This was supposed to be the Christmas in Europe where family and friends could once again embrace holiday festivities and one another. Instead, the continent is the global epicenter of the COVID-19 pandemic as cases soar to record levels in many countries. With infections spiking again despite nearly two years of restrictions, the health crisis increasingly is pitting citizen against citizen — the vaccinated against the unvaccinated. Governments desperate to shield overburdened health care systems are imposing rules that limit choices for the unvaccinated in the hope that doing so …

A chemical that babies give off from their heads calms men but makes women more aggressive, according to new research in the journal Science Advances. It could be a chemical defense system we inherited from our animal ancestors, the authors speculate, making women more likely to defend their babies and men less likely to kill them. Odors affect behavior in the animal world in plenty of ways. A rabbit mom will attack her pups if they smell like another female rabbit. Mice whose sense of smell is damaged don’t attack …