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So all animals are in different species to members of their same sex? I'm joking a little of course. But only to make the point that the definition of species
by sago 7y ago
So all animals are in different species to members of their same sex?
I'm joking a little of course. But only to make the point that the definition of species taught in high school is very difficult to pin down. You identified one way. Even more common: not all organisms reproduce sexually. But also: some organisms (protists) perform sexual recombination separately to reproduction. And even for well known higher mammals (which is where the 'offspring must also be fertile' clause comes from), 'fertile' is by no means binary! A sexual definition of species is simple, but rather difficult down in the nitty-gritty.
It is always worth bearing in mind that species is a human classification concept, not a biological reality. It's not surprising that it has very grey edges.
- virtuous_signal 7y agoAt least for sexually reproductive species, your first objection could be addressed by defining the species relation as the transitive closure of the relation A ~ B if A can reproduce with B. (so for instance male1 ~ female0 and male2 ~ female0 by the original definition, and then male1 ~ male2 via the closure)
- bayesian_horse 7y agoYou still assume you have animals that breed when you're looking. Lot's of them don't. And it's still about the genetic distance. You can't mate everyone to everyone. You need to cluster by phenotype,genotype or location.
- Scarblac 7y agoIt's also just an extremely impractical definition. Say you have two animals and you want to know if they are the same species. How are you going to find out whether they can or cannot mate (and produce fertile offspring, even)? What if they are the same species but just aren't that interested in each other?