An interesting op/ed piece in yesterday's Sunday Review of the New York Times unwittingly underscores Holly's point in her post last Friday, that saying that evolution is 'only' about survival and reproduction wrongly trivializes those fundamental aspects of life. Except that Holly said it much better than that, illustrated.
"Our Animal Nature" by Barbara Natterson-Horowitz and Kathryn Bowers (a tad confusingly written in the first person) tells of Natterson-Horowitz discovering that people are animals, too. Or is it that animals are people, too? She is an attending physician at UCLA but also consults at the Los Angeles zoo and she has been struck by the diseases and psychiatric conditions that humans and zoo animals share and was curious about what this might mean.
My medical education included stern warnings against the tantalizing pull to anthropomorphize. In those days, noticing pain or sadness on the face of an animal was criticized as projection, fantasy, or sloppy sentimentality. But scientific advancements of the past two decades suggest that we should adopt an updated perspective. Seeing too much of ourselves in other animals might not be the problem we think it is. Underappreciating our own animal natures may be the greater limitation.Animals are known to have melanoma, chlamydia, obesity, they binge eat, they grieve, they can become addicted to mind-altering substances and be overwhelmed by anxiety. And, according to the authors, the life circumstances of animals who suffer the same illnesses -- and pleasures -- that we do can tell us a lot about our own.
Evolutionary biologists would react to this statement with a resounding "Duh!" since animal models very different from humans, from squid to insect to mouse and beyond, have shown this, and genomes have shown why. Still, it is an interesting discussion that enumerates many different examples.
Among the examples are that dairy animals, cows and goats who lactate for a living, very rarely get breast cancer. Many non-dairy mammals do get breast cancer, and some even seem to have risk related to the mutations in the same gene that, when mutated, can confer risk in humans, BRCA1. Viruses can cause cancers in humans as well as other animals, dogs rarely get colon cancer, probably because of their diet, and so on.
It's difficult to say how useful these kinds of similarities and differences would be if we didn't already have an idea from epidemiological study of human diseases of the risk factors we think are causal. It has long been recognized that humans who give birth and lactate early seem to be protected from breast cancer, e.g., so it's not new knowledge to see this in dairy animals as well. Even so, it is true that just as evolution is a difficult concept for many to grasp, or accept, not everyone recognizes that humans are animals too, so another acknowledgement of this is welcome.
Non-human animals can gain weight, too, and wild animals can get fat with unchecked access to calories. Natterson-Horowitz and Bowers say that yellow-bellied marmots in the Rockies, blue whales in the Pacific and rats in Maryland have been getting fatter in recent years, and they suggest this is due to changes in circadian rhythms and light.
New research suggests that when, and how much, light beams through your eyes may play a quiet and unrecognized role in determining your dress or pants size. And the breaking up of light-dark cycles may be a culprit. Light pollution from suburban sprawl, big-city skyglow, electronic billboards and stadium lights has brightened our planet. A rodent study published in the Proceedings of the National Academy of Sciences showed that mice housed with constant light — whether bright or dim — had higher body mass indexes (B.M.I.’s) and blood sugar levels than mice housed with standard cycles of dark and light.The microbiome that inhabits our gut may also have more to do with our girth than we'd ever suspect. Thin people, and mice, have a different set of intestinal fauna than do the overweight, and this may be related to the fraction of calories they divert from us to them.
Cutting is a psychiatric disorder that has become rather prevalent among teens, but, the authors say, this is in fact a self-soothing behavior, and non-human animals do the same sorts of things, pulling out their hair, chewing on their skin.
In a way, self-harmers are actually self-medicators. That’s because, paradoxically, both pain and grooming cause the body to release natural opiates, such as endorphins, the same brain chemicals that give marathoners their runner’s high.The authors' ideas on addiction reinforce Holly's idea that survival and reproduction aren't such bad reasons for living. They write about lab animals that easily become addicted to opiates or other substances that induce pleasure, causing them even to forgo food and water in the interest of obtaining their drug, and mountain sheep apparently take pleasure in hallucinogenic lichen that grow on boulders in the Rockies and so on.
The usual evolutionary assumptions with or without foundation
Naturally, since we live in the evolutionary era in which everything has to have an adaptive explanation, and almost every author seems to know what it is, the authors suggest that addiction has long enhanced survival, because they mimic the feel-good rewards of behaviors that allow animals to survive and care for their young. And that feel-good reward comes from chemicals like dopamine naturally released in our brains when things are going well (or artificially induced by opiods or other drugs). Doing what enhances your fitness makes you feel good, doing what doesn't makes you feel bad and this is true in humans and non-humans alike, but in humans, because we have culture, those feelings can be induced by other than directly fitness-related behaviors, the authors point out.
We humans get drug rewards for life-sustaining activities just as animals do. We simply call those activities by different names: Shopping. Accumulating wealth. Dating. House hunting. Interior decorating. Cooking.It doesn't have to be this way. Not all organisms have to be bribed to do what makes us evolutionarily fit -- paramecia, mushrooms and oak trees don't make dopamine. But dopamine goes back a long way in the vertebrate lineage, to before the divergence of fish and tetrapods. Eels have dopamine receptors, frogs do too. This means that this response to doing well in ways that evolution rewards has been fixed for hundreds of millions of years.
Nonetheless, regardless of the specific reasons for the existence of these shared traits, they are entirely consistent with the web of connections that evolution produces, the similarities as well as the differences -- we are, after all, not exactly like mice or leopards! These traits are enabled by genes, regardless of the specific reason for those genes' functions.
More importantly, the genomic evolution that connects us, along with these traits, raises some interesting questions -- and may provide some important clues -- about genomes, with relevance to much that's going on in genetics today, having to do with the continued existence of, or variation in, or genetic basis of the many traits that we share with the menagerie in or out of the zoo. We'll discuss that tomorrow.