I’ve just belatedly read Mark S. Blumberg’s Freaks of Nature: and what they tell us about development and evolution. I’m sorry I missed this on publication (paperback 2010) because it is a powerful exposition of evo devo. Blumberg convincingly shows that the gene-centred view of life-forms is inadequate. He discusses the factors that play out in functions as different as limbs and sex and the way in which different forms can emerge from the same genome. The poster case for this is sex determination in crocodiles, some turtles, lizard and fishes. They do not have separate genetic sexes and whether an individual becomes male or female is regulated by temperature at a crucial stage of development. Some fishes switch identity several times over.
Human beings do have sex determining genes of course but even here things can happen such as genetic males appearing to be females until puberty when male genitalia suddenly appears. The reason is that a receptor for the hormone testosterone has been switched off in the foetus and is only activated at puberty. The genome has not changed but the results have. In general environmental factors, such as temperature in the case of crocodiles, can have drastic effects on development at key moments. All these phenomena belong under the heading of epigenetics.
There is another book somewhat similar to Blumberg’s: Armand Marie Leroy’s Mutants. I fear that neither book is as well known as it should be partly because of those titles. Both books do discuss abnormal development – freaks and mutants – but mostly for the light they shed on normal development. A great deal has been discovered about developmental mechanisms by observing what happens when it goes wrong. But some readers may have been put off by the titles. Blumberg, in particular, does make a strong case for a better attitude towards abnormalities of development. One’s understanding of life processes is greatly broadened by these books. It is safe to say that you will never see life in quite the same way again.
Human beings do have sex determining genes of course but even here things can happen such as genetic males appearing to be females until puberty when male genitalia suddenly appears. The reason is that a receptor for the hormone testosterone has been switched off in the foetus and is only activated at puberty. The genome has not changed but the results have. In general environmental factors, such as temperature in the case of crocodiles, can have drastic effects on development at key moments. All these phenomena belong under the heading of epigenetics.
There is another book somewhat similar to Blumberg’s: Armand Marie Leroy’s Mutants. I fear that neither book is as well known as it should be partly because of those titles. Both books do discuss abnormal development – freaks and mutants – but mostly for the light they shed on normal development. A great deal has been discovered about developmental mechanisms by observing what happens when it goes wrong. But some readers may have been put off by the titles. Blumberg, in particular, does make a strong case for a better attitude towards abnormalities of development. One’s understanding of life processes is greatly broadened by these books. It is safe to say that you will never see life in quite the same way again.
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