by Eric Rasmussen
New Year’s is a wonderful time for festivities and time with loved ones. And if you are anything like me, the holiday brings New Year’s resolutions.
But to make plans for where we’re going, it pays to know where we have been. In the case of the human species, ours is a story that encompasses continents, time and several species.
The key phrase here is speciation events— changes that lead one population of organisms to separate into two distinct species. Geographical separation is one way to trigger this kind of divergence. Imagine that something happens which causes half a population to separate for its other half. Over eons, these two populations will randomly mutate and adapt to their different environments. Eventually, these two populations may become so different that if the barriers were removed, they could no longer interbreed. The original population has speciated into two species.
Similar events played out across time and space with our numerous common ancestors in Africa.
The most recent event occurred about 400,000 years ago, when a population called Homo heidelbergensis gave rise to Homo neanderthal and Homo sapiens.
Amazingly, if we take a DNA test, most of us will likely have between 1 to 4 percent neanderthal DNA, a remnant of early interbreeding between the two (and perhaps later on, as the issue of whether Neanderthals and Sapiens are true distinct species is still undergoing debate).
This process did not happen overnight, of course, nor was there a sharp divide in time between one species and the next. Imagine three separate populations of Homo heidelbergensis existing at the same time, then one goes extinct and two continue.
Now rewind the clock even more. Crank that dial. Instead of the geological blink in the eye of 400,000 years, let’s go back 12 million years.
Africa’s Saharan desert was a rainforest back then, spanning the width of the continent. Lush Central Africa favored adaptations of primates to live in trees.
Because the northeastern portion of Africa straddles the East African Rift Zone, tectonic forces split the earth’s crust to form the Red Sea to the north and the Great Rift Valley to the east. These changes shifted the weather patterns, and a lack of rain created patches of shrub land.
Ancestral populations adapted, including the common ancestors of chimpanzees and humans. The western subpopulation continued to dwell in humid forests, while the eastern subpopulation adapted to an open environment to become the two-legged, walking organisms associated with genus Homo.
Over the next 12 million years, organisms continued to divide into a patchwork of lineages: Homo erectus, Homo habilis, Homo heidelbergensis, and today’s Homo sapiens.
Far-fetched as these changes may seem, in science, hypotheses are only as good as the supporting data, and evolutionary biology is among the most established theories in science, understood more than the theory of gravity.
To envision how radically different organisms can become, look no further than dogs. Through careful breeding techniques over a few generations, a lineage of two wolves has transformed from Great Danes to a Chihuahuas and from Mexican Hairless Dogs to Chinese Crested Dogs. Imagine the variety that evolved over billions of years.
While those aren’t exactly separate species, scientific literature brims with examples of observed speciation events, of extreme changes to physical forms as populations separate and adapt, and as evolution plays out before our eyes.
This writer is thinking a wise resolution might be to vow remain adaptable because the more things change, the more they…change.
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Eric Rasmussen, BS, M.Ed., obtained his bachelor of science degree at the University of Colorado at Boulder. He majored in ecology and evolutionary biology, and now serves as a Learning Technology Coach at Erie High School and Erie Middle School in the St. Vrain Valley School District, CO.