Charles Darwin spent nearly the whole of his writing career attempting to convince his colleagues, the general public, and, by extension, you and me, that change occurs gradually. Tiny slivers of difference accumulate over time like grains of sand in a vast hourglass. Change happens, in other words. It’s painfully slow, but it’s inevitable. By implication, two organisms that look different enough to us to be classified as separate species share, many tens of thousands or even millions of generations back, the same ancestors. (Inbreeding means we don’t even need to go back quite that many generations to demonstrate overlap, but you get the point.) But change that gradual means, as Darwin himself well recognized, that looking for “missing links” would be a pretty silly errand. Differences between one generation and the next look to our eyes just like common variation. It’s one grain falling from the top of the hourglass to the bottom. You can’t perceive the change. You would have to go back in time to find the very first individuals who possessed a particular trait – bat-like wings, say, or human-ish hands – and then, turning to their parents, you would see something almost identical.