Language Log

One of the oldest and most interesting arguments for evolution is Ernst Haeckel's theory of recapitulation: the idea that ontogeny recapitulates phylogeny. In the form that Haeckel proposed — that embryological development progresses though a series of fully-developed ancestral forms — this theory has been refuted many times over the past century. What remains is the idea that "one species changes into another by a sequence of small modifications to its developmental program". This is the basis of modern research in evolutionary developmental biology ("evo devo"), and a central theme of Neil Shubin's Your Inner Fish, from which I took that picture of the development of arm bones from fish to humans.

Evo devo is mainly about anatomical development, but sometimes, surprising claims are made in this framework about evolutionary conservation of neurological function. A striking example of this is offered by a paper in the July 18 issue of Science (Andrew H. Bass, Edwin H. Gilland, and Robert Baker, "Evolutionary Origins for Social Vocalization in a Vertebrate Hindbrain–Spinal Compartment", Science 321(5887): 417-421, 2008), which argues that "the vocal basis for acoustic communication among vertebrates evolved from an ancestrally shared developmental compartment already present in the early fishes", namely "a segment-like region that forms a transitional compartment between the caudal hindbrain and rostral spinal cord".

Stupid pet communication stories are back. (Did they ever go away?) Yesterday the BBC published a story (thanks to Sam Tucker for the reference) about a stray red-tailed African grey parrot that told police how to find its owner. It was in Chiba prefecture near Tokyo in Japan. After repeating its name and address at the local veterinary clinic (where police had turned it in after capturing it), the bird greeted people for a while, then sang some popular children's songs, and then supplied its name and address. From what it said, police tracked down its owner, and took the parrot home.

The story is probably true in outline. No one disputes that parrots can be trained to do a pretty good acoustic reproduction of a human utterance. And they will do just as well on an address as on a line from a children's song or a few verses from the Kor'an; the content doesn't matter — for them, there is no content. But a paragraph at the end of the story reveals that the BBC still brings out its most gullible writers (or perhaps its most cynical and dishonest writers) as soon as anything to do with the cognitive or linguistic sciences comes on the scene. The last para says this:

The African Grey parrot is considered one of the most intelligent birds and is said by experts to have the cognitive ability of a six-year-old.

They mean a human of age six. There are people writing purportedly serious stories for the British Broadcasting Corporation who think that a grey parrot has the cognitive ability of a normal six year old human child. Have these people never met a normal six-year-old human child?

Yesterday, I described Olga Feher's demonstration that species-typical songs emerge, over several generations, in an isolated colony of zebra finches founded by birds raised in isolation ("Creole birdsong", 5/9/1008). I compared this pattern to Derek Bickerton's "bioprogram" hypothesis, first put forward in his 1981 book Roots of Language, and discussed again in his 2008 book Bastard Tongues ("A Trail-Blazing Linguist Finds Clues to Our Common Humanity in the World's Lowliest Languages"). As the Wikipedia article on the "language bioprogram hypothesis" explains, Derek's idea is that

when the linguistic exposure of children in a community consists solely of a highly unstructured pidgin[,] these children use their innate language capacity to transform the pidgin, which characteristically has high syntactic variability, into a language with a highly structured grammar.

I also mentioned some of the subsequent debate over the bioprogram theory of creolization, quoting from an encyclopedia article by John Rickford and Barbara Grimes. Some of this debate has focused on whether the process of regularization in creole languages is complete in the first generation of native learners, or takes several generations. I observed that Bickerton's general idea ought to be consistent with a multi-generational emergence of a cognitive phenotype, where the species-typical pattern results from the accumulation of learning biases over several iterations.

However, some of Bickerton's critics have seen multi-generational creolization as evidence against his hypothesis. And to my surprise, it seems that he agrees with them. In an interesting comment on my post, he wrote:

Mark, you say that "Where social learning is involved, perhaps it's normal for the phenotype to emerge over multiple generations." And you may well be right, since social learning has nothing to do with creolization. How can you "socially learn" something for which you have no model, which didn't exist until you made it?

Yesterday, I spent a fascinating afternoon at Ofer Tchernichovski's lab at CCNY. And a couple of weeks ago, the Penn Linguistics Department colloquium featured Ofer talking about some of his lab's recent research, including this work: Olga Feher, Partha P. Mitra, and Ofer Tchernichovski, "Abnormal isolate birdsong evolves into normal song over a few generations".

Zebra finches are among the songbirds who learn their songs by imitating adults, just as human children learn their language by interaction with those who already know it. Male songbirds raised in isolation, without any conspecific adult models during the critical period for song learning, are handicapped for life: they develop only an ill-organized, infantile "subsong". From the example of abused or feral children like Genie, we know that something similar happens with human children.

In both cases, this raises a sort of chicken-and-egg question: if normal development requires an adult model, then which came first, the pupil or the tutor?