We all know natural selections occurs, well, in nature to select the genes most suited to adapt in a given ecosystem, but have there ever been cases of human-caused evolution? I know horse breeders and the like select for certain characteristics, but has there ever been a species of organism taken in by humans and evolved completely into a new species (read: can no longer breed with others of what it formerly was)? Do any of you know of any occurrences of this happening, intentionally or otherwise?
Ever wonder where cows come from?
Mules?
Yeah, but I don’t think it would be safe to say that modern cows are a completely different species from aurochs. Just because one went extinct doesn’t mean there couldn’t have been interbreeding.
The wiki site quoted is confusing on the issue containing both of these quotes:
and
Mules are sterile.
For clarity’s sake, i offer this definition
Species: a group of organisms that can interbreed in nature(or in this case under domesticated (or even lab) settings) to produce a fertile offspring
Arguably some very small dog breeds couldn’t reproduce with wolves, given that a female chihuahua or whatever wouldn’t have much chance of successfully giving birth to a wolf cross. I suppose the other way round would work, though.
I’m pretty sure fruit flies in some experiments have been warped to the point of infertility with regular fruit flies. I’ll look around a bit for some cites.
thanks, i would be very much interested in reading about documented examples where theyve watched it happen step by step.
Dogs are still considered to be one species, even the very large and very small, because even though some individuals may not be able to sucessfully interbreed, you can still get gene flow between them. That is, a Great Dane’s genes may be passed down to a chihuahua line through smaller and smaller intermediate generations.
As to the OP, I’d say probably not, though I’m willing to be proven wrong. If I had to hazard an explanation, I’d guess it’s probably due to two factors: one, that we haven’t been at it all that long - a few thousand years at most. Though it’s interesting to note that dogs, probably the oldest domestic animal, spring to mind first as being significantly different from their ancestral species. Two, we haven’t really been fiddling with our animals’ reproduction methods (with some exceptions like poultry). We’re typically breeding for body size, shape, muscle mass, that sort of thing, rather than trying to change when they mate or what kind of display they put on to attract one another.
Just my two cents.
Oh, and I’d classify fruit flies and other lab experiments as a separate phenomenon from domestic animals. In those cases, we’re deliberately trying to learn how it all works, so it’s more of a direct effect than in the case of a domestic.
You can read about various speciation experiments with fruitflies here starting at section 5.3. There don’t look to be many cases of really clearcut infertility though.
Sure, but the OP is asking specifically about interbreeding, and not gene flow. I realize it’s not a clearcut example, but it’s probably as close to it as we’ve come outside of short-lived insects.
As far as I know, all domesitic animals are still interfertile with their wild progentors. Whether a Chihuahua could produce an offspring with a wolf is perhaps doubtful, but certainly most breeds of domestic dogs can.
There have been some cases in which artificial selection in the lab has produced lineages which are analagous to natural species, because they can not interbreed with the ancestral form, but this is somewhat different from the case of domestic species, and these are not true species according to the Biological Species Concept.
The Biological Species concept recognizes as species those populations that interbreed regularly in nature. (Populations that can produce fertile offspring in captivity, or which hybridize rarely in nature, can still be recognized as separate species if they do not hybridize regularly in the wild.) The Biological Species Concept therefore cannot be applied to domestic animals, or to laboratory populations. However, by convention, the modern practice is to consider domestic animals to belong to the ancestral species.
Regarding cows, whose wild ancestor is extinct, you could also consult my Staff report What did cows evolve from? Modern domestic cattle are usually considered to belong to the same species as the Aurochs, their ancestor.
This is phrased a little clumsily, if you’ll allow me the nitpick. The genes which are expressed in a characteristic enabling the individual possessing that characteristic to be better equipped than other population members to survive and breed in a given environment - a selective advantage, in other words - are selected for. “The genes most suited to adapt” don’t enter into it: natural selection doesn’t - indeed, can’t - deal with future possibilities of adaptation to contingencies, only with current circumstances. Today’s garland may be tomorrow’s millstone.
