The Panda's Thumb. By Stephen Jay Gould

The Panda's Thumb

Stephen Jay Gould

Penguin Books. First published 1980.

A set of 31 essays on paleobiology and evolutionary biology by a master. I have read and enjoyed (and learnt much from) Gould's books before, and this one is no exception. Except that they are all about the above two topics, the essays are only loosely connected. In the first few pieces, Gould tells something, but not much, about his theory of punctuated equilibrium as an alternative to the (then?) commonly held theory of slow steady evolution by random variation and natural selection. As 'evidence' he talks about repeated sudden extinctions. He does not say anything about Kimura's theory of neutral drift which I find an attractive way of explaining biological diversity. This is not to discount natural selection as the prime agent of evolution, only that it does not operate to always make organisms 'better and better'. Gould also talks about the Piltdown fraud; the evolution of how Mickey Mouse is drawn to make 'him' look more and more childish, and therefore more attractive; about politically and racially motivated biological and evolutionary theories about such features as the size and weight of brains of women and black people; about how to define species; about cladism; about the intelligence of dinosaurs; and about whether birds are descended from dinosaurs (they are) or whether they are a product of convergent evolution that produced feathers in two separate events - archaeopteryx and birds (no, they are not). Some of the essays are, well, not outdated, but dated, since surely much evidence has accumulated in the last 30 years that would have settled some of questions raised in them. For example, Gould speculates that the evolutionary relationship between ciliates and acoeles (whatever they are) will be settled by analyses of DNA sequences, of which very little were available at the time Gould wrote his essays. With the enormous amount of sequence information now available, that question must have been settled. 


I record one final piece of information - magnetotactic bacteria carry nanocrystals (Gould calls them 'single domain crystals' - the 'nano' terminology was not known then) of magnetite (i.e. one of the iron oxides) to help them orient themselves to magnetic fields. But not, in general, North/South but Up/Down, using the force of Dip or the vertical component of the earth's magnetic field. The nano size (~ 500 Angstroms) is apparently just right - smaller and they would be paramagnetic, any larger and they would have too many domains to act as a proper magnetic sensing device.