0
$\begingroup$

I am asking this question as a layman in biology: What the title is supposed to mean is, as a species evolves, say humans and chimps from its common ancestor, at what point and why are humans or chimps not able to reproduce with it's common ancestor anymore? I'm asking this because two very different looking dogs can still reproduce, so how long would we need to keep breeding dogs until the resulting dogs can't reproduce anymore with the "older" dogs?

$\endgroup$
2
  • 2
    $\begingroup$ Your analogy here is a bit flawed - it is more like current dogs unable to breed with current dogs - which already happens. Very large dogs can't physically breed with very small for instance. The small males can't get up that high physically and the small females can't carry or birth the cross-breed pups as they are too large. $\endgroup$
    – bob1
    Jun 30, 2023 at 8:39
  • 4
    $\begingroup$ Does this answer your question? How many generations does it take for one species to become a new one? $\endgroup$
    – John
    Jul 2, 2023 at 12:58

1 Answer 1

1
$\begingroup$

Zooming out a bit, biologists are usually interested in what practically stops gene flow, not whether gene flow is technically possible or not. A good example of this is chipmunks on the north and south ridges of the Grand Canyon, USA. A human could pick up a few chipmunks from the northern side, bring them to the southern side, and they'll breed perfectly fine with the local population. But in real life, chipmunks cannot naturally cross the canyon and so there is actually no gene flow.

Now to answer your question about when it's literally impossible for two different populations to mix and have children, it's always genetic. There is simply too much genetic difference between the two species to have a viable offspring. A great example is mules, the offspring of horse and donkeys. Horses have 64 chromosomes, and donkeys have 63, which is a different number. For the first generation of mules, it just so happens to not matter. But the dissimilarity prevents mules from breeding and having offspring. Between any pair of species, there will be genetic differences, and at some point, the genetic differences just become too great to allow reproduction. For example, you could never cross a horse with a plant because they are simply too incompatible. However, there is no one compatibility issue that is always responsible. Different species will have different issues. It is not always having a different chromosome number.

$\endgroup$
1
  • 2
    $\begingroup$ worth noting chromosome number is not enough several species have different chromosome numbers within the species. like everything in biology its messy and blurry. $\endgroup$
    – John
    Oct 7, 2023 at 14:04

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .