New research suggests that for clovers the same evolutionary adaptation is destined to appear time and time again. Whilst chance events (such as a meteorite impact) have caused considerable shifts in evolution. These new results suggest that if we were able to replay evolution some adaptations might reappear everytime...
Some clover species have two forms, one of which releases cyanide to discourage nibbling by snails and insects and the other of which does not. A scientist found that this 'polymorphism' has evolved independently in six different species of clover, each time by the wholesale deletion of a gene. The clover species are in a sense predisposed to develop this trait, suggesting that evolution is not entirely free form but instead bumps up against constraints.
http://www.sciencedaily.com/releases/2014/06/140623225009.htm
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