Biological Anthropology

Why Anthropology Matters (now more than ever)

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Excited chatter echoes down the second floor corridor as a group of middle school girls approaches the door to the osteology lab. The young women file into the lab wide-eyed, curiously craning their necks to see the rows of bones on the shelves and tables. “Are those real?” They ask, pointing to a row of skulls or the complete skeleton on the table, “are those someone’s bones?”

Typically, I begin these GiST (Girls in STEM at Tulane) workshops by introducing myself and welcoming them to the New Life in Buried Bones workshop. Today, I tell them, you all will learn about the study of human skeletal remains from archaeological sites and in forensic cases. Using the examples of bones with dental disease and cranial modification, I show these young women how human bones inform us on ancient life. They always love to hear gory forensic cases, so I make sure to include a few examples of blunt-force trauma and gun-shot wounds. For those interested in medicine or biomechanics, I give demonstrations of how repetitive motions to two joint surfaces can result in boney changes and sometimes even osteoarthritis. Every once in a while, one girl will exclaim that she also wants to be a bioarchaeolgist or a forensic anthropologist when she grows up.

Today, this workshop felt as if it would be different. Today, my enthusiasm felt strained. I had spent the last few days deliberating over what I was going to say to these girls. I could not simply pretend that everything was okay. It certainly wasn’t. I could not think of words eloquent enough to express how distraught I felt. Today, it was my job to stand in front of these young women and tell them that her education was one of the most important things she’ll ever have. She shouldn’t feel discouraged when she fails, or when her peers let her down. I was supposed to tell her that the bullies don’t win in the end. Hard work and critical thinking are invaluable. Being bold, imaginative, and fearless is what leads to innovation and discovery. The world is full of its problems, but she has the ability to tackle the most insurmountable challenges. Pursuing science, I would tell her, is one way to do that.

Today, those words felt hallow, flippant, and simply untrue. I should be thinking of ways to encourage and inspire these women, but instead, in light of this week’s election, I was plagued with memories of all the troubles I had when I was their age. I thought of the bullies, male peers who harassed me for answering questions in class or commented on my appearance, as if that had something to do with my value or intelligence. How was I supposed to tell them that no matter how impressive her accomplishments, there will be that person who attempts to discredit her, belittle her, and make her feel worthless? Worst of all, how am I supposed to tell her that all of these problems are simply a phase, and that things will get better after middle and high school? She has a bright future, I should tell her. She would be accepted to university based on her merits. But would always be someone there, a real or fictions demon on her shoulder whispering in her ear that she only got in because she’s a woman, a woman of color, an immigrant, a LGBT? I shudder to think of those who said similar things to me (and I enjoy more privilege than most); those men who said or implied that I took their spot, that being a woman gave me a competitive edge they did not enjoy. Forgot that maybe my successes meant I was qualified. Someone had to be blamed, and I was the unlucky winner.

As much as I wanted to unleash my own frustrations, I knew that was not the best way to proceed. I am sad, I am angry, but I am certainly not going to back down and admit defeat.

Instead, I will look to my greatest comfort: anthropology.

What is anthropology? I ask the young women.

“The study of human bones!”

“The study of ancient societies!”

“The study of artifacts and archaeology!”

“The study of culture!”

You are all correct, I tell them, these are all important aspects of being human and they are intimately interconnected and manifest in infinite, fascinating ways. Anthropology is the science of human beings. We have the tool kit of a scientist: we ask questions, formulate hypotheses, make observations of the evidence, and evaluate our results. Our goal is to understand the complexities of human nature, why humans do what we do. It is during that fascinating, fulfilling, and sometimes frustrating journey that we discover how valuable and rare our open-mindedness and thirst for understanding is in the world.

My fellow anthropologists, all you linguists, cultural and medical anthropologists, forensic anthropologists, archaeologists, bioarchaeologists, and primatologists, you know this. And it thrills me to call you my friends and colleagues.

But to those who are unfamiliar with what I do, this is for you. Anthropology is not simply an intellectual oddity tucked away in the ivory towers of university campuses. It cannot be buried in piles of jargon-heavy books and articles, though that doesn’t mean some haven’t tried. Studying the interconnectedness of all aspects of human life enables us to understand why diseases spread and why crops fail. This science of human nature allows us to explore why societies commissioned art to inspire creativity or to evoke a sense of the divine. Anthropology explores how empires expand and collapse. It does not shy away from discussions of race, gender, and colonialism; in fact, it confronts these debates head-on, challenging us to critically evaluate our past mistakes so that our future is full of thoughtful, well-informed decisions. To an anthropologist, why early humans migrated out of Africa, over Beringia, and went to the moon seems almost obvious. Humans are wired to look to the horizon, across oceans, and up at the night sky: we want to go beyond our known world to see what lies just out of reach.

Anthropology has comforted me these last few days. Hatred and fear are simply the symptoms of ignorance, and it can spread like wildfire if left unchecked and unchallenged. To be an anthropologist is to understand human similarities and differences. We do not hate the unknown nor fear the challenges of this ever-changing world. Instead, we build connections with our global community and to the past by studying cultures, ancient societies, and their material correlates; we do not build walls. Anthropology is a discipline that has the power to understand who we were. It is more important now than ever that we recognize that anthropology also has the indispensable power to help us decide who we are and who we want to be.

So today, as I looked at those excited, hopeful, bright young women in the osteology lab, I tell them I decided to study anthropology because I wanted to fully comprehend and appreciate the complex, beautiful world around me. In the words of Ruth Benedict, I tell them, “the purposes of anthropology is to make the world safe for human differences.”

Death without Weeping: Maternal Bonds towards Deceased Offspring among Non-Human Primates

Nonhuman primate mothers do not weep in response to death of their infants. When a non-human primate mother has her offspring, she has already invested considerably time as well as physical and metabolic energy to gestation and birth of the infant. Death of an infant, therefore, is detrimental to the mother who already invested in her offspring, as well as the group’s genetic continuity. Whether or not the death of non-human primate mother’s offspring elicits an emotional or affectionate response is more difficult to identify.

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Primatologists have long acknowledged the importance of death of a primate for calculations of demographic trends and constructing life tables (Altman and Altman, 1970). Studies of behavioral responses to death among rhesus macaques include elevated grooming levels between group members, possibly to counteract the loss of a group member. The living also engaged with the deceased by grooming, inspection, as well as aggression towards the corpse (Buhl et al., 2012). Female hamadryas baboons show increase in stress hormone levels after the death of a conspecific (Engh et al., 2006). Studies of chimpanzees group responses to pre- and post-death care of members of their cohort indicate that behaviors typically include close inspection and tests for signs of life at the moment of death, male aggression towards the corpse, all-night attendance by family members, cleaning of the corpse, and even avoidance of the place where death occurred (see Goodall, 1977, Anderson et al., 2010, and Biro et al., 2010).

Whether or not there exists a general trend of maternal responses to primate death remains poorly understood. The mother-offspring bond is considered to be one of the longest and most essential social bonds among mammals (Cronin et al., 2011). The maternal reposes associated with the permanent, premature disruption of this social bond—the death of the offspring—has rarely been investigated (Cronin et al., 2011). Early primatological studies documented male responses to dead infants among semi-free-ranging Barbary macaques (Merz, 1978). A long-term study of wild geladas from Ethiopia recorded 14 cases of dead infants being carried by females was the first attempt to explore responses to death in non-human primates, focusing on allomaternal-like behavior towards dead infant (Fashing et al., 2010). Primate death and behavioral responses from group members have also been documented from several sites, including the Gombe, Tai Forest, and safari park in Scotland (Teleki, 1973; Boesch and Boesch-Achermann, 2000; Anderson, 2011, respectively).

Primatological studies have documented instances when mothers continue to handle the corpses of their infants. Given this prolonged interaction, I wonder, does maternal attachment continues after the death of her offspring? If so, what triggers this particular behavior?

