Brain size and complexity vary enormously across vertebrates, but it is not clear how these differences came about. Humans and frogs, for example, have been evolving separately for 350 million years and have very different brain abilities. Yet scientists have shown that they use a remarkably similar repertoire of genes to build organs in the body.
The key lays in the process that Blencowe’s group studies, known as alternative splicing (AS), whereby gene products are assembled into proteins, which are the building blocks of life. During AS, gene fragments — called exons — are shuffled to make different protein shapes. It’s like LEGO, where some fragments can be missing from the final protein shape.
AS enables cells to make more than one protein from a single gene, so that the total number of different proteins in a cell greatly surpasses the number of available genes. A cell’s ability to regulate protein diversity at any given time reflects its ability to take on different roles in the body. Blencowe’s previous work showed that AS prevalence increases with vertebrate complexity. So although the genes that make bodies of vertebrates might be similar, the proteins they give rise to are far more diverse in animals such as mammals, than in birds and frogs.
And nowhere is AS more widespread than in the brain.
Gueroussov showed that in mammalian cells, the presence of the second, shorter version of PTBP1 unleashes a cascade of AS events, tipping the scales of protein balance so that a cell becomes a neuron.
What’s more, when Gueroussov engineered chicken cells to make the shorter, mammalian-like, PTBP1, this triggered AS events that are found in mammals. More.
What we don’t hear is whether the chicken became more intelligent as a result of these interventions. Now that would be of much greater interest.
This thesis is worthy of a commission in the war against common sense created by trivial explanations of the human being. Like these:
Some say we evolved large brains alongside small guts, but another research team found no such correlation. Alternatively, fluid societies (relative to chimps) explains it. And, according to some, mental illness helped. Chimpanzees’ improved skills throwing excrement are also said to provide hints about human brain development. (The ability to throw projectiles at very high speeds is apparently unique to humans.) Our ancestors had to grow bigger brains anyway, we are told, to make axes and hunt something besides elephants. Collective intelligence (“ideas having sex”), whatever that means, has been really important to human evolution as well.
The obvious problems with all of these disunited and discordant theses can be summed up for convenience as: 1) If some aspect of chimpanzee behavior explains matters, why didn’t it produce the same result in chimpanzees? 2) If mere advantage (which every primate seeks) explains a development like the human mind, why did only humans experience it? More.
Remember, the more serious science stories tend to start after Labour Day. The ones that would show, for example, the chicken getting smarter.
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