Why can't two different populations have offspring that reproduce?

Question

Im not quite sure and have been wondering. I have a test coming up in Bio and would like to know why this happens. Thank you.

Answer 1

If you find two populations of organisms in the wild and cannot reproduce properly, it implies that these populations may be different species under the biological species concept. The biological species concept states that if a viable offspring (one that can live) is not created when individuals from two populations mate OR that offspring cannot have offspring of its own, then the two populations may be considered separate species. In both cases, these populations have what are known as reproductive isolating mechanisms (or RIMs) which means that there is something that is keeping the two populations from mating and/or having fertile offspring (offspring capable of having babies). There are pre-zygotic isolating mechanisms (things that keep a zygote or fertilized egg from forming) and post-zygotic isolating mechanisms (what you are referring to in the question, this is what happens after the zygote is formed). For post-zygotic isolating mechanisms, the baby can abort or if it is born and can live to an adult, it cannot produce babies of its own. The classic example (as given by an earlier poster), is when a horse and donkey mate, they make a mule. The mule may be perfectly healthy, but it cannot reproduce to make other mules. Thus, horses and donkeys are considered separate species.
I'm sorry if this is more information than you may have expected, but these concepts are typically covered on Biology exams, definitely on AP Biology exams and in other high school Biology classes (taught by good teachers). For more information about pre-zygotic isolating mechanisms please check your textbook, in general these mechanisms are much easier to understand than post-zygotic ones.

Answer 2

Your question is somewhat vague. Two different populations of what? Humans? Well, we humans don't have any problems producing offspring that can have more humans. Does not matter if that human is Chinese and America, Asian or Mongoloid.

Different wolf populations could reproduce successfully. After all they are the same species. There are examples. The federal government reintroduced what they called the "red wolf". The thinking was that these were a unique species and population that would not breed outside its population. Well no. Within a couple years these "red" wolfs were breeding with domestic dogs. Was not too long before there were not any red wolfs left. But plenty of wolf dog crosses.

Horse and donkey are NOT separate species, they are indeed both Equis.

Answer 3

OK, I think that by population, you're actually thinking two different species; maybe populations that have been isolated from one another for very long periods of time and can no longer breed successfully. The primary reason for this, I feel, is change in the chromosome number between species and/or, mutations in cell surface receptors on the membranes of their gametes, sex cells. If these receptors are not the same between male and female of a given species, sperm and egg cannot dock up properly and fertilization will not occur. There may also be physical limitations that have evolved in one population that will not permit successful intercourse to occur between species.

Answer 4

They are two separate species, like the horse and the donkey. Their offspring the mule is infertile, because its parents have different numbers of chromosomes..

Answer 5

Genetic/reproductive isolation/divergence, speciation.

The two populations have diverged genetically (through evolutionary forces; NOT just natural selection) enough that they can't reproduce. At that point, they'd definitely be considered separate species.