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Before I examine the behavioral responses to infant death, it is important to briefly describe what is considered “normal” mother-infant behavior among primate. Mothers and their infants represent a central focus of interest for other females in the group among species and groups of social primates (e.g. Hrdy 1976; Seyfarth 1976; Altmann 1980; Nicolson 1987; Maestripieri 1994a). Females visibly show their interest in interacting with newborn infants. When new infants are present in a group, subadult and nulliparous females approach the mothers and attempt to sniff, investigate, and pick up the young infants (Nicolson 1987). Females also have been observed grooming the mother in exchange for handling her new infant (Altmann, 1980, O’Brien & Robinson, 1991, Muroyama, 1994, Di Bitetti, 1997, Silk, 1999).

While female attraction to infants represents a common feature of primate species, maternal response to infant handling shows a certain degree of variability (Nicolson 1987; Maestripieri 1994b). Maternal responses to infant death have been attributed to several ecological and circumstantial explanations as well as several hypotheses in the primatological literature:

  • Unawareness of Death Hypothesis (Hrdy, 1999)
  • The Decomposition Hypothesis (Fashing et al., 2011)
  • Post-Parturient Condition Hypothesis (Kaplan, 1973; Biro et al., 2010)
  • “Learning to Mother” Hypothesis for Learning about Death (Warren and Williamson, 2004

Unawareness of Death Hypothesis

Extended carrying of a dead infant may indicate that the mother is unaware that her infant is no longer alive. According to the hypothesis, primate mothers of recently dead infants continue interacting with her infant exhibiting behaviors typical of new mothers, such as grooming and licking. For example, Kaplan (1972) recorded responses of captive female squirrel monkeys that were presented with the corpses of their dead infants. The infants had been dead for approximately two weeks. The mothers seemed unaware that their infant was no longer living, yet attempted to retrieve the corpse by lifting it or administer vocalizations regardless (Kaplan, 1972). However, these experiments do not simulate a situation that would occur in the squirrel monkeys’ natural environment. The mother’s infant was immediately retrieved after its death, which denied the mothers an opportunity to interact with her infant post-mortem.

Contrary to the hypothesis, there are examples of maternal behavior that shows the mother continues handling her infant while also exhibiting behaviors indicating that she is fully aware that her infant is no longer alive. A white-faced capuchin mother continued to groom and lick the body while trying to repel carnivorous insects from the corpse. She also allowed her dead infant to be fully submerged in water while she drank. Once she finished, she retrieved the corpse, and continued to transport her dead infant for several days (Perry and Manson, 2008). Similarly, chimpanzee mothers from Bossou, Guinea, appear to be aware that the bodies of the infants they carried were inanimate, and adopted carrying techniques not normally used with healthy juveniles (Biro et al., 2010).

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It is possible that uniparious mothers are unable to differentiation between living and non-living offspring due to a lack of experience. Studies have shown, however, that number of living offspring does not necessarily contribute to the duration for which in infant corpse is handled. Two multiparious snub-nosed monkey mothers carried and handled their dead infants for 4 days and one month. The mothers had had infants previously, and therefore could differentiate between normal, responsive infant behavior and abnormal, unresponsive infant behavior (Li et al., 2012). Similarly, multiparious chimpanzees mothers have been documented carrying their infant’s corpses for longer compared to the chimpanzee mothers carrying the corpse of their first and only offspring (Biro et al., 2010). Warren and Williamson (2004) also noted that two multiparious gorilla females also continued to handle their infants long after their death. Whether or not a primate mother is nulliparious or multiparious does not appear to influence how long she continues to interact with the corpse of her infant.

Overall, it appears that the unawareness of death hypothesis does not adequately explain the mechanism of maternal behaviors towards dead offspring. Continued handling of her infant does not necessarily suggest that she is unaware that her infant is not longer living; rather, the mother may be prolonging the separate from her infant for another reason.

The Decomposition Hypothesis

According to the decomposition hypothesis, any long-term carrying of the infant by the mother does not represent a sense of loss or attachment to the infant. Rather, mothers are unaware of the infant’s death and continue to carry the corpse until clear signals of decomposition (e.g. particular odor cues) indicate death (Fashing et al., 2010). Extreme climate conditions (such as cold or hot arid weather) slow the natural rate of decomposition of deceased bodies (Haglund and Sorg, 1997). Prolonged carrying (defined as longer than 10 days) of an infant corpse appears to be more likely in extreme climatic conditions, particularly in cold or hot arid weather, that naturally slows decomposition of infant body (Fashing et al., 2010).

Several studies of primates living in extreme climate conditions have supported the decomposition hypothesis. Gelada monkeys (Theropithecus gelada) of Guassa, Ethiopia, live in an extreme climatic condition that favors a slower rate of decomposition of dead individuals. Over a 3.75 year-long study period, 14 mothers carried and handled their mummified infants for 10 or more days. Extended carrying of dead infants has been documented among mountain gorillas that inhabit unusually cold environments (Fashing et al., 2010b, Nakagawa et al., 2010, Vedder, 1984) and chimpanzees living in extremely arid regions with a long dry season of Bossou, Guinea (Biro et al., 2010, Matsuzawa 1997).

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The decomposition hypothesis is based on another assumption that New World primates in tropical environments appear only to carry or care for dead infants rarely or for only a short period of time. For example, a tufted capuchin mother was reported to carry her dead infant for less than 24 hours after an infanticide attack (Izar et al., 2007). This behavior, however, may be due to the social dynamics of infanticide, rather than the maternal indifference towards her dead infant.

Despite the climatic circumstances that delay decomposition, primates have been documented to carry infants for a long enough period that the body does eventually decay. In this case, signs of decomposition, such as putrefaction and change in the infant’s appearance (e.g. loss of fur and limbs) do not repel mother and, in some cases, other kin and non-kin. For example, Bossou chimpanzee mothers as well as related and unrelated individuals from all age groups of both sexes attempted to handle, lift and drop limbs, and sniff the bodies of three dead infants. Juvenile and infants were even allowed to carry the bodies of infants some distance from the mother in bouts of play. Biro and colleagues (2010) state that they never observed a response that could be interpreted as aversion, despite the bodies’ intense smell of decay and usual appearance of mummified skin and missing fur.

Similarly, four female mountain gorilla continued to carry their dead offspring even when the corpses lost their hair and heads, and despite the pervasive smell of decaying flesh (Warren and Williamson, 2004). Observations made by Rumbaugh (1965) of captive squirrel monkeys in San Diego, California, noted that a mother continued to handle her infant for six weeks as the corpse began to putrefy. Over a 24-year study period of Japanese macaques, a total of 157 mothers continued to carry their dead infants between 1 to 17 days despite the quick progression of the decomposition, and the putrid smell and swarm of flies surrounding the dead infant and the mother (Sugiyama et al., 2009). In this case, however, non-kin avoided the mother and her dead infant, seemingly due to the smell, and she received less social grooming that before their infants had died (Sugiyame et al., 2009). Sugiyama and colleagues (2009) state that they cannot determine why mothers continue to carry the corpses given its bad state of decomposition. It is apparent, however, that mothers do not necessarily abandon their offspring due to aversion.

It is possible that “caretaking” behaviors rather than the environmental setting facilitates mummification. In the study conducted by Biro and colleagues (2010) in Bossou, Guinea, three chimpanzee mothers continued to carry the mummified corpses of their infants for 19, 27, and 68 days following their death, exhibiting extensive care of the body by grooming it regularly, sharing her day and night nests with it, and showing distress whenever they became separated. The mothers also chased away flies that circled the corpses, twice with the aid of a tool (Biro et al., 2010).

In sum, the decomposition hypothesis has several flaws. Infant handling is not limited to primates living in unusually arid, cold regions. In fact, mothers continue to handle their dead infants even though the corpses admit olfactory and visual signs of putrefaction and decomposition. Overall, it seems that the foul odor of decomposing flesh does not appear to deter mothers from transporting and manipulating corpses. Oftentimes, this “care-taking” behavior seems to (unintentionally?) preserve the offspring. Yet, this treatment towards dead infants will be explored in the post-parturient condition hypothesis.

