Follow the links below for new
anthropological research I mention during lecture that represent recent
anthropological research relevant to the course. These links will
accumulate during the semester.
TWEE RIVIEREN, South Africa - The educated city people - a government minister,
a chief executive and several directors of the nation's most important
scientific organizations - traveled at sunrise to this barren region of the
Kalahari Desert to see for themselves the cactus that has been trumpeted as a
natural wonder.
But when they stood before it, a puny cluster of spiny
stalks that looked like wrinkled cucumbers, the magnitude of the moment escaped
them.
"That's it, huh?" asked Dr. Ben Ngubane, minister of arts,
culture, science and technology. "How do you know this one is safe to eat?"
A grin from Petrus Valbooi, a leader of the San people, or
Bushmen, who scrape life from this barren landscape, reassured the skeptics. He
cut off a stalk, shaved off its spines, and sliced into its milky center,
bidding them to taste.
That's where its power lies, he told them. Indeed.
From a desert weed known as hoodia, one of the world's
oldest and least developed peoples hopes to enjoy its first taste of prosperity.
The San have sucked on hoodia for generations, principally
to raise their energy and fight hunger during long hunting trips.
Now, Pfizer, the international pharmaceutical giant, has
begun work on an appetite suppressant from the plant, and agreed to share the
profits. The deal, which includes the government, is considered a landmark in
the field of international property rights.
The company, with a British-based research partner, has
spent millions working to develop the drug from the active chemical in the
obscure runt of a cactus, hoping to make it as profitable as Viagra.
Here among the San, the concept of wealth has begun to
sink in. The first payment to the San, some $30,000, was made
last month, and there are already plans to buy land and build clinics.
But at the formal signing of the agreement in March, most
of the Bushmen seemed happy just knowing that the modern world had recognized
that there remained wealth in ancient knowledge, and that at least one tradition
in their dying culture might be saved.
"I am very happy because it was not written that this day
would happen," said Mr. Valbooi, who arrived at the
ceremony wearing traditional shorts made from deerskin and a crown made from the
tail of a wild cat. "Now I know that
God has not abandoned the Bushmen."
It was a happy ending to a protracted legal conflict that
began in 1996 when the Council for Scientific and
Industrial Research, a government-financed laboratory, patented the active
chemical of the hoodia, called P57,
without acknowledging the San.
The government then licensed rights to develop P57 to the
British pharmaceutical research company Phytopharm, which sublicensed the rights
to Pfizer.
After years of legal wrangling, an agreement was reached
between the San and the government. Under the agreement, some 100,000 Bushmen in
four countries - South Africa, Botswana, Namibia and Angola - will receive at
least three more payments during the clinical testing of the drug.
Then the South African government will pay the San some 6
percent of the royalties it receives once the drug goes on the market.
Roger Chennells, a lawyer who represented the San in their
legal fight, acknowledged that the community was getting the smallest slice of
what could be a multibillion-dollar pie. "If this is a cop-out," he said, "then
it is a cop-out I can live with because it is going to bring these people
benefits no government has ever given them."
The San trace their history back some 150,000 years, to
the world's first humans. The hunter-gatherers are still considered expert
trackers, with abilities to read animal movements from the sand.
But they became the prey under South Africa's colonial
rulers, who shot them for sport. Under apartheid, the San were enslaved and
robbed of their ancestral land. The South African military used them to find
black opposition leaders living on the run.
To the marvel of anthropologists, the San have been able
to cling to their traditions. After the end of white rule, South Africa's first
black president, Nelson Mandela, returned them to their lands, as arid as the
face of the moon.
Today, however, fewer than a dozen people speak their
language, and even fewer know how to hunt. Children learn traditional dances,
but prefer polyester T-shirts and tennis shoes over animal skins. Most young
people abandon the desert for schools and jobs in cities.
Jan Vander Westhuitzen, 47, a Bushman tracker, said hoodia
is struggling, too. "Hoodia used to cover the desert, " he said, cutting a
leaf from a shriveled specimen and stuffing it in a deerskin medicine pouch.
