We can assume that in a relatively short time — perhaps within 100 million years — the one celled organism evolved into a colony of cells. With the further passage of time, groups of cells within those colonies assumed specialized functions of food-gathering, digestion, the structural features of an outer skin, and so on; thus began the stage of evolution leading to the complex, many-celled creatures which dominate life today.
The fossil record contains no trace of these preliminary stages in the development of many-celled organisms. The first clues to the existence of relatively advanced forms of life consist of a few barely discernible tracks, presumably made in the primeval slime by soft, wriggling wormlike animals. These are found in rocks about one billion years old. These meager remains are the earliest traces of many-celled animal life on the planet.
Red Giants and White Dwarfs : Man's Descent from the Stars (1971), p. 249.
When a scientist writes about God, his colleagues assume he is either over the hill or going bonkers. In my case it should be understood from the start that I am an agnostic in religious matters. My views on this question are close to those of Darwin, who wrote, "My theology is a simple muddle. I cannot look at the Universe as the result of blind chance, yet I see no evidence of beneficent design in the details."
God and the Astronomers (1978), Ch. 1 : In the Beginning.
At this moment it seems as though science will never be able to raise the curtain on the mystery of creation. For the scientist who has lived by his faith in the power of reason, the story ends like a bad dream. He has scaled the mountains of ignorance; he is about to conquer the highest peak; as he pulls himself over the final rock, he is greeted by a band of theologians who have been sitting there for centuries.
God and the Astronomers (1978), p. 116; (p. 107 in 1992 edition).