Post-Parturient Condition Hypothesis

Post-parturient condition hypothesis proposes that postpartum hormones influence maternal behaviors toward dead infants. Physical characteristics and particular hormones are essential for the onset and maintenance of infant-carrying behavior and the development of the mother–infant bond towards living infants (Kaplan 1973; Biro et al. 2010). Neuroendocrine mechanisms and physical characteristics of the infant (such as natal attractiveness) stimulate and regulate motherly behavior to care for and protect her offspring (see Maestripieri, 2001, 1991). At birth, an infant’s attractiveness includes size at birth, vocalizations made by the infant (e.g. “purring” noises), infantile facial expressions, distinguishing morphological features such as bug ears or tail tufts, and distinctive coat color (Hrdy, 1976).

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Human, non-human primate, and non-primate mammal studies demonstrate that there are endocrine influences on mother-infant interactions and the formation of bond post-partum (Maestripieri, 1999). In non-primate mammals, pregnancy and lactation hormones enhance maternal responsiveness and behavior although they are not strictly necessary for their onset or maintenance (Stern, 1989). In New World monkeys such as red-bellied tamarins (Saguinus labiatus) and common marmosets (Callithrix jacchus), there is evidence that hormones influence both responsiveness to young during pregnancy and quality of maternal care during lactation (Pryce et al., 1993). Studies of group-living pigtail macaque females show that the females increased their rate of interaction with infants during the final weeks of pregnancy that corresponded with an increase in plasma levels of estradiol and progesterone (Maestripieri and Wallen, 1995; Maestripieri and Zehr, 1998). Fleming and colleagues (1997) showed that human mothers who maintained high levels of estradiol over the parturitional period also had higher feelings of attachment to their own infant in the early postpartum days than mothers whose estradiol levels dropped. Thus, these studies indicate that primate and human parenting is partially influenced by physiological variables.

The continued interaction and gradual separation between the mother and infants’ bodies appears to also be a by-product of hormonal condition of pregnancy and the formation of the mother-infant bond in post-parturient female primates. Behavioral studies note that mothers do not simply abandon the corpse of her dead infant. Rather, the mother continues to interact with the corpse, gradually separate herself physically from the body of her dead offspring.

There are several physiological characteristics that may be observed in female primates that indicate that hormone levels are fluctuating and therefore influencing her behavior. Postpartum amenorrhea in chimpanzees lasts around four years, but is shortened with the death of an infant (Wallis, 1997). The infant could no longer breastfeed and lactation ceased, triggering the mothers’ reproductive cycle to return.

To date, there are no studies that directly link changes in hormones during the mother’s transition from handling her infant until the moment she abandons its. Therefore, the post-parturient condition hypothesis relies on behavioral studies. Several behavioral studies report that mothers gradually separate herself from the corpse of her infant. For example, gelada monkey mothers also experience a graduate separation that includes a transition from only the mother handling the infant corpse, and then allowing other group members to handle to deceased juvenile (Fashing et al., 2010).

The post-parturient condition is best illustrated by observations conducted at Chimfunshi Wildlife Orphanage Trust, a chimpanzee sanctuary in Northwest Zambia (Cronin et al., 2010). Shortly after the death of her infant, the mother transitioned from maintaining close, constant proximity to the dead body to creating physical distance from the deceased infant (Cronin et al., 2010). She maintained visual contact with the body when not in immediate proximity to it. As time passes, mothers transition to lessening her contact with the body and allowing others to inspect the body (Biro et al., 2010; Hosaka et al., 2000). Other studies have also reported that chimpanzee mothers gradually transition from extreme attachment to the body of their dead infants immediately following death to weakened attachment to the body as time passes (Hosaka et al., 2000, Biro et al., 2010).

Ring-talked lemur (Lemu catta) mothers have been reported to continue to return to their dead infants several times for several hours after the infant’s death. Every time each female returned to the body, she would sniff, lick, and touch the infant (Nakamichi et al., 1996). Despite the increasing distance between the troop and the deceased infant, the mothers continued to return to her dead infant, even when the troop have moved 400 meters away from the corpse (Nakamichi et al., 1996). Six of the seven mothers attempted to lift the corpses, and one mother clumsily carried the corpse 15 meters and attempted to jump into a tree. Mothers were unable to maintain proximity between both the troop and the corpse concurrently because she was not able to carry her dead offspring (Nakamichi et al., 1996).

The post-parturient hypothesis appears to most adequately examine the mechanism of maternal handling and carrying of deceased infant remains. Carrying and handling a corpse after death expresses a strong attachment, and the gradual separation of mother from her dead infant are behavioral responses to hormonal changes. Whether or not death of an infant elicits a psychological or emotion response is difficult, possibly impossible to identify. To compliment the hormonal-centric tenants of the post-parturient hypothesis, I will explore literature that contemplates whether or not the prolonged carrying and handling of corpses is part of process in which primates “learn” about death.

“Learning to Mother” Hypothesis for Learning about Death

Studies of maternal responses to death among apes provide additional information investigating whether or not the extended interaction with infant corpses is a period during which primates engage in a learning process. The “learning to mother” hypothesis was first proposed by Hrdy (1976) to explain why female young and non-mothers interact so frequently with offspring. Warren and Williamson (2004) adapt this hypothesis to a population of mountain gorillas to illustrate that the prolonged handling of dead infants is a type of social learning for mothers, young, and non-mothers to acquaint themselves with cues typical of death.

Ateles geoffroyi vellerosus Spider Monkey Central America mother and baby

Primatologists have investigated the long-term benefits of young and non-mothers carrying living infants. The handling of live infants by non- mothers has been referred to as aunting, baby-sitting, kidnapping, play-mothering, allomaternal behavior, or allomothering (Hrdy, 1976; Maestripieri, 1994a, 1994b). According to the ‘‘learning to mother’’ hypothesis, young or nulliparous females who handle infants gain maternal experience, and recalling these skills later in life, making them more capable of raising their own offspring (Hrdy, 1976).

The benefits of “learning to mother,” could be gained with a corpse, since the motor skills required to carry an infant while traveling and foraging could still be acquired (Warren and Williamson, 2004). Furthermore, the extending carrying behavior by the mothers, as well as related and unrelated individuals, may be an example of observational learning that promotes prolonged transport of deceased young (Biro et al., 2010). These interactions with a corpse could be part of a process in which the primate learns to recognize death.

Observations of mountain gorillas at Karisoke Research Center, Rwanda, noted that two nullparious mothers in their final months of pregnancy, and two mothers who had recently lost offspring all handled and transported the mothers’ two dead infants (Warren and Williamson, 2004). As previously discussed, the hormonal disposition of the mother may contribute to the continued handle of her infant after death. The hormonal state of pregnant females similarly predisposes her to interact more frequently with infants, even ones that are recently dead. It seems it may be both an innate change in her physiology as well as an opportunity to practice handling infants.

Similarly, Cronin and colleagues (2010) suggest that chimpanzees handle and examine the body of deceased infants in order to recognize cues of a corpse and therefore “learn” about death. Studies conducted at Chimfunshi Wildlife Orphanage Trust, a chimpanzee sanctuary in Northwest Zambia, recorded that one chimpanzee mother touched the body and face of her dead infant, presumably an action that would have provided olfactory and gustatory information about the infant’s condition (Cronin et al., 2010). Every time she returned to the infant’s corpse, she would closely inspected its face and neck. Cronin and colleagues (2010) suggest that close inspection of the face could serve as the best location to assess the condition of the infant. No changes in eye gaze, breathing, or facial musculature could inform the mother that the infant’s condition had irreversible changed (Cronin et al., 2010). The mother was actively gathering novel sensory information about the dead infant, possibly remembering this information for the next time she encountered the same set of cues. In other words, the mother may have been “learning about death.” (Cronin et al., 2010: 420).

Whether or not prolonged handling of infants is indicative of a “cultural” behavior towards death that is passed on throughout the group and through generations may be impossible to prove. Yet, some researchers suggest that the transmission of knowledge for handling of dead infants that occurs throughout multiple generations and occurs among multiple members of a group may indicate that this learning and knowledge may be transferred (see Cronin et al., 2010; Warren and Williamson, 2004; and Biro et al., 2010). For example, three chimpanzee mothers at Bossou, Guinea, all had infants that died during the study period and all exhibited a similar manner of prolonged handling of dead infants. Biro and colleagues (2010) suggest that the similarities in treatments and behaviors may not be a rare occurrence in this particular community. In fact, the prolonged handling may part of the culture of that particular group. In sum, the learning to mother hypothesis provides an intriguing framework in which primatologists may explore prolonged infant handling among the great apes.

