Just like penguins and other primates, people trade sex for resources

Female penguins mate with males who bring them pebbles to build egg nests. Hummingbirds mate to gain access to the most productive flowers guarded by larger males.

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<p><a href="http://www.physorg.com/news127057451.html">Just like penguins and other primates, people trade sex for resources</a></p> <p>Female penguins mate with males who bring them pebbles to build egg nests. Hummingbirds mate to gain access to the most productive flowers guarded by larger males.</p>