Whatever size you are, you'll have to navigate your way around your world at some time or another. Bugs orientate towards decomposing food, and migrating birds aim towards remote destinations. Some species' rely for survival on their sperm successfully navigating through open water towards a single egg. But how tiny sperm locate their own species' eggs was largely a mystery, until Richard Zimmer's lab began analysing the essential essence released by abalone eggs. After purifying litres of egg-enhanced seawater,Patrick Krug and Jeffrey Riffell found that the eggs were secreting nothing more exotic than tryptophan to lure the sperm in their direction(p. 1439).
More is known about how birds navigate the heavens than how a single sperm cell locates its target. Creatures that release their gametes into the ocean must have developed some way of attracting sperm from their own species,otherwise evolution would have consigned them to the wastebasket....
