IT鈥橲 THE ultimate problem in family etiquette. The researchers from your
local lab phone to say they鈥檝e thawed out a 50,000-year-old ancestor of yours,
and they want to bring him over. The question is, should you welcome this
forebear into your home?
Perhaps, like palaeobiologist Simon Conway Morris of Cambridge University,
you believe that we differ very little from people who lived tens of millennia
before us. He suggests that, given suitable education, your long-lost kin would
have no problem holding their own in your business or at your local bistro.
鈥淭hey could walk into the room and, given a haircut, they鈥檇 fit right in,鈥� says
Conway Morris. In other words, our evolution has been all but over for quite
some time.
There is a certain comfort in that thought. After all, if you decide to go
for cryogenic preservation when you die, it could be you who鈥檚 cast in the role
of the defrosted dinner guest. But before you make those hotel reservations for
a family reunion in 50,000 years鈥� time, you should be warned that there are
those who strongly disagree with Conway Morris鈥檚 forecast for our species. Far
from slowing evolution down, they say, technology and culture could be
accelerating it to a furious pace. So instead of being welcomed as an equal, you
could be shunned as a primitive freak.
Advertisement
Despite their varying visions of our future, scientists on all sides of the
debate over our evolutionary destiny agree about how things started out. In the
beginning, all life on Earth was at the mercy of the same evolutionary forces of
natural selection. Competition, starvation, predators, disease and sometimes bad
luck took their toll on our ancestors and thereby pushed and pulled the gene
pool in different directions. Overall, those with genes that suited the
environment survived and reproduced, while those with an inappropriate genetic
constitution disappeared into oblivion.
Then, about 5 million years ago, primate evolution split along two tracks:
one leading towards humans, the other towards chimpanzees. A million years
later, our ancestors adopted an upright gait, and 2 million years after that
their bodies and brains began to grow and they started making primitive stone
tools. The first modern-looking humans appear in the fossil record about 130,000
years ago. By 50,000 years ago, there is evidence for folks who appear to have
distinctly modern bodies and lifestyles. They created complex tools and
jewellery, built shelters, buried their dead in graves and probably had the
language skills to chat about what they were doing.
And through these simple acts, the newly minted Homo sapiens
unintentionally thwarted the very forces that had created our species, says
Conway Morris. Effective weapons removed most of the threat of predators, and
agricultural development beat back starvation. 鈥淭he technological innovations
that took place during this period were astounding,鈥� he says. 鈥淏ut there is no
sign that this was due to genetic changes.鈥� And while we still haven鈥檛 banished
human hunger or disease from the planet, the trend is clear. We are cushioning
ourselves from the forces that shaped our biology for aeons.
Steve Jones, a geneticist at University College London and author of The
Language of Genes, agrees. Culture and technology, he says, spelled the
beginning of the end for evolution in its classic sense鈥攏atural selection
of genes better suited to their environment. In the developed world, child
mortality has declined drastically and family size tends to be small. Put
simply, natural selection doesn鈥檛 take place if everyone, regardless of the
genes they carry, has two children who survive to reproduce.
Too much alike
And this is only half the story, Jones adds. For evolution to proceed, there
must not only be environmental rigours that weed out the weakest, there must
also be genetic variation between members of the population so that some are
better suited to cope than others. Humans, it turns out, are already remarkably
similar at the genetic level. There is only about a 0.1 per cent difference
between your DNA and that of any passer-by. In contrast, among our close
relatives the chimpanzees, the variation is at least five times that.
Jones believes that modern life continues to chip away at the few remaining
differences. For instance, mutations in the chromosomes of eggs or sperm become
more common as parents age, but this source of genetic variation is disappearing
because parental age is decreasing as couples tend to stop at two kids. What鈥檚
more, in the past, some human mutations were preserved because they provided
protection from disease. But as public health measures eliminate deaths from
these diseases, the number of people who carry the mutation decreases.
All the while, says Jones, our knack for building machines that whisk us
around the planet dashes any hope that we might spin off a new species of human.
That鈥檚 because the spawning of new species requires reproductive isolation, and
geographic barriers often provide just the right type of genetic privacy. But
our wanderlust regularly gives the gene pool a good, homogenising stir. With
mutational fuel running low and the engine of natural selection idling, Jones
concludes that our evolution is, at most, coasting slowly to a standstill.
But according to Lynn Jorde, a human geneticist at the University of Utah, it
is just changing direction. Agricultural developments may have made famine less
frequent, he points out, but they have also caused people to live in larger,
more densely populated areas, increasing the likelihood and impact of epidemics
such as cholera and AIDS. In addition, our frequent globetrotting has allowed
disease organisms to hitch rides into even the most remote communities. 鈥淎ll
this presented our immune systems with greater challenges,鈥� he says.
