What we can learn from a sea creature orgy

For more than 400 million years, horseshoe crabs — 10-eyed, blue-blooded, dome-shaped sea creatures — have lived on our planet, crawling ashore in spring and summer to mate and lay thousands of eggs that look a bit like grains of millet. 

They were doing this before Pangea broke up into the continents we know today. They were doing this the year an Everest-sized, dinosaur-slaying asteroid smashed into what is now Mexico. 

And they continued doing this as humans transformed the planet...