I really like Richard Dawkins explanation of this, where he has you imagine taking a photo of yourself from your are born to you reach adulthood with 1 minute intervals.<p>If you stack these pictures, there is no single picture you can pull out and say: &quot;Here I transitioned from child to adult&quot; e.g. Likewise with animals and evolution. Changes are so minute that you can speak of a transition from one species to another happening at the point of birth.<p>Only when you look at pictures of yourself far away from each other in the pile can you start differentiating them. Likewise with animals.