Some penguins have been known to engage in "prostitution." They will have sex with males in exchange for food and pebbles.

AS ANIMAL TOTEMS GO,penguins take their place somewhere between the regal eagles and the hapless hippos. By virtue of their sleek lines, “formal wear,” and pure exotic appeal, penguins symbolize dignity and class. But their decidedly awkward waddles and round, fuzzy offspring also make them adorable and endearing.

So it might come as a surprise that, at times, penguins behave in ways that seem neither stately nor cute but rather what we humans might call sleazy. To wit, Adélie penguins regularly steal stones from other nests to fortify their own, even though they get pecked and chased in the process. More surprising yet is the recent discovery that some females resort to peddling their bodies in exchange for the precious pebbles.

And penguins are not the only creatures to exchange sex for a material benefit (aside, of course, from humans). A few other birds trade reproduction favors for food, and many insects have evolved elaborate quid pro quo sexual arrangements. In several cases, one or another of the individuals involved has even figured out a way to get something for nothing.

Animal behaviorists believe these “deals” could have evolved for several reasons: to encourage sex; to provide a kind of offspring support for the third party’s potential progeny; or to lay the groundwork for a possible future relationship. In any case, with some of the examples stretching back millions of years, prostitution seems to live up to its reputation as the oldest profession.