into a miniature pole vault, and the marathon-runners’ main aim in life is to drink the water-jump before the steeplechasers get to it and drink it first. This is the Evolympics, where everything happens at once.
The evolutionary competitions, and their outcomes, also depend on context. Climate, in particular, plays a big role. In the Galápagos, selection for beak size in Darwin’s finches depends on how many birds have what size of beak, and on what kinds of food – seeds, insects, cactus – are available and in what quantities. The amount and type of food depend on which plants and insects are competing best in the struggle to survive – not least from being eaten byfinches – and breed. And all of this is played out against a background of climatic variations: wet or dry summers, wet or dry winters. Observations published in 2002 by Peter and Rosemary Grant show that the main unpredictable feature of finch evolution in the Galápagos is climate. If we could forecast the climate accurately, we could predict how the finches would evolve. But we can’t predict the climate well enough, and there are reasons to think that this may never be possible.
That doesn’t prevent evolution from being ‘predictive’, hence a science, any more than it prevents meteorology from being a science. But the evolutionary predictions are contingent upon the behaviour of the climate. They predict what will happen in what circumstances, not when it will happen.
Darwin almost certainly read Paley’s masterwork as a young man, and in later life he may well have used it as a touchstone for his own, more radical and far more indirect, views. Paley succinctly expressed many of the most effective objections to Darwin’s ideas, long before Darwin arrived at them. Intellectual honesty demanded that Darwin should find convincing answers to Paley. Such answers are scattered throughout Darwin’s epic treatise The Origin of Species , though Paley’s name does not appear.
In particular, Darwin found it necessary to tackle the thorny question of the eye. His answer was that although the human eye appears to be a perfected mechanism, with many interdependent parts, there are plenty of different ‘eyes’ in the animal kingdom, and a lot of those are relatively rudimentary. They can even be arranged in a rough progression from simple light-sensing patches to pinhole cameras to complex lenses (though this arrangement should not be interpreted as an actual evolutionary sequence). Instead of half an eye, we find an eye that is half as effective at detecting light. And this is far, far better than no eye at all.
Darwin’s approach to the eye is complemented by some computer experiments published by Daniel Nilsson and Suzanne Pelger 4 in 1994. They studied a simple model of the evolution of a light-sensing patch of cells, whose geometry could change slightly at every ‘generation’, and which was equipped with the capacity to develop accessories such as a lens. In their simulations, a mere 100,000 generations were enough to transform a light-sensing patch into something approaching the human eye, including a lens whose refractive index varied from place to place, to improve its focus. The human eye possesses just such a lens. Moreover, and crucially, at every one of those 100,000 steps, the eye’s ability to sense light got better.
This simulation was recently criticised on the grounds that it gets out what it puts in. It doesn’t explain how those light-sensing cells can appear to begin with, or how the eye’s geometry can change. And it uses a rather simplistic measure of the eye’s performance. These would be important criticisms if the model were being used as some kind of proof that eyes must evolve, and as an accurate description of how they did it. However, that was never the purpose of the simulation. It had two main aims. One was to show that in the simplified context of the model, evolution constrained by natural selection could
The evolutionary competitions, and their outcomes, also depend on context. Climate, in particular, plays a big role. In the Galápagos, selection for beak size in Darwin’s finches depends on how many birds have what size of beak, and on what kinds of food – seeds, insects, cactus – are available and in what quantities. The amount and type of food depend on which plants and insects are competing best in the struggle to survive – not least from being eaten byfinches – and breed. And all of this is played out against a background of climatic variations: wet or dry summers, wet or dry winters. Observations published in 2002 by Peter and Rosemary Grant show that the main unpredictable feature of finch evolution in the Galápagos is climate. If we could forecast the climate accurately, we could predict how the finches would evolve. But we can’t predict the climate well enough, and there are reasons to think that this may never be possible.
That doesn’t prevent evolution from being ‘predictive’, hence a science, any more than it prevents meteorology from being a science. But the evolutionary predictions are contingent upon the behaviour of the climate. They predict what will happen in what circumstances, not when it will happen.
Darwin almost certainly read Paley’s masterwork as a young man, and in later life he may well have used it as a touchstone for his own, more radical and far more indirect, views. Paley succinctly expressed many of the most effective objections to Darwin’s ideas, long before Darwin arrived at them. Intellectual honesty demanded that Darwin should find convincing answers to Paley. Such answers are scattered throughout Darwin’s epic treatise The Origin of Species , though Paley’s name does not appear.
In particular, Darwin found it necessary to tackle the thorny question of the eye. His answer was that although the human eye appears to be a perfected mechanism, with many interdependent parts, there are plenty of different ‘eyes’ in the animal kingdom, and a lot of those are relatively rudimentary. They can even be arranged in a rough progression from simple light-sensing patches to pinhole cameras to complex lenses (though this arrangement should not be interpreted as an actual evolutionary sequence). Instead of half an eye, we find an eye that is half as effective at detecting light. And this is far, far better than no eye at all.
Darwin’s approach to the eye is complemented by some computer experiments published by Daniel Nilsson and Suzanne Pelger 4 in 1994. They studied a simple model of the evolution of a light-sensing patch of cells, whose geometry could change slightly at every ‘generation’, and which was equipped with the capacity to develop accessories such as a lens. In their simulations, a mere 100,000 generations were enough to transform a light-sensing patch into something approaching the human eye, including a lens whose refractive index varied from place to place, to improve its focus. The human eye possesses just such a lens. Moreover, and crucially, at every one of those 100,000 steps, the eye’s ability to sense light got better.
This simulation was recently criticised on the grounds that it gets out what it puts in. It doesn’t explain how those light-sensing cells can appear to begin with, or how the eye’s geometry can change. And it uses a rather simplistic measure of the eye’s performance. These would be important criticisms if the model were being used as some kind of proof that eyes must evolve, and as an accurate description of how they did it. However, that was never the purpose of the simulation. It had two main aims. One was to show that in the simplified context of the model, evolution constrained by natural selection could
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