Science may have spawned medicine, but it has also unleashed an industrial
and technological revolution that spews out radioactivity and chemicals that can
contribute to an increase in our mutation rate鈥攐r act directly as
selective forces. 鈥淎 thousand people a day die of cigarette smoking in the US
alone,鈥� says Jorde. 鈥淭hat鈥檚 got to have some impact.鈥�
Even a little impact, genetically speaking, could go a long way. Remember
that the vast difference between us and chimps comes down to a mere 1.5 per cent
difference in our DNA. In fact, our current genetic variability is still high
enough to pose a significant medical problem. Genetic factors mean that new
drugs often prove ineffective on a significant chunk of the population (New
Scientist, 4 November 2000, p 31).
Still, we may ultimately manage to thwart the health and pollution problems
of our own making. So would that lead to human evolution鈥檚 last breath?
Christopher Wills of the University of California in San Diego certainly doesn鈥檛
think so. He believes that as the deadly blows of past selective pressures
disappeared, we began to be shaped by more subtle but equally persuasive forces.
鈥淚t is less obvious. But you don鈥檛 have to pile up bodies in the street to have
evolution.鈥� In fact, he believes that rather than slowing us down, our culture
has probably propelled us into developing at unprecedented speeds.
Culture itself shapes our genes. In those societies where milk drinking is an
ancient practice, for example, people have genes that allow them to digest the
milk sugar lactose. People whose ancestors were not milk-drinkers tend to lack
these mutations. Wills argues that today鈥檚 globalisation increases the potential
diversity of the human gene pool by bringing together such specialised versions
of genes that had been separated through much of history. 鈥淭his creates new
combinations that may never have been seen before,鈥� he says.
In his book Children of Prometheus, Wills argues that the major
evolutionary influence of culture is to create new environments and select for
human genetic diversity. Fine motor skills, for instance, were probably not much
use when our ancestors were doing little more technical than smashing rocks. But
in a more modern society you can benefit from both big muscles, and the delicate
manipulations of a watchmaker. One talent of the human animal is to devise ever
more exacting mental and physical challenges. Wills cites the recent rise in
popularity of extreme sports. 鈥淭hese people are now succeeding based on skills
that didn鈥檛 exist even a few years ago,鈥� he says.
He also points out that diversity itself can be selected for. Outside our
species, for example, researchers have found that trees that are rare in forests
reproduce more often than more common varieties. The thinking is that a sparse
population gives species-specific parasites less of a chance to breed.
Similarly, he argues that rare traits are rewarded in our culture. Musical
geniuses thrive exactly because they are exceptional. If we all had perfect
pitch and virtuosity, we would clearly be less impressed.
It is in intellectual and psychological areas that our culture generates the
greatest advancement and diversity, according to Wills. The decision not to have
children, for example, has exactly the same evolutionary impact as losing a
child through predation or disease. Now consider that this form of selection
might be triggered by our genetic constitution. Wills points out that people who
cope badly with stress in their lives often choose not to have children, so the
effect may be a bloodless coup where those genes that allow us to deal with the
stresses of modern life emerge victorious.
Jorde agrees that the evolution of the brain is a neglected area. 鈥淭he best
new estimates say a third or more of our genes play a role in the development or
function of our brain. We鈥檙e only just beginning to understand what that means
for our evolution,鈥� he says. The dystrophin muscle gene, for example, which
causes muscular dystrophy when faulty, is also expressed in the brain. So too
are XRCC4 and Lig IV, which are involved in immunity. As a
result, genetic changes that have improved muscle tone or our ability to fight
disease could have had psychological or intellectual repercussions.
All this suggests that it would take a lot more than a haircut to bring our
primitive ancestors up to scratch. They may have been mentally incapable of
dealing with modern society.
But it isn鈥檛 always obvious how to chart the effects of culture on evolution.
Do increases in the use of birth control select for better parents, because only
those that really want children tend to have them? Or does it mean that a great
many more children are born to parents who mess up their use of pills or
condoms, selecting for parents who are less than careful?
Richard Dawkins of Oxford University questions whether a good case can be
made for close co-evolution of human genes and culture. He points out that much
cultural change is simply too fast and too fickle. It takes a reproductive
generation, say 25 years, for a slight change in the human gene pool to emerge,
while fashions change almost daily. Dawkins says that if the human gene pool
were a cork thrown into the ocean, then most cultural effects would be like
chaotic winds tossing it back and forth, without tugging it in any particular
direction.
Yet, continuing the metaphor, Dawkins admits there might be what he calls
鈥淕ulf Stream effects鈥濃�攍ong-term trends within society that draw our
species in a particular direction. One of his nominees for such a deep cultural
current is the growth of computational power. The density of transistors on
computer chips has doubled on average every 18 months since the integrated
circuit was invented, a phenomenon known as Moore鈥檚 law. Of course, this would
influence human evolution only if the ability to cope with this electronic
explosion provides some reproductive advantage.
Is that so crazy? The Internet has spawned a whole generation whose social
interaction is increasingly electronic. Chances are that some readers of this
feature will know couples who forged e-relationships that have blossomed into
e-marriages. And technology鈥檚 influence on mating choice extends beyond the
Internet鈥檚 great cyber-singles bar. Recently, researchers from the University of
Liverpool reported that young men in pubs and bars use their mobile phones as
lekking devices, meeting in groups and displaying their technology as a symbol
of status and wealth, in much the same way that male grouse congregate and show
off to attract mates (Human Nature, vol 11, p 93).
