Darwin's Theory vs. The Fossil Record

In my book Darwin's Doubt, I discuss a problem that Darwin understood about his own theory,

even in 1859 when he published The Origin of Species, and that is that the pattern of appearance

of new forms of life in the fossil record does not match the branching tree pattern that

he presented in The Origin of Species. But instead, in the fossil record, new forms of life

arise very abruptly, and there's one particular such event in the history of life that's especially

dramatic. It's known as the Cambrian explosion. Most of the first animals arise during

the Cambrian period, and these first animals exemplify very new ways of arranging body parts

and tissues called a body plan.