Speciation is a process where a population so much changes in design from the population they once were that they have gone their separate ways. Where still able to have offspring the entire population no longer chooses to pair-up together. Or a population that became isolated from another can experience genetic drift that forces them forever apart.
In some cases speciation happens very slowly by taking small learning steps. No single genome change was an event that made a new species. It is then impossible to put an exact time and date on the birth of the new species.
In other cases speciation follows a very sudden change in genome structure. This happened in humans, fruit flies (drosophilia) and mosquitoes following a chromosome speciation event from an ancestor much like us that in our case was very different from modern great-apes we know which did not exist back then.
How long it would take an isolated genome to slowly speciate much depends on its learning rate (how fast it gains or changes new information/genes). Sexual reproduction has a good amount of crossover exchange which greatly accelerates the ability to adapt and change. Asexual reproducers such as E. coli produce clones of itself which are identical to the parent. Fast responses to environment is then from exchanging plasmids. But these are transient additions to the genome that accomplishes reproduction.
There are "living fossils" that have changed so little it seems to us that they should have become a new species by now or at least new morphology. But this change is relative to how fast our genome changes in comparison to theirs. So it is not time alone that matters, we must also consider the genome learning rate in our calculation of how long it takes for a given genome to speciate.Home/Classroom Fruit Fly Speciation Experiment
In this experiment one or more people create unique environments inside an assortment of jars, coffee cans and other containers are given a unique food source and environment inside an aquarium or even trash-can with screen on top for some air flow but no escape. Open air hole(s) on the top of each environment container allows movement from one environment to another for the ones that would rather leave the environment to go in search of a new one where their sense of taste and smell will help them find another. When the food needs changing or rotating (so not all maggot young are removed) they can be brought outside where those that escape will not matter and in cold weather or short time in refrigerator will slow them down to a stop. Inside of each environment there is one or more small paper cups or other tiny food dish so the container itself will not need cleaning. Each member of group can bring a new supply of food of their choice to the experiment. In the case of food like soggy pizza the very salty toppings will help keep the food from spoiling but too much pepperoni might be toxic to them. A couple of grapes or other fruit can be included so they have more than dry salty pizza and sugary water source.
Each in a group can be as creative as they want in designing one. It can be an open flying space. Or include toys or other material to climb in and around where their wings will no longer do them much good anymore. Cleaning might be more difficult where not still but toys could be a tied together as a bundle to lift out to swap food then place inside. This will give some of the flies that would rather fly away the opportunity to do so while those that prefer their bundle will get to repopulate their environment.Behavioral Speciation
This experiment demonstrated how speciation is in part guided by what the organism itself finds desirable in the variety available to select as a mate. This includes extreme examples such as peacocks where females selecting the largest most attractive tail design has led to males with giant brilliant displays, even though this makes it more difficult to fly from predators.
In humans the looks of "sex symbols" are sometimes computer enhanced to represent the conscious ideals not yet common in our morphology. What gets added to or removed, helps show what human intelligence finds most desireable.
In a behavioral speciation there is no one day and time that a pivotal event occurred. And the genome must first have to be already drifting in that direction or else such morphological change is not possible. In the peacock example we can say that the peacocks are aroused by the direction their genome is already set to go anyway. Therefore what they in their mind find desirable is the same as what the genome finds desirable at the molecular level being expressed in the emergent peacock brain. What they find desirable is not here hard-wired into neurons it is an expression of the molecular genome itself that even responds chemically with hormones that increase to cause physiological change that in humans with just a picture of a member of same species inviting mating.
We can to some degree predict where a species is drifting towards, by how it idealizes itself. For our species there is all of art and culture where we find exaggerations of real life where the size of Betty Boops pupil alone is the size of her whole mouth yet we still recognize it as being human and sexy. What produces this may be that it is epigenetically possible to drift in that direction, or already are.Chromosome Speciation (Human, Fruit Fly)
In human speciation chromosome complexity suddenly increased when two entire chromosomes fuse at opposite ends to become one. This has made humans unique among their kind where such a fusion makes a total of 46 chromosomes, instead of the 48 of all great apes. Here, a parent passed to offspring a fused copy in one of the two parental gametes, to birth a being with 47 chromosomes. That fusion then passed into the population where the fusion would then on occasion have the fusion in both gametes to make the first 46 chromosome beings where from such man and woman (Chromosomal Adam and Eve) were born only 46 chromosome descendants, us.
Even though there was not a significant amount of gene scrambling the rearranging of the chromosome territories may have produced a very noticeable morphological change. If true then I would place the speciation event right there. Which happens to be about the same time that's currently estimated for our speciation. It might have literally happened overnight with the birth of our 46 chromosome ancestors.
The fusion event is not automatically the speciation event it depends on other factors especially what it is that makes the species most unique. In our case humans all have 46 chromosomes and great-apes 48 so it's not like gorilla having previously gone another way with the same 48 genome structure that humans throw in a zoo not send off to college. We also have two events first the fusion in one gamete then later present in both. With the final count eventually becoming 46 that is when the restructuring of the genome was complete. And without that fusion the human form may be impossible.
The mother of a 47 might have known there was something about them that was not like all the other children but still love them just the same. Then came the birth of 46's from 47's that were again of sudden different genome structure from their parents who might be able to tell they were somehow different from their 48 and 47 chromosome peers.
One giant chromosome may have advantage over two average sized ones, which would help explain why that sometimes happens with beneficial results. This would then be another way the genome takes a good guess. In this case by a little bit encouraging a beneficial chromosome fusion event by their having safely tangled protective ends, a mechanism to increase chromosome complexity. After occurring it can be enough to guarantee a very major speciation event.Hybridization Speciation
Common in plants and used in agriculture a hybrid species is created when two or more still reproductively viable species combine to form a new non-sterile species. In plants this is relatively easy. In animals can be more difficult. Horses and donkeys normally give birth to a sterile mule but on rare occasions a fertile mule is born.Polyploid Speciation
Polyploid speciation is the result of chromosome count (information content) doubling, tripling or more. With twice or more of everything the cells are proportionately larger, resulting in a larger plant or animal. This is relatively common in self-reproducing plants. In animals reproducing the new genome structure requires a genome compatible mate, therefore surviving polyploidy species are less frequent but are still found in some insects, fishes, amphibians, reptiles and rat.References
 Francisco J. Ayala and Mario Coluzzi
Colloquium Paper: Systematics and the Origin of Species: Chromosome speciation: Humans, Drosophila, and mosquitoes
PNAS 2005 102:6535-6542; published online before print April 25, 2005, doi:10.1073/pnas.0501847102http://www.pnas.org/content/102/suppl.1/6535.full
Polyploidy and Speciation, Kimball's Biology Pages.http://users.rcn.com/jkimball.ma.ultran ... loidy.html