Mother-Infant Bonds and Learning to Grieve?

Overall, it appears there is continued attraction and care towards dead infants occurs to some extent in all major taxaonomic groups (Anderson, 2011). Both the decomposition and unawareness of death hypotheses seem insufficient to explain why primate mothers continue to handle the corpses of offspring after death. Contrary to the unawareness of death hypothesis, primate mothers appear to handle their infants in ways that suggest they are aware that their offspring is no longer living. Similarly, primate mothers continue to handle their dead infants regardless of the environmental setting (arid verses humid) and despite putrefaction and decomposition of the corpse.

The post-parturient condition hypothesis, on the other hand, considers both the behavioral and hormonal responses of primate mothers across primate taxa. The formation of the strong mother-infant bond at birth does not simply disappear once the infant dies; rather, it seems that the mother transitions from physiological conditions typical of motherhood (e.g. cessation of lactation amenorrhea) is concurrent with the mother’s gradual separation from and abandonment of her deceased infant.

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It is particularly interesting that mothers slowly allow conspecifics to handle the corpse, and that recognition of particular cues that signal death may illustrate that young and non-mothers are “learning” to recognize death. Whether or not the handling of dead infants should be considered cultural learning is difficult and potentially impossible to identify. Given that multiple mothers of a particular group of chimpanzees and gorillas all exhibited similar behaviors in response to the death of their infant indicates that the behavior may be contributed to both physiological and social influences.

Studies of primate death are greatly biased towards chimpanzees, but long-term and behavioral studies of gorillas, baboons, and new world monkeys are also becoming more common. Overall, primate behavioral and hormonal studies indicate that continued handling and interaction with infant corpses signifies a connection between the mother and her offspring, even if the offspring has died.

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Physiological and Evolutionary Mechanisms of Fertility at High Altitude: Part 2

Birth weights, Stillbirth Rates, and Infant Mortality

Exposure to hypoxic environments may increase the stress on an already vulnerable growing fetus, thus result in a higher frequency of low birth weight, higher stillbirths, and increased infant mortality among high altitude populations. Several scholars have reported reduced birth weight with increasing altitude due to inadequate maternal oxygenation later in pregnancy (Yip, 1987; Haas et al., 1977; Ballew and Haas, 1986; Jensen and Moore, 1997; Khalid et al., 1997). For pregnant women, oxygen saturation and hemoglobin concentration naturally decrease towards term, resulting in a fall in arterial oxygen at the end of pregnancy. If a woman is at high altitude, she has even less access to oxygen which may explain the reduction in birth weight at high altitudes (Hartinger et al., 2006).

Hartinger and colleagues (2006) compared birth weights of 84,173 neonates between 1995 and 2002 from the cities of Lima (150 masl), Huancayo (3280 masl), Cusco (3400 masl), and Juliaca (3800 masl). The authors found that birth weight is lower at high altitude, but there is no linear relation between altitude of residence and birth weight (Hartinger et al., 2006). In fact, in Juliaca (3800 m) where the population has resided the longest, birth weight was higher than that of Huancayo (3280 m) where indigenous populations have resided the shortest. In Cusco (3400 m), where there is increased admixture among Spanish and indigenous populations, birth weight was also lower compared to Juliaca (Hartinger et al., 2006). The data suggests that women from families who had lived at high altitudes for at least 3 generations maintained their oxygenation better during pregnancy (McAuliffe, 2001), allowing for a higher birth weight and suggesting that adaptation occurs when groups are exposed to a hypoxic environment over generations (McAuliffe, 2001).

Several studies have confirmed an association between high altitude and a higher stillbirth rate (Gonzales et al., 2007; INEI, 2001) due to an effect of low barometric pressure and colder temperatures common in these hypoxic environments (Gonzales, 2007). For example, populations in the Sarata district of southern Peru almost 20 percent of children do not survive beyond age five (Collins, 1983). Local health personnel and native healers state that the leading cause of infant mortality is respiratory failure, possibly related to the hypoxic environment (Collins, 1983). In fact, respiratory symptoms are reportedly responsible for 58-68 percent of deaths among children under one year of age, and for 49-55 percent of deaths among children aged one to five (Collins, 1983).

To offset the effects of high altitudes, indigenous Peruvian mothers often tightly swaddle and enclose their infants in a set of clothes and blankets, referred to as a manta pouch. The manta pouch modifies the internal microenvironment so that, compared to the ambient environment, the temperature is higher and more stable, the humidity is higher, the partial pressure of oxygen is lower, and stimulation levels are reduced. It appears to be a solution the lower the infant mortality rate among indigenous women (Tronick et al., 1994).

Gonzales and colleagues (2007) compared stillbirth rates from a sample of 22,662 births between 2005 and 2006 for the cities of Lima (150 masl), Huancayo (3280 masl), Cuzco (3430 masl), and Puno (3850 masl), and reported that stillbirth rates were higher at high altitude (>3000m) compared with low altitude (Gonzales et al., 2007). Yet, inhabitants from the South Andes (i.e. Cusco, Puno) actually have lower stillbirth rates compared with the central Andes (Huancayo) (Gonzales et al., 2007). Similar to Passano (1983), Gonzales and colleagues attribute this discrepancy with a vague description of an “ancestry effect,” in which populations with longer multigenerational residence in the southern Andes population may be linked to lower still birth rates (Gonzales et al., 2007).

To summarize, there appears to be no association between an increase in fetal mortality with increasing elevation. High altitudes pose several environmental stressors (e.g. low oxygen and cold temperatures) which increase infant mortality; to counteract these stressors, Peruvian mothers tightly wrap and swaddle their newborns in mantas, creating a protective microenvironment. Interestingly, the rates of perinatal and neonatal mortality are, however, lower in populations that have resided at high altitude for longer; populations inhabiting the southern Andes have a longer antiquity at high altitude and lower rates of fetal and neonatal deaths than those in the central Andes with a shorter residence at high altitude.

Post-Partum Behaviors

Female physiology after birth may contribute to lower fertility levels, but most research has indicated that post-partum behaviors account for a decrease in reproductive rates. The National Institute of Statistics and Informatics of Peru documented longer durations of exclusive breastfeeding at high-altitudes than at sea level as revealed by an increased prevalence of lactation amenorrhea (absence of menstruation)(INEI, 2001). Yet, Gonzales (2007) noted that fertility rates among high altitude populations in Peru are higher compared to those at sea level despite the prevalence of lactation amenorrhea and prevalence of >2 years sexual abstinence after parturition.

Couples living in the Sarata district of Peru take an active role in preventing and regulating births family sizes after reaching the desired number of children size. Collins (1983) reported that women sought herbal specialists who provided herbs, fruits, and seeds thought to induce miscarriages if taken within a month or two of conception. Infanticide is also a common practice, especially if the infant was in some way abnormal, because the harshness of the environment and lack of health care services made the burden of raiding an abnormal or weak child too costly for many families. Other methods approved by the local Catholic nuns included abstinence and the rhythm method. Also, seasonal migration is sometimes prescribed to young couples that were having children more rapidly, and Collins (1983) noted two accounts in which fathers-in-law recommending that their sons–in-law migrate seasonally in order to space births.

Similarly, Laurenson and colleagues (1985) noted that females living in Central Nepal (12,400 feet) experienced lower fertility frequencies than females living at 8500 feet. Though the females at high altitudes reported longer post-partum ammenorhea and breast-feeding periods, the pregnancy gap was due to the later age of marriage and controlled birth spacing (Laurenson, et al., 1985). Overall, it appears that both male and female parents actively seek solutions to control birth spacing in order to achieve desired number of offspring.

Onset of Menopause

Similar to the age of sexual maturation, high altitudes may contribute to an earlier or later onset of menopause. Studies have documented that the age at menopause occurs earlier at high altitude than at sea level (Gonzales, 1994) and therefore result in a shorter reproductive span for women living at altitude (Gonzales and Villena, 1996). Women living at Cerro de Pasco (4340 masl) experienced accelerated menopause compared to women in Lima (150 masl) due to high levels of serum follicle stimulating hormone (FSH) and accelerated oocyte loss observed in regularly menstruating women at high altitude (Gonzales and Gonez, 2000).

