After a long layoff due to conference congestion, here’s a new installment of Linkage, our semi-regular round-up of science news from around the world and web.
The “Speech Gene” Gains a Function
One of the more intriguing genes discovered since the flood of genetic sequences began to arrive at the beginning of this decade is FOXP2. Encoding for a humble transcription factor (sort of a DNA light switch), FOXP2 nevertheless gained lofty status when it was found in the late 1990’s to be associated with human language – one of the most complex behaviors of all. Previously associated with speech and language disorders in humans, FOXP2 gained steam when a team of scientists (including University of Chicago professor of human genetics Molly Przeworski) compared our FOXP2 with our close primate relatives and found only two amino acids different between the human and chimpanzee versions of the gene. With only 715 amino acids total in the FOXP2 protein, that small difference suggests a recent evolution event, which that research group estimated at roughly 100,000 years ago – right around the time that “modern humans” appeared on the scene. This has led some to conclude that this fortuitous small change in the FOXP2 gene is one of the key moments in our evolutionary history that separated man from beast.
But what exactly does FOXP2 do, and how could such a minute change mean the difference between chimpanzee grunts and Shakespeare? One way to answer that question is to put the human version of the FOXP2 gene into another animal, an experiment that was published earlier this year by a very large team of German researchers. That mouse didn’t suddenly start reciting soliloquies, but it did show differences in “ultrasonic vocalizations,” as well as cellular changes in a part of the brain associated with movement – which makes sense given that FOXP2 is thought to mediate motions related to speaking. Still, changing just one gene to the “human version” in an animal and leaving all the other mouse genes intact would presumably limit the impact of the human FOXP2 gene in changing the mouse brain. (Jerry Coyne wrote about the media reaction to this paper here)
Thursday, another group got down to the dirty details of the human FOXP2 gene, examining how the protein it encodes is functionally different from the chimpanzee version. Despite the small changes (again, the two genes are only 0.2% different), the number of genes that respond in different ways to human vs. chimp FOXP2 is over 100, a dramatic change in function. Interestingly, the human FOXP2 gene actually changes the expression of fewer gene targets than the chimp version – another blow to the idea that complex behavior must result from greater numbers of genes (fruit flies have twice as many genes as humans, for instance). Many of the genes that FOXP2 turns on or off have to do, unsurprisingly, with the development of the brain. But as for how that combination of FOXP2-related genes work together to help humans talk where other animals cannot remains unanswered. Hence the conclusion of an accompanying commentary in Nature by Martin Dominguez and Pasko Rakic that the paper “does what important discoveries usually do: it answers many questions, but raises even more.”
When Sleestaks Roamed the Earth
Lizard creatures are a fixture of science fiction from Land of the Lost to the recently-revived V miniseries to David Icke conspiracies. But until reading this post at Darren Naish’s Tetrapod Zoology blog, I had no idea that upright lizards have actually been floated as a scientific theory of what dinosaurs might have evolved into had they not been wiped out 65 million years ago or evolved into birds. Okay, it’s not really an accepted theory or anything – Naish, who studies the theropod dinosaurs that Canadian paleontologist Dale Russell based his intelligent “dinosauroid” thought experiment on in 1982, is clearly irritated by the premise. But the reason slightly disturbing upright humanoid dinosaurs are back in the blog conversation is because they were name-dropped by none other than Richard Dawkins in a recent Scientific American article about whether aliens would resemble humans.
Russell’s basic idea (and again, this is all in the territory of what-if speculation), is that a dinosaur called a Troodon, with a brain six times larger than the average dinosaur, might have eventually developed a human-size brain if not for that whole extinction thing. Russell decided to estimate what a dinosaur with a human-size brain would look like, and came up with something that looked very similar to the denizen of many a sci-fi movie (pictured above). Since then, paleontologists have dismissed Russell’s hypothetical “dinosauroid” as being much too human in shape, arguing that there’s no reason “intelligence” would necessitate human-like features of standing upright and the lack of a tail or long, toothy snout.
On his blog, Naish points out that signs of intelligence have been observed in dinosaur descendants – we just know them as boring old birds. Birds such as parrots and crows can use tools, count and according to one recent paper, hold “funerals” for deceased relatives. Naish argues there’s no reason why standing upright on two legs should be considered the “best shape” for an intelligent organism with a big brain, it’s just the shape evolution happened to deal us. He also argues that Dawkins “should have known better” than to rely upon the poor, freakish dinosauroid even in the context of what is, for all intents and purposes, another scientific thought experiment. But I think it’s a pretty interesting cautionary tale about the difficulty of trying to predict what path evolution might take and a reminder that similar circumstances won’t necessarily produce similar creatures. Sorry, Sleestaks.