Deck 10: Human Biological Diversity in Context

Question 1

There are no biological races in humans today, but could there have been in the past? What conditions would have facilitated subspecies distinctions in humans in the past? Think about the debates over the number of species in the genus Homo. Could these also be seen as debates about subspecies? What about the potential overlap of modern Homo sapiens and Homo erectus or other archaic forms (such as Neanderthals) in Eurasia? Does this overlap reflect the presence of races?

Answer 1

The concept of race is a biological one; it is misunderstood in society and is often associated with an individual's ethnic, cultural or linguistic characteristics. There are two distinct concepts of race:
• The scientific concept of race is defined as a population, or a group of populations, within a species that has measurable, defining biological characteristics in relation to other populations in the species. This concept results in a subspecies, or race, within a species that is taking a different evolutionary path and is therefore becoming increasingly differentiated from the species at the genetic level.
• The socially constructed concept of race is a set of cultural or ethnic factors linked with observed morphological traits, in an effort to create a "biologized" and artificial category.
In understanding the scientific concept of race, one can infer there were most likely races of different humans in the past, those that ventured into a different evolutionary path from its original species. The evolution of cranial size and the enlargement of the brain, along with the development of the Olduwan tool, are conditions that can facilitate the distinction of subspecies. For example, in Spain, researchers speculate that at a dig site in Gran Dolina, the hominin fossils that were discovered next to Olduwan-type tools may have been an ancestor that gave rise to H. heidelbergensis , and itself evolved from early H. erectus. Is can be possible that the relation of this hominin fossil with H. erectus is more in-line with a subspecies type, having taken on a different evolutionary path away from H. erectus , instead of evolving from H. erectus. Similarly, H. heidelbergensis could have been a separate race, or subspecies, from this hominin fossil. Without additional fossil evidence for support, the contentious debate on this hypothesis is most likely.
Debates on the number of species from the genus Homo can also be perceived as debates about subspecies. In one main perspective, all members of the genus Homo are of one species, H. erectus. Another argument is that the genus Homo included at least three or four species. It is also argued that all fossils of the genus Homo are members of the same species, H. sapiens. From these three perspectives, it can easily be debated that the various species of genus Homo , including H. heidelbergensis, H. ergaster and H. florensiensis , could be subspecies of H. erectus , as they contain morphological distinctions that can very well categorize them as a subspecies.
One can infer that the overlap of H. sapiens and H. erectus or other archaic forms can reflect the scientific concept of race, in that fossilized evidence show that each species is set apart from another (for example, H. sapiens and H. erectus having differing morphologies). With each species having defining biological characteristics that show differentiation at the genetic level, H. sapiens and H. erectus can very well be subspecies of one another. One can also conclude that the overlap of the species reflect the presence of races, with both species existing simultaneously as a result of developing sub-speciation.

Question 2

How can there be more genetic variation in African populations if there are more people outside of Africa? How do the fossil record and the debate over the Recent African Origin model versus the Multiple Dispersal model (described in chapter 9) help resolve this quandary?

Answer 2

Based upon research of the human genome, especially from the Human Genome Project of 1998, researchers discovered that there were little genetic variations between populations. Further research and understanding concluded that despite the wide dispersal of our species across the planet, the vast majority of human genetic variation occurs between individuals within each human population, rather than between the populations themselves.
When applying statistical measure to assess genetic variation, Fst (the fraction of variation that is found between samples), an average between 83% and 97% of human genetic variation is found within populations, and between 3% and 17% is found between populations.
Applying this fact to the continent of Africa, there is nearly twice as much genetic divergence among African populations than non-African populations. When comparing the genetic variation in African populations to all the genetic variation in populations outside of Africa, researchers can conclude that all outside-Africa variation is found within Africa as well.
Both the Recent African Origin (RAO) and Multiple Dispersion (MD) models support the fact that there is more genetic variation in African populations than outside of Africa.
The abundance of genetic variation in African populations supports the MD model, which proposes multiple movements by the members of the genus Homo in and out of Africa, and that it is the African populations that contribute to modern gene pools. The pattern of genetic variation indicates that there is more DNA sequence variation within Africa than outside of Africa, indicating that modern humans have been in Africa longer than anywhere else on the planet. This fact supports the RAO model of the origin of modern humans, which a single movement occurred out of Africa between 150,000 to 200,000 years ago.

Question 3

How could modern, human-induced changes in the environment (such as the hole in the ozone layer) be affecting human variation? How do modern medical technology and the reduction in infant mortality rates worldwide affect human variation? Would you predict more or less biological variation in our species over the next few centuries? Why?

Answer 3

Human-induced changes and behaviors that impact the environment can have an effect on natural selection and ultimately, on human genetic variation. Consider the pressures of the environment on an organism and how natural selection limits its genetic variation by removing unnecessary traits. When this idea is applied to human variation, selection can influence the range of possible variants, as traits that do not benefit the overall fitness will be removed over time. As such, when selection pressures are strong, there is less genetic variation. Conversely, when selection pressures are weak, there is an increase in genetic variation.
With this knowledge of the relationship between selection pressure and genetic variation, any human-induced change that increases the selection pressure on the human species, such as creating a hole in the ozone layer, will most likely limit human genetic variation. Other human-induced changes, such as modern medical technology and increasing the infant mortality rates worldwide, will make selection pressures weaker and therefore, increase human variation.
In the next few centuries, one can infer that the biological variation of the human species will only increase. The reason for this resides in the fact that enhancements in nutrition, the future potential in the development of technology, communication, medicine and the ability of the human species to alter its environments and climate, can only contribute to weaken the selection pressures on the human species. As selection pressures weaken on the human species due to these advancements, there will be an increase in human genetic variation.

Question 4

Is there something about our biology and our primate heritage that predisposes us to use easily perceived traits in order to classify other humans? What role do popular misunderstandings about biology and genetics play in modern, everyday conceptualizations of human differences and "race"? What could one do to dispel these misunderstandings?

Question 5

Will the ways in which race is used as a biological classifier in the United States change as more people gain accurate information about the subject? Why or why not? Has your perspective on race changed in your own lifetime? Can socially constructed race ever be truly detached from notions of biological distinction?