Yellowstone National Park may be the best place there is to reflect on the fact that we are all pond slime. Every cell in our body acknowledges a deep history, a time when organelles floated free in a world we would have found insupportable. Our close mammalian relatives, the bears and the bison, all of us little twigs on the branches of the evolutionary tree, could not survive without the simple cells that are near to the base of the trunk. We could do without the horseshoe crab or the velvet worm, but we would be lost without bacteria. The lodgepole pines that line the lakeside in Yellowstone could not grow without help from the symbiotic fungi coating their roots and scavenging phosphates from the soil, molecule by molecule. The story of life is not only a narrative of the triumphs of one organism over another organism; rather it is as much about communal shelter and mutual benefit. It is a web or it is a crossword puzzle with no final answer. It is certainly not simple. When you touch a brown mat, blistered and glistening beneath a veneer of slime, you are communing with the deepest part of your own history: deeper than mind, deeper than sex. Now you know where you came from.

Richard Fortey, Horseshoe Crabs and Velvet Worms: The Story of the Animals and Plants that Time Has Left Behind.