According to Caroline Ross (1998: 54), Head of the Department of Life Sciences at Roehampton University (UK), questions pertaining to life history strategies such why “a large animal takes longer to mature than does a small animal” and why “small animals that breed rapidly and develop early, have many young per litter, and have short lives [as compared to] large animals that breed slowly and develop late, have few young per litter, and have long lives,” have emerged and researched in the field of Evolutionary Anthropology since the 1960s. Since then, evolutionary and biological anthropologists alike have vied to understand how different animals grow, reproduce, maintain energy inflow and outflow, and how they subsequently stand adaptive to their particular niches as a result of their species’ life strategy. Particular focus has been placed on understanding the life history strategy of humans, which, as Karen L. Kramer, Associate Professor of Human Evolutionary Biology at Harvard University, and Peter Ellison, Cowles Professor of Anthropology and Human Evolutionary Biology at Harvard University, deviates from our primate relatives such as chimps, bonobos and apes, “with respect to other developmental, reproductive, and parenting characteristics” (2010: 136). What is the human life history strategy and how has it resulted in Homo Sapiens forming a more resilient fit to our terrestrial, heterotrophic, extractive, and intensely social niche? In addition, how has it co-evolved with the brain and shaped the brain to become more efficient, rendering us humans to successfully function, survive, and thrive on a day to day basis in tandem with our niche? Allow me through this expository to firstly embellish upon and explain the human life strategy of prolonged early life periods, such as gestation, infancy and juvenility, and the slow growth and development within them (even more slower growth than does occur in primates and other terrestrial animals). I will further investigate how this strategy results in humans acquiring various adaptive features in resiliency and fit to their niche such as a more developed and efficient immune system and brain, longer lifespan, effective reproduction capability, and more post-reproductive success and efficiency. Secondly, I intend to emphasize how this life history strategy has particularly made the brain more adaptive, efficient, and allowed for its co-evolution.
As Langdon depicts in Figure 21.2 (Langdon, 2005: 275), compared to non-human primates such as Lemurs, Macaques, Gibbons, and Chimpanzees, Homo Sapiens have a longer gestation, infancy and juvenile period time span, which means that there is more time for growth and development in the human body during these prime, formative years. When babies are in the mother’s womb during gestation, they are being provided nutritive energy and resources through the mother’s placenta; they don’t have to forage for food yet and all the energy that they acquire can be utilized in the development of the body, and particularly the brain and immune system. According to Ellison, as he asserts in his book titled On Fertile Ground: A Natural History of Human Reproduction, this longer gestation period is beneficial for humans since it notably helps in the development of the brain, which is “not only expensive to maintain, but also expensive to grow” (Ellison, 2001: 289). Commenting upon brain development and the amount of energy it requires, Ellison further contends that human brains “grows dramatically in utero” and that ‘the burden of this expense must be born by the mother during pregnancy [in the womb]” (Ellison, 2001: 289). At the onset of birth, the infancy period starts, which is also another prolonged period of dependency and development for human babies. During this period, human babies have “continued dependency on the mother through nourishment for milk” (Langdon, 2005: 276). Thus, since babies don’t have to devote any energy upon foraging or extraction processes even yet and the parents are there to support and protect the baby, the energy can once again solely be directed towards the development of the immune system, brain, and other anatomical features in the body. Commenting upon the development that undergoes during infancy as a result of the energy coming from mother’s milk and being utilized solely for development, Langdon (2005: 276) propounds, “As the infant grows, it is able to develop muscular and locomotor coordination in the real world and to explore environmental and social challenges without having to face them entirely on its own.” Once weaning commences and the juvenile period begins, even though the child becomes a bit independent, he or she is still dependent on parents for energy and resources and most of his/her energy and nutritive resources yet still come from parents and “adults in the community called alloparents, or ‘other parents’ “ (Langdon, 2005: 277). Thus, having longer gestation, infancy and juvenility periods with slower growth within each, as opposed to other primate relatives who spend a shorter amount of time in these periods, refers to the human life history strategy which allows humans to form a resilient fit to their niche by allowing them to allocate incoming energy during the formative years, mainly to personal anatomical growth and development.
