This article is reposted from the old WordPress incarnation of
Not Exactly Rocket Science. When it comes to sex, it makes sense
to stick to your own species. Even putting aside our own innate
revulsion, inter-species liaisons are a bad idea because they
mostly fail to produce any young. In the few instances they do,
the hybrid progeny aren’t exactly racing ahead in the survival
stakes and are often sterile (think mules). But having poor
unfit young is still better than having no young at all and if
an animal’s options are limited, siring a generation of hybrids
may be a last resort. Karin Pfennig from the University of North
Carolina found that the plains spadefoot toad uses just this
strategy in times of need. Female toads breed just once a year,
so it pays for them to make the right choice. According to
Pfennig’s work, they take their health and their environment
into account when choosing mates. If their bodies are weak and
their surroundings are precarious, the benefits that another
species’ genes can pro