If I read your sentence in the way which I suspect you intended, “that in a given environment natural selection works to select the genes best adapted to that environment” it works much better. “Most suited to adapt” is confusing your meaning a little: “most suited to an environment” and “best adapted to an environment” amount to the same thing, since the suitability expresses the adaptation.
you are correct, the wording was atrocious, and my thoughts were not properly represented. Please to note: I am an idiot.
on another note, ive been perusing the interweb, and it appears the question i was really wanting to ask had more to do with directed mutation than evolution, per se. An example would be the bacteria discovered by some japanese scientists in 1975 that is capable of feeding on nylon waste This would be the sort of thing no one would bat an eye at if it werent for the fact that nylon is a synthetic material and does not exist in nature.
i am obviously incapable of asking my own questions, but if this would give you any idea of what ive got rattling around in my head i would very much appreciate further information and examples. thanks
What about plants? I thought there were some domesticated plant species that can no longer reproduce with the wild varieties from they were derived, but I could be wrong about that.
It’s quite possible, especially since some domestication events may have involved polyploidy. I can’t think of any definite examples right now, however.
With regards to the OP, as a followup to one of Smeghead’s points (that we haven’t been in the domestication business very long), it may be worth mentioning that frequently members of the same genus can produce fertile hybrids. This is true among all species of the genus Canis (dogs, wolves, coyotes, and jackals), as well as species in the genus Bos (cattle, including domestic cattle, gaurs, banteng, etc.). For that matter, species in different genera, such as domestic cattle and Bison, can produce fertile offspring as well. Even species as different as camels and llamas have been hybridized (although I don’t know whether it’s been determined if the offspring are fertile). Since humans have been domesticating plants and animals for only a few thousand years, it’s not to be expected that intersterility with ancestral forms would have resulted, unless that were a character being selected for directly.
That’s absolutely true, and a good point. Take the banana, for instance. On a wild banana plant, what we think of as the “fruit” is really a seed pod filled with ping-pong ball sized seeds, with just a little flesh surrounding them. The domestic banana plant is triploid, meaning it has three copies of every chromosome instead of two. This means that when it goes through meiosis, the chromosomes can’t be divided equally, and the seeds can’t develop, so the seed pod fills with flesh, with just a few black specks that are the aborted seeds.
So, are the two banana plants different species? Well…I don’t know, but I don’t think so, especially since the domestic plant isn’t fertile. Someone else will know more about plant classification than I do. The key difference is that the change here is in the number of chromosomes, not in the genes themselves. In animals, extra chromosomes usually lead to death or severe disability, but plants are much better able to deal with them. Many of our domestic plants have multiple copies of their chromosomes, because, as a general rule, more chromosome copies tends to correlate with larger size for some reason. Strawberries, IIRC, have eight copies. I think watermelons have seven (seedless watermelons, that is, since it’s an odd number, like with bananas).
Anyway. This is a slightly different method of speciation than the gradual change in physiology or behavior leading to lack of interfertility that we usually think of, but it is an important mechanism in the wild. A lot of new plant species have occured through hybrids, with one set of chromosomes from each parent species. The hybrid can then double the chromosomes to get two sets from each parent, at which point it will be a stable new species. This can happen through a failed cell division, where the chromosomes are replicated, but the cell doesn’t divide.
So, I don’t really know if domestic plants are considered separate species, though I suspect some of them are, but many of them definitely have changed enough that they can’t interbreed with their ancestral species.
Corn (or maize, as furriners usually call it) is definitely a different species than the wild form. A fairly recent discussion of the domestic species and the ancestor can be found here , including my sleep-deprived calling the ancestor by the name of a wheat species (triticum) instead of triticale (the correct name).
As of my last knowledge (which may be out of date), biologists were trying to find ways to import useful genes from triticale into domestic corn. It is, however, no easy task, as domestic corn has some really strange genetic mechanisms (“jumping genes” for one).
Not at all: I had to rewrite my post about four times to make sure it said what I wanted, and I’m sure a real biologist could drive a truck through it. Guests who ask sensible questions which spark good threads like this one are always welcome: please stick around.
No, triticale is wrong too. As was pointed out in the other thread, teosinte is the ancestral form you were thinking of. Triticum is wheat; Triticale is a cross between wheat and rye.
Whether or not domestic corn is considered a separate species from the ancestral form is a matter of convention, since as I mentioned the Biological Species Concept doesn’t apply to domesticates. This is especially true in this case since domestic maize is unable to survive in the wild. This Wikipedia article considers maize to be a subspecies of one of the wild species of teosinte, which would be the modern taxonomic convention.