One way to think of the job of
anthropologists studying human evolution is to divide it into two basic components:
the first is to arrive at a comprehensive and precise catalogue of the features
and behaviors that make humans different from the species most closely related
to us, and the second is to arrange all these differences in order of their
emergence in our ancestral line. Knowing what came first is essential—though
not sufficient—to the task of distinguishing between causes and effects. For
instance, humans have brains that are significantly larger than those of any
other primate, and we use these brains to fashion tools that are far more
elaborate than the stones, sticks, leaves, and sponges used by other apes.
Humans are also the only living ape that routinely walks upright on two legs. Since most
of us probably give pride of place in the hierarchy of our species’
idiosyncrasies to our intelligence, we can sympathize with early Darwinian thinkers
who felt sure brain expansion must have been what started our ancestors down
their unique trajectory, making possible the development of increasingly
complex tools, which in turn made having our hands liberated from locomotion
duty ever more advantageous.
This
hypothetical sequence, however, was dashed rather dramatically with the
discovery in 1974 of Lucy, the 3.2
million-year-old skeleton of an Australopithecus
Afarensis,
in Ethiopia. Lucy resembles a chimpanzee in most respects, including cranial
capacity, except that her bones have all the hallmarks of a creature with a
bipedal gait. Anthropologists like to joke that Lucy proved butts were more
important to our evolution than brains. But, though intelligence wasn’t the
first of our distinctive traits to evolve, most scientists still believe it was
the deciding factor behind our current dominance. At least for now, humans go
into the jungle and build zoos and research facilities to study apes, not the
other way around. Other apes certainly can’t compete with humans in terms of sheer
numbers. Still, intelligence is a catch-all term. We must ask what exactly it
is that our bigger brains can do better than those of our phylogenetic cousins.
 |
Lucy |
A
couple decades ago, that key capacity was thought to be language, which makes
symbolic thought possible. Or is it symbolic thought that makes language possible?
Either way, though a handful of ape prodigies have amassed some high vocabulary
scores in labs where they’ve been taught to use pictographs or sign language,
human three-year-olds accomplish similar feats as a routine part of their
development. As primatologist and sociobiologist (one of the few who
unabashedly uses that term for her field) Sarah Blaffer Hrdy explains in her
2009 book Mothers and Others: The Evolutionary Origins of
Mutual Understanding, human language relies on abilities and interests
aside from a mere reporting on the state of the outside world, beyond simply
matching objects or actions with symbolic labels. Honeybees signal the location
of food with their dances, vervet monkeys have distinct signals for attacks by
flying versus ground-approaching predators, and the list goes on. Where humans
excel when it comes to language is not just in the realm of versatility, but
also in our desire to bond through these communicative efforts. Hrdy writes,
The open-ended
qualities of language go beyond signaling. The impetus for language has to do
with wanting to “tell” someone else what is on our minds and learn what is on
theirs. The desire to psychologically connect with others had to evolve before language. (38)
The
question Hrdy attempts to answer in Mothers
and Others—the difference between humans and other apes she wants to place
within a theoretical sequence of evolutionary developments—is how we evolved to
be so docile, tolerant, and nice as to be able to cram ourselves by the dozens
into tight spaces like airplanes without conflict. “I cannot help wondering,”
she recalls having thought in a plane preparing for flight,
what would
happen if my fellow human passengers suddenly morphed into another species of
ape. What if I were traveling with a planeload of chimpanzees? Any of us would
be lucky to disembark with all ten fingers and toes still attached, with the
baby still breathing and unmaimed. Bloody earlobes and other appendages would
litter the aisles. Compressing so many highly impulsive strangers into a tight
space would be a recipe for mayhem. (3)
Over the past
decade, the human capacity for cooperation, and even for altruism, has been at
the center of evolutionary theorizing. Some clever experiments in the field of
economic game theory have revealed several scenarios in which humans can be
counted on to act against their own interest. What survival and reproductive advantages
could possibly accrue to creatures given to acting for the benefit of others?
When
it comes to economic exchanges, of course, human thinking isn’t tied to the
here-and-now the way the thinking of other animals tends to be. To explain why
humans might, say, forgo a small payment in exchange for the opportunity to punish
a trading partner for withholding a larger, fairer payment, many behavioral
scientists point out that humans seldom think in terms of one-off deals. Any
human living in a society of other humans needs to protect his or her
reputation for not being someone who abides cheating. Experimental settings are
well and good, but throughout human evolutionary history individuals could
never have been sure they wouldn’t encounter exchange partners a second or
third time in the future. It so happens that one of the dominant theories to
explain ape intelligence relies on the need for individuals within somewhat
stable societies to track who owes whom favors, who is subordinate to whom, and
who can successfully deceive whom. This “Machiavellian intelligence” hypothesis
explains the cleverness of humans and other apes as the outcome of countless
generations vying for status and reproductive opportunities in intensely
competitive social groups.
One
of the difficulties in trying to account for the evolution of intelligence is
that its advantages seem like such a no-brainer. Isn’t it always better to be
smarter? But, as Hrdy points out, the Machiavellian intelligence hypothesis
runs into a serious problem. Social competition may have been an important
factor in making primates brainer than other mammals, but it can’t explain why
humans are brainer than other apes. She writes,
We still have to
explain why humans are so much better than chimpanzees at conceptualizing what
others are thinking, why we are born innately eager to interpret their motives,
feelings, and intentions as well as care about their affective states and
moods—in short, why humans are so well equipped for mutual understanding.
Chimpanzees, after all, are at least as socially competitive as humans are.
