Breaking a truly ancient tradition

"Modal age at death" means the age at which the largest number of individual deaths occur. The modal age at death is determined by the interaction of two factors, the increasing risk to each individual with advancing age, and the decreasing number of individuals still alive with advancing age. As a population of adults gets older, each person is at ever increasing risk of death, so at first the number of deaths at each age goes up. But eventually, even though individual risk is still increasing, the number of people experiencing that risk is going down so fast that the number of deaths at each age (what demographers call dx) goes down. So modal age at death is neither at the age with the most individuals or the age at the highest risk, but somewhere in between. And studying the modal age at death, how it varies between populations and over time can tell demographers many useful things that I'm not going to go into because I am more interested in subverting the paradigm.

The paradigm in this case is that modal age at death is some time in early old-age, when death rate is going up but not too many people have died yet. Except that often it hasn't been. If one looks at life-tables for historical populations of humans, the highest dx (by far) is often d0, the number of individuals who die before their first birthday. Put another way, far more people died between birth and their 1st birthday than during any other year of age. The Human Mortality Database (the world's premier source for data on this sort of thing) estimates that of the baby girls born in Sweden between 1751 and 1759, slightly over 20% died in their first year. To put in perspective how the resulting distribution of deaths over age looks, please glance at this graph:

If I asked you to guess at what exact age a random female had died, by far your best guess would be age 0. And surely the people living in such a population must have been affected in all sorts of ways by the frequency that babies die. To ask how this population would have adjusted to such a thing is to ask a misleading question, because adjustment would imply that this is something new. In fact, the modal age at death is almost always 0, and modern humans are highly unusual in having it be much later in life. In fact, even in the cohort of Swedes born in the 1920s, modal age at death was still 0. In some countries it may still be 0, although such places are generally harder to get good demographic data from.

How far back does this go? Well it is 0 for hunter gather populations. It is zero for wild primates. It is zero for other mammals. It is zero for.... As far as I can tell, modal age at death has been zero for almost every population of almost every kind of organism for the entire history of life on earth. Contemporary wealthy humans still suffer much higher mortality in our first year than at any other pre-adult age, but infant mortality has been gradually brought down over the last centuries, so far that somewhere in the 1930s and '40s, many of the world's nations unknowingly broke with hundreds of millions of years of tradition by having a modal age of death that wasn't zero. So the right question to ask may well be not, "how did they adjust to zero being the mode?" but rather, "how are we adjusting to zero not being the mode?" And my impression is that one important way that we have adjusted is by very gladly forgetting that things were ever different than they are now.

Seen another way though, we haven't changed the modal age at death at all. If one is willing to classify the loss of an embryo or fetus as a death, modal age at death has never been zero. It has always been, and remains, -1. Minus one because far more individuals are lost in the year prior to birth (even if only nine months) than the year after it, or any other age. Where before many cultures avoided naming newborns until a week or month or even a year had passed, we still often avoid it for those not yet born, for the same set of emotional (some say superstitious) reasons.

Will science progress to the point that we feel safe naming that recently implanted embryo, knowing that she will almost surely make it? Perhaps. If so, modal age at death will finally, at long last, be in the age range that my demographer friends like to consider.

The boundries of personhood

A group of academics (psychologists, ethicist, biologists etc.) have recently endorsed a statement arguing that dolphins and whales do deserve the rights of humans, based on their intelligence, self-awareness, individuality, sociality and so forth.

 A curmudgeonly old man, who was an environmentalist but hated that he was because he didn't like to be associated with hippies, once opined to me as follows on this topic, only in much more colorful language: We can't start treating whales as though they have the same rights as humans, because if we give those rights to whales, we have to give them to apes too, and if we give them to apes pretty soon we'll be extending them to monkeys, and pretty soon antibiotics will be outlawed because they violate the inalienable rights of infectious bacteria.

