Biomedical Engineering Reference
In-Depth Information
ancestor lived.” Such calculations gave rise to the notion of an African
Eve: “the woman whose mitochondria were the last common ancestors
of all surviving mitochondria today” and who lived around 190,000
years ago.
13
A similar African Adam was found by developing techniques
to trace nucleotide mutations of the Y chromosome, and this African
Adam's age was dated at around 144,000 years ago. Thus modern genet-
ics, in addition to modern anthropology, demonstrates what seems to be
a significant human reality: “The continents were settled by Africans in
the expected order. Modern humans appear first in Africa, then in Asia,
and from this big continent they settled its three appendices: Oceania,
Europe, and America.”
14
Such migrations began eighty thousand to one
hundred thousand years ago. And as the populations grew and migra-
tion occurred, so began the process of adaptation to new environments
and climates that in turn led to the differences we currently observe
between and among modern humans. Such differences are environmen-
tal adaptations by groups, but they are not genetic, and can neither over-
ride the reality of our common origin nor provide any justification for
any claims to superiority, genetic or otherwise.
Individuality
Populations are essentially homogeneous with some variations—a func-
tion of the distance from the original ancestor. But even these differences
slow down as geographic distance increases. Scientifically, then, it is irre-
sponsible to use the term race to denote some sort of biological superi-
ority or the primacy of some genotype or some group. Such homogeneity,
however, is not the case in looking at individuals. The argument for this
comes from the various technologies involved in DNA fingerprinting that
identifies the probability of a DNA specimen coming from a particular
individual. “The chance of two [unrelated] individuals on average having
the same DNA profile is about one in a million billion,” according to
one researcher in the forensic application of this technology.
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And as
Cavalli-Sforza observes, “Regardless of the type of genetic markers used
(selected from a very wide range), the variation between two random
individuals within any one population is 85 percent as large as that
between two individuals randomly selected from the world's popula-
tion.”
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Additionally, through migration and increasing intermarriage,
we have a greater mixing of genes that will have two effects: first,
