The “species cannot breed with each other” thing seems like an argument from definitions on Eliezer’s part, because while there are often genetic, fertility, life-strategy and longevity issues with hybrids, they’re not all sterile, and they’re not all maladaptive. Indeed, there are some situations where hybridizing at the expense of the “pure” populations turns out to be an adaptive strategy. This can even be done in the lab with fruit flies.
Wild hybrids of fin and blue whales aren’t uncommon at all (we don’t know much about their lives as yet, though we’ve recorded them for quite a while now). Coyotes and wolves interbreed so frequently that some genetic analyses indicate that red wolves may all constitute coyote hybrids, implying the entire species “canis rufus” originated as a cross. Wolf-dog hybrids are quite common in the US. Beefalo and Zubron hybridize domestic cattle and wild bison, and are perfectly viable (and common in agriculture). Wild populations of grizzly and polar bears seem to produce viable hybrids; a few are known both as wild encounters and captive-bred. At least some camelid and feline hybrids are also reproductively viable. There are many, many interspecific bird hybrids.
The “species cannot breed with each other” thing seems like an argument from definitions on Eliezer’s part, because while there are often genetic, fertility, life-strategy and longevity issues with hybrids, they’re not all sterile, and they’re not all maladaptive. Indeed, there are some situations where hybridizing at the expense of the “pure” populations turns out to be an adaptive strategy. This can even be done in the lab with fruit flies.
Wild hybrids of fin and blue whales aren’t uncommon at all (we don’t know much about their lives as yet, though we’ve recorded them for quite a while now). Coyotes and wolves interbreed so frequently that some genetic analyses indicate that red wolves may all constitute coyote hybrids, implying the entire species “canis rufus” originated as a cross. Wolf-dog hybrids are quite common in the US. Beefalo and Zubron hybridize domestic cattle and wild bison, and are perfectly viable (and common in agriculture). Wild populations of grizzly and polar bears seem to produce viable hybrids; a few are known both as wild encounters and captive-bred. At least some camelid and feline hybrids are also reproductively viable. There are many, many interspecific bird hybrids.