November 10, 2003
Does Race Exist?
If races are defined as genetically discrete groups, no. But researchers can use some genetic
information to group individuals into clusters with medical relevance
By Michael J. Bamshad and Steve E. Olson
Look around on the streets of any major city, and you will see a sampling of the outward variety of
humanity: skin tones ranging from milk-white to dark brown; hair textures running the gamut from
fine and stick-straight to thick and wiry. People often use physical characteristics such as these--
along with area of geographic origin and shared culture--to group themselves and others into
"races." But how valid is the concept of race from a biological standpoint? Do physical features
reliably say anything informative about a person's genetic makeup beyond indicating that the
individual has genes for blue eyes or curly hair?
The problem is hard in part because the implicit definition of what makes a person a member of a
particular race differs from region to region across the globe. Someone classified as "black" in the
U.S., for instance, might be considered "white" in Brazil and "colored" (a category distinguished
from both "black" and "white"😉 in South Africa.
Yet common definitions of race do sometimes work well to divide groups according to genetically
determined propensities for certain diseases. Sickle cell disease is usually found among people of
largely African or Mediterranean descent, for instance, whereas cystic fibrosis is far more common
among those of European ancestry. In addition, although the results have been controversial, a
handful of studies have suggested that African-Americans are more likely to respond poorly to some
drugs for cardiac disease than are members of other groups.
Over the past few years, scientists have collected data about the genetic constitution of
populations around the world in an effort to probe the link between ancestry and patterns of
disease. These data are now providing answers to several highly emotional and contentious questions:
Can genetic information be used to distinguish human groups having a common heritage and to assign
individuals to particular ones? Do such groups correspond well to predefined descriptions now widely
used to specify race? And, more practically, does dividing people by familiar racial definitions or
by genetic similarities say anything useful about how members of those groups experience disease or
respond to drug treatment?
In general, we would answer the first question yes, the second no, and offer a qualified yes to the
third. Our answers rest on several generalizations about race and genetics. Some groups do differ
genetically from others, but how groups are divided depends on which genes are examined;
simplistically put, you might fit into one group based on your skin-color genes but another based on
a different characteristic. Many studies have demonstrated that roughly 90 percent of human genetic
variation occurs within a population living on a given continent, whereas about 10 percent of the
variation distinguishes continental populations. In other words, individuals from different
populations are, on average, just slightly more different from one another than are individuals from
the same population. Human populations are very similar, but they often can be distinguished.
Classifying Humans As a first step to identifying links between social definitions of race and
genetic heritage, scientists need a way to divide groups reliably according to their ancestry. Over
the past 100,000 years or so, anatomically modern humans have migrated from Africa to other parts of
the world, and members of our species have increased dramatically in number. This spread has left a
distinct signature in our DNA.
To determine the degree of relatedness among groups, geneticists rely on tiny variations, or
polymorphisms, in the DNA--specifically in the sequence of base pairs, the building blocks of DNA.
Most of these polymorphisms do not occur within genes, the stretches of DNA that encode the
information for making proteins (the molecules that constitute much of our bodies and carry out the
chemical reactions of life). Accordingly, these common variations are neutral, in that they do not
directly affect a particular trait. Some polymorphisms do occur in genes, however; these can
contribute to individual variation in traits and to genetic diseases.
As scientists have sequenced the human genome (the full set of nuclear DNA), they have also
identified millions of polymorphisms. The distribution of these polymorphisms across populations
reflects the history of those populations and the effects of natural selection. To distinguish among
groups, the ideal genetic polymorphism would be one that is present in all the members of one group
and absent in the members of all other groups. But the major human groups have separated from one
another too recently and have mixed too much for such differences to exist.
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Kind Regards, Robert Karl Stonjek.