(46)
 |
Meltzoff's famous experiment |
To bolster this
point, Hrdy cites research showing that infant chimps have some dazzling social
abilities once thought to belong solely to humans. In 1977, developmental
psychologist Andrew Meltzoff published his finding that newborn humans mirror
the facial expressions of adults they engage with. It was thought that this
tendency in humans relied on some neurological structures unique to our lineage
which provided the raw material for the evolution of our incomparable social
intelligence. But then in 1996 primatologist Masako Myowa replicated Meltzoff’s
findings with infant chimps. This and other research suggests that other apes have
probably had much the same raw material for natural selection to act on. Yet, whereas
the imitative and empathic skills flourish in maturing humans, they seem to atrophy
in apes. Hrdy explains,
 |
Myowa's replication with a chimp |
Even though
other primates are turning out to be far better at reading intentions than
primatologists initially realized, early flickerings of empathic interest—what
might even be termed tentative quests for intersubjective engagement—fade away
instead of developing and intensifying as they do in human children. (58)
So the question
of what happened in human evolution to make us so different remains.
*****
Sarah Blaffer Hrdy exemplifies a
rare, possibly unique, blend of scientific rigor and humanistic sensitivity—the
vision of a great scientist and the fine observation of a novelist (or the vision of a
great novelist and fine observation of a scientist). Reading her
1999 book, Mother Nature: A History of Mothers, Infants, and Natural Selection, was a watershed experience for me.
In going beyond the realm of the literate into that of the literary while
hewing closely to strict epistemic principle, she may surpass the
accomplishments of even such great figures as Richard Dawkins and Stephen Jay Gould. In fact, since
Mother Nature was one of the books
through which I was introduced to sociobiology—more commonly known today as
evolutionary psychology—I was a bit baffled at first by much of the criticism
leveled against the field by Gould and others who claimed it was founded on
overly simplistic premises and often produced theories that were politically
reactionary.
The theme to which Hrdy continually
returns is the too-frequently overlooked role of women and their struggles in
those hypothetical evolutionary sequences anthropologists string together. For
inspiration in her battle against facile biological theories whose sole purpose
is to provide a cheap rationale for the political status quo, she turned, not to
a scientist, but a novelist. The man single-most responsible for the misapplication
of Darwin’s theory of natural selection to the justification of human societal
hierarchies was the philosopher Herbert Spencer, in whose eyes women were no
more than what Hrdy characterizes as “Breeding Machines.” Spencer and his
fellow evolutionists in the Victorian age, she explains in Mother Nature,
 |
Herbert Spencer, coiner of the phrase "Survival of the fittest" |
took for granted
that being female forestalled women from evolving “the power of abstract
reasoning and that most abstract of emotions, the sentiment of justice.”
Predestined to be mothers, women were born to be passive and noncompetitive,
intuitive rather than logical. Misinterpretations of the evidence regarding
women’s intelligence were cleared up early in the twentieth century. More basic
difficulties having to do with this overly narrow definition of female nature
were incorporated into Darwinism proper and linger to the present day. (17)
Many women over
the generations have been unable to envision a remedy for this bias in biology.
Hrdy describes the reaction of a literary giant whose lead many have followed.
For Virginia
Woolf, the biases were unforgivable. She rejected science outright. “Science,
it would seem, in not sexless; she is a man, a father, and infected too,” Woolf
warned back in 1938. Her diagnosis was accepted and passed on from woman to
woman. It is still taught today in university courses. Such charges reinforce the
alienation many women, especially feminists, feel toward evolutionary theory
and fields like sociobiology. (xvii)
But another literary luminary much
closer to the advent of evolutionary thinking had a more constructive, and
combative, response to short-sighted male biologists. And it is to her that
Hrdy looks for inspiration. “I fall in Eliot’s camp,” she writes, “aware of the
many sources of bias, but nevertheless impressed by the strength of science as
a way of knowing” (xviii). She explains that George Eliot,
whose real name
was Mary Ann Evans, recognized that her own experiences, frustrations, and
desires did not fit within the narrow stereotypes scientists then prescribed
for her sex. “I need not crush myself… within a mould of theory called Nature!”
she wrote. Eliot’s primary interest was always human nature as it could be
revealed through rational study. Thus she was already reading an advance copy
of On the Origin of Species on
November 24, 1859, the day Darwin’s book was published. For her, “Science has
no sex… the mere knowing and reasoning faculties, if they act correctly, must
go through the same process and arrive at the same result.” (xvii)
 |
George Eliot (Mary Ann Evans) |
Eliot’s
distaste for Spencer’s idea that women’s bodies were designed to divert
resources away from the brain to the womb was as personal as it was
intellectual. She had in fact met and quickly fallen in love with Spencer in
1851. She went on to send him a proposal which he rejected on eugenic grounds:
“…as far as posterity is concerned,” Hrdy quotes, “a cultivated intelligence
based upon a bad physique is of little worth, seeing that its descendants will
die out in a generation or two.” Eliot’s retort came in the form of a literary
caricature—though Spencer already seems a bit like his own caricature. Hrdy
writes,
In her first
major novel, Adam Bede (read by
Darwin as he relaxed after the exertions of preparing Origin for publication), Eliot put Spencer’s views concerning the
diversion of somatic energy into reproduction in the mouth of a pedantic and
blatantly misogynist old schoolmaster, Mr. Bartle: “That’s the way with these
women—they’ve got no head-pieces to nourish, and so their food all runs either
to fat or brats.” (17)
A mother of three and an Emeritus
Professor of Anthropology at the University of California, Davis, Hrdy is
eloquent on the need for intelligence—and lots of familial and societal
support—if one is to balance duties and ambitions like her own. Her first
contribution to ethology came when she realized that the infanticide among
hanuman langurs, which she’d gone to Mount Abu in Rajasthan, India to study at age 26 for her doctoral
thesis, had nothing to do with overpopulation, as many suspected. Instead, the
pattern she observed was that whenever an outside male deposed a group’s main
breeder he immediately began exterminating all of the prior male’s offspring to
induce the females to ovulate and give birth again—this time to the
new male’s offspring. This was the selfish gene theory in action. But the
females Hrdy was studying had an interesting response to this strategy.
