Heterochrony and Evolutionary Processes

Historical Antecedents



Historical Antecedents

Recognising Heterochrony

Modern examples: Sexual Dimorphism

Cambrian trilobites

Cope's Rule

K- and r- selection: Tertiary echinoids

Consequences for debates on adaptation, constraints and evolutionary dynamics


Haeckel and the Biogenetic Law.

Forgive a little historical digression, but beginning a discussion of heterochrony with a brief look at its historical antecedents may be useful for getting a grip on both what heterochrony is all about and why we still hear the phrase "ontogeny recapitulates phylogeny". And it might even be interesting in its own light.

Ernst Haeckel, always a man for a catchy phrase, is probably best remembered for leaving us with the notion that:

Ernst Haeckel (1834 - 1919)

Did a little too much Goethe?

"Ontogeny is the short and rapid recapitulation of phylogeny"

This, the so-called "Biogenetic Law", held that evolution proceeded by organisms passing through stages corresponding to successively more advanced ancestors. Innovations and advances are then "tacked on" to the end of this succession. Thus, human ontogeny includes a protist stage, a worm stage, and a fish stage, among others.


This idea certainly predated Haeckel, but he managed to get his name associated with it, not least because of his gift with neologisms. Now, Haeckel was an interesting character: one of the foremost embryologists and biologists of his time, many people nevertheless have a bit of trouble accepting that what he did was truly "science". Haeckel was part of an intellectual movement known as Naturaphilosophie, which drew much of its inspiration from the works of Goethe and Hagel. Simply, it was held that the world was animated by a force or a spirit (Geist) that inexorably moved things from primal chaos towards perfection. Haeckel was one of the Darwin's biggest boosters, if only because he thought that evolution provided another example of the natural world's movement from chaos to perfection (i.e. human beings, the supposed pinnacle of the natural order).