We find that they vary in many different ways.

Some are stronger, some swifter, some hardier in constitution, some more cunning.

An obscure colour may render concealment more easy for some, keener sight may enable others to discover prey or escape from an enemy better than their fellows.

Among plants the smallest differences may be useful or the reverse.

The earliest and strongest shoots may escape the slug; their greater vigour may enable them to flower and seed earlier in a wet autumn; plants best armed with spines or hairs may escape being devoured; those whose flowers are most conspicuous may be soonest fertilised by insects.