One of Charles Darwin’s most enduring intellectual legacies was the idea of “common descent” – that the history of life is like a tree with different evolutionary lines sprouting from a common trunk.
Put another way, he recognised that all of life was traceable to a single common ancestor, with evolutionary history unfolding through the inheritance of common features, modified through time as organisms evolved in response to changes in their environment.
As we pass back in time, we humans, as a species, must have shared thousands of common ancestors with other organisms over the past three billion years or more of the history of life none of which we will ever firmly identify.
It begins for us with the Neandertals – our closest extinct cousin – onto chimpanzees – our closet living relatives – and ultimately back through the tree of life of primates, early mammals and even earlier animals back to the very earliest life when we shared a common ancestor will all living things.
For 150 years or so, biologists have studied the human body for the vestiges of our evolution in the form of apparently redundant features dubbed “vestigial” organs.