- Cochran, Gregory and Henry Harpending.
The 10,000 Year Explosion.
New York: Basic Books, 2009.
ISBN 978-0-465-00221-4.
-
“Only an intellectual could believe something so stupid”
most definitely applies to the conventional wisdom among
anthropologists and social scientists that human evolution
somehow came to an end around 40,000 years ago with the emergence
of modern humans and that differences among human population groups
today are only “skin deep”: the basic physical, genetic,
and cognitive toolkit of humans around the globe is essentially
identical, with only historical contingency and cultural inheritance
responsible for different outcomes.
To anybody acquainted with evolutionary theory, this should have
been dismissed as ideologically motivated nonsensical propaganda
on the face of it. Evolution is driven by changes and new
challenges faced by a species as it moves into new niches
and environments, adapts to environmental change, migrates and
encounters new competition, and is afflicted by new diseases
which select for those with immunity. Modern humans, in their
expansion from Africa to almost every habitable part of the
globe, have endured changes and challenges which dwarf those
of almost any other metazoan species. It stands to reason, then,
that the pace of human evolution, far from coming to a halt, would
in fact accelerate dramatically, as natural selection
was driven by the coming and going of ice ages, the development
of agriculture and domestication of animals, spread of humans into
environments inhospitable to their ancestors, trade and conquest
resulting in the mixing of genes among populations, and numerous
other factors.
Fortunately, we're lucky to live in an age in which we need no
longer speculate upon such matters. The ability to sequence the
human genome and compare the lineage of genes in various populations
has created the field of genetic anthropology, which is in
the process of transforming what was once a “soft science”
into a thoroughly quantitative discipline where theories can be
readily falsified by evidence in the genome. This book has the
potential of creating a phase transition in anthropology: it is
a manifesto for the genomic revolution, and a few years from now
anthropologists who ignore the kind of evidence presented here will
be increasingly forgotten, publishing papers nobody reads because
they neglect the irrefutable evidence of human history we carry in
our genes.
The authors are very ambitious in their claims, and I'm sure that
some years from now they will be seen to have overreached in some
of them. But the central message will, I am confident, stand: human
evolution has dramatically accelerated since the emergence of modern
humans, and is being driven at an ever faster pace by the cultural
and environmental changes humans are incessantly confronting.
Further, human history cannot be understood without first acknowledging
that the human populations which were the actors in it were
fundamentally different. The conquest of the Americas
by Europeans may well not have happened had not Europeans carried
genes which protected them against the infectuous diseases they
also carried on their voyages of exploration and conquest. (By some
estimates, indigenous populations in the Americas fell to 10% of
their pre-contact levels, precipitating societal collapse.) Why
do about half of all humans on Earth speak languages of the
Indo-European group? Well, it may be because the obscure cattle
herders from the steppes who spoke the ur-language happened to
evolve a gene which made them lactose tolerant throughout adulthood,
and hence were able to raise cattle for dairy products, which is five
times as productive (measured by calories per unit area) as raising
cattle for meat. While Europeans' immunity to disease served them
well in their conquest of the Americas, their lack of immunity to
diseases endemic in sub-Saharan Africa (in particular,
falciparum malaria) rendered initial attempts colonise that region
disastrous.
The authors do not hesitate to speculate on possible genetic
influences on events in human history, but their conjectures are based
upon published genetic evidence, cited from primary sources in the
extensive end notes. A number of these discussions may lead to the
sound of skulls exploding among those wedded to the dominant academic
dogma. The authors suggest that some of the genes which allowed modern
humans emerging from Africa to prosper in northern climes were the
result of cross-breeding with Neanderthals; that just as domestication
of animals results in neoteny, domestication of humans in agricultural
and the consequent state societies has induced neotenous changes in
“domesticated humans” which result in populations with a
long history of living in agricultural societies adapting
better to modern civilisation than those without that selection in
their genetic heritage, and that the unique experience of selection
for success in intellectually demanding professions and lack of
interbreeding resulted in the emergence of the
Ashkenazi Jews
as a population whose mean intelligence
exceeds that of all other human populations (as well as a prevalence
of genetic diseases which appear linked to biochemical factors
related to brain function).
There's an odd kind of doublethink present among many champions of
evolutionary theory. While invoking evolution to explain even
those aspects of the history of life on Earth where doing so involves
what can only be called a “leap of faith”, they dismiss
the self-evident consequences of natural selection on populations
of their own species. Certainly, all humans constitute a single
species: we can interbreed, and that's the definition. But all dogs
and wolves can interbreed, yet nobody would say that there is
no difference between a Great Dane and a Dachshund. Largely isolated
human populations have been subjected to unique selective pressures
from their environment, diet, diseases, conflict, culture, and
competition, and it's nonsense to argue that these challenges did not
drive selection of adaptive alleles among the population.
This book is a welcome shot across the bow of the “we're all
the same” anthropological dogma, and provides a guide to the
discoveries to be made as comparative genetics lays a firm scientific
foundation for anthropology.
May 2009 