Whether or not culture has shaped our biology in the past, John Campbell of
the University of California, Los Angeles, thinks we will soon consciously
control our own evolution. At a conference two years ago called Engineering the
Human Germline, which he helped organise, most experts agreed that the first
humans with designer genes will probably be born in the next two decades (
New Scientist, 3 October 1998, p 24). 鈥淚t will start in the areas that are
least controversial, such as treating genetic disease,鈥� says Campbell. 鈥淏ut
people will soon be dumbfounded by the possibilities.鈥�
For instance, certain fairly simple natural genetic mutations are now thought
to confer resistance to HIV or protection from high cholesterol. And researchers
are already hot on the trail of genes that might enhance longevity and cognitive
ability. Engineering these refinements into human chromosomes would involve
standard genetic manipulations of single human cells and then using these cells
to create a clone鈥攖he same technology that made Dolly the sheep
possible.
The chosen people
Though no one has yet crossed the line and grown genetically engineered human
clones, the prospect seems closer than ever. Dolly was a relatively new
phenomenon two years ago, but now she is just one of dozens of sheep, mice,
cows, goats and pigs rolling off the cloning production line. And only a few
months ago, a couple from Colorado caused an uproar by using genetic tests to
choose an embryo. They wanted a baby that would be a close tissue match for
their other daughter, who suffers from an inherited blood disease. Some
ethicists saw the episode as the slippery slope towards full-scale eugenics. If
parents are already willing to use genetic screening to create tissue donors,
will it be long before they begin to screen for babies with high IQ or superior
athletic ability?
While many people recoil at the idea of 鈥渄esigner babies鈥�, Campbell thinks
that small groups are bound to use the latest reproductive techniques to push
the boundaries of human evolution. 鈥淭he technology is going to advance beyond
what our conservative society will embrace,鈥� he says. 鈥淏ut I think we will see
some people evolve at rates we haven鈥檛 even imagined yet.鈥� Geneticist Lee Silver
of Princeton University predicts a similar cottage industry of human evolution
in his book Remaking Eden. He speculates that cloning and other genetic
technologies could create a genetic elite, or what he dubs the 鈥淕enRich鈥� class,
who would refuse to mate with 鈥渘atural鈥� human beings and ultimately become a
separate species.
But Jones doubts that even conscious effort could get us out of our
evolutionary rut. The GenRich would be hard pressed to keep their new genes to
themselves, he says. History shows that even in a highly stratified society, the
classes still mingle due to our basic, animal instincts. 鈥淚 believe in the
healing power of lust,鈥� Jones says. And a few improved genes among the 100,000
we possess, in a global population of 6 billion, is a drop in the ocean.
But even if Jones is right and there is no way on Earth that a new humanoid
species could arise, engineer Robert Zubrin is betting it will anyway. Zubrin,
who is president of Pioneer Astronautics in Colorado, thinks it will happen on
another planet.
He points out that the very factors which Conway Morris and Jones believe
have led to a lull in human evolution鈥攋et travel, light speed
communication and advanced medicine鈥攈ave made it possible for us to
venture into space. 鈥淪ome argue that this means we are at the end of the history
of humanity,鈥� says Zubrin. 鈥淏ut I think that means we are at our first
尘辞尘别苍迟蝉.鈥�
Our destiny, says Zubrin, is to leave the planet, just as our ancestors left
Africa and colonised the rest of the world. And our first stop could be Mars,
which might be made habitable through terraforming. In fact, he believes that a
fully functional Martian city with hundreds of residents will be built in this
century. And as surely as our descendants shape that world, it will shape
them.
There would be incredible selection for people whose genes help them survive
in the harsh environment, and even on a terraformed Mars this would long
persist. While providing Earthly children with genetic enhancements may seem
like a frivolity, it would just be good sense to endow Martian kids with the
ability to endure a thinner atmosphere and stronger solar radiation. And since
the gravity on Mars is only about one-third the strength of Earth鈥檚, Zubrin
suggests it might also be wise to give its inhabitants long, springy legs to
cover terrain more easily. The unprecedented geographic isolation of this new
civilisation and the speed of genetic selection among its inhabitants would make
it fertile ground on which a new species could arise.
While it might not be that surprising that a rocket scientist such as Zubrin
envisages a future in space, some biologists are quick to agree with him. 鈥淚f we
find even a distant planet that can support life, nothing will stop us from
getting there one way or another,鈥� says Wills. 鈥淭hat鈥檚 because our curiosity is
orders of magnitude above that of other species.鈥�
Perhaps that鈥檚 why you can鈥檛 help wondering what you should bring for that
family dinner party in the year 52,000. It might be wise to hedge your bets. A
good bottle of wine for the parents, perhaps, and extremely long elastic
trousers for the kids.