How Did We Get Here?
Kenneth R. Miller, November 30, 1996
I noted earlier that evolution consistently explains the interlocking evidence from paleontology, development, and DNA, and challenged you to present an alternative. You have not. Rather than present an alternative (and fail the tests evolution passes), I suspect you'd prefer just to raise objections, hoping to establish reasonable doubt. Good lawyering, weak science.
You made a serious mistake when you called the dog-to-dolphin sequence "propaganda," asking me to "try detailing the functional intermediate steps." A perfect example of criticism unrestrained by fact. I don't have
to "try" to detail the intermediates ... they existed. Beginning with a mesonychid mammal (your "dog") the intermediates are Pakicetus, Ambulocetus, and Rodocetus, leading to a true whale, Basilosaurus. Even Basilosaurus itself is intermediate. It had hindlimbs, a nose in front, and teeth like those of its carnivore ancestors, not modern cetaceans.
Once again, the fossils support evolution. Beaten on this score, you withdraw to attack the mechanism.
You wrote: "The mechanism is observed only at the micro level, and it certainly hasn't been shown capable of producing the kind of alterations in embryonic development which macroevolution would require." I note that you do agree that the mechanism of evolution - natural selection acting on variation - is observable fact. Thanks. Score one for evolution. However, you restrict that mechanism to the "micro level." Unfortunately for this argument, you are not correct.
First, many fossil sequences fit the "micro" pattern perfectly, including the evolution of mammals from reptiles. These alone disprove your contention. Second, a number of well-understood mechanisms, including single gene mutations, produce changes that qualify as macroevolution. These include heterochronic mutations that alter structures by changing growth rates, homeotic mutations that change the identities of whole body parts, and paedomorphosis, which converts juvenile stages directly to adult ones. Indeed, the most recent issue of Science (Nov-15, page 1082) reported that a single gene controls tunicate tail formation. Mutate it, the tail is lost. Restore it, tail comes back. Just another example of a genetic mechanism producing macroevolutionary change. Score two for evolution.
Phillip, could it be that your real concerns are philosophical, not scientific? You charge that one of my textbooks says "evolution is undirected and purposeless." Joe Levine and I actually wrote that "natural selection operates in a manner similar to artificial selection, but ... without any goal or purpose." We meant, of course, to contrast the forces of nature with the direct and conscious selection of the breeder. But science cannot determine "purpose," so (point taken) this poor choice of words will change at next printing.
Not even Michael Behe, who claims to have discovered "irreducible complexity " in biochemistry, disputes the common descent of vertebrates or the validity of the fossil record in depicting that descent. To date your only substantive criticisms are stabs at the old notion of ontogeny recapitulating phylogeny, a notion that author Scott Gilbert accurately notes "was not Darwinism." I enjoy answering these queries, but do wonder if you actually have a theory to put forward.
(go to next letter)
(go to previous letter)
(go to Debate contents)
Odyssey Home | How? | Morphing | Lens
Timing | Creepy Crawlies | Table of Contents
Support provided by
For new content
visit the redesigned