Now that we know that the human life strategy involves prolonged periods of slow and gradual development during the early life stages and allows for energy allocation to development, let’s discuss further how this strategical pattern has helped humans form a more resilient fit to their niche as well as influenced the co-evolution of the brain to form a fit to the niche. Since humans spend more time in these early stages and can allot more energy to developing anatomical features, our immune system gets well developed and thus enhances our survival in later life. As Kramer and Ellison (2010:142) point out, compared to other primates, humans have a much better of chance of survival after their first year. Humans become more resistive to inflammation and diseases and this directly impacts and correlates with our longer lifespan, which ranges around 60 to 70 to maybe even 80 years. In contrast, our non-human primate relatives spend much less time during these formative life periods and since they cannot allot most of their incoming energy to their immune system development–they are not fully dependent on their parents to forage and provide them food and energy resources–their immune system isn’t as developed and resistant to diseases and inflammation as ours, and thus they have relatively much lower life spans. Slower and more prolonged growth during the early life stages also results in effective reproduction, since we can delay the onset of becoming sexually mature adults until we become relatively developed. This is evident in the varying age of females at menarche; some reach it as early as the age of eleven whereas some reach it around the age of fourteen (Stutz 2015). As Langdon (2005: 277) also asserts, “The advantages of putting off adulthood are continued growth and storage of nutrients, to increase both future reproductive potential and survival.” Thus, humans grow slowly and over a prolonged period of time to become well developed adults, capable of effectively producing offspring, which we can then efficiently sustain and the raising of whom won’t cause a compromise in our own development. Since our life history strategy renders us with better immune systems, which result in longevity, humans also have much effective post reproductive success, as evident in Figure 21.2 (Langdon, 2005: 275). Hence, once we pass our reproductive prime, we can utilize our incoming energy—which is no longer needed for personal development—to forage and gather resources for young offspring as well as invest in taking care of them during their early life stages of prolonged and slow periods of growth. Thus, we can see how our life history strategy has allowed us to form a more resistive and resilient fit to our TOES niche by paving the development of a better developed immune system as well as longevity, efficient reproduction and effective post-reproductive success.
Now let’s move on to talk about how the life history strategy has specifically shaped and resulted in the co-evolution of a larger brain that helps us thrive and stay fit in tandem with our niche. Spending more time in these early life stages also helps us to allot more energy and invest in particularly a bigger neocortex, which is most beneficial in helping us navigate and thrive in the TOES niche. As Langdon (2005:279) contends, “A relatively larger brain is accompanied by slower development and maturation.” Bigger brains help us in foraging food, being extractive and also enhance the social aspect of our niche, which in turn allows us to bond, sustain relations, and cooperate with others in tasks such as hunting and foraging as well as taking care of each other’s needs. Since we can cooperate and forage for high nutrient based and calorie plenty food sources using our bigger brains, which we developed as a result of prolonged and slower development characteristic early life stages, we can also acquire more energy and thus grow bigger body sizes. In turn, bigger body sizes result in us growing more internal body cells, that help in the conservation of energy and increase metabolic efficiency, as opposed to outer body cells, which lose energy in the form of heat. Bigger brains also help us make complex decisions in our TOES niche, for example by helping us decipher and contemplate upon the advantages and disadvantages of different options and making rational decisions in our everyday lives. Thus, we can see how the human life history strategy of longer early life periods accompanied with slower growth has resulted in the co-evolution of the bigger neocortex based brain that helps us humans not only stay resilient and fit to our niche but also helps us thrive in it.
All in all, we can see how the human life history strategy involves prolonged early life periods such as gestation, infancy, and juvenility that are accompanied with slower development and growth. This strategic pattern then helps us humans form a much resilient fit to our niche by facilitating a better immune system, efficient reproduction and effective post-reproductive success, and in particular allows for the co-evolution of a bigger neocortex based brain that in turn also supplements our survival in our day to day life in tandem with the terrestrial, heterotrophic, omnivorous, and highly social niche.
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