"Molecular genetics analyses of species boundaries in the sea".

Blame is a mere cultural matter; it does not travel across species boundaries.

However, I've never heard of it crossing species boundaries.

Her prospects for romance here were nil, unless she wanted to cross species boundaries.

If you just look at E. coli, you see that nature shows far less respect for these species boundaries than we do.

Here was a disease with no respect for species boundaries.

This definition captures a number of intuitive species boundaries, but it remains imperfect.

Alangium has about 24 species, but some of the species boundaries are not entirely clear.

In addition, we now know that genes can be transferred laterally, usually by viruses, across species boundaries.

This approach has the advantage that the results are more likely to be valid across the species boundary.