Behavioral Adjustments Figure 14.1 Notice the lack of full spectrum color in this photo of a deep-water diver and the diver’s use of specialized equipment, such as a breathing apparatus to deliver gases for respiration, bodysuit to ensure thermal regulation, and flashlight to increase visibility in the low-light setting.
In general, the three main forms of adjustment are: behavioral, acclimatory, and developmental. As such, different individuals within a population may experience a wide range of possible adjustments in response to a similar stressor. Adjustments occur exclusively on the individual level. Although adjustments themselves are non-genetic in nature, the ability of an organism to experience or develop an adjustment is based in its phenotypic plasticity, which is linked to its evolutionarily guided genetic potential. The term “adjustment” refers to an organism’s non-genetic way of coping with the stressors of its environment. These mechanisms, which are referred to as adjustments (behavioral, acclimatory, and developmental) and adaptations, are explained in detail in the following sections. With respect to human phenotypic plasticity as well as evolutionary history, there are several primary mechanisms that have led to variations among individuals and between populations. Changes to the organism’s physiology, morphology, and/or behavior that are linked to its underlying phenotypic plasticity may result in changes that are merely temporary or those that are permanent. A special case of phenotypic plasticity, polyphenism, is broadly defined as the ability of a single genotype within the organism to produce multiple phenotypes when exposed to different environmental conditions or stressors. The range of changes in the physiology (function), morphology (form), and/or behavior of organisms in response to their environments and the potential stressors of those environments is regulated by its phenotypic plasticity. This cyclical fur development linked to seasonal weather changes is but one way that these organisms maintain their homeostasis. For example, some organisms, such as dogs, will develop a thicker coat of fur during cooler periods and they will shed this additional fur during warmer periods. Within limits, all organisms have evolved certain physiological mechanisms to respond to stressors in an effort to maintain homeostasis. These stimuli are referred to as stressors, exposure to which leads to a period in which there is a potential for the disruption of homeostasis. This constancy of internal functions is referred to as homeostasis however, homeostatic regulation may be challenged by a variety of both external and internal factors. STRESS AND HOMEOSTASISĪll organisms, including humans, must maintain a baseline of normal functions within their cells, tissues, and organs to survive. This chapter focuses on the complexities of modern human variation through the lens of human evolutionary history. The ways populations of humans met such challenges, coupled with their geographic separation throughout the majority of the last two centamillenia, have led to the many forms of adaptation in our species. Beyond genetically influenced changes in physiology as a result of evolution, humans have developed lifestyle strategies to cope with and even thrive in a wide range of habitats.
As early humans left Africa and spread across the globe, they faced numerous challenges related to their new environments. Genetic variability within and between modern populations of humans has been influenced by years of evolutionary forces, most notably natural selection and genetic drift. Within this framework, we now shift our focus toward examining the numerous challenges our species has faced throughout its evolutionary odyssey as well as how we have met those trials. In the previous chapters of this text, we explored the role of evolutionary forces in human evolution as well as the basics of genetic variation.
Compare and contrast the various genetic mutations present in Tibetan, Andean, and Ethiopian populations that allow them to survive at high altitudes.
Oxygen forensic 10.4 key skin#
In your explanation, include information as to why reduced pigmentation leading to lighter skin colors is advantageous for populations indigenous to northern latitudes.
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