Monday, June 09, 2014

Rapidity of human brain and muscle evolution - the downside of smarts?

Roberts does a summary of fascinating work by Bozak et al. He sets the context: 
Somewhat narcissistically, one of the spectacular changes in phenotype that we tend to be most interested in is the enhancement in our own brain power which has occurred over the 6 million years that separate us from our last shared ancestor with chimpanzees. The chimp genome is famously very similar to our own, but the technological, linguistic, and cultural phenotype is clearly profoundly different. Several studies have asked open-ended questions as to what happens between the genotype and phenotype to make us so different from our cousins, finding differences in levels, splicing, and editing of gene transcripts, for example. Now a paper just published in PLOS Biology by Katarzyna Bozek, Philipp Khaitovich, and colleagues looks at another intermediate phenotype—the metabolome—with some intriguing and unexpected answers...The metabolome is the set of small molecules (metabolites) that are found in a given tissue; by “small” we mean those with a molecular weight of less than 1,500 Daltons, which includes fats, amino acids, sugars, nucleotides, and vitamins (vitamin B12, for example, is near the top end of this range).  
...the metabolomes of human prefrontal cortex (and of combined brain regions) have changed four times as rapidly in the last 6 million years as those of chimps. While gratifying, this largely confirms for metabolites what was already known for transcripts. 
...brain is not the most spectacular outlier here. The real surprise is that the human muscle metabolome has experienced more than eight times as much change as its chimp counterpart. Indeed, metabolomically speaking, human muscle has changed more in the last 6 million years than mouse muscle has since we parted company from mice back in the Early Cretaceous.  
...the authors compared the performance of humans, chimps, and macaques in a strength test that involved pulling a handle to raise a weight. Human strength, as measured by this test, was barely half that of the non-human primates. Amazingly, untrained chimps and macaques raised in captivity easily outperformed university-level basketball players and professional mountain climbers. The authors speculate that the fates of human brain and muscle may be inextricably entwined, and that weak muscle may be the price we pay for the metabolic demands of our amazing cognitive powers.


  1. Anonymous6:30 AM

    Amazing !!

    In evolutive terms, wouldn't the diminishment of muscle power be a paramount disadvantage? where is the molecular coupling between the brain and muscle metabolomes? what is the direct relation between metabolomes and brain of muscle performance?

  2. Well... if the digestive system, GI tract, etc. can dish up only so much energy, it has to be parceled out between competing systems like muscle and brain. If the brain is getting more bang for the buck, it gets more.

    Also, brute strength, which is what they were testing, may not be as important as the specialized set of muscles needed for long distance running down of prey (and the brains to spear them). One of the unique features of humans is that they can outrun, have more endurance than, the fastest animals.