Barbarian on Great Dane/Chihuahua cross..
They can actually produce viable offspring (I suppose mom would have to be a great dane). There are species that are simply unable or unwilling to breed, but this isn't one of them.
I would say highly unlikely...
It's been done. There used to be a site with one, but the link is now broken.
http://www.google.com/search?hl=en&ie=U ... 22&spell=1
That would be a different species, then. If one evolves to the point that another population cannot produce viable offspring (and "viable" includes being able to reproduce) then it is a different species. Why is this a good point to go from microevolution to macroevolution? Because once reproductive isolation is a fact, then the genes of the two species can no longer be interchanged, and they will evolve increasingly from each other.
Not necessarily... you're forgetting the option of a third party. If two populations are unable due fertilize (although fertile) but a third population can reproduce with both then cross reproduction can occur. For example (and I'll use canines again for familiarity):
These are called "ring species". Leopard frogs in North America are an example. The ones on the far northern and far southern ends of the range can't interbreed, but they can interbreed with the ones in between. So, for now, leopard frogs are still one species. If for any reason the middle populations get eliminated, or northern or southern ones evolve further, we will have speciation.
Chihuahuas and Coyotes are isolated populations which do not interbreed naturally (which really would mean they are a different species if you consider Fransico Ayala's definition to be best). They are isolated from each other and they will not interbreed.
I live were the urban sprawl surrounded a patch of prairie and then encroached on it. Coyotes don't mind urban environments. They've become a problem. They see chihuahuas as coyote chow.
However... it could be hypothesized that it would be possible for chihuahua populations and beagle populations to interbreed. It is also probable that beagles and coyotes could and would interbreed. Thus, coyotes and chihuahuas should be in the same species since they are not isolated, they are bridged by another sub-species. Of course, you know that scientists commonly classify coyotes, wolves, and dogs (canus lupus for grey wolves, and canus latrans for coyotes) as different species.
Often, closely related species can interbreed, although they tend not to in the wild. Apparently, viable coyote/dog breeds are possible, although it takes some effort. Neither seems to find the other very attractive as a mate. Foxes, wild dogs, and jackels seem to have diverged long enough to make them completely infertile. Dogs and grey wolves have evolved apart in a geological instant.
Barbarian on the chances someone just never noticed a new species of flower:
That would assume that a very well-characerized biota had a distinct species of flower for hundreds of years with no one noticing. Seems pretty unlikely.
It is highly unlikely, but it isn't impossible. Of course, I don't have 10% of the details, so much of what I can say would only be speculation.
If it wasn't a prominently-flowering plant, there might be some possibility. But it is quite prominent.
Barbarian observes:
Grizzly bears and polar bears are two separate species, but they can interbreed and produce viable offspring.
Then are they really different species? Just because they are in a different location and thus isolated from each other, should that really count as "macroevolution"?
Yep. They are quite different. Polar bears have changed shape, the hairs have become specialized for retaining heat in water, the pads of the feet are specialized for walking on ice, and the front feet are webbed for swimming. The shape is streamlined for swimming as well.
A cross would not be viable in the wild. They would overheat on land (polar bears overheat if they run for any distance, even in winter) and they would not be able to swim and survive in arctic waters. So you'll never get a cross that lives, outside of zoos.
And if so, why such a double standard?: "By this definition of species there are over 6000 species of fruit flies (Drosophila) in Hawaii alone!"*
Yep. A species is defined as a reproductively isolated population. You'll never see polar bear genes mingling with brown bear genes in the wild. So they continue to diverge. This is the fourth carnivore return to marine envirionments, and these bears are probably going to found an incredible line of predators if they survive to become a completely marine animal. (the others are, in decreasing order of adaptation, seals, sea lions, and sea otters)
Barbarian observes:
Humans and Chimps, for example can probably form a fetus, but it would not survive.
Then I would contend that humans and chimps are not a seperate species. Of course, I would also doubt very much that they could create even a zygote. Otherwise, we would have already seen something of the sort - people do d-u-m-b things sometimes...
What makes you think they haven't? Remember, there would be a rather early spontaneous abortion.
Perhaps you could educate me by explaining to me finally (I have neve been able to find it) what exactly triggers sperm of one organism to unite with an egg of another, but other organism's sperm will not.
In primitive deuterostomes, like sea urchins, there are bindins that mediate the connection. In them, the bindins are different and don't work between species. On the other hand, guppies show that sperm from other species can fertilize eggs, but not as well as those of males of the same species. For extremely close species like humans and chimps, I bet it works fine. The problem is that through a fusion, humans have one less pair of chromosomes than a chimp, dooming any fetus in fairly short order.
I'm assuming it's something to do with the chemical make-up of the egg's surface - I've been told it's something like a key.
Yep. One of the researchers in the field is a feminist (forget the name). But she was put off by the "sperm coming and taking the egg" descriptions, so she wrote her paper from the "egg lures in the sperm and engulfs it" POV.
Funny stuff.
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