Some news that I've been waiting for seems to have come along. If so, a number of puzzles may have solutions and some suspicions I've held seem likely to be true. The news appears to be a confirmation of an idea put forth a couple of years ago by Terrence Deacon and which, when I heard it, set me thinking.
Deacon is best known on this blog for his book The Symbolic Species but he is also an expert on evolution and the brain. An interesting idea he has been promoting for a few years is that of "relaxed selection," a means of producing a random change and sheltering that change while it finds a role. Most changes to the genome are point mutations in genes and the results are immediately tested. If a mutation is harmful, it does not spread, while helpful genes do increase in a population. Neutral mutations are neither selected nor filtered out. They may increase over time through chance but probably will never amount to much of importance.
Deacon focuses on a more rare type of change in which a section of a chromosome duplicates. Although relatively rare, doubling has happened many times in evolution's long history. An example Deacon likes is the introduction of color vision into the primate line. It began with an accidental doubling of the genes that govern the retina. Color vision did not result immediately. The original genes provided normal vision. The doubling was basically useless but at least not ruinous. In essence, the doubling worked like a neutral mutation, neither selected nor discarded.
Once the doubling occurs, the doubled genes are of course subject to mutation and can change and sometimes produce something valuable. This process led to the eventual appearance of color vision as a neutral duplication evolved into something well adapted to the forest environment. Deacon calls this process "relaxed selection" because the doubled strand of genes is not immediately rejected and allows time for something new to appear.
Deacon has been arguing that the Homo brain's development is the result of a doubling and relaxed selection. Now comes news that a doubled section of the human genome controlling brain development has been identified. The doubling took place an estimated 2.4 million years ago, early in the history of the Homo line.
As far as I know, James Hurford never linked any of his ideas to Deacon's doubling but I did when I covered one of his presentations on subject and predicate. He talked about it as subject and news (see: The Word-Sentence Continuum). Hurford's approach enabled me to think of sentence and predicate as a kind of doubling.
Standard analysis of sentences defines the subject and predicate as a [noun phrase] + [verb phrase]. That rule allows for simple sentences like [Jesus] [wept] and complex ones like [Alexander and all his army] [defeated the Persians and their allies]. But Hurford got me thinking in a more functional way. News can come in many forms: verbs (e.g., died, as in Our neighbor died), adjectives (red, The leaves turned red), and nouns (book, Jack wrote a book).
Looked at this way, sentences can contain two elements and a link. The elements are the subject and the news. The startling thing is that a sentence can ask the listener to attend to both subject and news at the same time. This double attention is made possible by a link that fits with both ends of the elements: The leaves turned … turned red; Jack wrote … wrote a book. If the link does not work with both elements, the sentence is confusing and the doubled attention breaks: The leaves fell … fell red; Jack splintered … splintered a book.
I'm not proposing that sentences always come from doubled attention. Sometimes the link alone is sufficient for the news—Our neighbor died. Perhaps this kind of sentence is older than a doubled one, but ever since I combined Deacon and Hurford in my thinking I've been keeping an eye out for news that might support the idea that speech reflects a doubling that enables people to hold two points of attention at the same time.
Naturally I sat up straight when I came across a news item headlined, "Doubled Gene Means Extra Smarts," by Tina Hesman Saey. The gene in question is called SRGAP2 and has been previously identified as one of 23 genes that has been duplicated in humans but not in other primates. The gene was partially duplicated 3.4 million years ago and then 2.4 million years ago the partial duplicate was itself duplicated. The first duplicate is not found in all humans, but the second duplicate is fixed (i.e., universal) in the human population. 2.4 million years is considered a short time for a duplicate gene to become fixed, and suggests the change is important. Exactly what the changed gene accomplishes is unclear, but the research team—headed by Megan Dennis—proposes that it thickens the brain's cortex.
From my perspective, the date is good (before speech probably began, but not hopelessly before). It's something to keep an eye on.