Too much of the popular discussion of science focuses on what we know and understand, instead of what is really interesting to scientists, the areas where we have some vague guesses we are actively exploring. I am as guilty of this as anyone. When I talk about my research to non-experts, I mostly just talk about the background on which I am building, rather than putting in the effort to get to the enormous number of things nobody yet understands. But ultimately the attempt to identify and solve new mysteries, not the recounting of previous conclusions, is the essence of science. Most science classes never give students the opportunity to engage in science, only to memorize scientific facts and concepts. As someone who makes his living as both a scientist and a science educator, that pisses me off. It is like teaching someone to drive by having them memorize lists of auto safety statistics. Perhaps useful, but certainly not sufficient.
So this morning I will introduce you to a bit of my own research. But rather than just dumping facts on you, I'll ask you to try to explain a mystery that I don't know the answer to. Consider it an invitation to science.
The corner of biology I work in is called Evolutionary Demography. Evolutionary Demography is the attempt to understand how demographic patterns come about as a result of evolution. Living things, evolved organisms, are more likely to reproduce at some ages than others. They are more likely to die at some ages than others. Some species live longer than others. Males in some species live longer than females, in other species (such as humans) the females tend to live longer. In most species both sexes reproduce until they die. In humans and a few other species, females stop reproducing well before they die of age related illnesses. To explain how evolution shapes these patterns is the goal of evolutionary demography.
Evolutionary demography got started with the attempt to explain how it is that evolution, and in particular natural selection (the process that tends to maximize survival and reproduction) leads to aging (the decline in rates of survival and reproduction with age). How can aging be an evolved trait when evolution is supposed to increase just the factors which aging decreases?
The answer to this apparent paradox is that evolution, rather than simply increasing survival and reproduction generally, shapes these factors so as to maximize total lifetime reproductive success. So the force with which natural selection should weed out traits that cause mortality early in life, before one has had any kids, is much greater than the force with which it should eliminate traits that cause death late in life, when your genes have already been passed on and you may not have any more kids anyway. And, to oversimplify a bit, the young skimp on investment in the future in order to splurge in the present. Is it better to very slowly build a skeleton that will never break down, or throw together something that will let you start having kids? (Better in this context being defined as "on the average leading to having more kids." That is what natural selection maximizes.) This is a tradeoff, and tradeoffs, as in economics, tend to lead to seizing the sure short term gain over planning to avoid the long term decline. Breed now, die later. There is a sizable scientific literature on the evolutionary basis of aging, and while their are still plenty of controversies on the particulars, the broad outline is fairly well agreed upon.
So that is already known. But there is a huge amount we still need to figure out. A big piece of my current research focuses on trying to apply many of these same concepts to the opposite end of the lifespan. If the evolutionary basis of aging has been broadly mapped, the evolutionary basis of infant mortality is terra incognita. We know a huge amount about the health problems that cause infants to die, but understand next to nothing about why evolution has led to infant having so many problems and dying at such high rates. In many species the rate of mortality in the first minutes or days of life is hundred or thousands of times higher than at any other age. And remember, natural selection should act most strongly to decrease mortality rates in individuals who have not yet reproduced. On the face of it anything that makes an individual likely to die just after birth should be eliminated incredibly quickly by natural selection. Anyone who dies at birth passes on none of the genes that allowed her to die. Those genes have been selected out, right?
Apparently not, as all mammals and birds, and at least some (possibly all) reptiles, fish, amphibians, invertebrates, plants, fungi and algae have this pattern of very high mortality rates early in life.
So I'm all, "What the fuck Dude? Why haven't you done something about all these babies dying?"
And Evolution is all, "Get out of my face, primate. You're the biologist, figure it out."
And I'm all, "Well fine, maybe I will."
So I'm working on putting together a list of hypotheses that are out there in the literature, plus a few of my own, to explain why evolution sucks (that's the technical term) at keeping babies of so many species alive. I have half a dozen, which I won't explain yet. I'm interested in hearing what explanations occur to you. Any thoughts?