Nobody. If this is what you were taught the person who taught you was wrong. A species is an interbreeding population. Tigers and lions are separate interbreeding species and they can also produce fertile offspring when mated in captivity.
“Tigers and lions are separate interbreeding species and they can also produce fertile offspring when mated in captivity.”
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Really? Where can I see these fertile offspring? This is the first I have ever heard of this. When I look up Tiglon it is referred to as a sterile hybrid cross.