- Wade, Nicholas.
A Troublesome Inheritance.
New York: Penguin Press, 2014.
ISBN 978-1-59420-446-3.
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Geographically isolated populations of a species (unable to interbreed
with others of their kind) will be subject to natural selection
based upon their environment. If that environment differs from that
of other members of the species, the isolated population will begin
to diverge genetically, as genetic endowments which favour survival
and more offspring are selected for. If the isolated population is
sufficiently small, the mechanism of
genetic drift
may cause a specific genetic variant to become almost universal
or absent in that population. If this process is repeated for a
sufficiently long time, isolated populations may diverge to such
a degree they can no longer interbreed, and therefore become
distinct species.
None of this is controversial when discussing other species, but
in some circles to suggest that these mechanisms apply to humans
is the deepest heresy. This well-researched book examines the
evidence, much from molecular biology which has become available
only in recent years, for the diversification of the human species
into distinct populations, or “races” if you like,
after its emergence from its birthplace in Africa. In this
book the author argues that human evolution has been
“recent, copious, and regional” and presents the
genetic evidence to support this view.
A few basic facts should be noted at the outset. All humans are
members of a single species, and all can interbreed. Humans, as
a species, have an extremely low genetic diversity compared to
most other animal species: this suggests that our ancestors went
through a genetic “bottleneck” where the population
was reduced to a very small number, causing the variation observed
in other species to be lost through genetic drift. You might
expect different human populations to carry different genes, but
this is not the case—all humans have essentially the same
set of genes. Variation among humans is mostly a result of
individuals carrying different
alleles
(variants) of a gene. For example, eye colour in humans is entirely
inherited: a baby's eye colour is determined completely by
the alleles of various genes inherited from the mother and father.
You might think that variation among human populations is then
a question of their carrying different alleles of genes, but that
too is an oversimplification. Human genetic variation is, in most
cases, a matter of the frequency of alleles among the
population.
This means that almost any generalisation about the characteristics of
individual members of human populations with different evolutionary
histories is ungrounded in fact. The variation among individuals
within populations is generally much greater than that of populations
as a whole. Discrimination based upon an individual's genetic heritage
is not just abhorrent morally but scientifically unjustified.
Based upon these now well-established facts, some have argued that
“race does not exist” or is a “social construct”.
While this view may be motivated by a well-intentioned desire to
eliminate discrimination, it is increasingly at variance with
genetic evidence documenting the history of human populations.
Around 200,000 years ago, modern humans emerged in Africa. They spent
more than three quarters of their history in that continent, spreading
to different niches within it and developing a genetic diversity which
today is greater than that of all humans in the rest of the world.
Around 50,000 years before the present, by the genetic evidence,
a small band of hunter-gatherers left Africa for the lands to the
north. Then, some 30,000 years ago the descendants of these bands
who migrated to the east and west largely ceased to interbreed and
separated into what we now call the Caucasian and East Asian populations.
These have remained the main three groups within the human species.
Subsequent migrations and isolations have created other populations such
as Australian and American aborigines, but their differentiation
from the three main races is less distinct. Subsequent migrations,
conquest, and intermarriage have blurred the distinctions between
these groups, but the fact is that almost any child, shown a picture
of a person of European, African, or East Asian ancestry can almost always
effortlessly and correctly identify their area of origin. University
professors, not so much: it takes an intellectual to deny the
evidence of one's own eyes.
As these largely separated populations adapted to their new homes,
selection operated upon their genomes. In the ancestral human
population children lost the ability to digest lactose, the sugar
in milk, after being weaned from their mothers' milk. But in
populations which domesticated cattle and developed dairy
farming, parents who passed on an allele which
would allow their children to drink cow's milk their entire life would have more surviving
offspring and, in a remarkably short time on the evolutionary
scale, lifetime lactose tolerance became the norm in these areas.
Among populations which never raised cattle or used them only
for meat, lifetime lactose tolerance remains rare today.
