We
are storytelling creatures, the authors explain, before proceeding to tell
their own story about where we came from. The origins question is, of course,
one of surpassing breadth in our species. Evolve the ability to ask questions,
and that particular one emerges near the top of the list: Where did we come
from?
The
authors are eminently qualified to tell a story that is both authoritative and
engaging. Both are curators at the American Museum of Natural History in New
York (Tattersall now emeritus). Tattersall’s expertise lies in primate
anatomical evolution; DeSalle’s is in molecular evolution. They have written
many books separately, and have previously collaborated successfully on the
topics of beer, wine, and race.
What
does it even mean to be an “accidental” species, anyway? There are several
directions in which one could go. First,
one could argue that the nucleotide substitutions in the DNA that facilitated
bipedalism, canine tooth reduction, cranial expansion, and the like, were all
ultimately accidental miscopyings of the DNA in certain late Miocene apes.
Indeed the great bulk of DNA changes are in fact neither good nor bad, but
neutral, or close enough to neutral that they can be readily carried through
the generations within the gene pool. The fact that some accidental DNA changes
eventually proved valuable would be ignored here, for this would be a view of
human evolution through a lens of the caprice of mutation. Alternatively, one
could argue that, unlike many religious views, there is ultimately no reason or
telos for our existence; our species is just another accident of nature,
not special or central in the history of life, for they all come and go. This
was the thesis of Henry Gee’s recent engaging polemic The Accidental Species,[1] but suffers from the fact
that our undirected, decentralized, pedestrian development in the universe
can’t be proved without standing outside of that universe, which is manifestly
impossible, and consequently the point can only be vigorously asserted – even if
it may well be true. Yet a third possible aspect of our “accidental” existence
might be the stabilization of random variation in our species. Just as there are one-humped (Dromedary) and
two-humped (Bactrian) camels, and they both seem to work well as camels, maybe
the features that characterize our own species are simply physical variations
that work as well as their alternatives. An example might be the syndrome of
smallish face, roundish head, and linear body build that seems to have emerged
first in Africa about 200,000 years ago and now characterizes our entire
species. Indeed when methods have been applied to detect the effects of deterministic
natural selection on the evolution of the human form, they have generally
failed, suggesting that much of our body or head shape may indeed be
“accidental”.[2] A fourth understanding of being “accidental”
might be as the result of extraneous events: luckily surviving an asteroid
impact or volcanic eruption, and subsequently repopulating the area in one’s
own image. Yet a fifth might reside in the classical mathematics by which small
gene pools (like those of our ancestors) can deviate from mathematical
expectations over the generations, and large gene pools (like ours today) can sustain large amounts
of diversity – both of which come with unpredictable consequences.
The
story told in The Accidental Homo sapiens is by and large a normative
one, and the authors are on sure ground in their discussions of human
biological evolution. This is actually not a situation to be taken lightly, for
evolution is our particular origin myth, and everybody in science thinks they
own a piece of it – unlike, say, boron or electromagnetism. There are,
consequently, scientists who borrow and bend human evolution to construct
narratives of our origin and nature without a deep knowledge of, well, human
evolution. Exhibit A, this book’s
antagonists, are the evolutionary psychologists, who came to prominence in the
1990s with glib science bites about human nature. Tattersall and DeSalle argue
that the evolutionary psychologists see too much determinism, and not enough
accident, in the evolution of our species.
The
first two chapters provide a very accessible introduction to statistical
quantitative genetics, which is just as difficult to achieve successfully as it
sounds. The authors then introduce the
possibility of associating quantitative continuous variation in normal human
traits to DNA variations, and the limitations
of trying to do so. Indeed, given
the difficulties in establishing a classical Mendelian basis for a “hard”
character like height, the difficulties are compounded in trying to do it for a
“soft” character like extroversion or sexual inclination.
The
middle of the book recounts the broad features of our ancestry, from the
bipedal apes of five or six million years ago, through their descendants a
million years ago, who had learned to cut things and burn things, to our
(geologically-speaking) recent ancestors, talking and drawing. The evolutionary novelties are biological,
technological, and communicative. In the evolution of apes into humans, we can
record alterations in the throat and mouth (permitting us to speak), and to the
extent that it can be accessed comparatively, in the mind (giving us something
to say). We often refer to these properties as symbolic thought, referring to
the construction of meaningful imaginary connections between things, as in
pointing. In pointing, there is no physical connection between the fingertip
and the object, just a metaphorical extension of the fingertip in the mind of
the pointer and of anyone with a similarly built brain.