Studies have estimated medium age of menopause to be between 45.4 years and 46.1 years among rural Bolivian Aymara, (Crognier et al. 2002; Burch and Vitzthum, 2011). Among women living at high altitude in Nepal, menopause occurs between 45–50 years (Lang and Lang, 1971; Beall, 1983), an age range that is within the average onset of menopause worldwide. Vitzthum (2013) notes, however, that these ranges are similar to those of other populations that have poor living conditions and high mortality risks (e.g., India = 44.0 years; also see Wood, 1994). Like age at menarche, variation in age at menopause may be due to factors other than, or in addition to, hypoxia. Yet, there appears to be little, if any, demographic impact of perhaps a year less at the end of the reproductive life span of women (Vitzthum, 2013).

Evolutionary Mechanisms and Ethnicity/Ancestry Influences on Fertility

Evolutionary processes may have acted differently on the populations who originally migrated into high altitude environments and thus resulted in different patterns of adaptation. These results suggest that longevity of life at high altitude may be an important component of adaptation. For example, the reduced survival of Spanish children at high-altitudes suggests that the newcomers lacked an adaptation to the hypoxic environment (Gonzales, 2007). The indigenous Peruvian population—Aymara and Quechua—was later mixed with the Spaniards who colonized Peru during the 16th century. As a result, the Peruvian population has three important admixture groups: first, the Quechua or Aymara populations with long-term residence in highland zones particularly at the Southern Andes (Cuzco and Puno), and the second is admixture of Spanish with the indigenous Quechua and Aymara populations, and third, the Spanish who moved to high altitude relatively recently in the last four centuries (Rupert and Hochachka, 2001). This introduction and mixture of genes may have stopped or reversed the adaptive processes preformed during more than 10,000 years of life at high altitude. Natives with longer ancestry in high altitudes appear to have an unknown genetic component that make them better adaptive to their environments compared to individuals of Spanish descent.

Evolutionary processes may have acted differently on colonizing populations of the Andes verses those of the Himalayas, resulting in different pattern of adaptation (Beall, 2006). Compared to Andean residents, Tibetans with 20,000 years of antiquity at high altitude demonstrate less intrauterine growth retardation and elevated arterial oxygen content which increases uterus-placental oxygen delivery during pregnancy (Moore et al., 2004; Wiley, 1994). The ability to sufficient deliver oxygen to the fetus and the fetus’ ability to incorporate the oxygen into its system is necessary for the offspring’s survival (Moore et al., 2004; Wiley, 1994).

It appears that a phenotype of high saturation of oxygen may exist among populations with antiquity in high altitude environments. For example, Bealls’ (2006, 2007) research has supported the hypothesis that the higher oxygen saturation allele might be favored by natural selection among Tibetans, but not Andean peoples. To test the hypothesis that high oxygen saturation genotypes have higher Darwinian fitness, Beall (2006, 2007) gathered genealogical, oxygen saturation, and female fertility data from 905 households in 14 villages at 3800-4200 masl in rural areas of the Tibet Autonomous Region and found that infants who were homozygous and heterogygous for oxygen saturation gentoypes had higher likelihood of surviving infancy (Beall 2006, 2007, 2014). This suggests that high-altitude hypoxia acts as an agent of natural selection on the heritable quantitative trait of oxygen saturation via the mechanism of higher infant survival of Tibetan women with high oxygen saturation genotypes (Beall et al., 2004; Beall, 2006, 2007, 2014).

In sum, there are evolutionary forces selected for increased oxygen saturation among Tibetan populations with the greatest antiquity in the Himalayas. Though Andean samples lacked the allele associated with this mechanism, it is possible that similar adaptive forces have been acting on the indigenous populations of the Andes.

Discussion

Historic chroniclers found that indigenous Andean females maintained capacity to reproduce while Spanish colonists were reportedly unable to carry fetus to full term or experienced high infant mortality rates. Low oxygen environments may delay the onset of sexual maturation among Himalayan and Andean populations; however, menarcheal age is well within the range of variation worldwide. Whether or not socio-economic status impacts sexual maturity remains unclear. Overall, it appears to have no demographic consequence because marriage and sexual behaviors typical begin well after puberty between highland Himalaya and Andean populations. Studies documenting gamete formation and testosterone production have demonstrated that exposure to high altitudes negatively impact male reproductively abilities for a short period of time. Mechanisms of ovulation vary between highland and lowland females in both the Andes and Mongolia yet are well within the range of worldwide variation. At times, differential barometric pressures appear to impact female ovulation, but there appears to be no negative impact on female fertility. In fact, it appears that overall health and socioeconomic status may impact overall fertility among high altitude populations. Lower oxygen levels may be linked to lower birth rates among high altitude infants, yet there is no linear relation between altitude of residence and birth weight. In fact, better oxygenation during pregnancy appears to be an adaptation among women with greater ancestral antiquity in high altitudes. Low barometric pressure and cold temperatures are traits of high altitudes and are attributed to the high stillbirth and infant mortality rates. Infants born into populations with greater antiquity in the highlands, however, appear to be more likely to survive compared to infants born to recent immigrants to the highlands. Post-partum behaviors such as breast-feeding, abstinence, herb-inducing miscarriage, and rhythm method, indicate that females actively attempt to regulate reproduction and control birth spacing, thus actively attempt to control their fertility.Variation in age at menopause between highland and lowland populations may be due to hypoxic environments as well as poor living conditions and overall health. However, there appears to be little, if any, demographic impact on the earlier age of menopause among women in high altitudes.

The stressors associated with high-altitude environments impose severe, lifelong stress upon every resident regardless of age, sex, or individual characteristic. Populations living in high-altitude environments do not adapt behaviorally to create non-hypoxic microclimates, people must adapt biologically. In fact, genetic research is beginning to elucidate the how populations with the longest antiquity in high altitudes have certain genes that allow them to live, and thrive, in an otherwise physiological stressful environment.

Conclusion

High altitude environments appear to impact the reproductive physiology of males and females, yet individuals who have a longer ancestry at high altitude appear to have adapted to the low oxygen environments. While socioeconomic factors sometimes negatively impact fertility, it appears that high altitude ancestry appears to have a greater impact on reproductive success. Native populations with a long ancestry in high altitudes have fewer reproductive issues while those who have a mixed ancestry (e.g. Spanish verses Quechua or Aymara; Han Chinese verses Tibetans), are more likely to have issues with fertility. In sum, an examination of fertility in the Andes and Himalaya mountains illuminates complex relationship between proximate behaviors and dynamic evolutionary adaptations which together impact reproductive functioning in high altitude environments.

Physiological and Evolutionary Mechanisms of Fertility at High Altitude: Part 1

High altitudes have the potential to negatively impact normal bodily functions of individuals who are both accustomed, or not properly acclimated, to such environments. Air deficient in oxygen, colder temperatures, greater exposure to solar radiation, and higher energetic costs of subsistence compared to that of lowland environments are potentially detrimental to physiological function. Similarly, high-stress environments with riskier living conditions may lead to economic disparities and locally specific cultural practices. Despite these limitations, human populations have lived, and thrived, in high altitudes environments for thousands of years. I investigate how theses environmental stressors impact reproductive functioning and fertility of indigenous populations living at high altitude, particularly in the Andes and Himalaya Mountains. In particular, I assess whether or not altitude-related stressors and reproductive behaviors contribute to lower fertility rates among high altitude populations. Through analysis of the physiological, behavioral, and genetic properties of males and females living at high attitude, I argue that fertility rates are under strong evolutionary control that offset altitude-induced sicknesses (hypobaric hypoxia) thus limiting variation in fecundity among high altitude populations.

