How long will it take two populations of organisms to develop into different species?

Question

Assuming these two groups of organisms (not any particular species) are COMPLETELY seperated, approximately how long until they develop into seperate species? When I say "seperate species," I mean that if an individual from each population were to mate, conceiving offspring would either be impossible, or the offspring would at least be disabled or infertile.

If the environments in which they live are similar (two tropical rain forests seperated by mountains or some such obstacle), will the development of seperate species take longer? What if the environments are different? (Forest and tundra?)

Answer 1

It depends widely on the species, and is best measured in the number of generations, not years (as some species have a generation-length measurable in days, while in mammals this is decades).

However, under controlled conditions, speciation can be achieved in a surprisingly small number of generations.

For example, speciation has been achieved in the laboratory using fruit flies:

Diane Dodd's experiment (source 1, 2) showed reproductive isolation in as little as 8 generations (!). That means that the two subpopulations lost any interest in mating with each other, which in nature, would be sufficient to produce speciation (although it is difficult to tell if speciation has actually occurred, if you define "speciation" to mean that they are genetically *unable* to produce fertile offspring).

To demonstrate actual genetic incompatibility, the two would have to continue to show willingness to mate, but produce stillborn or infertile hybrids. This is harder to do in the laboratory, but has been demonstrated in as little as 30 or 40 generations (see source 3).

However, in mammals, it seems like the answer is more like thousands of generations.

And of course, in nature the answer is much longer, because there is no control over the selective pressures or the genetic isolation. Nevertheless, this has been documented as well. E.g. there is evidence that a species of mouse introduced accidentally by man on the Faroe Islands about 250 years ago, has become a separate species from the original species (source 4). And there are others in source 4.

But yes, if the two populations find themselves isolated geographically, and then those two geographies change in different ways (one becoming forest, the other tundra), then this will favor different types of individuals in each environment, and speciation will take less time (assuming neither population is *completely* wiped out).

Incidentally, source 3 has a long (and IMO, important) discussion of what "speciation" and "species" mean. Worth reading.

Answer 2

Hmm - I wouldnt say millions of years. Gotta be careful with that with educated people around (not just under educated college students taking evolution). Thats a cop-out or an answer barring no real thought. Once you hear "millions of years", you should understand that a fairy tale is coming next or no real science or thought went into the answer. Thus, the problems we evolutionists confront... we tend to clean up the mess with the "millions of years" trick. For instance - A. "How can you say a bird can create a non bird?" B. "Well, weve never observed such a feat or the beginning of such a feat, but maybe over millions of years it could happen according to some of the evidence Ive seen."

Instead, look at horses and donkeys... they are two animals from a common ancestor. When they mate, they produce a mule. However, the mule is infertile. A horse and donkey parted ways less than 1000 years ago. So the answer is <1000 yrs.

Answer 3

Why do you ask this in the R&S section? You need to ask these questions in the science section. First of all, one organism does not evolve. Nothing ever evolvues during it's lifetime. It's the species as a group that changes as natural selection determines what organisms survive. I have a feeling you won't ask this in the science section, so I'll try to answer them quickly. If you aren't satisfied, e-mail me or do some research online. Yes, life started in the sea. The fish that could go on land would escape predators in the sea. The fish that could go from ocean water to a tidepool would survive better than the ones that couldn't escape predators. Have you ever seen a lungfish? It looks like a fish, but can crawl around on land...it's alive today. Oaks didn't evolve into apple trees. Oaks and apple trees have a common ancestor. Roses don't evolve into lilys. Flowers need to be different because some need to attract specific insects in order to be pollinated. The climate is not right for palm trees in Alaska. Non-flying creatures came first. We don't know for sure why, some say to help catch prey. Have you ever seen a chicken up close? It's feet look a lot like a dinosaur's. Please contact me if you have any more questions.

Answer 4

There's no concrete answer. It depend tremendously on the environments, because selection pressures will drive evolution and speciation to work faster. Size of the populations also matters greatly, the smaller the starting population the faster speciation should go. Theoretically, if the two populations are both large and in identical environments, speciation should never occur. But sometimes it does anyway.

Answer 5

a really long time, especially in multicelled organisms. We're talking hundreds of generations

Answer 6

hundreds of thousands, if not millions of years.