Comment "Species" is a surprisingly fuzzy term (Score 1) 238
Identifying animals by species is usually convenient, but it's really an shorthand for clades of individuals. Are two individuals close enough to reproduce and have offspring that are capable of reproduction? That's a different question from whether Species X and Species Y are close enough, and the boundaries are a lot fuzzier than they taught us in high school. Lions and tigers aren't the same species, but they're close enough that ligers or tigons can be fertile, and there's at least one liliger out there. (It doesn't happen in nature, because lions and tigers don't live in the same areas, at least in modern times, but they're still close enough relatives.) And even mules are occasionally fertile.