Human Evolution Traded Brawn For Brains

Alan McStravick for – Your Universe Online

Have you ever wondered why it is that monkeys, chimpanzees, apes and other primates are frighteningly strong compared to us humans? If your answer was yes, you are not alone. And now a new study goes in depth in explaining why and how this phenomenon has occurred evolutionarily.

If we take the primate as the most logical known last point in human evolution, then describing primate strength and cognitive abilities as superhuman and subhuman, respectively, would be incorrect. In fact, human strength and cognition would better be described as subprimate and superprimate, again, respectively.

Humans were able to walk out of the forests and slowly civilize over millenia, eventually mastering and manipulating our environments. As we have progressed, we have done such things as create the car and the airplane, land men on the moon, and surf this virtual landscape we call the worldwide web. All of that brain power required more and more energy. With a finite amount of energy able to be ingested, some human features had to suffer. Muscle strength, it turns out, was an excellent candidate for energy to be siphoned from.

This finding was discovered as the result of a study conducted by scientists from Shanghai’s CAS-MPG Partner Institute for Computational Biology and other research teams based at the Max Planck Institutes in Germany. In their study, the teams investigated the evolution of metabolites – small molecules like sugar, vitamins, amino acids and neurotransmitters that represent key elements of our physiological functions. Their investigation showed how metabolite concentrations actually evolved in humans at a staggeringly fast pace compared to our primate cousins. This was especially true in two tissue areas: the brain and muscle.

The science world has been abuzz about the study of the human genome since the mid-1990s, and that field of study has yielded excellent research results. The genome, like the rings of a tree, is slow and methodical, recording steady changes that occur over time. However, this international team of scientists, led by Dr. Philipp Khaitovic from Shanghai, looked at an area that is regarded as far more responsible for the development of our distinctive human features, the metabolome. The metabolome is the compendium of metabolites that are present in human tissue. “Metabolites are more dynamic than the genome and they can give us more information about what makes us human,” stated Khaitovich. “It is also commonly known that the human brain consumes way more energy than the brains of other species; we were curious to see which metabolic processes this involves.”

The genome is the tortoise to the metabolomes hare, it appears. Though the metabolome has taken few rest breaks in this race, with the metabolome of the brain evolving some four times faster than that of the chimpanzee. If that figure is surprising, then learning that human muscle has undergone metabolic change ten times that of the chimp is mind blowing.

As humans have driven towards civilization, our lifestyles have become far more sedentary than our evolutionary ancestors. To account for this, the researchers simulated a high-sugar, high-fat, low movement environment for a group of macaque monkeys they used as subjects in their study. “For a long time, we were confused by metabolic changes in human muscle,” commented Dr. Kasia Bozek, lead author of the study, “until we realized that what other primates have in common in contrast to humans is their enormous muscle strength.”

Echoing Bozek’s statement, Dr. Josep Call of the Wolfgang Kohler Primate Research Center in Leipzig, Germany said, “This is common knowledge to all the zoo keepers, but it was never tested systematically.” To test this scientifically, the team devised a pull test in which several primates abilities were matched against the strength of university students and professional athletes. In each pull test, all human participants were woefully outmatched by the animal participants. Of course, ask any of the human participants to effectively communicate the answer to a math problem and you will realize primates have nothing on humans.

It was this last point that began to open up an hypothesis that was just too tantalizing to the team of researchers. Perhaps the metabolic roles of the human brain and brawn are intertwined. “Our results suggest a special energy management in humans that allows us to spare energy for our extraordinary cognitive powers at a cost of weak muscle,” contends Bozek. “The world of human metabolomics is just starting to open up its secrets to us,” Dr. Patrick Giavalisco, leader of the metabolome measurement effort at the Max Planck Institute for Molecular Plant Physiology in Golm said. “Such human-specific metabolic features we find could be related not only to physical or cognitive performance but also to common human metabolic diseases,” he concluded.

The full article detailing the study and the findings of this international team was published this week in the open-access journal PLOS Biology.