"Now the land is too dry."
He said the plant had been a center of life for the
Bushmen for as long as he could remember. A sip of its bitter
liquid gave them enough energy to walk all day or make love through the night.
It cured a morning hangover, or, brewed like tea, soothed an aching stomach.
He seemed to delight at the idea that its secret was out.
"I do not think we are being robbed of our knowledge," he said. "I think that
people who know how to live from the earth should share."
Invisible People Airs Sunday, Apr 06 at 4
p.m. on the National Geographic Cable Channel, #48
Meet Brazilian adventurer Sydney Possuelo. This 'Amazon Ambassador' has
trekked through a landscape in
which anacondas and ambush seem to lurk around every jungle bend. He's been
assailed by malaria 37 times, nearly lost an eye and broke a rib in a plane
crash. Along the way, he has fought to protect the way of life some of the most
isolated peoples on Earth as head of Brazil's Department of Isolated Indians (FUNAI).
FUNAI itself has also withstood the hardships of its work - 50 staff members
have died in the field,
from both violent conflicts and the jungle itself. The fate of isolated Indians
has become increasingly precarious in the more than forty years since Possuelo
first made their cause his life's work. Invisible People offers a unique
insight into a career spent wrestling the forces of modernity, as we follow
Sydney on an emergency visit to the recently contacted Korubo tribe, known
locally as the "head smashers" - a reference to their unusual method of waging
battles. Traveling into Korubo territory we learn about the plethora of forces
that threaten Amazonian tribes; from drug smuggling and disease, to tribal
conflicts, and Sydney's struggle to protect their land and preserve their way of
life.
robably the single most common motive mentioned by
tribal warriors when asked why they go to war, is revenge, according to a Penn
State anthropologist. "The impulse for revenge is far from being uniquely
human," says Dr. Stephen Beckerman, associate professor of anthropology.
"Clutton-Brock and Parker show how widespread in the
animal kingdom is the behavior of returning injury for injury. Animals as varied
and as far from us as blue-footed boobies, elephant seals, side-striped jackals
and European moorhens are called punishers; they regularly respond to injuries
by attacking the culprit who has injured them."
Beckerman notes that among some primates, injured
individuals may punish one of his or her attacker's relatives rather than punish
the attacker or, in other primates, the punishment may be meted out not to a
relative, but to a friend or ally of the victim. Presumably, they intend this
behavior to be negative reinforcement; training others to act so they do not
damage the fitness of the punisher.
"When we come to blood revenge among human beings, it is
helpful to remember that we seem to be dealing with something that is not so
different from behaviors we already see in primates," Beckerman told attendees
today (Feb.
14) at the annual meeting of the American Association for
the Advancement of Science in Denver.
Human revenge is concerned with dominance and status as is
that of other primates, and often revenge is taken on a relative or ally.
Perhaps one difference is that animal punishment as defined by Clutton-Brock and
Parker disavows "a conscious decision or a moral sense on the part of the
punisher."
Humans add to the widespread, angry animal impulse to
punish, a conscious sense of what the reception of punishment will be and
achieve, and that consciousness moves the act from animal punishment to human
revenge.
"Revenge is a desire to not just punish the culprit, but
to change his mind, to make him see, if only in his death throws, that he was
wrong," said Beckerman.
This idea of revenge colors the methods and approaches of
tribal warfare. After the psychological basis for revenge in providing negative
reinforcement there are the social rules developed to carry out this revenge.
The idea of blood revenge - a life for a life, an eye for an eye - is of concern
to social groups because the injured party is usually already dead.
"The general rule is that you are prohibited from taking
blood revenge on those who would be obliged to avenge you, if you were killed,"
said Beckerman.