In the early
1970s, it was still widely assumed by Darwinians that females were sexually
passive and “coy.” Female langurs were anything but. When bands of roving males
approached the troop, females would solicit them or actually leave their troop
to go in search of them. On occasion, a female mated with invaders even though
she was already pregnant and not ovulating (something else nonhuman primates were
not supposed to do). Hence, I speculated that mothers were mating with outside
males who might take over her troop one day. By casting wide the web of
possible paternity, mothers could increase the prospects of future survival of
offspring, since males almost never attack infants carried by females that, in
the biblical sense of the word, they have “known.” Males use past relations
with the mother as a cue to attack or tolerate her infant. (35)
Hrdy would go on
to discover this was just one of myriad strategies primate females use to get
their genes into future generations. The days of seeing females as passive
vehicles while the males duke it out for evolutionary supremacy were now
numbered.
I’ll never forget the Young-Goodman-Brown experience of reading the twelfth chapter of Mother Nature, titled “Unnatural Mothers,” and
covering an impressive variety of evidence sources that simply devastates any notion of women as nurturing
automatons, evolved for the sole purpose of serving as loving mothers. The
verdict researchers arrive at whenever they take an honest look into the
practices of women with newborns is that care is contingent. To give just one
example, Hrdy cites the history of one of the earliest foundling homes in the
world, the “Hospital of the Innocents” in Florence.
Founded in 1419,
with assistance from the silk guilds, the Ospedale delgi Innocenti was
completed in 1445. Ninety foundlings were left there the first year. By 1539 (a
famine year), 961 babies were left. Eventually five thousand infants a year
poured in from all corners of Tuscany. (299)
What this means
is that a troubling number of new mothers were realizing they couldn't care for their
infants. Unfortunately, newborns without direct parental care seldom fare well.
“Of 15,000 babies left at the Innocenti between 1755 and 1773,” Hrdy reports, “two
thirds died before reaching their first birthday” (299). And there were fifteen
other foundling homes in the Grand Duchy of Tuscany at the time.
The chapter amounts to a worldwide tour of
infant abandonment, exposure, or killing. (I remember having a nightmare after
reading it about being off-balance and unable to set a foot down
without stepping on a dead baby.) Researchers studying sudden infant death
syndrome in London set up hidden cameras to monitor mothers interacting with
babies but ended up videotaping them trying to smother them. Cases like this
have made it necessary for psychiatrists to warn doctors studying the
phenomenon “that some undeterminable
portion of SIDS cases might be infanticides” (292). Why do so many mothers
abandon or kill their babies? Turning to the ethnographic data, Hrdy explains,
Unusually
detailed information was available for some dozen societies. At a gross level,
the answer was obvious. Mothers kill their own infants where other forms of
birth control are unavailable. Mothers were unwilling to commit themselves and
had no way to delegate care of the unwanted infant to others—kin, strangers, or
institutions. History and ecological constraints interact in complex ways to
produce different solutions to unwanted births. (296)
Many scholars
see the contingent nature of maternal care as evidence that motherhood is
nothing but a social construct. Consistent with the blank-slate view of human
nature, this theory holds that every aspect of child-rearing, whether
pertaining to the roles of mothers or fathers, is determined solely by culture and
therefore must be learned. Others, who simply can’t let go of the idea of women
as virtuous vessels, suggest that these women, as numerous as they are, must all
be deranged.
 |
Daly and Wilson |
Hrdy demolishes both the purely
social constructivist view and the suggestion of pathology. And her account of
the factors that lead women to infanticide goes to the heart of her arguments
about the centrality of female intelligence in the history of human evolution.
Citing the pioneering work of evolutionary psychologists Martin Daly and MargoWilson, Hrdy writes,
How a mother,
particularly a very young mother, treats one infant turns out to be a poor
predictor of how she might treat another one born when she is older, or faced
with improved circumstances. Even with culture held constant, observing modern
Western women all inculcated with more or less the same post-Enlightenment
values, maternal age turned out to be a better predictor of how effective a
mother would be than specific personality traits or attitudes. Older women
describe motherhood as more meaningful, are more likely to sacrifice themselves
on behalf of a needy child, and mourn lost pregnancies more than do younger
women. (314)
The takeaway is
that a woman, to reproduce successfully, must assess her circumstances,
including the level of support she can count on from kin, dads, and society.
If she lacks the resources or the support necessary to raise the child, she may
have to make a hard decision. But making that decision in the present
unfavorable circumstances in no way precludes her from making the most of future
opportunities to give birth to other children and raise them to reproductive
age.
Hrdy goes on to describe an
experimental intervention that took place in a hospital located across
the street from a foundling home in 17th century France. The Hospice des Enfants Assistes
cared for indigent women and assisted them during childbirth. It was the
only place where poor women could legally abandon their babies. What the French
reformers did was tell a subset of the new mothers that they had to stay with
their newborns for eight days after birth.
