Monday, February 15, 2016

The limits of adaptation

Evolution has populated the earth with an utterly remarkable range of life. Even today we are don't know exactly how many forms its takes and there are constant surprises, with life been found in the most unlikely places (extremophiles)

However as a process it has three fundamental limitations. 

Firstly it is essentially reactive. Most often most creatures thrive best when their environment is stable during which time there will be little if any evolution. Major changes are most often brought about through upheaval. There are many examples of creatures that, essentially have not changed much over hundreds of millions of years. The coelacanth  is a famous example but many others have not really changed much over the millennia, e.g. sharks, crocodiles.

The second problem is that it relies on chance. External catastrophes such as such as the rogue comet hitting earth as happened for the dinosaurs mentioned above are one example. However equally important are the random mutations that happen purely by luck, the vast majority of which are deadly. Just a tiny proportion have the capacity to be beneficial and even these will be useless if they do not happen to coincide with other propitiative conditions.  

The last issue is that it is constrained by the limits imposed by reality, especially 1 and 2. For example there was a time when all vertebrae were water bound. Vast areas of dry land were filled with plentiful supplies of food and no predators, a veritable paradise. However the fish of the time could not take advantage of this. The characteristics they had evolved for life in the water prevented them, they would be starved of oxyen as their gills failed, their streamlined forms lacked the means necessary for propulsion. They were trapped in water and it would take millions of years for them to make the transition. Even then it was through the very unstatisfactory route of the amphibian, still very limited through the need to remain close to water for reproduction.

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