So, among the inner circle, or within the social group,
revenge is forbidden. However, at a further distance, with those groups a tribe
has close contact with, reciprocal exchange and trade, revenge is acceptable,
but constrained by rules. At this intermediate social distance, the groups share
enough values and beliefs on what injuries need revenge and how that revenge is
carried out to have rules as to who is an acceptable target of revenge. These
rules, which include who can carry out revenge against whom, where it can occur
and for what reason, are attempts to achieve an equal balance of injuries.
"Sometimes feud goes on for centuries, but reciprocal
violence at this middle social distance can also be self-limiting," said the
Penn State anthropologist.
At the greatest social distance, the people are
essentially strangers and evoke the bloodiest revenge without an attempt at
balance. Revenge against foreigners is often disproportionate to the initial
injury and often deliberately full of atrocities. The aim is not to achieve
balance, but to attain total submission or extermination.
While within group revenge episodes are unusual, tribal
members cannot always prevent someone who is so angry they inflict revenge on an
in-law, brother or cousin, but taking that revenge is outside the rules. On the
intermediate level, the value of ritualized revenge, seems to be that any group
that is not willing to retaliate blood for blood finds its resources, land and
homes plundered, women carried off and men bullied.
Revenge is not always an immediate act. Sometimes a group
must wait for adequate manpower, resources and opportunity. During the recent
fighting in the former Yugoslavia, some leaders rallied their forces by evoking
the defeat at the hands of the Moslems that occurred 900 years before they were
born. Revenge has a long memory.
Beckerman notes, however, that currently we do not operate
on the tribal level and that a watershed in human history occurred when the
decision to go to war was no longer made by those who fight the wars.
ORONO - With America and its allies poised to attack Iraq
and the U.S. and North Korea locked in a showdown over nuclear weapons,
diplomats and politicians would do well to remember that humans may have nuclear
technology but still only possess stone-age brains. This is often a lethal
combination, says University of Maine anthropologist Paul Roscoe who will
present a paper on tribal warfare in New Guinea today at the annual meeting of
the American Association for the Advancement of Science in Denver.
Roscoe has extensively studied revenge as a motive for war
among tribes in New Guinea and concludes that killing enemies to avenge the
death of kin - something only humans do - is probably not a useful evolutionary
adaptation. This is because lethal revenge most frequently fuels more killing
rather than deterring it, says the professor of anthropology and cooperating
professor of Quaternary and Climate Studies at UMaine.
"I argue that revenge is probably not an adaptive feature
because revenge is not good for you," Roscoe says. Evolutionarily speaking, it
does not make sense to engage in behavior that may not only kill yourself but
also other members of your clan or tribe. Writ large in a thermonuclear
exchange, revenge killing could theoretically wipe out your entire species. "It
makes evolutionary sense to fight and then back off."
Humans have, in a sense, deviated from the evolutionary
path by engaging in revenge killings and warfare. They do so because their
technical ability to harm one another has outpaced their social and cultural
abilities to deal with behavior that might not be so wise, Roscoe surmises. Only
in the last 10,000 years of human existence have people evolved from hunters and
gatherers with spears to glorified hunters and gatherers with thermo-nuclear
weapons.
"We may have nuclear technology, but we still have
stone-age brains," Roscoe says. "Our social and political systems are slow to
adapt in comparison to the pace of technological development."
Previous theories on motives for revenge, based on
socio-biology, have centered on an escalating tit-for-tat complex. This theory
holds that humans have simply taken behavior routinely practiced by other
animals to the next step. Many animal species engage in escalating aggressive
behavior. Male red deer competing for territory or mates, for example, will
first roar at one another. If neither backs away, the animals then walk back and
forth side-by-side sizing one another up. If this fails to resolve the conflict,
the two animals may fight, but the results are typically not lethal.
Humans, however, are the only animals to seek out enemies
and to kill them for past actions. Roscoe argues that this is because humans
have a large, highly developed neo-cortex, the region of the brain known for
intellectual thought and creativity. The neo-cortex is believed to have evolved
for positive purposes such as enabling humans to develop tools, to communicate
through language, and to plan cooperative hunting trips. However, it has not
always been used for positive purposes.
