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My students have heard me say many times that it would take a sample of thousands of people to test the hypothesis of neutrality within today's population. Well, Framingham is one such sample, and it's not surprising that some things would be found significantly to affect fitness.

The Time article mentions our work on recent evolution in a very positive way. Of course, the Framingham sample isn't suitable for testing what has been going on during the last 40,000 years; it is about mass selection on phenotypes in the present American population. That will involve mostly selection on standing variants, things that are already common in the population. Some of those may be things that were increasing in the past, others not -- some may even be reversals in direction compared to pre-industrial times. And there's no predicting how they might change in the future, as we continue to change our environment out from under ourselves.

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Our skulls and our genes show that we're still evolving, but not always in the ways you might expect.

For example, the typical human head has actually been getting smaller over the past few thousand years, reversing the earlier evolutionary trend. Meanwhile, East Asians are becoming lighter-skinned - and appear to have more sensitive hearing than their ancestors did 10,000 years ago.

John Hawks, an anthropologist and blogger at the University of Wisconsin at Madison, points to such trends as evidence that "recent evolution is real."

Hawks delved into a few of his favorite scientific tales over the weekend in Austin, Texas, at the annual CASW New Horizons in Science meeting.

You've no doubt heard some of those tales already. There's the one about the genetic mutation about 7,500 years ago that enhanced Europeans' ability to digest milk in adulthood - which in turn encouraged the rise of dairy farming. And then there's the still-debated claim that early humans' skin became lighter as they migrated northward because the need for vitamin D absorption outweighed the risk of skin cancer.

Other researchers have found that several genetic strategies for fighting off malaria have arisen among populations in sub-Saharan Africa, including a mutation that can also lead to sickle-cell anemia.

Such findings have come about thanks to detailed studies of how genetic mutations are passed along - and how beneficial mutations tend to become more widespread, even if those benefits are accompanied by secondary risks. The fingerprint of such changes, Hawks said, is a phenomenon known as linkage disequilibrium, in which characteristic snippets of genetic code show up in combination among members of a population. The level of genetic linkage can indicate how much of a role natural selection is playing in particular genes.

Hawks said about 3,000 of the genes that distinguish humans from chimpanzees show signs of linkage disequilibrium - and that suggests that a quarter of the evolutionary divergences between the two genomes are continuing today.

It's not just genes that are revealing these changes. One of Hawks' specialties is measuring how the typical shape of human skulls has changed over the course of thousands of years. The current view, based on skull measurements as well as genetics, is that the modern head isn't as "long" as it was 10,000 years ago, with a resulting reduction in brain volume. "Brains are shrinking," Hawks said.

This isn't necessarily a bad thing: The brain is the human body's hungriest organ, consuming half of the glucose we take in. The modern brain may be packing more power into a smaller space and as a result cutting down on the biological energy requirements - with the help of external memory devices.

"What do we need these brains for? We've got iPods," Hawks joked.

But often we're too close to the situation to second-guess what natural selection is doing to us. "Efficiency demands that the brain should be smaller," Hawks said. "Maybe we got better with smaller brains, but I gotta tell you that maybe we're getting dumber. How can we know?"

That aura of uncertainty applies to other ongoing evolutionary changes as well. One of the genes under heavy selection in East Asian populations plays a role in the development of the inner ear's machinery. That suggests that more sensitive hearing may be conferring some sort of advantage on those populations, and Hawks speculates that it may have something to do with the tonal character of most Asian languages. That's only a guess, however.

The guesswork becomes even murkier when it comes to figuring out why genetic coding linked to redheadedness and lighter skin color is becoming more prevalent among Asians. "Our species is evolving like crazy in pigmentation in different ways in different populations, presumably because of the same underlying selection pressures," Hawks said.

Hawks doesn't think the vitamin D factor alone can explain why skin color is being affected by natural selection. Some theorists, including Charles Darwin himself, have suggested that sexual selection may be at work - that having lighter skin somehow improves an individual's reproductive prospects. But in this more evolved age, voicing that kind of view can make your typical researcher sound like a Neanderthal.

