Why Bother Getting Old?

Live fast, die young, and leave a good-looking corpse. Sounds like an awesome plan, right? Read on to find out why natural selection says otherwise...

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This is a follow-up to my previous entry The Capacity to Learn?

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Again, with credit to Jared Diamond's The Third Chimpanzee, let's consider the question: why do we have old people? Forgive me if you've already thought about this – for me, it was one of those questions that seems blindingly obvious in retrospect, but I'd never asked myself before. (Sort of like – Q: “Why would the First Nations people of Vancouver Island invent a bed that folds up into a couch?” A: “It's a hide-a-bed, not a Haida bed, you complete moron.”)

So, why have old people? As we know, the purpose of all life is to propagate itself – whether bacterium, mosquito, baobab tree, hamster, or human being, the basic drive is to survive to reproductive age, and then reproduce as much as possible. Caveat: the offspring should survive to reproduce themselves. No good having 100 babies if they all die before adulthood. Anyhow, summed up: leave as many children as you can. Most animals, quite sensibly, die as soon as they accomplish this goal.

Take salmon as an example. They hatch, try not to get eaten, grow a bit, then leave their native stream for the ocean. Next, they swim around in the ocean getting fat and reaching adulthood, and then – incredibly – they swim right back to their very own native stream, charge upstream, mate, spawn (SPAWN! SPAWN!), and promptly die. This gory sight can be witnessed at any number of salmon spawning streams: the salmon arrive, lay eggs, and DIE. They know what's up. There is no point – in an evolutionary sense – in surviving past the birth of your babies.

Some animals - for example cats - for example my cat, who is pregnant again - have babies and don't die. Why? Just to annoy me! But seriously, two reasons: (1) They need to nurse their babies, something that the lucky mother salmon are not required to do. (2) They can have more than one round of babies. Again, see example: Jenn's cat.

Human beings, however, have an even crazier level of longevity, exemplified by seemingly the most illogical of phenomena: MENOPAUSE. Why bother with menopause at all? You are no longer nursing babies. You are no longer having babies. Quite possibly, you are no longer supporting your children at all. So, if you are no longer nursing or otherwise keeping your children alive – so that they, in turn, can have more babies and further propagate your genetic material – and you can no longer have more children of your own, why stay alive? Indeed, very old people become a drain on the resources of their children and community, requiring special help and no longer contributing to the communal tucker pot. This seems like a disadvantage, doesn't it? Why would natural selection ever favour the development of such a long lifespan in human beings? We are stuck with two questions:

1. Why do we have old people?

2. If, for whatever reason, there is an advantage in staying alive for such a long time - why menopause? Why don't human females remain fertile, as human males remain virile?
   
   

The answer to “why do we have old people” is difficult to divine in modern society. I love my grandmother very much, but if I had to say how much she has directly contributed to the survival of myself or my parents over the past 10 years, I'd be forced to admit that it's not much. I suppose there are vague emotional/spiritual benefits, but in the hypothetical situation of balancing those benefits against an extra mouth to feed, it wouldn't come out too favourably. Fine. In comparison, take an example from my past week of life in D'Kar.

On Thursday evening I was out in the field with some guys from the office, and we were camped out in the bush, making dinner. Suddenly there was a great rumbling, and of all things, a massive hailstorm descended upon us. BAM BAM BAM, chunks of ice bashing the car, sliding down my shirt, falling in the soup, and all melting away in about 30 seconds. This, clearly, is not a common occurrence in the Kalahari. When I got back to D'Kar, all the talk was about the storm. “Were you scared?” I asked one young girl.

“No,” she replied. “I know about hail.”

“You've seen it before?” I asked, incredulously.

“No,” she rolled her eyes. “Of course not. The old man, JM, told me about it.”

Often, this is the answer to such questions. “The old man told me about it.” It's another cultural blind spot for me: if it doesn't hail here, I think to myself, and they don't have television, how can they know about hail? Well, simple. If it has happened in the past 70 or so years, the old people will know. This is oral knowledge, oral history, and it is powerful. As human society became ever more complicated, the amount of useful knowledge there was to pass on increased, and therefore the advantage in keeping people around longer and longer to pass on that knowledge. So selection favoured more and more energy spent on repair of the body, because it paid off in terms of advantage passed on to the offspring. (More energy spent repairing the body as it deteriorates --> longer lifespan.)

A more hard-core example comes from Diamond: “When I visited Rennell Island in the Solomons in 1976, many islanders told me what wild fruits were good to eat, but only one old man could tell me what other wild fruits could be eaten in an emergency to avoid starvation. He remembered that information from a cyclone that had hit Rennell in his childhood (around 1905), destroying gardens and reducing his people to a state of desperation. One such person in a preliterate society can thus spell the difference between death and survival for the whole society.”

So, humans have longer lifespans than any other animals because we have a unique advantage in sticking around: passing on complex knowledge. Sometimes the knowledge of old people can provide life-or-death information about rare events. I cannot overstate the immense respect that San people have for their elders - “the old man,” which perhaps sounds derisive when typed out in this blog, is in fact a term of greatest respect and affection. It's not just a convention of etiquette, as respect for elders so often is in modern Western society – it's a genuine respect for the unique and extremely valuable knowledge that old people possess. They are the original Wikipedia.

Which leaves us with – why menopause? If we must get old, why not continue having babies the whole time? Why only women, and not men? The answer in brief is that childbirth is an extremely risky enterprise for human females, much more so than almost all other animals. Menopause is another compromise, another evolutionary trade-off: it's worth it to keep you around for your knowledge, which increases the fitness of your offspring. But after a certain age, the risk of dying in childbirth outweighs the possible advantage of having more children. (Stating the obvious: men don't risk death by spreading their seed.)

Why do human women have particular trouble giving birth? Most likely because human heads got out of proportion with the rest of us – our giant brains grew and the pelvis didn't have time to catch up.

And that, my friends, is that. We have giant heads, and we get old. Personally, I cannot wait to be “the old woman,” and I look forward to demanding the respect I am due. I do not care if other sources of information have rendered my elder-knowledge somewhat obsolete; I will take the best seat in all situations, hit on younger men, own dozens of cats, and insist that I know best about everything. LOOK OUT WORLD.