"Humans developed the ability to model actions before they
happen. This means we can plan collective violence. It explains why we have
warfare," he says. Research on chimps confirms that, once you can gang up and
launch a surprise attack on outnumbered victims, killing becomes a dramatically
more attractive option than it is in the one-on-one confrontations typical of
other species.
The neo-cortex also allow humans to manipulate their
emotional states. Warriors, for example, can whip themselves into an angered
frenzy by recalling slain kin and engaging in repetitive, war-mongering chants.
A highly developed neo-cortex also allows people to
de-humanize their enemies. Many tribes in New Guinea, for example, refer to
their enemies as "our game" and world leaders have equated their enemies with
mad dogs and rats. This is how humans circumvent their built-in aversion to
killing members of their own species, Roscoe says.
This portion of the brain has also allowed humans to
develop sophisticated weapons whereby they can kill one another without
face-to-face contact. This not only can make killing more efficient, but also
gets around our in-bred aversion to killing other humans.
Roscoe has focussed his research on tribes in New Guinea
because surprisingly little work has been done on the wars waged by these
people, many of whom did not have contact with outsiders until the 1930s. In
addition, the island presents a potential treasure trove of information on
warfare because, at the time of contact, there were thousands of groups that
spoke more than 1,000 languages. These groups were often at war with one
another. With funding from the National Science Foundation, Fulbright-Hays Area
Studies Program and the American Philosophical Society, Roscoe has traveled to
archives around the world to collect data about warfare in contact-era New
Guinea. Since anthropologists usually arrived many years after contact, Roscoe
often has had to rely on other sources, especially the writings of missionaries
who visited the South Pacific island. Much of the writing Roscoe reviewed is in
German and Dutch.
He found that much of the warfare in New Guinea was, in
fact, precipitated by revenge and that the motive was to weaken the enemy and to
forestall further aggression. Some tribes believed they must fight until the
number of dead on both sides were equal. Others believed they must inflict
lethal revenge to be spared from the ghosts of clansmen who were killed. However
the fighting began, it often escalated, sometimes involving groups not party to
the initial clash, and continued for generations. This raises problems for
theories that revenge stops further aggression.
"My hope is that somewhere down the road, we will use this
knowledge to get around killing one another. War is the most costly thing in the
world in terms of blood and treasure. We need to figure out why we have war
before it wipes us off the planet," Roscoe concludes.
Miners Killed by Cinta Larga of Brazil
--------------------------------------------------------------------------------
THURSDAY April 22, 2004
Chief defends killing of diamond prospectors
THURSDAY April 22, 2004 Chief defends killing of diamond prospectors
A female Cinta Larga warrior aims her arrow at reporters at the Roosevelt
Indian Reservation in Rondonia state, Brazil, on Wednesday. (Victor R. Caivano/The
Associated Press)
The Associated Press
ON THE ROOSEVELT INDIAN RESERVATION, Brazil -- An Amazonian tribal chief said
Wednesday the killing of 29 diamond prospectors on his remote Indian reservation
came after they were repeatedly warned to stay away. In his first comments to
the media since the April 7 killings, Chief Pio Cinta Larga told The Associated
Press that Indians in the area carried out the killings, but he denied ordering
the attack or taking part in it. "There are some very angry Indians and not even
the leadership can control their actions," he said, adding that members of other
tribes have joined the Cinta Larga on the 6.7-million-acre reservation, where
prospectors frequently trespass. "We told them we didn't want them here and they
kept coming back. The warriors lost patience and this is what happened," said
Cinta Larga, who uses the tribe's name as his surname. Federal police have said
the 29 miners were killed by the Cinta Larga Indian tribe in a dispute over
diamond mining. The reservation is believed to have South American's largest
diamond reserves. Investigators indicated most of the miners were lined up and
killed at short range with arrows, clubs, spears and firearms. Many of the
bodies appeared to have been tortured or mutilated. Though denying links to the
attack, he said the Indians have a right to defend their culture. "We are
warriors," said Cinta Larga. "Before the white man came, none of the tribes here
were friends. We fought and killed each other, that is how we resolved things."