So what does Hawks think is behind the skin-color issue? "That's a box I don't want to open," he told me.

Further thoughts from John Hawks:

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Some genetic mutations confer clear benefits on the folks who have them but may not spread widely among populations because they don't enhance reproductive fitness, Hawks. Classic examples would be mutations that tend to extend longevity, such as the one that gives Italian villagers in Limone sul Garda extra resistance to cardiovascular disease.

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The recent analysis of a 4.4 million-year-old hominid fossil known as Ardi could lead to big changes in how we view our evolutionary family tree. "It's not a tree. It's not a bush. It's like a network where things reconnect," Hawks told me. The latest findings suggest that the common ancestor for chimps and humans was less chimplike than previously thought. In some areas - for example, the hands - humans may be considered more "primitive" than chimps, Hawks pointed out.

Conall

Nov 1 2009, 05:01 AM

In the future everyone in the west will look fat and lazy, perfect food for the morlock third world working classes that are soon to take over the whole world.

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Humanity may split into two sub-species in 100,000 years' time as predicted by HG Wells, an expert has said.

Evolutionary theorist Oliver Curry of the London School of Economics expects a genetic upper class and a dim-witted underclass to emerge.

The human race would peak in the year 3000, he said - before a decline due to dependence on technology.

People would become choosier about their sexual partners, causing humanity to divide into sub-species, he added.

The descendants of the genetic upper class would be tall, slim, healthy, attractive, intelligent, and creative and a far cry from the "underclass" humans who would have evolved into dim-witted, ugly, squat goblin-like creatures.

Race 'ironed out'

But in the nearer future, humans will evolve in 1,000 years into giants between 6ft and 7ft tall, he predicts, while life-spans will have extended to 120 years, Dr Curry claims.

Physical appearance, driven by indicators of health, youth and fertility, will improve, he says, while men will exhibit symmetrical facial features, look athletic, and have squarer jaws, deeper voices and bigger penises.

Women, on the other hand, will develop lighter, smooth, hairless skin, large clear eyes, pert breasts, glossy hair, and even features, he adds. Racial differences will be ironed out by interbreeding, producing a uniform race of coffee-coloured people.

However, Dr Curry warns, in 10,000 years time humans may have paid a genetic price for relying on technology.

Spoiled by gadgets designed to meet their every need, they could come to resemble domesticated animals.

Receding chins

Social skills, such as communicating and interacting with others, could be lost, along with emotions such as love, sympathy, trust and respect. People would become less able to care for others, or perform in teams.

Physically, they would start to appear more juvenile. Chins would recede, as a result of having to chew less on processed food.

There could also be health problems caused by reliance on medicine, resulting in weak immune systems. Preventing deaths would also help to preserve the genetic defects that cause cancer.

Further into the future, sexual selection - being choosy about one's partner - was likely to create more and more genetic inequality, said Dr Curry.

The logical outcome would be two sub-species, "gracile" and "robust" humans similar to the Eloi and Morlocks foretold by HG Wells in his 1895 novel The Time Machine.

"While science and technology have the potential to create an ideal habitat for humanity over the next millennium, there is a possibility of a monumental genetic hangover over the subsequent millennia due to an over-reliance on technology reducing our natural capacity to resist disease, or our evolved ability to get along with each other, said Dr Curry.

He carried out the report for men's satellite TV channel Bravo.

Toiletman

Nov 4 2009, 09:12 PM

Or the few non-multiplying super-humans will get killed and eaten by the much more numerous humans

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"While science and technology have the potential to create an ideal habitat for humanity over the next millennium, there is a possibility of a monumental genetic hangover over the subsequent millennia due to an over-reliance on technology reducing our natural capacity to resist disease, or our evolved ability to get along with each other," said Dr Curry.

jojocircus

Nov 7 2009, 02:08 AM

He says sexual selection will take place further into the future...Uh okay, hate to tell him that sexual selection has been going on since forever.