While
tools and art were certainly important products of the symbolic capacity, and
hugely important in the latterly success of our species, they figure
disproportionately in our narratives because they are preserved in the
archaeological record. Yet along with tools and art, humans imagined a new
social world into existence, which left no material traces yet certainly aided
our survival in the material world. This was kinship, and its effects were very
far-reaching, if often downplayed.
The
final turn of The Accidental Homo sapiens brings us back into the
present, trying to explain who we are and how we got here. Was there meaning
inherent in the transition from ape to human?
Where
the primary antagonists of Henry Gee’s similarly-titled book were those who
tried to read purpose or direction into the history of life (No! Our species
was accidental!), the targets here are principally modern scholars who
see our bodies and minds as finely-tuned machines, having been twiddled and
tweaked to precision over the ages by natural selection (No! Our species was accidental!).
Hardly anyone doubts today that natural selection has acted upon the human
species – the authors are not claiming that our ancestors’ brains grew by
accident, but rather by virtue of the persistent long-term survival and
proliferation of those bipedal apes that had bigger ones. Their claim is more specifically about how
universal and stringent natural selection has been. If natural selection is a
sieve, are its pores large or small in any particular case?
When
it comes to human behavior, the authors argue that the pores are large. That is
to say, once we attained the biological ability to think, act, and speak
symbolically, our species was capable of thriving with many different
alternatives. This was arguably the “big discovery” of 20th century
anthropology: that people all over the world are smart and can survive in
places that you can’t, so if you find yourself among them, you had better hope
they help you, because you’ll die if they don’t. While this may not sound like
much, it was different from the knowledge brought by the early English settlers
to America, with often tragic consequences for them.
The
modern view, then, is that natural selection worked stringently on the pre-human
brain up to a few hundred thousand years ago, when the adaptive value of the
collective intelligence of cultures began to overwhelm the adaptive value of
individual minds, and classical natural selection accordingly diminished. Nearly
all of what people do consequently has negligible relative survival or
reproductive value and is not the result of natural selection, but of
historical contingency, or accident. That is as well the view of Tattersall and
DeSalle, but not of their antagonists, the sociobiologists and evolutionary
psychologists. These latter scholars generally assume that natural selection
acts on individual human behaviors, and consequently they generate
biologically-based narratives for each one. By so promiscuously invoking
natural selection, which is a genetic process, these scholars imagine the genes
to be doing an awful lot of heavy lifting; but since they are mostly drawn from
ethology and psychology, not genetics, it generally doesn’t bother them. Tattersall and DeSalle are bothered, however,
and argue against analytically atomizing human behaviors, against ascribing
biological bases to the behaviors, and against invoking natural selection
wantonly as their cause. That obviously leaves the sociobiologists and
evolutionary psychologists in a limbo of bad evolutionary theory.
The
criticism is welcome, as the abuse of evolution has a long and embarrassing
history. The central problem that Tattersall and DeSalle highlight is the
difficulty in reconciling binary Mendelian alleles (wrinkled/round,
green/yellow, tall/short) to the quantitative and developmentally sensitive
human organism, much less to its context-specific behaviors.
This
problem has existed since the dawn of Mendelian genetics. In the early 20th
century, America’s leading geneticists generally adhered to the proposition
that people came in two Mendelian flavors, smart and “feebleminded”. Their
arguments helped pass legislation to restrict the immigration of Italians and
Jews into the US (1924) and to sterilize the poor involuntarily (1927), before
the Germans even got the idea. Today’s abusers of Mendel are only slightly less
crude, with genes “for” homosexuality, schizophrenia, aggression, or
religiosity regularly touted, although with remarkably short scientific
shelf-lives.
Tattersall
and DeSalle rather favor a model in which genes could not do that much work,
because they do not “code for traits” but set a range of possibilities, often
quite broad, that can be expressed in various ways, dependent upon various
factors. The pedagogical model we most often rely on imagines the phenotype
(i.e, detectable physiology) to be readily predictable from the genotype (i.e,
genetic status). And sometimes that is
true. If you have the alleles for cystic fibrosis, you will generally express
the disease. If you don’t, you generally
won’t. If you have the alleles for lactate dehydrogenase A, you will generally
express the enzyme. If you don’t, you generally won’t. But aside from
pathologies and biochemicals, one hardly ever finds binary patterns. Rather, we
find genes expressed in diverse ways (pleiotropy), genes affecting the
expression of other genes (epistasis), traits that may not appear in spite of
the genes (penetrance), and context-dependent gene expression (reaction norms).
