They need to interbreed, inject some vitality back into the family bloodlines.

In the hill country, sika interbreed with red deer and with elk.

Traditional agronomy transfers genes between plants whose kinship lets them interbreed.

Dogs do not become cats, nor interbreed to produce another species.

How long did they interbreed before the gap became too wide?

Because they range over huge areas, and interbreed freely, wolf genes are widely spread.

Yet in Gombe they now apparently mistake one another, because they have begun to interbreed.

It was common among the demon world to interbreed.

Such bestial couplings are generally infertile; after all, species are defined as groups that cannot interbreed.

For one thing, they will not interbreed.

Brown trout will never interbreed with rainbow trout in the wild, but do occasionally breed with salmon.

If those desirable mutants proceeded to interbreed with normal plants, the mutation would immediately be diluted or lost.

There is also evidence domestic cats continued to interbreed with their wild cousins much longer than domesticated dogs.

Of these, there are three sorts which keep apart from each other, and are thought not to interbreed.

And they can't interbreed either.

That is, they can interbreed.