Introduction
Evolutionary Health
Co-Evolution of Disease & Living Conditions
Diabetes
Malaria
Health Effects
What is Risk?
Environmental Risk
Risk Assessment
Risk Abatement
Risk Perception
Risk Management
Uncertainty & Other Features of Risk Assessment
Precautionary Principle
Appendix 1: Contaminants
Appendix 2: Environmnet & Reproductive Health
Exercises
Internet Links
Other Resources
Health & Risk System PDF
Printer-Friendly Web Version

Evolutionary Health:
Human Evolution, Climate, Diet, and Migration

Exercise:

In what respects do the old large-scale dread diseases, like small pox, cholera, plague, and typhoid differ from large-scale diseases of today, like heart disease, diabetes, depression and AIDS?

 

Human health is the result of the 2 million year history of the hominid species. The hominid species is a family of the “superfamily” of apes and contains orangutans, African apes, and humans. The superfamily of apes is of the larger order called primates. The hominid family has two subfamilies: (1) ponginae, consisting of orangutans and gibbons, and (2) Homininae, consisting of the African apes (gorillas and chimpanzees) and humans. The relationship between the members of the hominid family is close. Enzymes and other proteins of man and chimpanzee are identical.

About five million years ago, the hominid species split off from the chimpanzees. Two million years ago, there were several vegetarian and meat-eating hominid species in Africa. For the last 30,000 or so years, the only remaining hominid species is the Homo sapiens, which originally emerged around 80,000 years ago in Africa and then slowly spread world wide. See http://www.becominghuman.org for more information about human evolution.

Figure 1: The major dispersal routes by the modern human species Homo sapiens during the past (approximately) 75,000 years. The sea level was 100-140 metres lower during the most recent (Wurm) glaciation, which extended from around 85,000 to 15,000 years ago. Dispersal dates are only approximate, and derive from studies of fossil humans and stone tools. The dates shown here are averaged from several sources. (Image and caption from Human Frontiers, Environments, and Disease: Past Patterns, Uncertain Futures, by Tony McMichael; Cambridge University Press, 2001.)

 

At the most fundamental level, we can think of health as proper biological functioning. An important aspect of health often not recognized in the technological paradigm is that good health or "normal" health is a product of evolutionary biology. The natural environment in which we evolved over millennia has provided for each of us a set of conditions requisite or at least most desirable for our well-being. These environmental factors have predisposed our physiology to function best under certain types of conditions, such as climate and food. Even our genetics which determine some of these predispositions and susceptibilities have been subject to natural selection over hundreds of thousands of years. For example, people in sunny and hot climates have developed darker skins because of an abundance of melanin in their skins, giving it a darker coloring. Melanin is a pigment that helps absorb sunlight without burning the skin, and particularly the ultraviolet from causing skin cancer. Thus the dark pigmentation of people living in equatorial regions has a positive effect. This pigmentation also plays a role in moderating the necessary absorption of ultraviolet by our skin. Ultraviolet radiation converts 7-dehydrocholestorol, a compound made by the liver and brought near the skin through the blood, into Vitamin D. Vitamin D is necessary for healthy bones as it helps the absorption of calcium produced in the intestines during digestion. So pigmentation, like many other features of nature, has a dual function.

So what happens when people move from equatorial regions to higher latitudes? Dark-skinned immigrant children living at high latitudes and in dark urban areas develop Vitamin D deficiency. Prehistoric bones recovered from Norway and Denmark show evidence of a large rate of rickets. Thus early populations show deviations from good health resulting from the migration. As time goes on, the people with less susceptibility to that disease survive and reproduce. Thus natural selection eventually restores the population to a smaller equilibrium rate of that defect or with only the non-susceptible surviving, with very little of the defect in the populations. Certain diseases—especially the auto-immune diseases—therefore show a difference in rates depending on latitudes, reflecting the fact that humans originally evolved in the equatorial region. Auto-immune diseases are those caused when the body reacts to suppress its own immune system. Examples are child-onset (Type 1) diabetes, rheumatoid arthritis, and multiple sclerosis.

 

 

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  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.