Introduction to Paleoanthropology/Modern Humans/Population Variation

One of the notable characteristics of the human species today is its great variability. Human diversity has long fascinated people, but unfortunately it also has
led to discrimination. In this chapter we will attempt to address the following questions:
Variation and evolution.
Human genetic variation generally is distributed in such a continuous range, with varying clusters of frequency.
The significance we give our variations, the way we perceive them (in fact, whether or not we perceive them at all) is determined by our culture.
Many behavioral traits are learned or acquired by living in a society; other characteristics, such as blue eyes, are passed on physically by heredity. Environment affects both.
The physical characteristics of both populations and individuals are a product of the interaction between genes and environments.
For most characteristics, there are within the gene pool of Homo sapiens
variant forms of genes, known as alleles.
This kind of variability, found in many animal species, signifies a rich potential for new combinations of characteristics in future generations. A species faced with changing environmental conditions has within its gene pool the possibility of producing individuals with traits appropriate to its altered life. Many may not achieve reproductive success, but those
whose physical characteristics enable them to do well in the new environment will usually reproduce, so that their genes will become more common in subsequent generations. Thus, humankind has been able to occupy a variety of environments.
A major expansion into new environments was under way by the time "Homo erectus" appeared on the scene. Populations of this species were living in Africa, Southeast Asia, Europe and China. The differentiation of animal life is the result of selective pressures that, through the Pleistocene, differed from one region to another. Coupled with differing selective pressures were geographical features that restricted or prevented gene flow between populations of different faunal regions.
Genetic variants will be expressed in different frequencies in these geographically dispersed populations.
In blood type, H. sapiens shows four distinct groups (A, B, O or AB):
The Meaning of Race.
Early anthropologists tried to explore the nature of human species by systematically classifying H. sapiens into subspecies or races, based on geographic location and physical features such as skin color, body size, head shape and hair texture. Such classifications were continually challenged by the presence of individuals who did not fit the categories.
The fact is, generalized references to human types such as "Asiatic" or "Mongoloid", "European" or "Caucasoid", and "African" or "Negroid" were at best mere statistical abstractions about populations in which certain physical features appeared in higher frequencies than in other populations.
These categories turned out to be neither definitive nor particularly helpful. The visible traits were found to occur not in abrupt shifts from population to population, but in a continuum that changed gradually. Also one trait might change gradually over a north-south gradient, while another might show a similar change from east to west.
Race as a biological concept.
To understand why the racial approach to human variation has been so unproductive, we must first understand the race concept in strictly biological terms.
In biology, a race is defined as a population of a species that differs in the frequency of different variants of some gene or genes from other populations of the same species. Three important things to note about this definition:
The concept of human races.
As a device for understanding physical variation in humans, the biological race concept has serious drawbacks:
There has been a lot of debate not just about how many human races there may be, but about what "race" is and is not. Often forgotten is the fact that a race, even if it can be defined biologically, is the result of the operation of evolutionary process. Because it is these processes rather than racial categories themselves in which we are really interested, most anthropologists have abandoned the race concept as being of no particular utility. Instead, they prefer to study the distribution and significance of specific, genetically based characteristics, or else the characteristics of small breeding populations that are, after all, the smallest units in which evolutionary change occurs.
Physical variables.
Not only have attempts to classify people into races proven counterproductive, it has also become apparent that the amount of genetic variation in humans is relatively low, compared to that of other primate species.
Nonetheless, human biological variation is a fact of life, and physical anthropologists have learned a great deal about it. Much of it is related to climatic adaptation. A correlation has been noted between body build and climate:
Certain body builds are better suited to particular living conditions than others.
Anthropologists have also studied such body features as nose, eye shape, hair textures and skin color in relation to climate.
Continuing human biological evolution.
In the course of their evolution, humans in all parts of the world came to rely on cultural rather than biological adaptation for their survival. Nevertheless, as they spread beyond their tropical homeland into other parts of the world, they did develop considerable physical variation from one population to another.
The forces responsible for this include:
Although much of this physical variation can still be seen in human populations today, the increasing effectiveness of cultural adaptation has often reduced its importance. Cultural practices today are affecting the human organism in important, often surprising, ways.
The probability of alterations in human biological makeup induced by culture raises a number of important questions. By trying to eliminate genetic variants, are we weakening the gene pool by allowing people with hereditary diseases and defects to reproduce? Are we reducing chances for genetic variation by trying to control population size? We are not sure of the answers to these questions.