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When you have a continuum, species don't diverge. They interbreed. So the whole will just carry on. If a mutation occurs that stops interbreeding, then that
by mikekchar 10y ago
When you have a continuum, species don't diverge. They interbreed. So the whole will just carry on. If a mutation occurs that stops interbreeding, then that line is likely to die out because of competition with the main line.
However, imagine rabbits on an island. There are zillions of them everywhere and there is a wide variety of mutations. Mostly it doesn't matter because most of them can interbreed, and the ones that don't die out. But one day the rabbits get a terrible disease and almost all of them die. The ones that don't die have a mutation that makes them resistant to the disease. Now you have a different kind of rabbit where they are all resistant to the disease.
This keeps happening. Not always disease. Sometimes their food source disappears. Sometimes a new preditor arrives. Sometimes the weather changes. Each time, they almost all die. Only the ones that could survive live.
After all of that, the island rabbits are very specialised. They might not even be specialised for the current conditions. For example the disease may no longer exist. The weather may have changed back. The predators may have died out. But it doesn't matter. They are very different than the original rabbits, and also very different from the rabbits on the mainland. So much so that the two can't interbreed.
There is no intermediate forms because they all died. If they had not died, the specialised form would not have developed.
We can observe this both in the wild and in laboratory conditions. Especially with short lived insects (usually fruit flies) we can actually see evolution happening in this way. But with rabbits... we tried to kill all the rabbits in Australia with a disease and ended up with lots and lots of rabbits who are resistant to the disease.
This is why it is important to teach evolution in school.
- barking 10y agoThat makes sense thanks. I'm not sure how a mutation that prevents breeding would be disseminated from the animal in which it occurred?
- tremon 10y agoI'm not sure I fully understand your question, but probably this: https://en.wikipedia.org/wiki/Speciation https://en.wikipedia.org/wiki/Speciation The point is that as long as two minimally diverse populations remain in close contact and can interbreed, most of their mutations will cross the population boundary and we will probably classify them as one species, even though both populations may look nothing like their ancestors of 10,000 years earlier. Mutations that prevent interbreeding usually don't occur in a single generation, they are the result of a long period of no interbreeding (and therefore divergent mutations).
- barking 10y agoThat makes sense to me. Take two groups of animals from one species and put them in different environmental conditions, isolated from the other for long enough (maybe millions of generations?) and eventually you will end up with 2 distinct species.
- splawn 10y agoyes, that is true. However even if you take a single group in one environment and gradually change it over long period of time you can end up with something completely different even though the individual changes were extremely small. Imagine a RGB LED that very slowly goes through the full color spectrum over a year. From day to day the colors would look almost identical to the point that you could swap them and no one would notice. You would probably call all the colors during January "red". Once you got into July you would call the colors "green" and would never be able to swap those hues with their "ancestors" from January. This was a convoluted analogy to explain the concept of "gradual change", but hopefully it makes sense.
- loudmax 10y agoAn even more impressive demonstration is the existence of ring species: https://en.wikipedia.org/wiki/Ring_species https://en.wikipedia.org/wiki/Ring_species Here, you have a population whose geographic range is in the shape of a ring. Say, around the base of a mountain range. Members of the species may display some regional variation, but they can interbreed with their nearby kin. At some point on the ring though, there is a break. Here, regional variations will have accumulated to the point where the members are not able to interbreed and you have what appears to be two distinct, if similar, species. Only by following the line of population the long way around the ring do you find that the populations are still connected and actually the same species.
- barking 10y agoYou sent me off on a tour of the internet about this topic that I'd never previously heard of and it ended here: https://whyevolutionistrue.wordpress.com/2014/07/16/there-are-no-ring-species/ https://whyevolutionistrue.wordpress.com/2014/07/16/there-ar... There are no known examples of ring species, which is a pity because it would be really cool.
- marcosdumay 10y ago> Each time, they almost all die. It's a detail, but I think it's an important one. Evolution drivers do not have to kill most individuals. In fact, it does not have to kill any single one. Just a small decrease in fertility is enough to extinguish a genetic trait. Killing a huge number of individuals does make it act faster, but is by no means necessary.
- fapjacks 10y agoRight! It's about populations, not individuals.