Posted by: Dan | May 4, 2009

Nurture’s Learning is Dictated by Nature

I was tempted to steal Razib’s expression Nurture on Nature’s Leash, as the allusion to the eternal nature vs. nurture debate is obvious. That is, just how much of animal behavior is instinctual and biologically determined, and how much of said behavior is purely learned? This question and its answer, whatever it may be, have implications for ourselves, Homo sapiens, in the immediate sense of how we learn language, as well as in the ultimate sense of whether our behaviors are really ours to determine by choice.

The question came up in a study to be published in Nature regarding the De novo establishment of wild-type song culture in the zebra finch. As Razib notes, ScienceDaily has a good writeup with Birds Raised In Complete Isolation Evolve ‘Normal’ Species Song Over Generations. They explain the significance of this study:

During infancy, each of us emerges from a delightful but largely incoherent babble of syllables and learns to speak – normally, in the language of those who care for us. But imagine what would happen if we were somehow raised in utter isolation from other people, not only our parents but also from surrogates such as nurses and nannies. What sort of culture might we evolve if reared in isolation? Would we learn to speak? Would such a language evolve over multiple generations? If so, would it eventually resemble existing ones?

Their results:

Young zebra finches learn to sing by imitating adult male songbirds. But when raised in isolation, the young sing a raspy, arrhythmic song that’s different from the song heard in the wild. To find out what happens to this “isolate song” over generations, the scientists designed experiments in which these isolated singers passed on their song to their progeny, which in turn tutored the next generation, and so on. The tutors were either paired one-on-one with their progeny, or to mimic a more natural social setting, introduced into a colony of females (who, as it happens, do not sing) and allowed to breed for a few generations.

The team found that in either social setting, birds of every successive generation imitated their tutor’s song but also modified it with small, systematic variations. These improvisations weren’t random, however. Accumulating over generations, the introduced changes began to bring the innate, “isolate” song into approximate conformity with the song learned within normal zebra finch “society.” (This “cultured” song has been labeled “wild-type” by the scientists.) By the 4th or 5th generation, birds that were descendents of the experimental “isolates” were singing songs that very closely resembled the song sung by birds raised under social conditions in the wild.

As previous studies have suggested as well in the past, it would appear that “innate” behavior is different from “learned,” but the learning process is itself innate, if I’m not greatly mistaken.

Olga Fehér, Haibin Wang, Sigal Saar, Partha P. Mitra & Ofer Tchernichovski. Nature, 2009 [advance online publication]
DOI: 10.1038/nature07994



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