The Roosevelt Indian reservation in Roaondonia state, some 2,100 miles
northwest of Rio de Janeiro, is cloaked within the dense Amazon rainforest,
reachable only over nearly 100 miles of rutted dirt roads. Travel inside the
reservation is mainly over jungle footpath or by river. The Cinta Larga Indians
were first contacted by outsiders in the late 1960s, but development has been a
mixed blessing. Many of the Indians are fairly well-off, dressing in
western-style clothing and driving pickup trucks. About two-thirds of the
1,300-strong tribe have learned Portuguese, Brazil's national language, but the
remaining Indians maintain the tribe's fierce warrior traditions. The president
of Brazil's Federal Indian Bureau has said he considered the Indians to be
acting in legitimate self-defense because both mining and trespassing by
non-Indians are illegal on Indian reservations. Those comments only served to
fuel already high tension between the heavily armed Indians and prospectors.
"It's illegal to mine on Indian land, it's also illegal to kill," said Celso
Antim of the prospector's union in Espigao d'Oeste, about 60 miles from the
reservation. Antim said the killings would not keep prospectors off the
reservation for long. "There will be a little pause, but then they'll all go
back because they're all going hungry," he said. "This time, though, they'll go
back armed." Clashes between Indians and prospectors have claimed at least 70
lives since diamond mining began. Cinta Larga warned that prospectors who
returned should know they were taking their lives in their hands. He said the
solution is to change the law so Indians can legally mine on their lands.
Currently, the Indians mine the diamonds in violation of federal law and sell
them on the black market in violation of the international Kimberly protocol,
which governs the sale and trade of diamonds. A task force composed of hundreds
of state and federal agents has been deployed in and around the reservation and
is expected to remain in the region for up to six months. The unit is disarming
prospectors and Indians and will try to put an end to mining and prospecting
activities in the reservation. But officials here said ending the illegal
prospecting will not be easy. Brazil's Mines and Energy Ministry estimated some
$2 billion in diamonds have been mined in the area since prospecting began in
1999. "Prospecting isn't something that ends from one day to another. It will be
reactivated there is a great desire for diamonds and the diamonds on the
reservation are very good," said Amoss de Mello Oliveira, a geologist working
with the police.
When it comes to the matter of desire, evolution leaves little to chance.
Human sexual behavior is not a free-form performance, biologists are
finding, but is guided at every turn by genetic programs.
Desire between
the sexes is not a matter of choice. Straight men, it seems, have neural
circuits that prompt them to seek out women; gay men have those prompting
them to seek other men. Women’s brains may be organized to select men who
seem likely to provide for them and their children. The deal is sealed with
other neural programs that induce a burst of romantic love, followed by
long-term attachment.
So much fuss, so intricate a dance, all to achieve success on the simple
scale that is all evolution cares about, that of raising the greatest number
of children to adulthood. Desire may seem the core of human sexual behavior,
but it is just the central act in a long drama whose script is written quite
substantially in the genes.
In the womb, the body of a developing fetus is female by default and
becomes male if the male-determining gene known as SRY is present. This
dominant gene, the Y chromosome’s proudest and almost only possession,
sidetracks the reproductive tissue from its ovarian fate and switches it
into becoming testes.
Hormones from the testes, chiefly
testosterone, mold the body into male form.
In puberty, the reproductive systems are primed for action by the brain.
Amazing electrical machine that it may be, the brain can also behave like a
humble gland. In the hypothalamus, at the central base of the brain, lie a
cluster of about 2,000 neurons that ignite puberty when they start to
secrete pulses of gonadotropin-releasing hormone, which sets off a cascade
of other hormones.
The trigger that stirs these neurons is still unknown, but probably the
brain monitors internal signals as to whether the body is ready to reproduce
and external cues as to whether circumstances are propitious for yielding to
desire.