History of the Study of Fertility at High Altitudes

Populations and small-scale societies have a long antiquity at high altitudes, yet much of our early knowledge of whether or not males and females had normal reproductive fitness comes from chronicles written by Europeans colonizing the Andes. Archaeological investigations in the Andes are numerous and are ongoing (Rademaker et al., 2014), yet are still in a very early stage in the Himalaya Mountains (Aldenderfer, 2011). Similarly, studies of the genetic components associated with high-altitude living are novel avenues of investigation among researchers working with populations in both the Andes and Himalayas (Beall, 2006, 2007). Given this incomplete picture, fertility studies conducted among populations living in other high altitudes (e.g. ovulation among Mongolian females) will also be presented when relevant. Because both the Andes and Himalaya Mountains are both extreme high altitude environments, I will explore research on reproductive fitness from both areas while recognizing that the entire picture elucidating the nature of fertility at high altitudes remains incomplete.

It is generally assumed that the human ancestral phenotype of oxygen transport system evolved mainly in environments with normal oxygen levels, or “normoxia” at sea level (Beall, 2006; Hochachka et al., 1998). Geological, vegetational, and archaeological analyses of hominin fossil sites in rift valleys formations in Ethiopia spanning approximately 3 million years indicate that hominid habitation sites were at an altitude of 500-600 meters above sea level (masl), well below an altitude thought to induce hypoxic stress (Bonnefille et al., 2004; Redfield et al., 2003; Quade et al., 2004). Thus, it is assumed that hominid evolution occurred under normoxia, and the corollary that high-altitude hypoxia is a physiological stress seems reasonable (Beall, 2006).

Laguna Cullicocha (4635 masl)

Laguna Cullicocha (4635 masl)

Altitude stress, medically known as hypobaric hypoxia, is cased by the fall in barometric pressure with increasing altitude, resulting in fewer oxygen molecules in a breath of air compared to sea level (Beall, 2006). Barometric pressure decreases with ascending altitude, decreasing oxygen availability in ambient air. Conditions are especially prevalent in the altiplano/puna, a treeless, tundra-like landscape higher than 4000 masl, with little fuel for campsites, and is an area that requires twice the sea-level caloric intake needed to maintain normal metabolic function (Marriot, 1996). Hypobaric hypoxia becomes progressively more severe with increasing altitude and stresses biological systems because a steady, uninterrupted supply of oxygen is required for metabolism in the mitochondria (Beall, 2006). Aside from supplemental oxygen or descent, there is no such strategy to avert the effects of environmental hypoxia (Gonzales, 2007; Julian, 2011). Though hypobaric hypoxia is the most pervasive physiologic challenge associated with high-altitude exposure, lower humidity, colder temperatures, increased solar radiation, and high energetic costs of subsistence that also accompany higher elevations may also threaten physiological well-being and reproductive behavior (Baker and Little, 1976).

Despite these stressors, human populations have occupied high altitudes for thousands of years. Archaeologists have uncovered ample evidence of human residency in high altitude environments as early as 20,000 years ago (Rademaker et al., 2014). The Tibetan Plateau of the Himalaya Mountains exhibits archaeological evidence of worked stone (Aldenderfer, 2011) and handprints and footprints (Quesang site) at 4200 masl (Zhang et al., 2002). Butchered animal bones, stone artifacts, and small-scale hearths dating from 14,600 to 7500 calendar years before the present (cal yr B.P.) at Jiangxigou 1 (~3200 masl); Heimahe 1 (~3200 masl) (Brantingham and Gao, 2006); at Xidatan 2 (~4300 masl) (Brantingham et al., 2013); and at Yeniugou (3800 masl) in the northeastern part of the plateau (Tang et al., 2013).

Tibetan Plateau (approx 4500 masl)

The earliest archaeological evidence of human occupation in the South American Andes dates to as early as 10,000 to 12,000 years BCE (Rademaker et al., 2014; Bonavia, 1991). The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world (4355 masl) dating to 12,800-11,500 (Rademaker et al., 2014). Additional evidence of human occupation above 4000m of altitude with an antiquity of 10,000 years also has been found at the sites of Lauricocha, Huanuco (3850m) (Cardich, 1960) and Telarmachay, San Pedro de Cajas (4400m) in the Peruvian Andes (Bonavia, 1991).

Spanish chroniclers began to note the effect high altitude environments in the Andes had on living organisms during the 16th and 17th centuries early after colonization of the New World. Conquistadors such as Cieza de Leon (1553) described much about life among the Inca during the Spanish conquest and noted that the Inca had a surprisingly high fecundity rate. It was evident that Spaniards could produce offspring up to 3400 masl, yet infertility and stillbirths were frequent among Spaniards living in settlements around and above 4000 masl (Gonzales, 2007). Early chroniclers such as de la Vega and Cobo were of the opinion that the altitude effects on organisms were mainly attributable to the cold (de la Vega, 1609; Cobo, 1653). De la Calancha (1639) remarked in his chronicle that in Potosi (4300 m), in modern-day Bolivia, the natives had normal fertility and the offspring survived, whereas Spaniards encountered problems in having descendants. In fact, it was not until 53 years after then Spaniards settled the Andes did de la Calancha (1639) describe the birth and survival of the first child from two Spaniards in Potosi (4300 masl). Overall, chroniclers found that indigenous Andean females maintained capacity to reproduce while Spanish colonists were reportedly unable to carry fetus to full term or experienced high infant mortality rates.

Drawing by Guaman Poma de Ayala (1615/1616)

Given the discrepancy of fertility rates between newcomers to the Andes and the indigenous peoples, local biologists, biological anthropologists, and geneticists began to investigate the manner in which high altitude environments impact reproduction. Yet, many studies tend to produce contradicting results. The first fertility studies investigated the effects of altitude on fertility among sheep, cattle, cats, and rabbits, and demonstrated that short-term exposure to high altitude resulted in temporary infertility (Monge, 1942, Monge and Mori- Chávez, 1942; Monge et al., 1945).Studies in the late 20th century have shown that fertility is lower in the economically underdeveloped areas of the Andes than in the more prosperous Spanish-speaking parts (Collins, 1983). Studies documenting the fecundity rate (as calculated by the number of viable offspring per female) among Peruvian highlanders has found to be from one to two births less than that of lowland Peruvians of the same ethnic background. In fact, highland natives who move to low altitudes show markedly higher rates of fertility than their counterparts who remain in the highlands (Abelson, 1976). Conversely, studies have also noted that population fertility appears to be unaffected among natives to high altitude environments (Hoff, 1984). A retrospective hospital-based study performed on women of La Paz (3600 m), Bolivia shows that high altitude does not impair fertility (Suarez-Morales, 1967). In fact, the number of viable offspring born per female in the Andes has also been documented to be higher amongst high-altitude populations compared to those at sea level, suggesting that high altitude does not reduce fecundity in human populations (Gonzales, 2007). Additionally, scholars have noted that highlanders of both the Andes and Himalayas have distinctive morphological and physiological characteristics that seemed adaptive in the sense that they might offset hypoxia stress (Baker and Little, 1976; Monge, 1978). Given the complex and sometimes conflicting nature of the fertility data, considerations of the physiological mechanisms of reproduction as well as behavioral and genetic profiles will elucidate the nature of fertility at high altitudes.

Physiological and Behavioral Impacts on Fertility and Reproduction

At high altitude, the oxygen transport system must offset ambient hypoxia in order to maintain tissue oxygen levels to support maintenance, growth and development, and reproduction. Altitude-induced stress, hypoxia in particular, may act to affect the process of reproduction at several stages: formation of gametes and gametogenesis, the ovarian cycle and menstruation, birth weights, still birth rates, infant mortality, post-partum behaviors, and age of menopause.  Assessing how hypoxic stress impacts fertility alone is problematic because fertility is also affected by many cultural, social, and behavioral factors. Populations residing at high altitudes may have less developed health, social, and communication infrastructures than those residing at sea level. These reproductive categories will be explored while considering socioeconomic disparities and cultural practices impacting fertility. Over the next few weeks, I will address each of these reproductive systems beginning with development and formation of gametes and testosterone levels.

Development and Formation of Gametes and Testosterone Levels

Delay in the development of and abnormal formation of gametes may also impact fertility. In particular, research has documented whether or not male reproductive functions are negatively affected during and after high altitude sojourns. Early studies conducted on guinea pigs taken to Morochocha, Peru (4500m), observed degenerative alterations in the seminiferous tubules, which serve a crucial role in the production of male gametes (Guerra-Garcia, 1959).

