Ten years ago today, Carl Sagan died. I lost one of my great heroes, and the world lost one of its greatest popularizers of science.

Sagan’s efforts were not limited to physics and astronomy but extended to molecular biology and evolution, as in this clip from his famous series Cosmos. Here, he describes two tales of artificial selection (of the Heike crab in Japan, and of domestic animals), using these stories to create a foundation from which to discuss natural selection. In the meantime, he takes a couple of premonitory shots at intelligent design (a nonsense that he was mercifully spared, but which it would have been breathtaking to see him demolish):

Carl Sagan

Sagan was not the first to use artificial selection, a notion to which few would object, to demonstrate the reasonability of natural selection. From The Origin of the Species first chapter, “Variation Under Domestication”:

Thus, a man who intends keeping pointers naturally tries to get as good dogs as he can, and afterwards breeds from his own best dogs, but he has no wish or expectation of permanently altering the breed. Nevertheless I cannot doubt that this process, continued during centuries, would improve and modify any breed … by this very same process, only carried on more methodically, did greatly modify, even during their own lifetimes, the forms and qualities of their cattle. Slow and insensible changes of this kind could never be recognised unless actual measurements or careful drawings of the breeds in question had been made long ago, which might serve for comparison.

It may well have been Sagan’s introduction of artificial selection to me as a rapt nine-year-old on the family room sofa that made it so simple for me as an adult to accept the logic of evolution by natural selection.

Whenever people ask why I became a biologist, my answer invariably includes Cosmos. Sometimes it’s the story of the Heike crab; other times it is my clear memory of a computer animation of DNA polymerase, methodically adding nucleotide blocks to a new growing strand; at yet others it is Carl’s willingness to entertain fanciful projections of the possible appearance of life on other worlds. Cosmos provided rich food for my young mind, and I will always be grateful.

Thank you, Dr. Sagan.

“…and sometimes I despair the world will never see another man like him.”

For other entries in the Sagan blog-a-thon, see: