While dinosaurs ruled the world some 200 million years ago, a
group of nocturnal, shrewlike proto-mammals unwittingly sniffed
out a strategy for survival that eventually led to the evolution
of larger brains. Fossil skulls of two ancient, mammal-like
reptiles suggest that natural selection for a keener sense of
smell was the initial spur behind bigger brains in early
mammals, according to a report online today in Science. “Mammals
didn’t get our larger brains for thinking,” says co-author Zhe-
Xi Luo, a paleontologist at the Carnegie Museum of Natural
History in Pittsburgh, Pennsylvania. “We got it for a more
urgent and more basic need—our sense of smell was far more
important.” Birds and mammals have brains that are up to 10
times larger, relative to body size, than those of reptiles and
other animals. Why? Some researchers have proposed that the
early, nocturnal mammals evolved larger brains to boost their
hearing, because sight was less important at night. Others have
suggested that mammals’ brains are prop