We note that the Spedicato paper cited above proposes that the last glaciation began with a cometary collision or explosion over land. Perhaps we find here a clue to the sudden appearance of Cro-Magnon man?

I have here on my desk a paper by Rhawn Joseph and Chandra Wickramasinghe entitled Comets and Contagion: Evolution and Diseases From Space. They write in their conclusions:

"Correlation is not causation and thus no firm conclusions can be drawn despite the wealth of evidence suggesting a link between comets and diseases from space. Nevertheless, comets are an ideal vehicle for sustaining and transporting a variety of microbes, including viruses, from planet to planet and even from solar system to solar system. In consequence, when these organisms are deposited on a world already thriving with life, genes may be exchanged, the evolution of new species may ensue, or conversely contagion may be unleashed, and disease, death, and plague may spread throughout the land."

Let us speculate that the genes that produced Cro-Magnon man may have been brought to earth as the result of a cometary impact. The simplest version of this panspermia theory is that proposed by Sir Fred Hoyle and Chandra Wickramasinghe who suggest that life forms continue to enter the earth's atmosphere, and may be responsible for epidemic outbreaks, new diseases, and the genetic novelty necessary for macroevolution. The mechanisms proposed for interstellar panspermia may include radiation pressure and lithopanspermia (microorganisms in rocks), deliberate directed panspermia from space to seed Earth. Interplanetary transfer of material is well documented, as evidenced by meteorites of Martian origin found on Earth. [...]

Now, 'panspermia', as the DNA-transported-by-comets-seeding-life-on-earth theory is called, may get us off the hook as far as human evolution on earth is concerned, but it does not get us off the hook when considering where that DNA came from originally and how the individuals who carried it evolved, if the arguments against evolution that the panspermia scientists employ apply everywhere. Obviously, they are under the same constraints. On the other hand, that may be a way out in a different direction: DNA could be a pure manifestation of consciousness, a sort of first-level physicality, the interface between the material and non-material worlds. Pure information might be able to geometrize itself in the form of DNA and, voilà! the building blocks of life that are complex and capable of inducting consciousness itself into matter come into being in an instant. Sort of a mini-Big Bang with consciousness present to guide the 'explosion'.