Life+History+Theory

= Life History Theory = toc

Definition
Life history theory defines the stages of gestation, infancy, childhood, adolescence, and adulthood and seeks to explain the differences in the timing of development, fertility, and death of living organisms. By studying the variations in life events of these organisms, life history theory helps us understand how biological patterns evolved and why specific behaviors surrounding activities such as feeding, nurturing, and aging exist. Factors that are studied include mortality, diet, growth, and lifestyle choices. “The life history of an organism can be thought of as a complete description of that organism.” The study of life history theories uncovers the reasons behind specific behaviors that seem to go against the biological drive to further propagate an organisms genes, such as individuals willingly putting themselves in danger for the sake of thrill and excitement. Life history theory seeks to explain these factors by evolutionary explanation and define a schedule for biological events. Each species has different life history traits that govern life events from conception to mortality. By outlining the specific adaptations that come with each developmental stage, quantitative data can be gathered and compared with the different life history stages of other cultures.

History and Application in Anthropology
Life history theory is not as developed as other evolutionary theories, but it is making progress. It is useful in anthropology because it compares the life histories of organisms and illustrates how human life history evolved from patterns seen in life histories of apes. Life history theory also explains how tradeoffs work and manages to successfully track biological tradeoffs over time. By illustrating how certain traits developed at the expense of other traits we can better understand what is more beneficial for us. The function of tradeoffs is central to life history theory and is used to explain evolutionary adaptation and short term development. In comparison across humans populations, these tradeoffs shed light on how humans are able to adapt differently within varying environments and how much of an influence external factors have on the growth and development of the human body.

All anthropological studies will at some point investigate the habits of other primates in comparison to ours, and it is in such studies that life history theory can be used to make sense of any disparities. For humans, there is an ongoing battle to increase longevity and avoid any hazardous situations that may cause mortality even though our lifespan is longer than any other primate; the early hunter-gatherer lifespan was almost four times as long as the slightly smaller wild chimpanzee. Life history theory does not have to be limited to the comparison of humans and chimpanzees but may also be used to explain variations between different human cultures.

Having a method such as life history theory that seeks to explain cultural differences will make improvements in how different populations are treated in terms of health and nutrition. Anthropologists can better understand what a population needs to strive if they understand how it is these differences across cultures came to exist and how this translates into our development. In the practical application of life history theory, there is also a growing effort to use the theory to explain the development of the human immune system and study the variations in different human populations. From an anthropological perspective, this would be helpful to understand how different cultures have established their immune systems and how the body's defenses adapt to the environment.

Life History Theory and Health
The ongoing attempts by physicians and public health officials to improve patient health and increase longevity and reduce factors that cause mortality are influences that influence a human’s life history. Because different cultures are exposed to varying ailments and conditions, no single life history will be exactly the same across populations. Each life history will be influenced towards a more or less successful reproductive lifespan and it is the goal of medical anthropologists to seek ways in which longevity and health can be achieved in the specific way an individual will benefit.

Examples
A prime component of life history theory is understanding how trade-offs work. For example, although humans develop slower than other mammals, the long growth period known as “childhood” enables us to grow more complex brains. While chimpanzees reach maturity early and reproduce for the greater part of their lifespan, humans grow relatively slow and most of their life is spent in a post-reproductive state yet will live to raise many more offspring due to their longer lifespan.

An example central to different human populations is one that measures the growth and fertility of females across cultures. Females that were raised in developed and well-nourished populations grew larger and reached sexual maturity quicker than females in poor nutritional surroundings yet both populations had no changes in the age of menopause. Life history theory, which seeks to uncover why these disparities exist, could be employed to explain such differences.

Case Study
Barry Bogin is a physcial anthropologist who uses life history theory to explain disparities between humans and chimpanzees and uses a personal example, his grandmother, to illustrate the reproductive difference of the two species. Ethel, a Ukranian woman born in 1908, is able to produce more offspring in her lifetime than Fifi, a chimpanzee born in 1958. Ethel’s human life history allows her to wean offspring quicker and shortens the intervals of time between birth, while Fifi must nurse her offspring until they are able to forge for themselves. By comparing these different life histories, the biological and social differences that give Ethel more reproductive success are able to be quantified to better understand what makes humans different than other primates.

Another case study that illustrates how to life history can be used to gather data is seen in the remarkable plasticity of Maya children growing up in the United States compared to that of Maya children living in Guatemala. Using reference data from the National Health and Nutrition Examination Surveys, the height of these two groups of children differed dramatically and the Maya children living in the United States were measured to be taller than those in Guatemala. The average height difference was record to be 10.24 centimeters, which is one of the largest differences in mean stature between migrants and those remaining in their native country. Such plasticity is a benefit of the childhood stage of development and this data can be used to uncover what it was about living in the United States that attributed to the differences in height.

Behavior and Biocultural Mechanisms
The tradeoffs that are fundamental to Life History Theory can be thought of as strategies that organisms take to adapt to their environment in order to maximize fitness. Such tradeoffs are also apparent in different stress environments, such as how early experiences shape development and behaviors. For example, in nutrition crises, baby cats show more play-hunting behaviors, which ultimately hone skills that help adult survival. This behavior is the result of environmental pressure and cues from the queen.

//Behavioral Responses to Stress and Resource-Poor Conditions// In some cases, high levels of competition and few resources restrict successful procreation. In situations where reproductive failure is imminent, an organism will often trade short-term profits for long-term fitness. One example is the adoption of high-risk behavior with the aim of achieving reproductive success. In a sense, an organism has everything to gain and nothing to lose by rolling the dice, because in doing so there is at least a slim chance of success. Human behavioral development responds in the same way to these environmental stressors. Three examples given by James Chisholm (1999) include Absent Father Syndrome, Young Male Syndrome, and Young Female Syndrome. All of these include youths with increased sexual activity, violence, aggression, delinquency, and sexual activity in stressful environments. Additionally, demographics that display the most altered development and high-risk behavior match those demographics with a resource handicap (e.g.: young men).

//Emotional and Social Responses to Stress and Resource-Poor Conditions// Emotions are believed to have evolved as chemical indicators of advantageous or detrimental behaviors. Good feelings (e.g.: love, pride, excitement) reinforced and created incentives for behaviors that increased fitness. Bad feelings (e.g.: fear, anger) warned against dangers. Because mammals are often extremely community-based, emotional systems are reactive to social interactions, with feelings of affection indicating an advantageous social circumstance. Of course, social bonds have the potential—but not the guarantee—to offer better fitness via increased resources and reproduction, decreased morbidity and mortality, and reciprocal altruism.

Attachment models develop in early life, and are one way that organisms react to environmental pressures. During fearful experiences, strong, secure attachment models condition a reduction in response intensity, thereby decreasing cortisol levels and associated psychosomatic outcomes.Although healthy models improve offspring fitness, they are not free. Secure attachment models can form in resource-poor areas; however the circumstances require more protection and investment from parents. Weak, insecure attachment models detract from offspring fitness, and form when parents do not make the necessary investment to develop healthy models in their children. They also may occur in cases when the family is the source of the stress. The result of negative models is often a deactivation (or apparent deactivation) of emotional systems, and an inhibition to acknowledge needs or dangers. Here again, long-term benefits are traded-off for short-term payoffs. Often, a feedback loop begins to develop. High-stress circumstances foster high-risk behavior such as sexual activities, drug use, violence and aggression; which, in turn, forms unhealthy attachments that bring on stress. Additionally, closed internal models render the individual less receptive to novel information and change. Thus, a repetitive pattern of behavior is continued.

Resources
[|An article about the theory of aging]