In Darwin 's own words : `` Thus the small differences distinguishing varieties of the same species , will steadily tend to increase till they come to equal the greater differences between species of the same genus , or even of distinct genera . ''
In Darwin 's own words : `` Thus the small differences distinguishing varieties of the same species , will steadily tend to increase till they come to equal the greater differences between species of the same genus , or even of distinct genera '' .