It can be inconvenient when new information comes along and changes things. A few years ago this happened to me in a small way (ok, a very small way), and it forced me to revise the exams I give students and Master Beekeeper candidates. The original question and answer went like this:
(True or False) Honey bees are native to the North American continent. False
But now it looks like this –
(True or False) Honey bees are native to the North American continent. True
All this came about because of a new paper announcing a fossil honey bee, member of the genus Apis, recently found in a shale deposit in Nevada dating from 23-5 million years ago. It was named Apis nearctica by its discoverers1 (Fig. 1) and represents members of the genus that moved northeast from their native southern Asia, crossed the Bering land bridge during the early to mid-Miocene epoch, were cut off from retreat by rising seas, and settled down as residents of western North America for a few million years. Absence of additional fossils leaves us ignorant whether A. nearctica was the sole North American representative of Apis, but it seems unlikely that others didn’t make the trip or that the group didn’t spin off new species during its long tenure here. In any case, its history is a story of the power of contingent events, in this case weather. Just as climate-induced low seas allowed its arrival, climate-induced high seas cut off its retreat, and climate shifts from warm-wet to cool-dry spelled its demise. Bottom line – this native American honey bee went extinct and left no living descendants, leaving North America empty of honey bees until humans reintroduced another Apis in historic times, our beloved western honey bee, Apis mellifera.
This story is interesting in its own right, but it also reminds us that every species we know on Earth today is the outcome of a similar string of contingent events in the history of our planet, a history in which organisms and their genes are constantly being challenged and shaped by conditions or accidents of nature. Sometimes members of a population possess a “survivable” set of genes that lets their possessors reproduce and pass those “good” genes on to the next generation. In this manner, successful genes tend to accumulate in a population and over time literally shape the species, whether behaviorally or morphologically, into a finely-tuned member of its ecosystem. Natural selection operates in an extravegance of time which means that a species becomes adapted to most of the extremes its habitat can throw at it. This is what makes it different from non-natural selection, ie., human-guided breeding: in the window of our short lifetimes we cannot see all the ramifications of our selections which may work well for our narrow purposes, but fall short given a new turn in the climate or other natural event that to us appears anomolous, but is nevertheless within the range of normal for that environment in geologic time. Thus, outcomes of natural selection are comparatively stable and intimately connected to geography of origin whether that means a continental region if you’re a honey bee or this pool of water versus that one if you’re a snail.2 This is why organisms aren’t randomly dispersed around the world: zebras in America or elephants in Europe.
It is also true that individuals, as well as whole species, eventually miss the boat and fail in this high-stakes game. Individuals die; species go extinct. Death applies to all, and the vast majority of species that ever existed in Earth’s history are now extinct.
But the glory of natural selection is not death, but its participation in the effusive generativity of life. Just as individuals can give birth to new individuals, species can give birth to new species. This happens through a process called speciation. It begins when a subset of a species’s population is cut off from others.