We – we anthropologists, we scholars, we folk who act like we know what we’re talking about – tend to talk about complicated phenomena in ways that simplify them. This is necessary in teaching, in public outreach, and even in presenting work to our colleagues. We need to first make ourselves understood and then to try to come ever closer in our approximation to the real complexity of an idea or phenomenon. These technically untrue approximations of complex truths are sometimes called “lies to children”.*
Talk about evolution tends to be replete with metaphors about natural selection. We talk about the “goals” of evolution or the “choices” that species or individual genes make, even if we don’t believe that there is any intelligence at work in the process. Even talk about the “reasons” for a particular evolutionary outcome are usually imprecise approximations.
I was thinking about all of this after listening to a recent Fresh Air radio broadcast. Terry Gross interviewed Daniel Lieberman, Harvard professor of human evolutionary biology, about his recent book, The Story of the Human Body.
Now I hate to complain about this. I am pleased when news media interview scientists directly rather than relying on journalists or publicists to explain scientific work, and Fresh Air works hard to get excellent interview subjects. But while listening to the interview I was deeply uncomfortable about the ways Gross and Lieberman talked about evolution. It was really more of a feeling than a well-formed idea at the time, so I went back later and listened again to the podcast of the interview to try to understand what made me so uncomfortable.
I’m still thinking about the question of what made me feel that there was something misleading in the description of evolution, but this is a first approximation.
Lieberman and Gross discussed how changes in human diet and lifestyle lead to “mismatch diseases”, non-infectious, lifestyle-related illness. I’ve transcribed part of the interview to illustrate two issues.
Terry Gross: Why are our bodies ill-equipped for the kinds of foods and fats and sugars, and the quantity of food that we’re eating now?
Daniel Lieberman: Yeah well this is an important topic, obviously. You know, in India and China for example rates of diabetes are going up by almost an order of magnitude over the last generation, and they’re going up very rapidly in the US, too. And the reason they’re mismatch diseases is that diabetes, for example, is caused by essentially the body being unable to cope with sugar in the bloodstream. So, we evolved to crave sugar because sugar is an energy-rich food, but we didn’t evolve to digest large amounts of it rapidly.
Gross: So our bodies, the basic operating system of our bodies was designed for the hunter-gatherer era, right?
Lieberman: To a large extent. I mean hunter-gatherers, and even before hunter-gatherers, chimpanzees for example, eat plenty of foods that have carbohydrates. For example chimpanzees eat almost all fruit, right. … [But] Most wild fruits are only about as sweet as a carrot. So we love sweetness, but until recently pretty much the only food that we got that was very sweet was honey, and honey of course was a special treat. That was pretty much the only form of dessert in the paleolithic.
(The bit I’ve left out, marked by the ellipsis and bracketed [But], is Lieberman’s description of the sugars in fruit.)
There are two problems I see here. One problem is that Gross’s second question and it’s evocation of “the hunter-gatherer era” seems to suggest a view of evolution more in tune with Herbert Spencer than Charles Darwin, let alone contemporary evolutionary biology or anthropology. For Spencer and some other nineteenth century thinkers, evolution was thought to have a goal, a specific end-point. In biology, the “survival of the fittest” (Spencer coined the phrase) ensured that “higher” species would survive while “lower” ones eventually failed to reproduce. In human societies, hunting and gathering would give way to agriculture, and eventually to industrial “civilization”. Such theories were the the cause of, shall we say, considerable problems with early anthropology.
Now I have no reason to believe that Lieberman or Gross subscribe to such notions of evolutionism or social Darwinism. But the presupposition that there was, and no longer is, a “hunter-gather era”, and the failure to note the presupposition as problematic, may have contributed to my discomfort.
A second problem I see in this excerpt is its treatment of time. According to Lieberman, the mismatch he is describing has developed “over the last generation”, but also since “the paleolithic”. (No matter what my nieces may think, we were not actually living in the Stone Age a generation ago.) There is even a suggestion, in the discussion of chimpanzees “even before hunter-gatherers” that this mismatch developed around the time that the Homo and Pan genera diverged. So the problem of mismatch diseases is approximately 20 or 15,000 or 2.5 million years old. That’s a pretty rough estimate.
Now as I said, this kind of rough, even technically false approximation is a necessary step in explaining complex phenomena, and I shouldn’t criticize anyone too strongly for failing to get into all the messy complexity of advanced scholarship in a half-hour radio broadcast. Nevertheless, it makes me uncomfortable.
Lieberman’s answer to Gross’s last question suggests that he is able to explain things in a way that even I will not find discomforting.
Gross: Have we stopped evolving?
Lieberman: Definitely not. Evolution is always churning along. Evolution, after all, is just change over time, and natural selection, which is the kind of evolution we tend to be thinking about the most, is caused by just a few phenomena that are always there. … [But] what’s a more dominant form of evolution today is cultural evolution. It’s how we learn and use our bodies and interact with each other based on learned information. And that’s also a kind of evolution. It’s not Darwinian evolution, it’s not biological evolution, but it affects our bodies. We’re evolving slowly through natural selection and rapidly through cultural evolution.
This, I fancy, captures Lieberman’s point nicely. Biological change through natural selection is slow, while cultural and technological change is fast. This suggests one possible treatment for my current discomfort. I’ll need to go out and read Lieberman’s book.
*Wikipedia says that the label “lies-to-children” is due to science fiction author Terry Pratchett. Who knew?