Exposure to hypoxia and physical stress of high altitudes may induce reversible spermatogenic and/or Leydig cell dysfunction, a condition that decreases testosterone production (Saxena, 1995). Analysis of gamete production conducted on three subjects who trekked for 21-24 days between 5100-6700 masl revealed an increased rate of abnormal sperm shape (Abramsson et al., 1982), which would present an important problem if the subjects wanted children (Okumura et al., 2003). Additionally, scholars have observed that sperm counts had not recovered 3 months after subjects returned from the expedition. Yet, all subjects had normal gamete production and formation after 2 years (Okumura et al., 2003). Okumura and colleagues (2003) also observed an increase in abnormally shaped sperm 1 month after the subjects returned to sea level. Sperm shape had nearly recovered to the pre-expedition state after 3 months (Okumura et al, 2003).

Mount Everest (8848 masl)

In addition to hypoxia, physical stress while trekking and carrying heavy loads may also contribute to the initial decline in testosterone levels (Okumura et al., 2003). Endocrine tests conducted on the three subjects revealed slightly lower levels of testosterone in the blood 1 month after the expedition and decreased still further after 3 months. After 2 years, testosterone levels were normal. The subjects in the study also complained of erectile dysfunction after returning from the expedition, which may have been partly due to decreased testosterone (Okumura et al., 2003).

Semen analysis and recorded reproductive hormone levels taken from seven male mountaineers trekking through the Himalayas (approximately 5900 masl) found that physical exercise at high altitudes is associated with a testicular dysfunction leading to a reduced sperm concentration probably through an altered spermiation (Pelliccione et al., 2011). Interestingly, the physical exercise improved the male’s overall body composition, which increased testosterone levels after the expedition (Pelliccione et al., 2011).

In sum, studies have demonstrated short-term exposure to high altitudes negatively impact male gamete formation and testosterone production, ultimately affecting his ability to reproduce. It should be noted, however, that male gametes production and testosterone levels return to normal once he returns to sea level for several months to 1-2 years.

These are very high altitudes where people do not reside. Historically and in the archaeological record, however, there is evidence that people would take occasional sojourns to high mountain summits in the Andes. Spanish chronicler Cobo (1653) described how the Inka embarked on ritual pilgrimages (qhapaq huachas) to mountain summits were they would leave female and male children of exemplary physical perfection as immolate tribute to the Inka Empire and mountain gods. Freeze-dried bodies of these sacrificed children have been recovered from mountain summits up to 5200 masl in Chile, Argentina, and Peru (Reinhard and Ceruti, 2000). Physiologically, even brief sojourns to extreme altitudes has a minor impact on the reproductive system.

Ovarian Cycle and Menstruation

Ovulatory disorders are a major cause of infertility (Urman et al., 2006). While follicle phase ranges vary among women, a luteal phases lasting for less than 2 weeks is considered a “luteal defect” due to low levels of the hormone progesterone and an insufficient production of uterine lining, which inhibits a female’s reproductive abilities. Fecundability may be correlated to cycle length, which determines the number of opportunities for conception in a given time span (Wood and Weinstein, 1988). Because ovarian follicle growth is characterized by cell growth and rapid cell divisions, hypothetically, hypoxia may slow this process and thereby disrupt phase lengths (Wood and Weinstein, 1988).

Recent studies have suggested that short-term exposure to high-altitude hypobaric hypoxia may negatively impact the development and function of the corpus luteum. Parraguez and colleagues (2013) examined the corpus luteum among sheep living in high altitudes and found a significant decrease the growth and function of the corpus luteum, which resulted in decreased fertility (Parraguez et al., 2013). However, it is important to note that sheep used in the study were Creole ewes, a mixed breed developed from Churra and Manchega Spanish breeds brought to the Americas by Spanish colonists and therefore do not have a long ancestry in high altitude environments (Parraguez et al., 2013).

Among indigenous Aymara women on the altiplano (3800+ masl) of the Peruvian and Bolivia Andes, Vitzthum and colleagues (2000) reported a mean cycle length of 29.1 days (n = 612 cycles, 191 women). Cycle length among nomadic herders from the Mongolian high steppe (~1,500 masl) was 27.8 days, with the mean follicular-phase length averaging 14.7 days, and mean luteal-phase length 13.2 days (Jurado et al., 2009). According to Vitzthum (2009), neither the Aymara nor Mongolian cycle ranges were particularly low or high compared to cycle length of female populations worldwide. If hypoxia does slow follicle growth, the effect is insignificant (Vitzthum, 2013).

Differential hormone profiles, specifically time between the gonadotropin peak/release of luteinizing hormone (LH) and ovulation, between high and low altitude populations may indicate an ovulatory disorder. Escudero et al. (1996) compared samples from Lima (150 m) (N=10) and Cerro de Pasco (4340) (N=10), Peru. Females in Cerro de Pasco had smaller pre-ovulatory follicle diameters and lower estrogen production during the late follicle phase. Estradiol levels only increased 80% between Cerro de Pasco females compared to 137.3% among females in Lima. Additionally, the luteinizing hormone peaked earlier among women in Cerro de Pasco compared to women in Lima. Yet, both groups of females exhibited the same duration of the luteal phase and the same endometrium measurements between high and low altitudes (Escudero et al., 1996). Escudero and colleagues (1996) conclude that the differences in hormone profiles during menstrual cycle between high altitude and sea level samples are a result of low barometric pressure.

Conversely, Vitzthum and colleagues (2001a) compared ovulation rates between indigenous “middle-class” women in La Paz (3650 masl), Bolivia, and rural women living outside La Paz in El Alto (4150 masl), and reported that the rural participants had lower ovulation rates compared to the urban middle-class women, indicating that the difference in ovulation rates is not attributed to hypoxia because the two samples reside at similar altitudes (Vitzthum et al., 2001a, 2009). It is possible that overall health and socioeconomic status may impact overall fertility, yet the differences in ovulation lengths between the middle class and rural women may reflect normal variation (Vitzthum et al., 2001). The differences in ovulation may be correlated to socioeconomic status; ultimately, however, the high altitudes and sea level samples fall within the normal ranges of phase length and do not negatively impact reproduction.

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Anatomy and Behavioral Strategies of Human and Nonhuman Primate Parturition

In March of 2000, Sofia Pedro’s village in Mozambique was ravaged by floods. People were forced to higher grounds to avoid the floodwaters, and many people, including the heavily-pregnant Sofia Pedro, were climbed to shelter in the treetops. She was trapped in the tree for four days. On the third day, she gave birth to her daughter, Rositha.

Giving birth in the treetops is unusual for humans, but not for many primate species.

Stories like Sofia’s are particularly interesting because they pose the question: are humans unique in that they alone experience difficulties during birth? Do both human and nonhuman primates therefore adopt methods and strategies to minimize the risk and maximize survival of themselves and their offspring?

In other words, is there a gap in human and nonhuman primate parturition behavior?

To investigate the similarities and differences between human and nonhuman primate parturition strategies, one must examine 1.) the Anatomical characteristics to examine the physical difficulties humans and primates face when giving birth and 2.) Parturition strategies, in other words, how human and nonhuman primates manage birth and improve probability of survival of both the mother and infant.

Anatomical Characteristics 

The human and nonhuman birth canal divided into three transverse planes: the inlet, midplane, and outlet (fig. 1). Each plane is described as being either longest at either the anterior-posterior diameter or widest at the transverse diameter. Each plane may be aligned, meaning all three planes parallel to one another, or misaligned, the planes are perpendicular to one another, with the greatest diameter varying among the three planes

Figure 1. Pelvic inlet, midplane, and outlet

In the genus Pan birth canal, for example, the anterior-posterior diameter exceeds the transverse diameter. In Australopithecine (specifically A. aferensis) the pelvis inlet transverse diameter exceeds the anterior-posterior diameter, resulting in a platypelloid shape (i.e. a flat, oval shape). Among humans the three transverse are all misaligned; the inlet is widest transversely, and the outlet widest anterior-posteriorly; thus creating two perpendicular planes.

