From Donald I. Williamson
I can’t deny James McCartney’s point that the caterpillar and the butterfly are products of the same genome (6 March, p 32). I do contend, however, that this genome resulted from the fusion of two genomes when two distantly related animals hybridised.
A caterpillar-like animal (an onychophoran) hybridised with an ancestor of modern butterflies to give the first lepidopteran with a caterpillar larva. Metamorphosis thus represents a change in taxon during development. The drastic changes that take place in the lepidopteran pupa give an indication of the degree of difference between an onychophoran and a lepidopteran.
Hybridisation with onychophorans also gave caterpillar larvae to scorpion flies (Mecoptera) and to sawflies (Hymenoptera).
The forms of insect larvae are not well correlated with the forms of adult insects. The basic forms of all larvae were transferred from foreign taxa, and in most cases the donor group can be identified. The occurrence of caterpillar larvae is one of dozens of examples explained by the theory of larval transfer. The theory and its implications are the subject of my recent book, The Origins of Larvae (Kluwer).
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Port Erin, Isle of Man
