Sex and Animals

One definition of "species" is a group of animals that can breed to produce viable offspring that can themselves breed.

Many birds do not breed with each other for the simple reason that they are of different species. In contrast, all dogs are of the same species, so every dog can, in principle, breed with every other dog. Similar, an Angas cow can breed with a Hereford, because both are the same species.

 

You're confusing breed (or race as it's called in humans) with species. All humans are the same species (Homo sapiens) as are all dogs and wolves (Canis lupus). Stay tuned for cats, DNA analysis suggests that they are the same species as the wildcat, Felis silvestris, rather than a distinct species Felis domesticus. But birds are a class, which contains many families, most of which contain multiple genera, most of which may contain several species. The House Sparrow is class Passeriformes (sparrow-like birds) family Fringillidae (finches) genus Passer (all sparrows) species domesticus (the one that lives around houses. The hyacinth macaw is class Psitacciformes (parrot-like birds) family Aridae (parrots with long tails and bare skin around their eyes) genus Anodorhyncus (giant macaws) species hyacinthus (the purple one).

Birds can and do hybridize, but "breeds" of birds are difficult to tell apart except in captivity. A Bantam hen will happily mate with a Rhode Island Red rooster. Different species of birds can hybridize as long as they belong to the same genus, as discussed further down. And as is also discussed further down, this hybridization is not common in the wild but--in birds more than mammals--rather easy to make happen in captivity.

Most warm-blooded animals (mammals and birds) have a courtship ritual that the male performs for the female when she is in estrus (fertile, "in heat"). If this mating dance is not done properly, her instincts don't kick in and she simply does not become aroused and choose him for a mate. (Humans are almost unique in our reversal of the sexual roles, which makes us either special or weird, depending on your point of view. We're also practically the only species whose females are physically capable of copulation when not in estrus.) For example, tigers need the sensation of being clawed in order to be aroused and mate. Lions just absolutely hate that, so lions and tigers never mate in the wild.

Kingdom-Phylum-Class-Order-Family-Genus-Species. (Memorize as King Philip Called Out For Good Service.) Kingdom: Animalia. Phylum: Vertebrata. Class: Mammalia. Order: Carnivora. Family: Felidae. Genus: Panthera. Species: tigris.

We customarily call organisms by their genus and species only, with the genus capitalized. Homo sapiens (modern humans), Pheucticus melanocephalus (the black-headed grosbeak) Escheria coli (the intestinal bacteria most commonly responsible for food poisioning), Prosopis juliflora (the mesquite tree), Acer palmatum (the Japanese maple). If we're discussing several species in the same genus and we all know it, we'll abbreviate the genus, e.g. C. for Canis: C. lupus (wolves/dogs), C. latrans (the coyote), C. aureus, C. adustus, C. mesomelas (the three species of jackals).

Since, as noted above, species rarely interbreed in the wild, that is unlikely. The courtship ritual is the issue.

Species will interbreed in a few unusual circumstances.

One is a decline in population so that mates are hard to find. Wolves in eastern Canada have been hunted almost to extinction so they've taken to mating with coyotes. It helps greatly that both are highly pack-social species. The courtship ritual is not quite so important to them; the instinct to socialize with a pack-mate kicks in and enables copulation. As a side note we're getting our payback for that hunting-almost-to-extinction thingie. Those hybrids are coming back down into the Eastern U.S. and breeding back into the coyote population. They've got gigantic, fearsome fifty-pound "coyotes" out here in Maryland now. I think their deer problem is solved.

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Another is the creation of a new habitat: Human settlements. Most animals are a little wary of giant herds of humans. But scavengers or hunter-scavengers tend, out of necessity, to be a little more inquisitive and opportunistic than most species. In every species of scavenger there are a few individuals whose "comfort" distance from humans is much shorter than the others, and they take up residence on the fringes of our settlements, eating the bounty of perfectly good food we throw in the trash, or the produce of our farms. It's no surprise that these individuals, so comfortable in the proximity of another species, are the same ones who have no taboos about inter-species dating and are not put off by a slightly odd mating dance. People tell me they've seen gaudily colored hybrid macaws diving dumpsters in Latin America.

