An example of the contribution of developmental and ecological flexibility to the evolutionary origin of characters (see previous post) involves barn owls recently migrated to Malaysian oil palm plantations. Lenton (1983) describes the owls fifteen years after the first pair bred in a Malaysian plantation, by which time they had spread throughout southern Malaysia. The owls have two to three clutches a year, do not rigidly defend their territories, and perch to wait for their prey-the rats abundant in the plantations. In contrast, owls of the same species in Europe have only one clutch per year, rigidly defend their territories, frequent open areas, and quarter those areas in search of prey. Moreover, the juveniles in the Malaysian plantations, before the age of establishing their own nesting sites, congregate at the end of the day’s hunting-social behavior not observed elsewhere.
Now, if Darwinian biologists first observed the character differences between the Malaysian owls and their relatives without knowing about the recent immigration, my guess is that they might explain the increased fecundity and contracted territories as selectively advantageous in the environment of abundant rats. They would assume that there must have been some variation in fecundity and territory size in the original owls. The juvenile congregation would probably be passed over as simply a by-product of the other selected changes.
Suppose we then informed the biologists of how few generations there had been to accumulate any differentials that could have emerged from the offspring of the one founding pair. They would probably shift the focus of their explanation and postulate that barn owls have the flexibility to develop responses to novel environmental circumstances in appropriate ways, even if we have not observed the responses elsewhere. Flexibility would be seen as an adaptation resulting from previous selection. But I doubt that modern Darwinian biologists would go further and conclude that the owls have in fact evolved and adapted without any significant genetic change in the population.
Even if the biologists did not modify their definition of evolution to incorporate non-genetic change, the case indicates how the historical conjunction of circumstances and the previously unobserved ecological flexibility of the pre-immigrant owls elicited the new characters. This conjunction becomes crucial to the explanation of the changes that were observed in the population of oil palm owls—as important as, perhaps more important than, the genetics of character variation or any differential representation among variants after migration into Malaysia. Understanding evolutionary change does not license our focusing on the characters of individuals and not attending to the dynamic relationship between individual and contextual change.
Development is central to this story. Instead of single characters directly linked to genes, typically hypothetical, that arise through mutations or random rearrangement of DNA, we see that new characters arise within integrated sets of characters that develop over the organism’s lifetime. Instead of inheritance as the transmission from parent to offspring of Master Molecules, we have a picture of characters always being reproduced (imperfectly) through flexible developmental processes, processes that are only conditioned, not determined, by genes.
In the next post in the series I return to the original question of what it might look like to make evolutionary studies more ecological.
Lenton, G. (1983) “Wise owls flourish among the oil palms,” New Scientist, 97: 436-437
An extract from Taylor, P. (1998) “Natural Selection: A heavy hand in biological and social thought,” Science as Culture, 7 (1), 5-32.