That’s a very tricky question! Very few species can breed with each other (called interbreeding), so there is a countless number of “impossible” pairings. The more closely related two species are, the more likely it is that they can breed with each other. Some examples are tigers and lions: http://en.wikipedia.org/wiki/Liger and http://en.wikipedia.org/wiki/Tigon (a male lion and a female tiger produce a “liger” but a male tiger and a female lion produce a “tigon”!)
If I had to pick two animals that are least likely to breed with each other it would have to be animals that are the least related to each other (farthest away from each other on the tree of life). So that would be an insect (let’s say a fly) and a mammal (like a mouse or a monkey).
One of the definitions of what makes up a species is a group of animals that can reproduce to make fertile offspring. Natalie’s right – tigers and lions can make ligers and tigons (which can be enormous) but these animals are sterile and can’t make babies of their own. This can happen in a number of animals: Mules are the product of a male donkey mating with a female horse and are normally sterile (except in very rare cases and no one’s quite sure why).
The concept of a species gets difficult once you get to bacteria and viruses because they can transfer genetic material much more easily than animals can, so they are often just classified as groups of similar organisms (though viruses might not even be organisms)
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James commented on :
One of the definitions of what makes up a species is a group of animals that can reproduce to make fertile offspring. Natalie’s right – tigers and lions can make ligers and tigons (which can be enormous) but these animals are sterile and can’t make babies of their own. This can happen in a number of animals: Mules are the product of a male donkey mating with a female horse and are normally sterile (except in very rare cases and no one’s quite sure why).
http://news.bbc.co.uk/1/hi/sci/tech/1408717.stm
The concept of a species gets difficult once you get to bacteria and viruses because they can transfer genetic material much more easily than animals can, so they are often just classified as groups of similar organisms (though viruses might not even be organisms)
princessphoebe commented on :
hi my names phoebe i am wondering if eneyone knows how many eggs do spiders lay.