Which gets me around to answering your question. Those hybrid macaws will encounter a little birdie racism if they ever wander back into the forest. They don't do the Scarlet Macaw mating dance quite right but they don't do the Greenwing Macaw mating dance quite right either. In a couple of centuries (macaws take seven years to reach sexual maturity) you'll probably see rainbow flocks of thoroughly gene-mixed macaws roaming the suburbs of Brazil, but in what's left of the rain forest the individual species will dominate.

However there are always exceptions. The Black-headed grosbeak of the western U.S. and the Rose-breasted grosbeak of the eastern U.S. were always separated by the mighty forest on both sides of the Mississipi River. You remember that beautiful place, right? Oh that's right, we clear-cut it and replaced it with farms. Both species of grosbeaks love fruit and descended on the farms with vigor. These are the only two species in genus Pheucticus and therefore each is the only one that the other could possibly mate with. They are both really brash little birds--the black-headed is one of very few species in which the females sing--and after feeding together and getting to know each other they started crossbreeding. Apparently the grosbeaks who live nowhere near the Mississippi are just as amenable to inter-species dating, because the hybridization is spreading. We've seen hybrid grosbeaks at our feeder back home in California; they crossed the Rocky Mountains in only forty years. It's a good bet that in another forty or another eighty there will be only one hybridized species of Pheucticus grosbeaks in North America. But this is highly unusual, one for the record books.

Hybridization of birds is fairly easy to do in captivity because of "imprinting." Baby birds think they're whatever species raises them. If you take them from their parents when their eyes open and take over the feeding (and most domestic adult birds are happy to turn the job over to you), they grow up thinking they're people. If you raise several related species together, they think you're all one big happy flock. When they reach sexual maturity they'll mate with one of their flock mates even if it's a different species. Those rainbow macaws I mentioned in the Brazilian suburbs have been deliberately bred in commercial aviaries. You can buy a Lavender Macaw, which is just exactly what you're picturing in your head, if you've got the money for a fourth-generation hybrid that somebody spent thirty years creating.

 

Yes. Zoologists prefer the term "variety" or "subspecies." All dogs and wolves are Canis lupus, but if you want to talk about the domestic dog specifically, it's Canis lupus familiaris.

Absolutely. They've done the DNA analysis. The DNA of the average mongrel dog is closer to a wolf than a human from Borneo is to a human from Norway.

There is indeed more genetic variation with some species than others. This is a fact of biology that I'm not qualified to explain. But obviously a genetic bottleneck where the whole species is descended from a small group of individuals could have that effect. But I do know something about dogs because I'm a dog breeder. Dogs have been deliberately bred in captivity for thousands of years to isolate certain characteristics. That has never happened with humans, our separation is purely due to geography and is rapidly breaking down as the world shrinks.

A responsible breeder breeds his dogs when they're two years old, which gives them about ten times as many generations as humans in a given time period, so there's quite a lot of selective breeding that can be done in a short time. Entire new breeds have been developed in just a hundred years. The Pharaoh hound for example. It looks like the dogs in the Egyptian statues, but those have been extinct for almost 2000 years. So they just took a bunch of sighthounds (greyhounds, Afghans, salukis, whippets, borzoi, etc.) and crossbred them until they got what they were looking for. After a couple more decades they start to "breed true" and you can petition the AKC to recognize it as a breed.

The differences between dog breeds are pretty ephemeral. Size, coat length, tail shape, temperament. That's easy to breed for. They turned the Maltese--a 25-pound athletic performing dog used in British circuses--into the little teacup version Liz Taylor carries in her purse in just a couple of decades. They just look so different because that's what we strove for in the breeding and it's easy to do. The difference between the wolf/dog and the coyote, a distinct species that is its closest relative here in jackal-free America, is far greater than between a Great Dane and a Chihuahua.

Dogs are a pack-social species and that's just a dominance behavior used to establish the pack hierarchy. In breeds with a high incidence of alpha traits, like the Lhasa Apsos we breed, even the females do it.