"...it used to mean ..." When did it not mean that? The mechanism of natural selection was Darwin's main contribution to explain how evolution worked, even if t

"...it used to mean ..." When did it not mean that? The mechanism of natural selection was Darwin's main contribution to explain how evolution worked, even if they didn't understand genetics at the time. Darwin's famous finch example is a great demonstration of that. Finches with shorter, stouter beaks were able to take advantage of harder berries that were available on one island that other birds couldn't as easily eat. And once there was some geographic separation, birds with that same feature tended to breed more birds with that same trait. It wasn't some wild stroke of genetic luck where bird was born with a short beak -- it simply selected an existing trait that had previously been neutral (or close to it). Evolution happens to populations, not individuals. Selection pressure is exactly what shapes population genetics. During times of stability, genetic diversity is introduced through gene drift, but it is selective pressure that leads to population-level shifts. (Please don't nitpick -- everything is statistical a neutral change can spread through a population even without pressure, but that isn't the main vector). The article was about frogs, so my comment is in that context. In the case of bacteria, which are asexual and which exist in much greater numbers and have much shorter generation times, the "eureka" model of evolution you seem to be thinking of is more defensible, where one lucky bacterium out of a trillion gets a mutation that gives it some significant new ability (say, like being able to metabolize plastic or something) that allows its descendants to out-compete the rest of the population and take over.