The origin of life on Earth took a puzzlingly short time. Panspermia is appealing because it means that the origin of life
need not be confined to a few million years on one planet. Similar puzzles arise in the evolution of higher life forms.
Punctuated equilibrium, for example, seems to violate the darwinian account of gradual evolution by trial-and-error, a
few DNA nucleotides at a time. The strong version of panspermia alleviates this puzzle as well. If all of life comes
ultimately from space, genes may appear to be older than necessary, evolution by the acquisition of whole genes or suites
of genes, by horizontal gene transfer (HGT), becomes much more important, and punctuated equilibrium is not
surprising. Does evidence support this supposition? How common are old genes? How important is HGT versus the
gradual composition of genetic programs? We will look at these questions.
|