February 26th, 2018
I’ve been engaged with a very smart friend in an extended discussion of the meaning of life. The subject of death arose as a natural part of that discussion, and we ran into a rare disagreement. My friend is optimistic that someday medical science will extend our life spans to infinity — to eliminate death. I believe that medical science can extend our life spans by a few more years, perhaps as much as a hundred years, but beyond that I see little hope of further extensions to our life spans. I shall therefore present here my arguments for the inevitability of death despite all technical efforts to the contrary.
First Argument: Evolutionary Necessity
My simplest argument arises from evolutionary theory. Any species with an infinite lifespan will be unable to respond to changes in the environment, because its population will eventually reach the maximum amount permitted by the available resources. In fact, any such species will surely expand its population over the resource ceiling, accepting insufficient resources to induce famine. At that point, the weaker members of the population will die off, not because they have insufficient life spans, but because they starve to death.
Worse, such a species will be very slow to respond to environmental changes, because the oldsters will continue consuming resources necessary to permit newborns. With a very low reproduction rate, the species will be driven to extinction by any significant change in the environment.
There’s an interesting balance here between the frequency of changes in the environment and the pace of genetic change. Our genetic system currently requires something on the order of 10^4 generations for a species to respond to a significant change in the environment. For germs like Escherichia coli, that takes a few years at most. For humans, that will take about 250,000 years. Yes, there have been minor changes in the genome of Homo Sapiens in recent times, but nothing substantial. If a genome changes too rapidly, it suffers from a high rate of dead babies, because the great majority of genetic mutations are detrimental. If a genome changes too slowly, then the species risks being unable to adapt to environmental changes.
None of this works with creatures that live forever. A species can adapt to a changing environment only by getting rid of the old obsolete genes to make room for the new-fangled genes. Species need to kill off their oldsters. This is best handled by building in genes that guarantee that each individual eventually dies. The most efficient way to accomplish this is to design body parts to wear out after some period of time.
Henry Ford once sent out agents to all the junkyards to take a census of what parts of his cars were in greatest abundance. I believe that they discovered that the shock aborbers were the most common re-usable parts. Ford then ordered his engineers to use lighter-duty shock absorbers. There’s no point in building a long-lasting component if it outlasts the utility of the other parts.
Second Argument: Telic Decentralization
While I was an undergraduate student I took a pschology course in pain. (The labs were really tough!) The primary text in the course was a strange book by Daniel Bakan entitled Disease, Pain, and Sacrifice. This book is a bit on the woo-woo side, but it has a lot of good ideas, the most important of which he calls telic decentralization. The idea is not immediately obvious. The best way to see the concept in action is to perform a double experiment. First you ask a child to point to herself; she will likely point to her chest. Then ask an adult the same question and he will likely point to his face. The observation is that children identify with their entire bodies, while adults have a narrower perception of the relationship between themselves and their bodies.
Bakan argues that pain serves to shorten our lifespans by reducing our care for parts of our bodies. When we are born, we are “whole-body” creatures; we see every part of our body as “me”. But the most common response to pain is to flee from it, to put distance between our self and the source of the pain. If you keep stubbing your big toe, you’ll end up feeling less “close” to your big toe. It will become less and less “me” and more and more “that thing at the end of my foot”. And as we lose touch with our bodies, we care for them less.
This phenomenon also shows up in adult responses to pain. An adult’s perception of pain is based primarily on the risk of death imposed by the source of pain. This shows up when a child falls down and runs to mommy, crying that she hurt her foot. Mommy quickly scans the foot and establishes that nothing is broken or bleeding, and then reassures her child that “You’re not hurt. You’ll be fine!” The child cannot understand this response; she is most definitely hurt. Her foot is giving her pain, and that pain is hurting her. Eventually mommy teaches the child that injury to distant parts of the body is of no consequence.
I experienced a manifestation of this a few weeks ago. I was cutting down a dead tree with the chainsaw. This was a particularly tricky tree to cut down; it had been damaged while young and was twisted and tilted. But it was a Douglas Fir, which grows straight after such damage. I felt that I could readily predict where it would fall if I cut it. This information is vital to avoiding a dangerous accident. So I set to work, first “limbing” the lower part of the tree: cutting off all the branches to give me a clear working area. Next, I cut the tree close to the ground. But for some reason, when I cut through, it did not fall in the direction I expected; instead, it fell about 30º away from the expected direction. This caused it to lodge in the branches of a nearby madrone tree.
Cursing my poor evaluation of the tree, I decided to make a second cut about four feet from the ground. This, I reckoned, would cause the tree to drop four feet so that it could clear the madrone branch and fall freely. Again I cut through the tree. But this time, something went horribly wrong; I had misjudged the forces at work. The base of the tree, instead of shoving sideways and dropping, came straight at me. My reactions were pretty good; in an instant I had started to turn away from the tree and shove the still-running chain saw away from me for safety. The safest thing to do in a situation like that is to toss it away from you.
But again weirdo forces were at work and the base of the tree shifted direction and ran straight into the chain saw, propelling it towards me as it fell. Fortuately, in the intervening milliseconds I had propelled myself away from tree and chainsaw, falling backwards. But somehow that damn chainsaw swiped my leg above the knee as it fell. When the dust settled, I was lying on my back; my jeans were shredded and a nasty gash on my leg was bleeding. I quickly shut off the chainsaw and my first thought was, “Damn, you idiot, you really screwed up this time!” The pain wasn’t bad, or at least I didn’t feel any pain. I walked the hundred meters back to the house, with barely a limp. I cleaned up the mess and bandaged my leg (with a BIG bandage) and decided not to do any more outside work that day.
When she saw the injury that night, my wife was furious with me for not calling her so that she could rush me to the Emergency Room. It must have looked worse than it was. I never felt much concern over it because it was never life-threatening or even incapacitation-threatening. After 67 years, I am so disconnected from my body that even an injury such as this is only an inconvenience to me.
This disconnection from our bodies makes us callous about them, and ultimately harms our longevity. Mr. Bakan argues that it is a built-in mechanism for culling old useless people. I don’t quite buy his thesis, but I think that it sheds light on the issue.
Third Argument: Brain Obsolescence
My third and most powerful argument is also the most complicated. Consider the deterioration of cognitive skills with age. We all know that neurons die with time and in our dotage we lose mental function. Our memories dim, our judgement gets fuzzy, our reaction times lengthen. We normally attribute this to loss of neurons, but that’s not the only force at work. There’s something else going on that guarantees our eventual mental breakdown: learning. The key bit of evidence is that our short-term memory is usually the first mental function to decline. If neurons were randomly dying, we would expect all of our mental faculties to decline in unison.
The mechanisms by which neurons learn inside the brain have been subjected to intense scrutiny, but no clear answer has arisen. There are two ways that a neural network can learn:
1. Adding new connections to strengthen favorable responses.
2. Deleting existing connections to discourage unfavorable responses.
(There are a couple of secondary factors deserving consideration, but for the purposes of this essay I think it safe to ignore them.)
We can argue all day about which approach is better, but in theory each has its own advantages. In practice, however, we can provide two basic observations that throw a lot of weight in favor of #2.
The first is to consider the very first learning process for any human; motor control. A newborn baby responds to stimuli with its entire musculature. Poke it in the tummy and all the arms and legs wave around wildly. Similarly, a baby learns to crawl not by lying motionless on the floor and experimenting with individual muscles. Its first attempts involve too many muscles triggering in an uncoordinated mess. The baby learns motor control by deleting connections to muscles, not by adding them. The baby’s nervous system starts out over-connected; it’s got neural connections everywhere, so that any stimulus sets off wild storms of neural and muscular activity. It learns by paring back on this activity.
A second observation concerning the nature of pain lends weight in favor of #2. Pain is communicated in the nervous system by saturated signals. Neurons generally fire intermittently; they seldom fire pulses in rapid succession. Imagine your retina sending signals to your brain. As the light impinging on retina grows brighter, it sends more and more pulses. When the light becomes so bright that the signals are saturated — at the maximum possible rate — we experience the light as painful. In the same fashion, sounds become painful when they are too loud. The maximum pulse rate of sensory organs is indistinguishable from pain.
If you think about it, you can see that this makes perfect sense. If you’re designing a nervous system, you want to guarantee that the highest priority messages get through despite any damage to the system. Pain is certainly a high priority message — it signals damage to the body requiring immediate attention. What better way to insure priority by saturating the signal line with the maximum number of pulses?
There’s another, weaker argument in favor of #2. When neural activity results in pain, a flood of pulses pours into the brain from many channels. Any neuron that participated in that decision will be machine-gunned with zillions of pulses. Neurons operate by an electrochemical process in which the membrane on their dendrites shifts its chemistry, permitting ions to flood in. I speculate — and I emphasize that this is speculation on my part — that an avalanche of incoming pulses damages a neuron in such a manner as to make it less receptive to stimuli in future. In other words, the connections into it are rendered less effective.
If I am correct in my claim that the nervous system starts off life over-connected and then slowly eliminates connections as party of the learning process, then there’s a natural limit to the amount of information a brain can absorb. As the neurons become more and more resistent to stimuli, cognitive activity declines. This would suggest that old people are resistant to new ideas. The old codgers just don’t get it. Sounds a lot like the old codgers I know. Me? Well, that’s another story...
