Sex with a partner is better than sex alone. At least for worms and specifically in the context of Evolutionary Biology.  Going it alone (for lack of a better term) has failed to help worms in reproduction over the long term. 

Although worms have the ability to reproduce either “alone” or “with a partner”,  new research done at the University of Oregon suggests that the worm progeny from parents who self-fertilized themselves had shorter lifespans than the those  who were conceived by two parents.

In addition the benefits to their offspring, the worms who were “sans partner” had less coping strategies and a more difficult time with their environments, leading the researchers to believe that they might eventually become extinct.

Are we as people really so different from the worms? Strangely enough, a majority of  people prefer sex with a partner to masturbation.  Of course, this may depend on which particular partner that you have. And although without the assistance of modern-day science and possibly a petri-dish, it’s difficult for us procreate on our own, we are similar to our worm friends in that single people typically are less happy their their married counterparts. (This is changing a little, too, though.)