Figure 2. Comparison for the mechanism of birth in Pan, A.L. 288-1 (Australopithecus aferensis) and Homo (Tague and Lovejoy, 1986: 247)

The Australopithecine birth canal is an example of how useful it is to reconstruct and understand changes in birth and parturition among human and nonhuman primate ancestors.

Australopithecus serve as one of the earliest sources of fossil material for examining early human bipedalism, and for the purpose of this post, mechanisms of birth.  The cranial capacity of Australopithecus similar to that of modern chimpanzees. Pelvic and limb morphology indicate Australopithecines was bipedal, not but obligatory like our hominid ancestors. Australopithecines also had an increase in shoulder breadth co-occurs with bipedalism, helping with balance.

Australopithecine birth canal would have restricted fetal head rotations at all levels within the canal. Yet, the birth canal was adequate to allow passage of a neonate’s cranium only if the infant’s head entered with its occipital bone oriented transversely with ansynclitism, meaning the neonatal head tilted towards its left or right shoulder, and exited without rotating. The shoulders which followed probably would not have been able to pass through without changing orientation.

It is more difficult, if not impossible, to determine whether or not Australopithecines gave birth in solitude, among conspecifics, or sought attendants to assist with birth. Trevathan (1987) suggests that the presence of attendants at childbirth has been part of the genus heritage for at least one million to two million years, originating with encephalization in our linage. Hominid ancestors would have been able to give birth without assistance, but having that assistance and support would have made the difference between life and death for mothers and their infants. A slight reduction in mortality would lead to selection for the behavioral characteristic of seeking companionship during parturition, resulting in its widely universal distribution in the modern human species.

Anatomical Features of Human and Nonhuman Primate Birth

Sherwood Washburn referred to the human birth as the “obstetric dilemma,” resulting from the shrunken dimensions of the human birth canal mandated by the mechanical requirements of upright bipedal locomotion and the evolution of progressively larger human brains (Washburn, 1960). Among humans, the fetal head must be flexed as it passes underneath the subpubic arch/pubic symphysis, with the occiput against the pubic bones, the frontal bone passing along the concave anterior surface of the sacrum.  The infant’s head then emerges from the canal occiput anterior: meaning that the infant generally emerges from the birth canal facing the opposite direction from the mother.

Primate mechanism of parturition is slightly more difficult to investigate because observations and accounts of primate births in the wild are scarce. Primatologists who have observed primate births note the difficulties in differentiation between pregnant and non-pregnant females until the pregnant female is actually in labor. Also, some primates give birth nocturnally, thus lower the changes that they will be observed, and some even seclude themselves in the foliage of trees during parturition. Among greater apes, the spacious birth canal and large body size allow for the neonate to easily navigate the birth canal. Small-bodies primates and lesser apes (Ateles), proboscis monkeys (Nasalis), macaques (Macaca), and lesser apes or gibbions (Hylobates), have a smaller head-to-body proportions, thus potentially complicated the birthing process. In her PhD dissertation, Stoller (1995) examined radiographs of laboratory animals during parturition showed that squirrel monkey and baboon neonates entered the birth canal in various positions, but then rotate to exit face first, facing the maternal pubic bones with their heads in an extended position.

Human Primate Birthing Strategies 

Humans have adopted many strategies to combat the risks and difficulties in childbirth, one of which is seeking assistance from medical professionals or family members during the birth. Humans do have the ability to give birth without assistance, yet today many women giving birth prefer not to do it alone. Before the advent of modern obstetric care, pregnancy and childbirth were risky and dangerous, and the complex anatomical features involved in parturition predisposed humans to certain conditions, such as obstructed labor, which could result in a myriad of injuries to both the mother and infant (Roberts and Mancester, 2007; Arrowsmith et. al., 1996; Wall et. al., 2005). Thus, many women in developed societies view childbirth as an event to be managed with the presences of a trained professional using technological intervention (Liamputtong. 2007) to ensure that their pregnant bodies and fetuses are completely controlled, and therefore, safe (Liamputtong, 2007). To be sure there are benefits in having a trained medical professional present at the birth.

Obstructed births are a common complication humans face, one type in particular is shoulder dystocia, which occurs when the shoulders are unable to pass through the pelvis after delivery of the head when the neonate is too large and the pelvis too small. The typical medical intervention is a surgical incision to remove obstruction, which may be dangerous as it sometimes results in tearing or hemorrhaging, either of which might cause permanent damage or be fatal to the mother, infant, or both. Midwifes, on the other hand, adopt different strategies to combat shoulder dystocia: typically the maneuvers the parturent mother into different positions to widen the birth canal.

Birth positions in particular vary cross-culturally. Even though the semi-upright positions of kneeling and sitting are the best positions for parturition, the supine position is the most common in developed countries where birth typically occurs in a hospital. It is possible that many women do not have the stamina to remain in kneeling or sitting position for the length of time usually required to deliver a child. The supine position allows the medical professional to have optimal access to the birth canal as well. Interestingly, Friedman (1978) found that in general, the upright position is optimal for increasing intra-abdominal pressure and the diameter of the pelvis. Women who were upright in a seated or semi-reclined position during labor had a shorter labor length compared to women in a supine position (Friedman 1978).

Many women assign certain meanings to the birthing process; they feel a sense of achievement and pride in their ability to cope with intense pain. Mayan women living in Guatemala stated that they accept pain as an obligation of a woman’s life, and consider it a point of pride to confront the birth with stoic dignity and courage. In fact, the indigenous word for birth (patan) literally translates into “burden.”

Expressing and vocalizing any pain was, to some women, considered shameful because they believe such actions like screaming diverted energy needed to give birth. This is particularly true for Chinese women, who are also expected to use soft voices and demonstrate quiet demeanor during parturition.

Parturition Behaviors Among Nonhuman Primates 

Anatomically, it appears that the mechanism of parturition varies between primate species, specifically between large bodied and small-bodied apes. When scholars opine that primates have little to no problems during parturition, they do not consider the extrinsic challenges primates encounter when giving birth in their natural habitat. Observations of baboons reveals that females give birth among conspecific group members. Squirrel monkeys give birth within their group as well as a form of cooperation against predators, anti-predator vigilance, and defense of neonates. Among Chimpanzees, Goodall (1971) noted that pregnant females become more solitary as parturition approaches. Among some primates, females seek seclusion and take advantage of the tree foliage that provides a natural protection from terrestrial predators (Rosenberg and Trevathan 2002). In a study published in Primates in July 2014, primatologists observed a bonobo birth for the first time, and found that the parturent female was accompanied by two other females who, according the researchers, were “offering companionship and support.” After the birth, the mother as well as the so-called birth attendants all consumed the placenta.

Primate births may be diurnal verses nocturnal; in fact, primates give birth at times of day that offer the lowest predation risk. Among squirrel monkeys labor may being at dawn, and if the infant has not been birthed by daytime, labor will spontaneously stop and start again during the appropriate time, most likely during dusk.

Primates also maneuver into positions to widen pelvis, particularly among smaller-bodied primates with a very close caphalopelvic fit (e.g. macaca mullata). Primates also express pain when giving birth. Patas, Rhesus macaques, and bonobos have been observed having pained looks on faces and express said pain with vocalizations. Breeched births might occur among primates with a close cephalopelvic dimension, such as macaca mullata, rhesus macaques, spider monkeys.

So How Wide is the Parturition Gap?

The mechanism of birth appears to be more complex for humans, small-bodied primates, and lesser apes than compared to larger-bodied, greater apes. Humans opt to seek assistance during birth and while primates sometimes opt to give birth among group members, it is unclear whether or not primates actively seek birth attendants. Primates maneuver in positions optimal for birth while humans in medicalized cultures give birth in a less optimal, supine position; maybe humans should consider a primate model for birthing positions! Both human and nonhuman primates experience pain when giving birth, yet humans are unique in that they assign cultural meaning to their pain.

In sum, both face similar challenges when giving birth, yet the adaptive methods to overcome those challenges varies between species worldwide. It seems to be that the parturition gap between human and nonhuman primates is not a wide gap after all.

             

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