Human Variation in Adaption

In humans, the cold disturbs homeostasis, the equilibrium that the body maintains for normal functioning, by decreasing core body temperature. The human body can survive for a great deal under 98.6˚F, but after a point develops hypothermia and begins to break down normal functions, like the temperature regulation of the hypothalamus.

But in order to live in the varied climates that humans do, we have developed several different adaptations (i.e. short term, facultative, developmental, and cultural adaptations) that allow us to inhabit subnormal temperatures.

Short term adaptations occur to maintain the body's homeostasis on a short-term basis. The response is quick, and the return to the normal trait expression is equally as fast once the stress has been removed. For example, in the extreme cold, humans shiver to produce heat from the muscles, therefore limiting the amount that the body has to do to warm up the periphery of the body, and conserving the heat of the internal body temperature. Also, in the human body blood vessels constrict to preserve the core body heat in a similar way as shivering, so blood flow is reduced to the extremities.

Facultative adaptations are genetic traits not requiring a change in DNA, but rather an alteration of the expression of traits in response to environmental stress. This is different from short term adaptatio
ns because they take longer to return to the normal trait expression. In the same subnormal temperature example, the human body would respond in a facultative adaptation with an increase in metabolism, which is controlled through the hypothalamus. The increase in metabolism would produce extra body heat, therefore warming the core body temperature. However, this adaptation would take much longer than shivering to return to its normal levels.

Developmental adaptations are actual changes in the DNA of an entire population that has been exposed to a particular long-term stress. Evolutionary forces (i.e. natural selection) have produced a phenotypic change, and therefore these adaptations are those an individual is born with and will have throughout their entire life. If a person is part of a population, and their parents and prior ancestors have been as well, particular environmental stresses may cause that individual to be born with shorter limbs and an overall more compact body and higher body mass. The loss of surface area would conserve body heat better, therefore making this person's physical stature, something they were born with, an adaptation.

Related to the increase in the facultative adaptation of metabolism is actually the cultural adaptation of a change in diet. Consuming large quantities of high calorie fatty foods would help those who lived in consistently subnormal temperatures to develop a faster metabolism, warmer their core body temperature.

There are many benefits to studying adaptations across clines, but especially that as we learn about how the human body naturally responds to environmental stresses, we can use this information to advance cultural adaptations that can work alongside the body's natural processes. So for example, in addition to the cultural adaptation of a change in diet, there is also the development of insulation in clothing that works along with the body's natural chemistry to retain just the right amount of body heat to maintain homeostasis. Without studying adaptations across the clines, like the trait of shivering, or that of an increased metabolism, or a naturally compact build, certain technological advances in clothing would be rather pointless. If a clothing designer wanted to create clothes for people in these environments, they would need to know how those people store heat and energy, otherwise the clothes created might release too much heat, and therefore be rendered useless.

However another way that people try to understand adaptations is by applying race to the mix. One might say that because of race, an African male would not be able to live in the arctic regions because his arms and legs are so long, so he's not well suited for the environment. Many people attribute qualities such as long arms and legs to being black, when it's a completely varied number of circumstances that can make an individual tall and have long limbs. And that doesn't necessarily mean that he cannot survive in the subnormal temperatures, just that he will have to cope differently than a person of compact build.

The study of environmental influences on adaptations is a much better way to understand human variation because race won't give any indication of how a person might adapt to an environment. Just because a person is part of a certain culture doesn't mean their body won't react the same way as a person with an Alaskan Indian culture. Culture has nothing to do with how their bodies react and adapt to stress. The traits they inherited from their parents may give them a genetic advantage/disadvantage to living in a certain climate, but that is only noted through the study of environmental influences, of the study of developmental adaptations. To understand how to survive, we have to focus on what we can biologically bring to a situation and then enhance that trait with whatever cultural technologies we can apply to that biological base.