Comment »Posted on Thursday 9 October 2008 at 9:25 pm by Jacob Aron
In Evolution

At the end of my review of episode one of Richard Dawkin’s series on Charles Darwin, I wondered whether the next episode would talk about how the modern world has affected human evolution.

In the end it didn’t (unfortunately), but earlier this week Professor Steve Jones of University College London weighed in with a lecture lecture entitled “Human evolution is over”. I wasn’t at the lecture myself, but The Times spoke to Professor Jones about his talk.

I didn’t know this, but apparantly one of the key factors in introducing mutations into our DNA is an ageing male population. As a man grows older cell division becomes more common, and each time a new cell splits off the likelihood of a mistake increases. It’s a bit like being made to write out lines (do they still do that at schools?) – copying out the same sentence 10 times is fairly trivial, but after 100 or 1,000 you’re much more likely to make a mistake. The sperm of an average 29-year-old male (the average reproductive age in the West) is the result of around 300 divisions from the sperm that created at him, whilst a 50-year-old’s sperm follows over a thousand divisons.

What has this got to do with evolution then? Professor Jones says that a shortage of older fathers means that less genetic diversity is being passed on, and without genetic diversity there can be no evolution. I find this a bit strange – surely if people are living longer they are also having children later? Professor Jones says not, comparing the modern man to Moulay Ismail of Morocco, who supposedly fathered 888 children well in to his old age.

I think it has got more to do with natural selection, which Professor Jones also agrees is a factor. It used to be in ancient times half of all children would not make it past their 20th birthday, but now (in the West at least) 98% survive to 21. Thanks to our modern healthcare and diet the evolutionary playing field has been levelled out, and survival of the fittest no longer applies.

Tim Dowling of the Guardian has a humorous but sadly scientifically-lacking response to the lecture. He makes four points showing an “upside” to the halt of evolution. I want to point out the inaccuracy of the first two.

His first is that “We’re not going backwards”. Immediately, this is a misunderstanding of the concept of natural selection. Evolution does not go “forwards” or “backwards”, which implies some sort of grand scheme that will lead us to the pinnacle of being as long as we continue onwards. Evolution is literally a random genetic walk that goes in any direction it pleases.

Next, “This will give chimps a chance to catch up”. We are not evolved from chimpanzees. This is a key misunderstanding, which often angers anti-evolutionists into uttering “I ain’t no damn monkey!” What happened is this: at some point in the past a species was separated, going one of two ways. One group evolved into Homo sapiens (i.e., us), whilst another became chimpanzees. This means that the chimps aren’t our ancestors, but more like cousins. Some scientists believe this last common ancestor to be the 7 million year old Sahelanthropus tchadensis, but the matter is still open for debate.

So are we evolving or not? In a way, the question is unimportant. If 29 is the average age of male reproduction, even your great-great-great-grandchild is only 200 years or so away. Evolution is a slow process taking millions of years, so any major changes to what we call human are far, far into the future.

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