The primate ancestors of Homo sapiens diverged from our chimp cousins some seven million years ago and we have rarely looked back since. We rapidly developed larger brains, possibly in response to climate change, underwent upright bipedalism, acquired dozens of other distinctly human things—and now we have developed a new method for identifying the cellular and molecular differences between our two species. Using what they call a comparative loss-of-function approach, researchers at MIT’s Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, performed a genome-wide CRISPR-interference screen in human and chimp stem cells to see how our genes vary from our closest primate cousin. They uncovered a specific set of 75 genes that affect cell proliferation, shedding new light on human evolution and possibly explaining the origins of our larger brains. The same approach could open the doors to understanding the molecular secrets of other species, they say. Cell

Study on human evolution demonstrates how to identify differences in how genes are used between closely related species. Jennifer Cook-Chrysos/Whitehead Institute

Strokes are a leading cause of death in the United States, and effectively treating them usually means intervening surgically or, if appropriate, administering the clot-busting drug tPA. Every second counts during treatment, and successful interventions can mean a world of difference between saving lives and preventing long-term disability or not. Doctors at UCLA have piloted a new stroke treatment based on cathodal transcranial direct current stimulation (C-tDCS). In a first-in-humans clinical study involving 10 people, they showed that C-tDCS can be efficiently applied in emergency settings—though larger, multicenter trials are still needed to determine if it’s effective as a treatment. JAMA Network Open

Researchers in most countries who wish to study embryonic development are governed by something known as the 14-day rule, which says that human embryos cannot be grown in the lab more than two weeks beyond fertilization, though some have called for relaxing this rule in recent years. It’s an ethical consideration because at 14 days embryos undergo a crucial stage of development called gastrulation, where the three main cell layers begin to form, which leads to the formation of distinct tissues and organs. But that’s a stage of great interest to research because it’s also when epigenetic aging begins, among other questions. Now researchers at the University of Cambridge in England and the Weizmann Institute of Science in Rehovot, Israel, have developed workarounds, and in the process the most advanced synthetic human embryos ever created. Both workarounds are described in unpublished preprints, and involve developing embryos from stem cells, which fall outside the letter of the 14-day rule law. Nature

Homologous recombination is a vital molecular process for helping cells routinely repair DNA and mixing chromosomes during reproduction, which create genetic diversity in our offspring. But cancer can emerge when the DNA repair process goes awry. One of the most well-known genes involved in homologous recombination is BRCA2, famous for increasing the risk of breast cancer. Several other recombination genes, called RAD51B, RAD51C, RAD51D, and XRCC2, are also implicated in cancer, but they are less well characterized. Now researchers at the Francis Crick Institute in London have determined the structure and functions of the proteins encoded by these mysterious genes, showing they form a complex called BCDX2 that plays a key role in DNA repair that’s critical for tumor avoidance. The work could lead to new therapies for breast, ovarian, and prostate cancer. Nature

When a person travels into space, rapid changes in gene expression may weaken their immune system, according to researchers at the University of Ottawa in Ontario, Canada. This could explain why astronauts have been known to suffer skin rashes and shed more varicella zoster and herpes simplex virus in space. Sampling white blood cell counts in blood draws from 14 astronauts who lived on the International Space Station for 4–6 months, the researchers found 15,410 genes that were differentially expressed during and after spaceflight. One cluster of 247 genes were all dialed down when the astronauts reached space but ramped back up when the travelers returned to Earth. Another cluster of 29 genes were ramped up in space and dialed down back on Earth. They hypothesize the effect is due to the redistribution of blood from the lower to the upper extremities in zero gravity. Frontiers in Immunology

Rats experiencing distress and panic can transmit that fear to other nearby rats by releasing pheromones. Now researchers at the University of Tokyo have discovered that a non-stressed rat can ameliorate the fear nearby rats feel through the same sort of mechanism. Analyzing the pheromones of the common brown rat Rattus norvegicus, they found a stress-free rodent can evaporate the fear in another by emitting a chemical from its neck called 2-methylbutyric acid. This is significant, they say, because as anyone who has spent any time on the street at night in a large city almost anywhere in the world can attest, the wild brown rat is a major pest. Understanding how to chemically manipulate their fears could make our streets vermin-free and design safer, more humane ways to control their movements and breeding. iScience