This is an immensely valuable presentation of the way genetics actually
functions in human affairs, in contrast to the simplistic models underpinning
the evolutionary psychology literature.
Where
the authors come up just a bit shy, I think, is when they try to explain why
reductive, hereditarian ideas about behavior and intelligence persist in the
scholarly literature after all this time. They present a few possibilities :
“the human mind … seems naturally drawn to reductionist explanations” (p. 45);
“scientists may sometimes be uncomfortable with uncertainty, and … genetic and
genomic hypotheses promise clear-cut cause-and-effect explanations (pp.72-72);
and “when humans are told that something is very difficult or even impossible
to do, the immediately attempt it anyway.” ( p. 73).
There
is, however, something else at work, which scientists are generally loath to
confront, for it exposes an embarrassing side of the practice of science. The
sad fact is that arguments about genetic determinism take place upon a
biopolitical and moral ground as well as upon an empirical scientific one.[3] The same philanthropies
and demagogues that promote hereditarianism also promote scientific racism
(i.e., the recruitment of authority of science in support of the evil politics
of racism).[4] The hereditarian
psychologists Arthur Jensen and Thomas Bouchard, the racist psychologist
Philippe Rushton, and the hereditarian political scientist Charles Murray are
all linked through networks of right-wing interests. And a lot of money has
been spent to get wacko ideas into the scientific mainstream, with distressing
levels of success.[5]
Classically,
the argument looked like this: Blacks are inherently dumber than whites,
therefore they do not deserve equal rights.[6] The updated, subtler version goes: Low-IQ
people are inherently dumber than high-IQ people; IQ determines social and
political status; therefore social programs intended to ameliorate extreme
social stratification are doomed to failure, and federal funding should be
directed elsewhere.[7]
This
is not a scientific problem, but a problem for science, and one that scientists
are not trained to resolve – the problem of evil. The problem is social,
political, and moral, and requires the constant vigilance of the scientific
community to avoid sullying the good names of Darwin and Mendel.
After
challenging the reification of genes, the attribution of human behaviors to
them, and the blithe assumption by the evolutionary psychologists that acts are
adaptive and governed by natural selection, Tattersall and DeSalle’s narrative
winds down by engaging with our uniqueness as a species. If, as the authors tell us, “no creature in
the world today is more unlike its ancestor of two or three million years ago
than we are,” then does that fact come with scientific implications? They toy
with the idea of such a newly-arisen evolutionary gulf implying that our
species alone ought to be placed in a new Subkingdom Psychozoa, as the
biologists Julian Huxley[8] and Bernhard Rensch
suggested many years ago. But they quickly reject it, because modern scientific
sensibilities value phylogeny (how closely related we are to the apes) more
highly than divergence (how different from them we have become). I wish they
had pursued this point a bit further, because it is ultimately an arbitrary
decision, which is nevertheless imbued with scientific meaning in spite of
itself being largely “accidental”.
The Accidental Homo sapiens is a short,
straightforward book that tells a very scientifically validated story of who we
are and how we got here. There are
various classes of data and evidence to work with. But making up imaginary
genes as part of a narrative of human origins doesn’t do much credit to the
scientific endeavor. The authors
strongly discourage it, and so do I.
[1] Henry Gee, The Accidental
Species: Misunderstandings of Human Evolution (Chicago: University of
Chicago Press, 2014).
[2] Lauren Schroeder and Rebecca Rogers
Ackermann, "Evolutionary processes shaping diversity across the Homo
lineage." Journal of Human Evolution 111(2017):1-17.
[3] John P. Jackson and David J Depew, Darwinism,
Democracy, and Race: American Anthropology and Evolutionary Biology in the
Twentieth Century. (New York: Taylor & Francis, 2017).
[4] William H. Tucker, The Funding
of Scientific Racism: Wickliffe Draper and the Pioneer Fund. (Urbana, IL:
University of Illinois Press, 2002).
[5] Angela Saini, Superior: The
Return of Race Science (Boston, MA: Beacon Press, 2019).
[6] Carleton Putnam, Race and Reason (Washington,
D. C.: Public Affairs Press, 1961.)
[7] Richard Herrnstein and Charles Murray, The
Bell Curve (New York: Free Press, 1994).