Several advances in the last decade have underlined the bizarre fact that
the brain is a full-fledged sexual organ, in that the two sexes have
profoundly different versions of it. This is the handiwork of testosterone,
which masculinizes the brain as thoroughly as it does the rest of the body.
It is a misconception that the differences between men’s and women’s
brains are small or erratic or found only in a few extreme cases, Dr. Larry
Cahill of the
University of California, Irvine, wrote last year in Nature Reviews
Neuroscience. Widespread regions of the cortex, the brain’s outer layer that
performs much of its higher-level processing, are thicker in women. The
hippocampus, where initial memories are formed, occupies a larger fraction
of the female brain.
Techniques for imaging the brain have begun to show that men and women
use their brains in different ways even when doing the same thing. In the
case of the amygdala, a pair of organs that helps prioritize memories
according to their emotional strength, women use the left amygdala for this
purpose but men tend to use the right.
It is no surprise that the male and female versions of the human brain
operate in distinct patterns, despite the heavy influence of culture. The
male brain is sexually oriented toward women as an object of desire. The
most direct evidence comes from a handful of cases, some of them
circumcision accidents, in which boy babies have lost their penises and been
reared as female. Despite every social inducement to the opposite, they grow
up desiring women as partners, not men.
“If you can’t make a male attracted to other males by cutting off his
penis, how strong could any psychosocial effect be?” said J. Michael Bailey,
an expert on sexual orientation at
Northwestern University.
Presumably the masculinization of the brain shapes some neural circuit
that makes women desirable. If so, this circuitry is wired differently in
gay men. In experiments in which subjects are shown photographs of desirable
men or women, straight men are aroused by women, gay men by men.
Such experiments do not show the same clear divide with women. Whether
women describe themselves as straight or lesbian, “Their sexual arousal
seems to be relatively indiscriminate — they get aroused by both male and
female images,” Dr. Bailey said. “I’m not even sure females have a sexual
orientation. But they have sexual preferences. Women are very picky, and
most choose to have sex with men.”
Dr. Bailey believes that the systems for sexual orientation and arousal
make men go out and find people to have sex with, whereas women are more
focused on accepting or rejecting those who seek sex with them.
Similar differences between the sexes are seen by Marc Breedlove, a
neuroscientist at
Michigan State University. “Most males are quite stubborn in their ideas
about which sex they want to pursue, while women seem more flexible,” he
said.
Sexual orientation, at least for men, seems to be settled before birth.
“I think most of the scientists working on these questions are convinced
that the antecedents of sexual orientation in males are happening early in
life, probably before birth,” Dr. Breedlove said, “whereas for females, some
are probably born to become gay, but clearly some get there quite late in
life.”
Sexual behavior includes a lot more than sex. Helen Fisher, an
anthropologist at
Rutgers University, argues that three primary brain systems have evolved
to direct reproductive behavior. One is the sex drive that motivates people
to seek partners. A second is a program for romantic attraction that makes
people fixate on specific partners. Third is a mechanism for long-term
attachment that induces people to stay together long enough to complete
their parental duties.
Romantic love, which in its intense early stage “can last 12-18
months,” is a universal human phenomenon, Dr. Fisher wrote last year in The
Proceedings of the Royal Society, and is likely to be a built-in feature of
the brain. Brain imaging studies show that a particular area of the brain,
one associated with the reward system, is activated when subjects
contemplate a photo of their lover.
The best evidence for a long-term attachment process in mammals comes
from studies of voles, a small mouse-like rodent. A hormone called
vasopressin, which is active in the brain, leads some voles to stay
pair-bonded for life. People possess the same hormone, suggesting a similar
mechanism could be at work in humans, though this has yet to be proved.
Researchers have devoted considerable effort to understanding
homosexuality in men and women, both for its intrinsic interest and for the
light it could shed on the more usual channels of desire. Studies of twins
show that homosexuality, especially among men, is quite heritable, meaning
there is a genetic component to it. But since gay men have about one-fifth
as many children as straight men, any gene favoring homosexuality should
quickly disappear from the population.
