One of the ongoing, animating questions for this class is whether we should—or even can—break free of the anthropocentric view of history.

All year in Big History, we’ve been gradually zooming in on the time and place we call home. Starting out from the Big Bang, we’ve followed the action to galaxies and stars, to our own solar system, to Earth and its biosphere; now, we’re beginning the story of humanity’s ancestors. Is this a chauvinistic way of framing the history of the cosmos? Maybe not: after all, the universe as a whole is expanding and cooling, with energy becoming ever more dispersed. There truly is something special about those little pockets of space where complexity, from the range of exotic elements forged in supernovas to the variety of life itself, manages to thrive.

Then again, there could be billions of worlds like Earth. We started the year by testing and invalidating the geocentric view of cosmology. One of the ongoing, animating questions for this class is whether we should—or even can—break free of the anthropocentric view of history.

It was in this spirit that we started our unit on biology by questioning the very definition of life. Students began by classifying a set of objects—lichen, a refrigerator, a tornado, a seedless orange tree, a computer virus, a real virus—as living or nonliving. There was near consensus of the answers, but every attempt to codify the essential traits of life in a way that agreed with our intuition seemed to break down under the weight of edge cases and counterexamples. For example, what does a refrigerator do if not metabolize energy to maintain homeostasis? Or if reproduction and adaptation are the keys to life, what are we to make of the seedless orange tree? One member of the class observed that there were different ways a criterion for life could operate: it could be a necessary condition or a sufficient condition, and the real definition might require a combination of several criteria. Even so, we weren’t able to come up with any perfect demarcation.

Pressed as to why it matters to have a definition, students responded: How else would we be able to recognize another form of life if we found it? Or if we created it? And how else can we know when life begins and ends? I am not sure if the class was more disturbed or relieved to learn that biologists have hardly fared any better than themselves in answering these questions!

Undaunted, we pressed forward under a mutual agreement that life exists and that we want to know how it works. This part of the course was guided by Dobzhansky’s famous dictum that “nothing in biology makes sense except in the light of evolution”. We began by tracing the roots of Darwin’s big idea back to earlier scientific paradigm shifts, particularly the “uniformitarianism” of Lyell that had overturned geology in the preceding decades. Scientific breakthroughs are often portrayed as outbreaks of unique genius, so it was eye-opening for students to learn that some of the ideas behind evolution had been in the air for a while before Darwin managed to fit them into a coherent whole. We also saw some of the questions Darwin couldn’t answer in his own time, such as the mechanism of heredity. (Our own discussion of heredity—much aided by post-Darwin developments—brought to bear many examples students could relate to, from camellias to Manx cats to human blood type.)

For such a “simple” idea, evolution is notoriously prone to misunderstandings. To get a visceral sense of how evolution works, we played a game in which students played the role of animal species trying to survive in an environment buffeted by change. Card draws and rolls of the dice determined who died, who reproduced, and what mutations their offspring carried. While the game left plenty to be desired as a simulation of actual evolution, it nevertheless served to illustrate many surprising phenomena. Students saw traits favored by conditions early in the game become liabilities as conditions changed; saw the role of extinction in creating opportunities for adaptive radiation; saw the fragility of communities when biodiversity dropped, or when the rate of environmental disruption overwhelmed the pace of adaptation. Above all, the game served to make clear that adaptation is a matter of luck—the right chance mutation at the right time and place.

I wrote the evolution game in a weekend, and one of the most fun experiences of the Big History course to date has been watching the students find ways to improve on it. One student proposed a scientific naming system to track the species that were being born and killed off, using linear descent as the basis for classification. Another (responding to the uniformitarian idea) suggested a more realistic distribution of event magnitudes, with small environmental changes accumulating constantly and major catastrophes being rare. A third student noted that the game was, in one way at least, unfixable: to properly simulate evolution would require billions of organisms undergoing billions of events, something that groups of six students cannot pull off in half an hour. Not content merely to raise this objection, he did something about it, writing his own evolution simulator as a computer program that could take advantage of the rapid pace of CPU cycles.

To close our unit on biology, we touched on two more big questions. The first of these—what is a species?—was directly inspired by a student’s comment about the inadequacy of the common definition that a species is a population of individuals that can interbreed and produce fertile offspring. Where, the student asked, does this leave bacteria that reproduce by cloning themselves? Just as in our previous discussion of what distinguishes life from non-life, we found that no answer to this question is entirely satisfactory, and we must navigate with several criteria that produce similar answers… most of the time. The second big question was, how are human beings influencing the course of evolution on Earth? This question brings us full circle, and will follow us through the rest of the year as we try to understand what makes our own epoch truly unique.

--Austin Shapiro