New research from Jonathan Weissman, a professor of biology at MIT Alex Pollen, an assistant professor at the University of California at San Francisco Richard She, a postdoc in the Weissman lab Tyler Fair, a graduate student in the Pollen lab and colleagues uses cutting-edge tools developed in the Weissman lab to narrow in on the key differences in how humans and chimps rely on certain genes. However, it can be hard to tell which of the many small genetic differences between us and chimps have been significant to our evolution. These physical differences are underpinned by subtle changes at the level of our DNA. In the time since - brief, from an evolutionary perspective - our ancestors evolved the traits that make us human, including a much bigger brain than chimpanzees and bodies that are better suited to walking on two feet. Evolutionarily speaking, the wimps won after all.Humans split away from our closest animal relatives, chimpanzees, and formed our own branch on the evolutionary tree about 7 million years ago. It was these factors - brains and legs - that played a major role in humans' eventual global dominion. The Homo genus began developing larger brains that sucked energy away from muscles and selected for more economical muscle fibers. As we became bipedal, muscles primed for endurance would have also won out as our ancestors began walking long distances on their migrations across the globe. The researchers think we began getting weaker roughly 8 million years ago, when our lineage diverged from chimpanzees. These two factors likely explain much of the human-chimp strength gap, but other factors such as joint mechanics and muscle-tendon interactions play a role as well, with chimp arms better suited for the hanging and grabbing movements that they do every day. Chimp muscle fibers are longer than ours too, and the net result is that, pound-for-pound, their muscles are more powerful. Chimpanzee muscles, on the other hand, are more evenly balanced with less efficient but powerful MHC II muscle fibers they're the kind that come in handy when swinging from tree to tree in the forest. Humans tend to favor a type of muscle fiber called MHC I that allows for greater endurance and reduced energy consumption, but at the cost of raw strength. Where we differ, however, is in the type of fibers that together make up our skeletal muscles. Chimp and human muscles fundamentally work the same, they say, with filaments of actin sliding past thick myosin bands to produce contractions. In terms of static strength and contraction speed, human muscle fibers kept pace with chimp muscles. Direct tests of muscle fibers actually found many similarities between our cells and theirs. Their computer model found that chimps are only 1.35 times stronger than a human on average, a number that agrees with more recent lab tests pegging them at 1.5 times as powerful. Their study, published Monday in the Proceedings of the National Academy of Sciences, indicates our common conceptions of primate strength may be blown slightly out of proportion. Or, put another way, researchers wanted to know why humans are so weak. A new study from researchers at the University of Arizona and Ohio State University took a different approach to the problem: They performed direct tests of both human and chimp muscle fibers, and used computer models to determine how strong chimps really are. These estimates are likely based on experiments from the 1920s, when a researcher by the name of John Bauman recorded a chimp at the Bronx Zoo pulling 847 pounds with just one hand. When a human is attacked by a chimp, you'll see reports claiming the primates are anywhere from two to eight times as strong as a human, despite their small stature. Even when compared to our closest cousins, chimpanzees, the strength gap is obvious. Still, without the aid of tools and traps, creatures who call the wilderness home present a clear threat. Our lack of brawn is a result of our our big, energy-hungry brains, an adaption that seems to have worked out pretty well, all things considered. Relatively speaking, our physical prowess just doesn't match up to the rest of the animal kingdom. (Credit: Everett Collection/Shutterstock) Humans are sort of nature's wimps.
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