Such genes could be retained if gay men were unusually effective
protectors of their nephews and nieces, helping genes just like theirs get
into future generations. But gay men make no better uncles than straight
men, according to a study by Dr. Bailey. So that leaves the possibility that
being gay is a byproduct of a gene that persists because it enhances
fertility in other family members. Some studies have found that gay men
have more relatives than straight men, particularly on their mother’s side.
But Dr. Bailey believes the effect, if real, would be more clear-cut.
“Male homosexuality is evolutionarily maladaptive,” he said, noting that the
phrase means only that genes favoring homosexuality cannot be favored by
evolution if fewer such genes reach the next generation.
A somewhat more straightforward clue to the origin of homosexuality is
the fraternal birth order effect. Two Canadian researchers, Ray
Blanchard and Anthony F. Bogaert, have shown that having older brothers
substantially increases the chances that a man will be gay. Older sisters
don’t count, nor does it matter whether the brothers are in the house when
the boy is reared.
The finding suggests that male homosexuality in these cases is caused by
some event in the womb, such as “a maternal immune response to succeeding
male pregnancies,” Dr. Bogaert wrote last year in the
Proceedings of the National Academy of Sciences. Antimale antibodies
could perhaps interfere with the usual masculinization of the brain that
occurs before birth, though no such antibodies have yet been detected.
The fraternal birth order effect is quite substantial. Some 15 percent of
gay men can attribute their homosexuality to it, based on the assumption
that 1 percent to 4 percent of men are gay, and each additional older
brother increases the odds of same-sex attraction by 33 percent.
The effect supports the idea that the levels of circulating testosterone
before birth are critical in determining sexual orientation. But
testosterone in the fetus cannot be measured, and as adults, gay and
straight men have the same levels of the hormone, giving no clue to prenatal
exposure. So the hypothesis, though plausible, has not been proved.
A significant recent advance in understanding the basis of sexuality and
desire has been the discovery that genes may have a direct effect on the
sexual differentiation of the brain. Researchers had long assumed that
steroid hormones like testosterone and
estrogen did all the heavy lifting of shaping the male and female
brains. But Arthur Arnold of the University of California, Los Angeles, has
found that male and female neurons behave somewhat differently when kept in
laboratory glassware. And last year Eric Vilain, also of U.C.L.A., made the
surprising finding that the SRY gene is active in certain cells of the
brain, at least in mice. Its brain role is quite different from its
testosterone-related activities, and women’s neurons presumably perform that
role by other means.
It so happens that an unusually large number of brain-related genes are
situated on the X chromosome. The sudden emergence of the X and Y
chromosomes in brain function has caught the attention of evolutionary
biologists. Since men have only one X chromosome, natural selection can
speedily promote any advantageous mutation that arises in one of the X’s
genes. So if those picky women should be looking for smartness in
prospective male partners, that might explain why so many brain-related
genes ended up on the X.
“It’s popular among male academics to say that females preferred smarter
guys,” Dr. Arnold said. “Such genes will be quickly selected in males
because new beneficial mutations will be quickly apparent.”
Several profound consequences follow from the fact that men have only one
copy of the many X-related brain genes and women two. One is that many
neurological diseases are more common in men because women are unlikely to
suffer mutations in both copies of a gene.
Another is that men, as a group, “will have more variable brain
phenotypes,” Dr. Arnold writes, because women’s second copy of every gene
dampens the effects of mutations that arise in the other.
Greater male variance means that although average IQ is identical in men
and women, there are fewer average men and more at both extremes. Women’s
care in selecting mates, combined with the fast selection made possible by
men’s lack of backup copies of X-related genes, may have driven the
divergence between male and female brains. The same factors could explain,
some researchers believe, why the human brain has tripled in volume over
just the last 2.5 million years.
Who can doubt it? It is indeed desire that makes the world go round.
