Re: Ch. 5: Even the Ranks of Tuscany (A Devil's Chaplain)
5 Even the Ranks of Tuscany 187
5.1 Rejoicing in Multifarious Nature 190
5.2 The Art of the Developable 194
5.3 Hallucigenia, Wiwaxia and Friends 203
5.4 Human Chauvinism and Evolutionary Progress 206
5.5 Unfinished Correspondence with a Darwinian Heavyweight 218
This chapter is devoted to Dawkins' reviews of the work of Steven Jay Gould, with whom he had a combative rivalry. Dawkins accepts Gould's accolade that they are the two best writers on evolution. I mentioned essay 5.4 in the thread on evolutionary progress
and hope it makes sense to leave that discussion in that thread. Here I want to look at 5.3, Dawkins' review of Wonderful Life
, Gould's book on how the Cambrian explosion is revealed in the Canadian fossils of the Burgess Shale. These fossils were laid down 530 million years ago and are perfectly preserved with soft body tissues to reveal some of the most bizarre organisms ever.
Dawkins says that Wonderful Life
is a sorry mess. I think this goes too far. His main criticism is that Gould "really seems unable to comprehend that animals are continuously variable functional machines. It is as though he sees the great phyla not diverging from early blood brothers but springing into existence fully differentiated."
I read Wonderful Life
a few years ago and was intrigued by precisely this question, and find Dawkins' criticism hard to accept. It made me wonder how the Cambrian revolution, the emergence of macroscopic life, occurred. My understanding is that algae had been pumping oxygen into the air for billions of years, and at the Cambrian an oxygen threshold was reached, a tipping point that allowed multicellular life to be sustained. If this is the case, then it makes sense that multiple macroscopic life forms would have emerged simultaneously. If so, then the phyla were not "blood brothers" in Dawkins' term, but separate mutations from microbial forms. It is quite conceivable to me that the multiple body plans (phyla) of the Cambrian were twigs on a much older tree, not siblings born of a single macrobial ancestor.
An analogy is bubbles of methane rising from a bog, with each phylum as a separate bubble. Each bubble comes up independently from the mud, they do not rise in a single large bubble and separate near the surface.
Once the Cambrian was underway, the different phyla found themselves in competition. The most efficient body plans (eg chordata) won out over the strange and bizarre, which went extinct. I find it easy to imagine that at a major threshold such as the Cambrian that evolution occurred at the phylum level rather than at the species level, responding to a climatic phase change.
This model of phylum evolution applies in all major phase changes. For example at the dawn of aviation, inventors tried out all sorts of body plans. Only the most efficient survived, with subsequent technological evolution of aeroplanes at the equivalent of the genus and species level. Whether jet engines are equivalent to a new genus could be debated, but they did retain many features of the propellor planes, in steering and body plan. Helicopters and rockets are obviously separate phylum equivalents, as is the extinct form of the biplane. This same evolutionary model of an initial broad range of options followed by narrower evolution among the initially successful forms can be seen in fields such as music and computing. The successful pioneer subsequently crowds out innovation at the body plan level, until a new revolution comes along.
Dawkins says "Survival of the fittest means individual survival, not survival of major lineages. Any orthodox Darwinian would be entirely happy with major extinctions being largely a matter of luck. Admittedly there is a minority of evolutionists who think that Darwinian selection chooses between higher-level groupings."
I find this strange. It seems to make far more sense that, for example, tetrapods, four legged vertebrates, outcompeted other body forms because of the inherent efficiency of the form, not just because of luck. There is obviously an element of contingent accident in evolution, but I wonder if Dawkins' comment here scoffing at higher-level groupings overstates that contingency, against the alternate hypothesis that the most efficient phylum is most likely to succeed best.