Evolution Prevented By Competition

Most of the history of life is about changelessness, not evolution. A relentless struggle for existence produces creatures good at winning that particular struggle, not creatures that can open up new possibilities.

Creating novel creatures turns out to be relatively easy, provided that they are free from competitive pressures. This happens on islands, with rare and interesting creatures like the finches and giant turtles of the Galapagos Islands. And it can also happen in isolated lakes:

“Michael Bell has his children to thank for his discovery. Back in 1990, they were getting restless as he was driving past Loberg Lake in Alaska. Bell, a biologist who studies the evolution of sticklebacks, had not planned to collect any fish, as the native sticklebacks had been exterminated in 1982 to improve the lake for anglers. ‘But we saw the lake, and we had to do something,’ Bell says.

“To Bell’s surprise, they found that marine sticklebacks had recolonised the lake. This in itself was not all that unusual: marine sticklebacks can live in fresh water, and most freshwater species are descended from marine ones that colonised streams and lakes as the ice retreated at the end of the last ice age.

“But there was something odd about these sticklebacks. Ten thousand years on from the ice age, freshwater sticklebacks are quite different from their sea-going ancestors. The most obvious change is loss of armour plates, which seem to take longer to develop in fresh water. In lakes, lightly armoured fish may outgrow and outcompete fully armoured fish.

“This trait was assumed to evolve slowly, over thousands of years, so Bell was surprised to find that some of the fish he caught in Loberg Lake had fewer plates. In 1991 he asked a friend to collect some more fish. Sure enough, more had lost their armour.

“Bell, who is based at Stony Brook University in New York, began collecting sticklebacks every year. Each time, he found more lightly armoured fish. By 2007, 90 per cent were of the low-armour form. Far from taking millennia, the trait had evolved in a couple of decades…

“More examples keep turning up. A species of fish in a lake in Nicaragua has split in two in only 100 years. The new variety has evolved a narrower, pointier head and fatter lips, ideal for nibbling insects from crevices. The original variety has sturdier jaws and extra teeth to crack snail shells. Lab studies suggest the strains do not mate with each other even when put together, which would mean they are on their way to becoming separate species…

“As the list of examples grew, Kinnison and his colleagues began to pull them together and look at what they tell us about evolution. ‘We started to realise that maybe this was not the exception, that this was the norm.’

“In fact, he now argues that the term ‘rapid evolution’ is misleading, because it implies evolution is normally slow. Instead, he and his colleagues prefer ‘contemporary evolution’.

“Nowadays, most biologists with a background in evolution appreciate this, Kinnison thinks. Of course, proving that contemporary evolution is the norm in a world of millions of species is a challenge. To those who remain sceptical, though, Kinnison’s response is simple: ‘Take a look.’

“If rapid evolution really is the norm, how come fossil and genetic studies suggest it is slow? The answer may be that new species and traits not only evolve rapidly, they also disappear fast too and do not leave their mark on the fossil or genetic record…

“Put it all together and the picture of evolution that is emerging is radically different to the way most people envisage the process. As Kinnison puts it, the popular view of evolution is upside down. People think evolutionary changes are imperceptible in the short term but add up to big changes over millions of years. In fact, the opposite is true. It now appears that organisms evolve very rapidly in response to any changes in their environment, but in the longer term most evolutionary changes cancel each other out.” [Issue 2806 of New Scientist magazine, page 32-36]

So much for the ‘struggle for existence’. A fierce struggle produces nothing very new. Spectacular new advances tend to occur on the margins. The ancestors of all land-walking tetrapods were a minor group of fish. Mammals emerged after the death of the dinosaurs from a collection of obscure little creatures that had no mattered before. Humans evolved as part of a minor group of primates, the apes, which on the whole had lost out to the smaller and more versatile monkeys.

I don’t think it’s that different in human culture. People long ago found the benefits of leaving some people alone to do whatever may interest them: most achieve nothing much but just a few achieve something spectacular. Science sprung from this habit and remains dependent on it.

From Newsnotes, May 2011.

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