Under this “experimental”
regimen, the proportion of destitute mothers who subsequently abandoned their
babies dropped from 24 to 10 percent. Neither cultural concepts about babies
nor their economic circumstances had changed. What changed was the degree to
which they had become attached to their breast-feeding infants. It was as
though their decision to abandon their babies and their attachment to their
babies operated as two different systems. (315)
Following the
originator of attachment
theory, John Bowlby,
who set out to integrate psychiatry and developmental psychology into an
evolutionary framework, Hrdy points out that the emotions underlying the bond
between mothers and infants (and fathers and infants too) are as universal as
they are consequential. Indeed, the mothers who are forced to abandon
their infants have to be savvy enough to realize they have to do so before these
emotions are engaged or they will be unable to go through with the deed.
Female strategy plays a crucial role
in reproductive outcomes in several domains beyond the choice of whether or not
to care for infants. Women must form bonds with other women for support,
procure the protection of men (usually from other men), and lay the groundwork
for their children’s own future reproductive success. And that’s just what
women have to do before choosing a
mate—a task that involves striking a balance between good genes and a high
level of devotion—getting pregnant, and bringing the baby to term. The demographic
transition
that occurs when an agrarian society becomes increasingly industrialized is
characterized at first by huge population increases as infant mortality drops
but then levels off as women gain more
control
over their life trajectories. Here again, the choices women tend to make are at
odds with Victorian (and modern evangelical) conceptions of their natural
proclivities. Hrdy writes,
Since, formerly,
status and well-being tended to be correlated with reproductive success, it is
not surprising that mothers, especially those in higher social ranks, put the
basics first. When confronted with a choice between striving for status and
striving for children, mothers gave priority to status and “cultural success”
ahead of a desire for many children. (366)
And then of
course come all the important tasks and decisions associated with actually
raising any children the women eventually do give birth to. One of the basic
skill sets women have to master to be successful mothers is making and
maintaining friendships; they must be socially savvy because more than with any
other ape the support of helpers, what Hrdy calls allomothers, will determine
the fate of their offspring.
*****
Mother
Nature is a massive work—541pages before the endnotes—exploring motherhood
through the lens of sociobiology and attachment theory. Mothers and Others is leaner, coming in at just under 300 pages,
because its focus is narrower. Hrdy feels that in attempting to account for
humans’ prosocial impulses over the past decade, the role of women and
motherhood has once again been scanted. She points to the prevalence of
theories focusing on competition between groups, with the edge going to those
made up of the most cooperative and cohesive members. Such theories once again
give the leading role to males and their conflicts, leaving half the species
out of the story—unless that other half’s only role is to tend to the children
and forage for food while the “band of brothers” is out heroically securing
borders.
Hrdy doesn’t weigh in directly on
the growing controversy over whether group selection has operated as a
significant force in human evolution. The problem she sees with intertribal
warfare as an explanation for human generosity and empathy is that the timing
isn’t right. What Hrdy is after are the selection pressures that led to the
evolution of what she calls “emotionally modern humans,” the “people preadapted
to get along with one another even when crowded together on an airplane” (66).
And she argues that humans must have been emotionally
modern before they could have further evolved to be cognitively modern. “Brains require care more than caring requires
brains” (176). Her point is that bonds of mutual interest and concern came
before language and the capacity for runaway inventiveness. Humans, Hrdy
maintains, would have had to begin forming these bonds long before the effects
of warfare were felt.
Apart from
periodic increases in unusually rich locales, most Pleistocene humans lived at
low population densities. The emergence of human mind reading and gift-giving
almost certainly preceded the geographic spread of a species whose numbers did
not begin to really expand until the past 70,000 years. With increasing
population density (made possible, I would argue, because they were already
good at cooperating), growing pressure on resources, and social stratification,
there is little doubt that groups with greater internal cohesion would prevail
over less cooperative groups. But what was the initial payoff? How could hypersocial apes evolve in the first
place? (29)
In other words,
what was it that took inborn capacities like mirroring an adult’s facial
expressions, present in both human and chimp infants, and through generations
of natural selection developed them into the intersubjective tendencies
displayed by humans today?
Like so many other anthropologists
before her, Hrdy begins her attempt to answer this question by pointing to a
trait present in humans but absent in our fellow apes. “Under natural
conditions,” she writes, “an orangutan, chimpanzee, or gorilla baby nurses for
four to seven years and at the outset is inseparable from his mother, remaining
in intimate front-to-front contact 100 percent of the day and night” (68). But humans
allow others to participate in the care of their babies almost immediately
after giving birth to them. Who besides Sarah Blaffer Hrdy would have noticed
this difference, or given it more than a passing thought? (Actually, there are
quite a few candidates among anthropologists—Kristen Hawkes for instance.) Ape
mothers remain in constant contact with their infants, whereas human mothers
often hand over their babies to other women to hold as soon as they emerge from the
womb. The difference goes far beyond physical contact. Humans are what Hrdy
calls “cooperative breeders,” meaning a child will in effect have several
parents aside from the primary one. Help from alloparents opens the way for an
increasingly lengthy development, which is important because the more complex
the trait—and human social intelligence is about as complex as they come—the
longer it takes to develop in maturing individuals. Hrdy writes,
 |
Marmoset |
One widely
accepted tenet of life history theory is that, across
species, those with bigger babies relative to the mother’s body size will also
tend to exhibit longer intervals between births because the more babies cost
the mother to produce, the longer she will need to recoup before reproducing
again. Yet humans—like marmosets—provide a paradoxical exception to this rule.
