![]() “The problem with looking at expression changes or changes in DNA sequences is that there are many of them and their functional importance is unclear,” says Weissman, who is also a member of the Whitehead Institute for Biomedical Research and an investigator with the Howard Hughes Medical Institute. If a difference in gene use between species has a large, measurable effect at the level of the cell, this likely reflects a meaningful difference between the species at a larger physical scale, and so the genes identified in this way are likely to be relevant to the distinguishing features that have emerged over human and chimp evolution. The researchers looked for instances in which a gene was essential in one species but not the other as a way of exploring if and how there were fundamental differences in the basic ways that human and chimp cells function.īy looking for differences in how cells function with particular genes disabled, rather than looking at differences in the DNA sequence or expression of genes, the approach ignores differences that do not appear to impact cells. If the cells stopped multiplying as quickly or stopped altogether, then the gene that had been turned off was considered essential: a gene that the cells need to be active - producing a protein product - in order to thrive. Then they looked to see whether or not the cells multiplied at their normal rate. The researchers used CRISPRi to turn off each gene, one at a time, in a group of human stem cells and a group of chimp stem cells. CRISPRi uses a modified version of the CRISPR-Cas9 gene editing system to effectively turn off individual genes. Their approach, using stem cells derived from human and chimp skin samples, relies on a tool called CRISPR interference (CRISPRi) that Weissman’s lab developed. The researchers developed an approach to narrow in on these impactful differences. However, only some of the many differences in gene use between the two species underlie big changes in physical traits. Differences between the species often come down to when and how cells use those nearly identical genes. Only a handful of genes are fundamentally different between humans and chimps the rest of the two species’ genes are typically nearly identical. Studying function rather than genetic code Their findings, published in an open-access paper in the journal Cell on June 20, may provide unique clues into how humans and chimps have evolved, including how humans became able to grow comparatively large brains. 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. It may be that humans traded strength for endurance when the lineages separated millions of years ago, giving us the ability to travel farther to find food.Humans split away from our closest animal relatives, chimpanzees, and formed our own branch on the evolutionary tree about 7 million years ago. This gives us greater endurance, but less strength in bursts.Ĭhimp muscle fibre was found to be 1.35 times more powerful that that of humans. On average, humans have 70 per cent slow twitch and 30 per cent fast twitch muscle fibre. ![]() Why Chimps are Handy But Bonobos Aren't.(Eric Kilby/Wikimedia Commons) In chimps, one third of their muscles are slow twitch fibres and the other two thirds are made up of two types of fast twitch muscle fibres. Fast twitch muscle contracts more quickly and provides more force in quick bursts, but fatigues faster. This accounts for a chimp's ability to climb and jump rapidly over short distances. Having more fast twitch muscle fibre than humans give chimps the strength to climb.
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