In the most common system of taxonomy, as we should all have learned in high school, human beings are Animalia Chordata Mammalia Primata Hominidae Homo Sapiens. The first bit essentially means that we eat something other than sunlight. The second bit means we are descended – like all other vertebrates – from Pikaia gracilens. This creature lived about 570 million years ago and was part of the Cambrian explosion: so spectacularly displayed in the Burgess shale near the border of British Columbia.
Pikaia was initially mis-categorized as a worm. Now, it seems that the combination of segments, muscles, and a flexible dorsal rod embodied in this little creature may mean that it was the first vertebrate: the template for all those alive today. From the first vertebrate species, all amphibians, reptiles, birds, and mammals evolved. From tuna fish to orangutan, we may all be descendents of Pikaia. Writing about the animal in Wonderful Life, Stephen Jay Gould highlights both its huge evolutionary legacy and the degree to which it arose as the result of many change occurrences. If we could go back all those millions of years and let time unroll again, it is highly likely that we would have a profoundly different world at the end.
You can begin to imagine how staggeringly different the contemporary world would be if this little creature hadn’t survived and spread. The old view of evolution as a linear and predictable progression towards ‘higher’ organisms – a surprisingly common teleological view – is laid to rest by the contemplation of the degree to which chance can nudge history down one or another track.