Blackwell Publishing

Coevolution - What is an evolutionary 'arms race' ?


Evolutionary arms races

Predators and prey may often show an evolutionary pattern called escalation. By escalation, we mean that life has become more dangerous over evolutionary time: predators have evolved more powerful weapons and prey have evolved more powerful defences against them.

Escalation and evolutionary progress

We must distinguish escalation from evolutionary progress. If evolution is progressive, organisms will become better adapted to their surroundings through evolutionary time; if it is escalatory, the improvement in predatory adaptations may be matched by improvements in prey defences, and neither ends up any better off.

The two concepts are easy to distinguish by a thought experiment. If evolution is progressive in predators (for example), then later predators would be better at catching their prey than were earlier predators. If, however, evolution is escalatory, later predators will be no better than their ancestors at catching their contemporary prey types; but if transported in a time machine and set loose on the prey hunted by ancestral predators, they should cut through them like a modern jet fighter in a dog-fight with an early biplane.

The evidence suggests that the relative brain size of both carnivores and ungulates (like this zebra opposite) have increased through the Cainozoic. It has been suggested that this is through escalatory evolution.

Richard Dawkins provides a definition of the concept of an arms race.

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