Humans in Africa originally lived close to the equator and had
dark skin to protect them from the ultraviolet radiation of the
Sun. As human bands occupied northern latitudes in Europe
and Asia, dark skin would prevent them from being able to synthesise
sufficient Vitamin D from the wan, oblique sunlight of northern
winters. These populations were under selection pressure for alleles
of genes which gave them lighter skin, but interestingly Europeans and
East Asians developed completely different genetic means to lighten
their skin. The selection pressure was the same, but evolution
blundered into two distinct pathways to meet the need.
Can genetic heritage affect behaviour? There's evidence it can.
Humans carry a gene called
MAO-A,
which breaks down neurotransmitters that affect the transmission of
signals within the brain. Experiments in animals have provided
evidence that under-production of MAO-A increases aggression and
humans with lower levels of MAO-A are found to be more likely to
commit violent crime. MAO-A production is regulated by a short
sequence of DNA adjacent to the gene: humans may have anywhere from
two to five copies of the promoter; the more you have, the more the
MAO-A, and hence the mellower you're likely to be. Well, actually,
people with three to five copies are indistinguishable, but those with
only two (2R) show higher rates of delinquency. Among men of African
ancestry, 5.5% carry the 2R variant, while 0.1% of Caucasian males and
0.00067% of East Asian men do. Make of this what you will.
The author argues that just as the introduction of dairy farming
tilted the evolutionary landscape in favour of those bearing the
allele which allowed them to digest milk into adulthood, the
transition of tribal societies to cities, states, and empires
in Asia and Europe exerted a selection pressure upon the population
which favoured behavioural traits suited to living in such
societies. While a tribal society might benefit from producing
a substantial population of aggressive warriors, an empire has
little need of them: its armies are composed of soldiers,
courageous to be sure, who follow orders rather than charging
independently into battle. In such a society, the genetic traits which
are advantageous in a hunter-gatherer or tribal society will be
selected out, as those carrying them will, if not expelled or
put to death for misbehaviour, be unable to raise as large a
family in these settled societies.
Perhaps, what has been happening over the last five millennia
or so is a domestication of the human species.
Precisely as humans have bred animals to live with them
in close proximity, human societies have selected for
humans who are adapted to prosper within them. Those who
conform to the social hierarchy, work hard, come up with
new ideas but don't disrupt the social structure will have
more children and, over time, whatever genetic predispositions
there may be for these characteristics (which we don't know
today) will become increasingly common in the population.
It is intriguing that as humans settled into fixed communities,
their skeletons became less robust. This same process of
gracilisation is seen in domesticated animals compared to
their wild congeners. Certainly there have been as many
human generations since the emergence of these complex societies
as have sufficed to produce major adaptation in animal
species under selective breeding.
Far more speculative and controversial is whether this selection
process has been influenced by the nature of the cultures and societies
which create the selection pressure. East Asian societies
tend to be hierarchical, obedient to authority, and organised
on a large scale. European societies, by contrast, are
fractious, fissiparous, and prone to bottom-up insurgencies.
Is this in part the result of genetic predispositions which have
been selected for over millennia in societies which work that
way?
It is assumed by many right-thinking people that all that is needed
to bring liberty and prosperity to those regions of the world
which haven't yet benefited from them is to create the proper
institutions, educate the people, and bootstrap the infrastructure,
then stand back and watch them take off. Well, maybe—but the
history of colonialism, the
mission civilisatrice, and
various democracy projects and attempts at nation building
over the last two centuries may suggest it isn't that
simple. The population of the colonial, conquering, or
development-aid-giving power has the benefit of millennia of
domestication and adaptation to living in a settled society
with division of labour. Its adaptations for tribalism have
been largely bred out. Not so in many cases for the people they're there to
“help”. Withdraw the colonial administration or
occupation troops and before long tribalism will re-assert
itself because that's the society for which the people are
adapted.
Suggesting things like this is anathema in academia or political
discourse. But look at the plain evidence of post-colonial
Africa and more recent attempts of nation-building, and couple
that with the emerging genetic evidence of variation in human
populations and connections to behaviour and you may find yourself
thinking forbidden thoughts. This book is an excellent starting
point to explore these difficult issues, with numerous citations
of recent scientific publications.
December 2014 