Humans, who of all the apes produce the largest, slowest-maturing, and most
costly babies, also breed the fastest. (101)
Those marmosets turn out to be central to
Hrdy’s argument because, along with their cousins in the family Callitrichidae, the tamarins, they make up
almost the totality of the primate species whom she classifies as “full-fledged cooperative
breeders”
(92). This and other similarities between humans and marmosets and tamarins
have long been overlooked because anthropologists have understandably been
focused on the great apes, as well as other common research subjects like
baboons and macaques.
Callitrichidae, it so happens,
engage in some uncannily human-like behaviors. Plenty of primate babies wail
and shriek when they’re in distress, but infants who are frequently not in
direct contact with their mothers would have to find a way to engage with them,
as well as other potential caregivers, even when they aren’t in any trouble.
“The repetitive, rhythmical vocalizations known as babbling,” Hrdy points out,
“provided a particularly elaborate way to accomplish this” (122). But humans
aren’t the only primates that babble “if by babble we mean repetitive strings
of adultlike vocalizations uttered without vocal referents”; marmosets and
tamarins do it too. Some of the other human-like patterns aren’t as cute
though. Hrdy writes,
Shared care and
provisioning clearly enhances maternal reproductive success, but there is also
a dark side to such dependence. Not only are dominant females (especially
pregnant ones) highly infanticidal, eliminating babies produced by competing
breeders, but tamarin mothers short on help may abandon their own young,
bailing out at birth by failing to pick up neonates when they fall to the ground
or forcing clinging newborns off their bodies, sometimes even chewing on their
hands or feet. (99)
It seems that
the more cooperative infant care tends to be for a given species the more
conditional it is—the more likely it will be refused when the necessary support
of others can’t be counted on.
 |
Kristen Hawkes |
Hrdy’s cooperative breeding
hypothesis is an outgrowth of George Williams and Kristen Hawkes’s so-called
“Grandmother Hypothesis.” For Hawkes,
the important difference between humans and apes is that human females go on
living for decades after menopause, whereas very few female apes—or any other
mammals for that matter—live past their reproductive years. Hawkes hypothesized
that the help of grandmothers made it possible for ever longer periods of
dependent development for children, which in turn made it possible for the
incomparable social intelligence of humans to evolve. Until recently, though,
this theory had been unconvincing to
anthropologists because a renowned compendium of
data compiled by George Peter Murdock in his Ethnographic Atlas revealed that there was a strong trend toward
patrilocal residence patterns in all the societies that had been studied. Since
grandmothers are thought to be much more likely to help care for their daughters’
children than their sons’—owing to paternity uncertainty—the fact that most
humans raise their children far from maternal grandmothers made any
evolutionary role for them unlikely.
But
then in 2004 anthropologist Helen Alvarez reexamined Murdock’s analysis of
residence patterns and concluded that pronouncements about widespread
patrilocality were based on a great deal of guesswork. After eliminating
societies for which too little evidence existed to determine the nature of
their residence practices, Alvarez calculated that the majority of the remaining
societies were bilocal, which means couples move back and forth between the
mother’s and the father’s groups. Citing “The Alvarez Corrective” and other
evidence, Hrdy concludes,
Instead of some
highly conserved tendency, the cross-cultural prevalence of patrilocal
residence patterns looks less like an evolved human universal than a more
recent adaptation to post-Pleistocene conditions, as hunters moved into
northern climes where women could no longer gather wild plants year-round or as
groups settled into circumscribed areas. (246)
But Hrdy extends
the cast of alloparents to include a mother’s preadult daughters, as well as
fathers and their extended families, although the male contribution is highly
variable across cultures (and variable too of course among individual
men).
With the observation that human
infants rely on multiple caregivers throughout development, Hrdy suggests the
mystery of why selection favored the retention and elaboration of mind reading
skills in humans but not in other apes can be solved by considering the
life-and-death stakes for human babies trying to understand the intentions of
mothers and others. She writes,
Babies passed
around in this way would need to exercise a different skill set in order to
monitor their mothers’ whereabouts. As part of the normal activity of
maintaining contact both with their mothers and with sympathetic alloparents,
they would find themselves looking for faces, staring at them, and trying to
read what they reveal. (121)
Mothers, of
course, would also have to be able to read the intentions of others whom they might
consider handing their babies over to. So the selection pressure occurs on both
sides of the generational divide. And now that she’s proposed her candidate for
the single most pivotal transition in human evolution Hrdy’s next task is to
place it in a sequence of other important evolutionary developments.
Without a doubt,
highly complex coevolutionary
processes were involved in the evolution of extended lifespans, prolonged
childhoods, and bigger brains. What I want to stress here, however, is that
cooperative breeding was the pre-existing
condition that permitted the evolution of these traits in the hominin line.
Creatures may not need big brains to evolve cooperative breeding, but hominins
needed shared care and provisioning to evolve big brains. Cooperative breeding
had to come first. (277)
*****
Flipping
through Mother Nature, a book I first
read over ten years ago, I can feel some of the excitement I must have experienced
as a young student of behavioral science, having graduated from the
pseudoscience of Freud and Jung to the more disciplined—and in its way far more
compelling—efforts of John Bowlby, on a path, I was sure, to becoming a
novelist, and now setting off into this newly emerging field with the help of a
great scientist who saw the value of incorporating literature and art into her
arguments, not merely as incidental illustrations retrofitted to recently
proposed principles, but as sources of data in their own right, and even as
inspiration potentially lighting the way to future discovery. To perceive, to
comprehend, we must first imagine. And stretching the mind to dimensions never
before imagined is what art is all about.
