Has evolution ended with Homo sapiens?

On this question, Tom Chivers at the Telegraph reports a fascinating disagreement between Sir David Attenborough and Dr. Adam Rutherford.

We have chosen some excerpts. Read it all here.

Like every other species on Earth, Homo sapiens is the product of more than three billion years of evolution: random, blind changes put through the filter of natural selection, leading from one simple original form to all the startling variety of life we see around us. Humanity’s lineage split with that of our closest relatives, the chimpanzees, six million years ago, and our ancestors have been evolving separately ever since. In that time we have gone from short, robust, hairy apes – perhaps partly tree-dwelling and knuckle-walking, like chimps – to tall, gracile, naked humans. It has been quite a journey.

But is that journey over? It might be, according to Sir David Attenborough, who said … “I think that we’ve stopped evolving. Because if natural selection, as proposed by Darwin, is the main mechanism of evolution – there may be other things, but it does look as though that’s the case – then we’ve stopped natural selection.”

To support his case, he points out that, unlike any other species, we can use technology to keep ourselves alive until breeding age, when otherwise we would have died. Specifically, he points towards the vast improvement in infant mortality rates: “We stopped natural selection as soon as we started being able to rear 95-99 per cent of our babies that are born. We are the only species to have put a halt to natural selection, of its own free will, as it were.” …

And what will happen next fascinates us even more. …

Attenborough … is suggesting something at once prosaic and startling: that human evolution ends here,that we are the final stop on the journey. You can understand his reasoning. After all, if we (at least in the affluent, technologically advanced West) can take even the most vulnerable babies, babies who would have died within hours of birth a hundred years ago, and keep them alive – essentially repair them so that they can live into adulthood and breed – have we not ended the cruel process of natural selection?

It’s not that simple, says Dr Adam Rutherford, a geneticist, author of Creation …  “He is absolutely right that the selection pressures on humans have radically changed, … And he’s right that one of the most profound changes to those pressures is infant mortality rates. But that’s not really, in a pure scientific sense, how evolution works.”

The fact that certain evolutionary pressures have been reduced – for example, the requirement for a baby’s lungs to be fully developed and functional by birth, now that we can keep that baby alive on a respirator until its lungs are grown – does not mean that all of them have gone. “The robust answer to the question ‘are humans evolving?’ is: we don’t know, because the timespans are too short to make a judgment,” says Dr Rutherford.

While we can watch evolution happen in viruses and bacteria – or fruit flies, or mice – human generations are just too slow; even the longest-lived of us can only reasonably hope to see great-grandchildren. Our split with the chimps takes us back to our great‑times-250,000-grandparents.

We can look at our own recent history, though, and at our genes. Several studies have suggested that human evolution has actually speeded up, not slowed down, since the advent of agriculture in the last 10,000 years – an eyeblink in evolutionary terms. In the past few thousand years some humans have evolved the ability to digest milk, unlike any other adult mammals. …

“If you look at changes in the frequency of genes in a population, which is the true measure of evolution, then I don’t think there’s any evidence to suggest that we’re not evolving,” says Dr Rutherford. The question, of course, is how we’re evolving.

There have been various suggestions, of varying stupidity, up to and including the suggestion that we’ll evolve fatter thumbs to help us text. (“That’s called Lamarckism, and it’s just wrong. The Jewish people have been cutting foreskins off their boys for 5,000 years and one hasn’t been born without a foreskin yet,” snorts Dr Rutherford.) More obviously plausible hypotheses include the idea that our tendency to have children later in life will select against people who are unable to do so.

What won’t necessarily happen is that we’ll become cleverer, or in any arbitrary way “better”, than we are now. Evolution doesn’t work that way.

The 2006 film Idiocracy suggested that clever people are having fewer and fewer children, while stupid people are having more, so the future of humanity is one of everyone being thick. That was a joke, but it illustrates quite neatly that evolution is not a stairway to a glorious pinnacle called “humanity”; intelligence is not the culmination of evolution, it’s just one tool that works for one species at the moment, just as sonar works for bats.

If powerful brains become less useful in future, then we can expect them to dwindle away, like the eyes of cave fish – they’re expensive, energy-draining things, and natural selection is a brutal accountant.

And if we contemplate the intellectual quality of those who have risen in recent years to the commanding heights of political power and academic authority in the West as a whole, we might suppose that the decline of brain-power in the human species has already begun.