why cant any species of animal breed with another?

Answer 1

It's correct that different species often have different numbers of chromosomes, but that alone doesn't always mean they can't mate. (Otherwise different chromosomes numbers would never evolve.)

Here are a few proximal reasons for an inability to breed:

Mechanical isolation: Two species that are from very different groups, like a fox and a cricket for example, are just plain unable to perform the act of copulation. The parts don't fit.

Gametic incompatibility: Again, with very different groups, sperm cells and egg cells don't recognize each other. Sperm cells can penetrate egg cells because chemicals on the outside of the sperm are recognized by receptors on the outside of the egg. If those receptors don't recognize the sperm, then fertilization doesn't take place.

Zygotic inviability: Sometimes the two gametes recognize each other and fertilization can occur, but then the fertilized cell (or zygote) cannot develop further. This processes occurring because of one parent's genes might fatally inhibit the processes of the other parent's genes.

Hybrid infertility: Some closely related species can have an offspring, but that offspring cannot reproduce. Horses and donkeys are the classic example. A mule is the offspring of a horse and donkey, but mules are infertile. This may be because the chromosomes inherited from the two different species are too dissimilar to allow the first stage of meiosis (in which homologous chromosomes pair up and divide.)

Answer 2

Species can't breed with other species, because groups of animals are classified as a species when they can't breed with something else. So it's in the definition.

In biology there are different definitions of 'species'. One is that if you have a population of, say, cats (just using this for a thought experiment), cats are labelled as a group because they can breed with other cats but not with things outside of the group (like dogs). So the definition of species is given when the animals can't breed with something different.

Thought experiment: You have a big group (A) of cats, all descended from the same ancesteral cats. One day a small group (B) of these cats gets cut off from all the other cats and can no longer breed with the big group. This means that in group B there is a smaller pool of genes, so any characteristics in this smaller group might become more common than in the bigger group. You could also add in environmental pressures. Imagine that the place the B group is in is much colder than where they were before. If the B group of cats contains a few cats with something useful for survival, like very furry coats, these cats are more likely to survive and have kittens. As parents pass on some characterists to their offspring, the kittens would have furry coats and would also be more successful. Over enough time the B group would evolve to have very different characteristics. In the end this could mean that even if the A group and B group met up again, their characteristics would be very different and their underlying genetics would be very different. This could mean that their behaviour (e.g time of year when the breed) is too different and they are incompatible, or if they did mate their genetic differences might mean that the kittens had problems and didn't survive. There could be physical problems so if group B had evolved to be very big and group A were still quite small, if a large male from B fertilised a small female from group A, the female could well die because the kitten was too big for her birth canal.

It can happen that two different species mate and produce offspring. If the offspring are fertile and go on to produce healthy babies themselves, then biologists would have to reconsider the classification - perhaps the species were closer than was thought. However, often if two different species mate and produce offspring, because of the genetic differences and incompatibility, although the baby will grow up, it will be infertile (it won't be able to have babies itself).

Example: Donkeys are related to horses, but not the same species. If a male donkey mates with a female horse they produce a mule (a hybrid). Mules are infertile although there have been rare cases when a mule has gone on to mate successfully. (This is so rare that some remote cultures believe that if it occurs, the world will end.) The infertility of the mule is probably because a horse has 64 chromosones and a donkey has 62. This leaves the mule with 63, an odd number, which can not easily divide. When mules have been fertile it has usually been when the chromosones have divided strangely when the mule is mated to a horse.

Hope this helps

Answer 3

There is not a clear definition of species.
A species is, however, broadly defined as the set of animals that can interbreed. Therefore, by definition animals of different species cannot breed.

However this is an arbitrary definition with many discrepencies.
The Tiger and Lion have already been mentioned - different species but they can interbreed.

Even animals from different genera have interbred (false killer whale and dolphin)

http://www.creationontheweb.com/content/view/271

What determines whether two animals can interbreed is not an arbitrary assignment of a species label, but which of the created kinds they are in.
From Genesis 1, the ability to produce offspring, i.e. to breed with one another, defines the original created kinds.

Refrering to Genesis for answers is deeply unpopular amongst the bigoted evolutionary community, but is always fruitful for the diligent.

Answer 4

I believe that a tiger and a lion can, which produces a liger. also a Horse and an Donkey, producing a mule, as the name implies. Im sure there are many more. If two Ligers could breed then you'd have a completly new breed of animal. As with Mules!

Answer 5

chromosome's are different
but some animals can breed with other animals in the same category
for example horses can breed with zebras, and donkeys

Answer 6

"And God said, let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earh after his kind: and it was so. And God made the beast of the earth after his kind, and the cattle after their kind, and every thing that creepeth upon the earth after his kind: and God saw that it was Good." this is why evolution isnt true. it is tru about ligers, but 2 ligers cant reproduce. as with the mule. dogs are not different kinds of animals. same kind, difference in appearance. same with humans. read the Bible.
its the manual for life God bless

Answer 7

what about different breeds of dog is this sub species?

Answer 8

They can e.g a lion and a tiger

a liger they are massive...fact!!

Answer 9

differences in number of chromosomes

Answer 10

i dunno but if they could then i'm pretty sure that a human would hav done with a camel ages ago!!!