Yet
there is an inescapable drawback to massive books like Mother Nature—for writers and readers alike—which is that any
effort to grasp and convey such a massive array of findings and theories comes
with the risk of casual distortion since the minutiae mastered by the experts in
any subdiscipline will almost inevitably be heeded insufficiently in the attempt to
conscript what appear to be basic points in the service of a broader
perspective. Even more discouraging is the assurance that any intricate
tapestry woven of myriad empirical threads will inevitably be unraveled by
ongoing research. Your tapestry is really a snapshot taken from a distance of a
field in flux, and no sooner does the shutter close than the beast continues
along the path of its stubbornly unpredictable evolution.
 |
Kim Hill |
When
Mothers and Others was published just
four years ago in 2009, for instance, reasoning based on the theory of kin
selection led most anthropologists to assume, as Hrdy states, that “forager
communities are composed of flexible assemblages of close and more distant
blood relations and kin by marriage” (132). This assumption seems to have been central to
the thinking that led to the principal theory she lays out in the book, as she
explains that “in foraging contexts the majority of children alloparents
provision are likely to be cousins, nephews, and nieces rather than unrelated
children” (158). But as theories evolve old assumptions come under new
scrutiny, and in an article published in the journal Science in March of 2011 anthropologist Kim Hill and his
colleagues report
that after analyzing the residence and relationship patterns of 32 modern foraging
societies their conclusion is that “most individuals in residential groups are
genetically unrelated” (1286). In science, two years can make a big difference.
This same study does, however, bolster a different pillar of Hrdy’s argument by
demonstrating that men relocate to their wives’ groups as often as women
relocate to their husbands’, lending further support to Alvarez’s corrective of
Murdock’s data.
Even
if every last piece of evidence she marshals in her case for how pivotal the
transition to cooperative breeding was in the evolution of mutual understanding
in humans is overturned, Hrdy’s painstaking efforts to develop her theory and lay it out so comprehensively, so
compellingly, and so artfully, will not have been wasted. Darwin once wrote that “all
observation must be for or against some view to be of any service,” but many
scientists, trained as they are to keep their eyes on the data and to avoid the
temptation of building grand edifices on foundations of inference and speculation,
look askance at colleagues who dare to comment publically on fields outside
their specialties, especially in cases like Jared Diamond’s where their efforts
end up winning them Pulitzers and guaranteed audiences for their future works.
 |
Mutual gazing in gorillas (de Waal's FB page) |
But
what use are legions of researchers with specialized knowledge hermetically
partitioned by narrowly focused journals and conferences of experts with
homogenous interests? Science is contentious by nature, so whenever a book
gains notoriety with a nonscientific audience we can count on groaning from the
author’s colleagues as they rush to assure us what we’ve read is a misrepresentation
of their field. But stand-alone findings, no matter how numerous, no matter how
central they are to researchers’ daily concerns, can’t compete with the grand
holistic visions of the Diamonds, Hrdys, or Wilsons, imperfect and provisional
as they must be, when it comes to inspiring the next generation of scientists.
Nor can any number of correlation coefficients or regression analyses spark
anything like the same sense of wonder that comes from even a glimmer of
understanding about how a new discovery fits within, and possibly transforms,
our conception of life and the universe in which it evolved. The trick, I
think, is to read and ponder books like the ones Sarah Blaffer Hrdy writes as
soon as they’re published—but to be prepared all the while, as soon as you’re
finished reading them, to read and ponder the next one, and the one after that.
12 comments:
DJ: "For instance, humans have brains that are significantly larger than those of any other primate, and we use these brains to fashion tools that are far more elaborate than the stones, sticks, leaves, and sponges used by other apes."
Isn't it local size rather than overall size? How else to explain larger than human Neanderthal brains and the small chimp-sized brains of floresiensis who used tools? Sneaky little hobbitses.
DJ: "Isn’t it always better to be smarter?"
Of course not! Large brains are costly developmentally and metabolically. What happens when you slowly starve brains/neurons of energy? dementia.
DJ: "Yet, whereas the imitative and empathic skills flourish in maturing humans, they seem to atrophy in apes."
We are in arrested development: pedomorphosis.
DJ: "Such charges reinforce the alienation many women, especially feminists, feel toward evolutionary theory and fields like sociobiology"
Yes! because it's still with us. Exhibit A: Satoshi Kanazawa.
DJ via Hrdy via Eliot: "a cultivated intelligence based upon a bad physique is of little worth, seeing that its descendants will die out in a generation or two."
The father of social darwinism may have been on to something as there is a bit of evidence for a correlation between intelligence and body symmetry. The idea is that since body symmetry roughly equates to good health, developmentally speaking, brain development, an indicator of general intelligence, naturally falls under body symmetry. Read the paper to see what interesting mechanisms are behind it all: "Third the importance of possible 'intelligence-boosting genes" (i.e., alleles at specific genetic loci that increase intelligence above the population average…) will need to be considered in the context of variation in intelligence maintained by fitness-reducing (and hence intelligence-reducing) mutations."
"Intelligence tests with higher g-loadings show higher correlations with body symmetry: Evidence for a general
fitness factor mediated by developmental stability"
Mark D. Prokosch, Ronald A. Yeo, Geoffrey F. Miller
DJ: "…maternal age turned out to be a better predictor of how effective a mother would be than specific personality traits or attitudes."
How did they evaluate mothering and what are the age ranges? It has to be largely independent from the health of the child in order to square it with the reams of data showing the accumulating effect of deleterious de novo mutations in both sperm and eggs as would-be parents get older, increasing overall risk to any number of developmental disorders. In other words, while older women may be more psychologically fit for childrearing their ovaries certainly aren't. Oh and fecundity decreases with age. A little OT, but intense competition among male mammals increases sperm production. Increase sperm production, you increase mitotic cell division which means increased mutation rates. This is what they call male-biased mutation (female germ line cell division/mutation rate is much lower of course) So we can tie male biased mutation to mutation load (possibly implicating general intelligence among other things). The take-home message is complicated. Hows that for a Grand Theory?
DJ: "Indeed, the mothers who are forced to abandon their infants have to be savvy enough to realize they have to do so before these emotions are engaged or they will be unable to go through with the deed."
Whether they are savvy or not the "Republicans in your vagina" legislation in the southern states increasingly seeks to force doctors to force women to listen to their infant's heartbeat and gape at the little pupae from an ultrasound before they abort it.
DJ: "When confronted with a choice between striving for status and striving for children, mothers gave priority to status and “cultural success” ahead of a desire for many children."
I like it...demonstrating your cultural fitness by not having kids.
DJ: "Ape mothers remain in constant contact with their infants, whereas human mothers often hand over their babies to other women to hold as soon as they emerge from the womb."
Re: Barbara Tuchman's "A Distant Mirror: The Calamitous 14th Century." Pretty much universally across Europe parents (nobles because literacy and record-keeping) placed little value on children until they reached their teens, limiting contact and even handing them off to be raised by others. Medieval Europe was maybe unique and the level of parent involvement in childrearing regardless of class is an area of contention among historians. Point being there seems to be dramatic variation throughout just recorded history on this subject.
DJ via Hrdy: "if by babble we mean repetitive strings of adultlike vocalization uttered without vocal referents"; marmosets and tamarins do it too."
Apparently Macaques (and lemurs, bushbabies and squirrel monkey) infants do it as well, and macaques (as a genus) and humans are the most widely distributed primates.
Can you share Hrdy's citation (122)?
The only evidence I found of marmoset babbling is from your wikipedia link linking to a longitudinal study of 8 monkeys in the mid-90s.
"Babbling in Pygmy Marmosets: Development After Infancy"
"Although the occurrence of Pygmy Marmoset Babbling declined between infant and juvenile ages, there is still a question of why babbling should
occur at all outside of infancy. If babbling is solely for vocal practice and young monkeys still need further practice to develop adult call structure,
then some continued babbling would be useful. However, there may be social consequences associated with babbling. As we reported for infants
(Elowson et al., 1998a, b) there was an increased probability of social interaction when juveniles produced babbling bouts so juveniles might use babbling to increase social interactions."
Based on the study design it wasn't possible to separate age from babbling in parent response; as age increased babbling decreased and parent response decreased. it's not contested that babbling is practice at adult vocalization, as it is in songbirds, the rest seems anthropomorphized driven speculation.
No…not the grandmother hypothesis!
"Menopause in Nonhuman Primates." Walker M., Herndon J.G. Biology of Reproduction, 2008. This is not something unique to humans and according to Hawks and Smith, "Do Women Stop Early? Similarities in Fertility Decline in Humans and Chimps" 2010, human menopause is ancestral not derived (i.e., virtually identical to chimps). Post-menopause lifespans are a byproduct of being kept alive long enough, as we see in captive mammals such as mice.
Two models that tested whether post-reproductive females, in providing help to younger kin, offset the reproduction they forfeited with menopause.
1)Rogers "Why Menopause" Evolutionary Ecology, 1993 used a surrogate model of Paleo human life to show "the presence of a postmenopausal 'mother' would have had to double the number of children all of HER children had and completely eliminate infant deaths for evolution to have produced menopause by natural selection.
2)Hill and Hurtado, "The evolution of premature reproductive senescence and menopause in human females: an evaluation of the "grandmother hypothesis." 1991, found any benefit postmenopausal women gain through assisted rearing of grandchildren (inclusive fitness) is insufficient to offset the direct fitness benefits of reproductive senescence: increase age, increase health risk in childbirth.
These are discussed in Austad's 1997 "Between Zeus and Salmon. pg11
"Fertility is well below its physiological maximum in hunter-gatherers today, and aggregate growth rates over human prehistory seem to have been fine-tuned remarkably close to zero. There may, therefore, have been little marginal cost to foregoing extra births and high marginal returns to parental survival and investment, especially in the face of recurrent scarcity. Calculations done without assuming homeostasis, cited Chapter 9, have suggested that the help provided by postmenopausal human females to their kin is not sufficient to offset the losses to their own reproductive potential imposed by menopause. […] If postreproductive survival were a feature of our evolutionary past, then, as Lee points out, the question of whether the postreproductive elderly were net economic contributors remains distinct from the question of whether they contributed enough to their descendants' reproduction to make menopause an adaptive trait."
So we don't know when menopause evolved in our lineage, we don't know how it evolved and we don't even know which genes are involved. It seems more likely, based on what we do know, that there's no menopause allele transmitted from mother to daughter but instead (maybe) a longevity allele being passed down, making menopause an artifact of increased longevity. As Gould would say functional differences cannot be equated to adaptive changes.
DJ: "But what use are legions of researchers with specialized knowledge hermetically partitioned by narrowly focused journals and conferences of experts with homogenous interests?"
Every field has its Journal of Thoracic Imaging and yet everyone strives for Nature and Science and PNAS.
"Nor can any number of correlation coefficients or regression analyses spark anything like the same sense of wonder that comes from even a glimmer of understanding about how a new discovery fits within, and possibly transforms, our conception of life and the universe in which it evolved."
Don't you agree, the grand visions of the Diamonds and Sagans and Hrdys live and die by those stand-alone findings they glom together?