I have mixed feelings about slippery slope arguments generally. Letting even minor instances of objectionable predilections (sexism, racism, etc.) slide really does seem to be a problem, on the principle that once people are used to these sentiments going unchallenged, they will feel freer to get more egregious. But we can and frequently do make different rules about the treatment of different categories of animals, and there is little likelihood of the rules that now apply to the study of chimpanzees being extended to include studies of bacteria, let alone infections. My research with live animals legally requires no review by any ethics board because I am working with invertebrates. Back when I studied birds, I needed committee approval just to go out in the woods and watch birds for scientific purposes, and my friends who study humans have sometimes had to get such approval just to reuse preexisting published and publicly available data on long-dead populations.

The fact of the matter is that we can and do make arbitrary decisions, often influenced by scientific knowledge but also influenced by emotional predilections, about who and what deserve what rights and protections. Before the US Civil War, southerners quibbled with the evidence that slaves were fully human, but more fundamentally they didn't admit that this implied that they deserved the same rights as other people. These days, American conservatives tend to want to extend the full rights of personhood to fetuses, embryos and potentially fertilized eggs. American liberals often want to extend these same rights to smart charismatic non-humans. Each side sees the other as both ridiculous and morally bankrupt. The difference underlying these wants are philosophical, moral, ethical and political, sometimes economic, but not generally founded in disagreements on scientific fact. Those factual disagreements usually follow, as each side looks for ways to justify its conclusions. I don't expect cetaceans will ever be granted the same rights as humans, but as we learn more about their mental and emotional lives, I do think it will become harder to treat them little different from large endangered fish. In other words, I think we will go part way down the slope.

The dead blackbird thing.

Much has been made of the news that 5000 dead blackbirds fell from the sky onto a small Arkansas town at the turning of the year. ~11:30PM on New Year's Eve. Conspiracy theories and omens abound, but I will propose my own theory: a conspiracy between fireworks and the migratory behavior of blackbirds.

There are several species of blackbirds in North America (e.g. Red-winged Blackbirds, Grackles, Starlings), that tend to migrate in large mix-species flocks. And when I say large, I mean blot out the sun, river in the sky, ornithophobe's nightmare large. Frequently in the hundreds of thousands, not rarely in the millions of birds. I was working at the Long Point Bird Observatory (in southern Ontario) one day in late November when one of these blackbird flocks went by, too thickly to count, for an hour and a half. As soon as we saw them we rushed out and closed the mist-nets we had put up to catch birds. While these nets work well for catching a flock of a dozen chickadees (which we would then measure, band and release), a thousand blackbirds hitting the nets all at once will collapse them, potentially killing large numbers of the birds. Many of the nets had several dozen blackbirds in them within the first minute, and it was a struggle to free them faster than new birds got caught. We couldn't close the nets until they were empty, and we couldn't stop catching them without closing the nets, so thick and fast they came, despite the fact that the main stream of birds was far above our heads, and despite each bird tending to avoid places where humans were standing. We put brightly colored cloths in the nets to make them more visible, but still we couldn't keep up. The nets began to sag under the weight of birds, each of which weighed only a few ounces. Only when the course of the avian river shifted significantly to one side were we able to empty and close the nets, and then stand and gape at the immensity of the flock. That night they all settled in a nearby wetland, densely and within a surprisingly small area.

Now by New Years Eve, these flocks would not be in Ontario, but in places more like Arkansas. It is reported that a wooded area in Beebe was being used as a nighttime roost for several hundred thousand blackbirds. My guess is that somebody was setting off fireworks near that wood, and scared the bejesus out of at least half a million blackbirds. Fireworks are used in agriculture to scare blackbirds out of fields, and to uninitiated birds, they are quite terrifying. So this river of blackbirds leaps into the air whirl around and around as the rockets and fountains go up. Now blackbirds, like most songbirds, have very poor night vision, and frequently smack into things if startled up at night. So maybe one in a thousand in the whirling disoriented mass smacked into a lamp, a sign, a building, each other. They go quite fast enough to kill themselves crashing headlong into hard objects, and can rebound several feet. The birds seemed to have died of blunt trauma, as from a crash.

Or it could be a sign of the end times.

What I'm literature searching for now..

how does one tell if a fruit fly egg has died, other than waiting to see if it hatches, which doesn't tell me at what developmental stage it died, which is what I want to know.

So far I can't find any evidence that anyone has a method for this.