What I often see in these Theories of Everything is more often than not a misconception of noise to signal, when noise is overwhelming complexity, diversity and natural variation--the good stuff--while signal is like squinting to drown out all but the general, roughest hues and forms. I want the next generation of scientists to embrace the noise.
It should be obvious, I think you've written a fantastic review.
Several of your points are useful supplements to the essay. For instance, Hrdy tries pretty hard to argue in Mother Nature that there was no evidence for a connection between health and fertility and beauty—even at the time I’m pretty sure she was wrong. So, yes, Spencer had a point, but he was exaggerating it. And from our historical perspective he seems like a dick.
But to respond to some important issues: First, on the grandmother hypothesis, I may have inadvertently exaggerated its similarity to Hrdy’s social breeding hypothesis. You rightly point to some major evidence and reasoning against the idea that menopause evolved as a trait to serve the function of freeing women from reproductive duty to benefit grandkids. Hrdy makes similar points. Looking back, I see I may have given the impression that she endorses that view, when in fact she doesn’t. I was only trying to situate the theory in some historical context. The key quote: “The proposal… that menopause might have evolved to produce in humans a sort of “sterile caste” to forestall competition between older and younger breeding females overlooks the fact that what is different about human apes is not cessation of reproduction around age 40—that is, menopause itself—but how long women go living afterward” (267). Interestingly, she cites a work on which Hawkes collaborated, so she too has moved beyond the menopause as an adaption view, which really was Williams’—Hawkes’ idea was that after women started living longer, for whatever reason, menopause made it possible for them to help grandkids take longer to develop. (“The Derived Features of Human Life History.”) Actually, I’m pretty Hawkes’s theory has always been separate from Williams’ strict adaptationist one.
The marmoset babbling citation was Margaret Elowson’s: http://www.ncbi.nlm.nih.gov/pubmed/21244960
I’m not sure I follow your point about it not being contested that babbling is practice at adult vocalization, since the article proposes a different function for the practice. As for the other primates you point to, Elowson states: “Similar periods of vocal development have not been described previously for non-human primates.” Not sure if it’s a matter of using a narrower definition.
To your point about the variability of mothering practices--or not-mothering practices: of course, variability poses a problem for any hypothesis about a trait serving an evolutionary purpose--but the universal pattern central to Hrdy's argument is that human mothers share care and the evidence you cite actually supports that.
Of course, anthropologists often go to the ethnographic record to learn about hunter-gatherers because their practices are thought to be more similar to our ancestors (but Diamond is catching hell right now for saying it out loud). But universals among hunter-gatherers are probably the best candidates for ancestral behaviors.
Hrdy incorporates variability of parenting practices into her argument. That's why she doesn't just focus on grandmothers (though they're often important figures.) She cites dozens of studies from several societies, but the key general study is Sears et al. "Who Keeps Children Alive". I haven't finished reading it yet--but from the abstract: "while help from kin may be a universal feature of human childrearing, who helps is dependent on ecological conditions."
http://eprints.lse.ac.uk/21225/1/Who_keeps_children_alive_(LSERO).pdf
Finally, I don't think it's fair to label Hrdy's cooperative breeding hypothesis a theory of everything; she sets out to explain a key difference between humans and other apes, and she suggests a key transition in our evolution as an important factor.
But I take your point. Yes, of course, if a large synthesizing, contextualizing book didn't use citations--or if I caught the author out on misrepresenting the sources--I'd give up on it.
The analogy I'd use would be with reading Science News every week. Sometimes I see a write-up on a study I'm interested in, so I look it up and read it. But these stand-alone studies seldom get me as excited as watching NOVA, or reading a really good book which takes a wider view.
Noise, complexity, variability--well, yes, theories shouldn't be any simpler or any more broadly applied than the evidence warrants. But detail without context doesn't have any meaning, is all but impossible to learn and remember, and even failed theories are useful.
Your challenges are what makes writing these fun. At some point, I'll get around to reading "Social Conquest." I'll have to have my druthers good and up for that one.
DJ: " Elowson states: “Similar periods of vocal development have not been described previously for non-human primates.” Not sure if it’s a matter of using a narrower definition. "
(Elowson, 2001)
""The reports that other marmoset species (Epple, 1968; Omedes, 1985) produce complex sequences of vocalizations, the large amount of variable vocalizations produced by infant bushbabies and lemurs (Zimmermann, 1995), the high rate of vocalizations of infant squirrel monkeys (Biben &
Bernhards, 1995), and the vocal variability of separated macaque and marmoset infants (Newman, 1995) suggest that infants in many primate species
produce complex, variable vocalizations."
I suppose it's a matter of definition.
DJ: "I’m not sure I follow your point about it not being contested that babbling is practice at adult vocalization, since the article proposes a different function for the practice."
I was referring to the work done on songbirds.
(Elowson, 1998)
"Until now, the closest animal parallel of human babbling has been the subsong of male passerine birds, a species that is far removed taxonomically from humans. In a now classic paper, Marler suggested that the process by which these male birds master song (to attract mates and proclaim ownership of a territory) is heuristic in understanding the ontogeny of human language. He proposed that subsong, a preliminary stage in song acquisition, was analogous to human infant babbling."
And supported here:
(Elowson, 2001)
"This is the first evidence that individual variation in early vocal behavior is related to the quality of vocal production and provides suggestive evidence that babbling might serve as a practice for later vocal production….If babbling is solely for vocal practice and young monkeys still need further practice to develop adult call structure, then some continued babbling would be useful.
All very minor points here
This is one of the most interesting, educational, and well written reviews I've ever read. Great work.
This is one of the most interesting, educational, and well written reviews I've ever read. Great work.
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