Aging - why and how

Much of what I am going to say here goes against Christian doctrine and Feminist ideals. For those who believe that Genesis is the literal truth, I would suggest that you probably don’t want to read this. For the feminists, I sympathise. What I will describe here is about how we are made. We can change how we think of each other and how we act but we can’t change our genes or our past.

People get older. We are all familiar with that and the outward signs. Skin becomes less elastic and wrinkles. Hair loses colour. In men, there is hair loss to a greater or less degree. Women do not experience significant hair loss as it is an effect of male hormones. Women undergo the menopause and there are attendant changes such as osteoporosis. These are macro level changes. However, we have to consider what the human body actually is. We are a collection of cells that cooperate, a complex organism composed of simpler but still complex organisms. To really understand aging, we have to consider how aging affects the cells.
Let us consider why we age. We age because we do not repair ourselves as fast as we are damaged by our environment. This is not terribly obvious at a macro level although you will often hear comments about how the young heal faster. If you are no longer in the first flush of youth (and I am surely in this camp) then this might seem an unfortunate feature of the human body. However, it exists for reasons that make good sense from an evolutionary perspective.

The purpose of an individual from a species perspective is to make more individuals. From our own personal perspective, we might regard our purpose as to play a perfect flute solo or make a million dollars or write the last great novel. From a biological perspective, our purpose is to breed. Moreover, we have evolved to do tolerably well when resources are not so plentiful. We are relatively cheap to build. We could have evolved with better repair systems but that isn’t an evolutionary advantage since each individual would require more resources. Picture this:

Subspecies A (repairers) have good repair mechanisms and can live indefinitely barring predation and accident. For a given level of resources, they can produce 2.1 offspring for each couple. They begin to reproduce at age 30 since they will mature more slowly.

Subspecies B (breeders) have poor repair mechanisms and can live for up to 30 years barring predation and accident. For a given level of resources, they can produce 3.0 offspring for each couple. They begin to reproduce at the age of 14 since they will mature more quickly.

After 14 years, generation 2 of Breeders is on its way. By year 28, the second generation is working on a third. At year 30, the first generation of Breeders is on its way and the first generation of Breeders is dying off. Allowing some time for gestation, that gives us 6 of Breeders (2 died) and 4 of Repairers (none died). Clearly, if unchecked, Breeders will do best.

What happens if we allow for predation and accident? Let us assume that deaths among the young can be replaced because this is what happens in nature. Well, this tilts the balance further in terms of Breeders. Because each individual is “lower cost”, loss of an individual has a less effect. Loss of individuals who have already reproduced hardly has any effect because they would be dying soon anyway and will produce no more offspring. Because the individuals age, it will be mostly the very young and the older members who are caught by predators or freeze in the winter – the young are quickly replaced by Breeders. Repairers will not lose seniors preferentially because of their superior repair mechanisms but they will still lose the very young and they cost more to replace due to the higher resource needs of a fully self repairing mechanism.

So, in both those cases, the cheaper but short lived species wins. What happens if we give both groups a hard time and reduce resources? Repairers can only produce 1.5 individuals per generation and Breeders can only produce 2.5 individuals per generation. Both can still increase but let us factor in accident and predation. Let us assume that .5 individuals per generation are killed in 20 years. This will mean that many of Breeders will die before reproducing and the population will struggle to remain at its previous level. Since Repairers do not reproduce until much later, many more of them will die before reproduction. Again, Breeders do better. This model is conservative since many species can produce more than 4 individuals per generation.

So, although it doesn’t suit the individual to age and die, it does suit the species. If we look at populations of species, we se that this pattern is followed everywhere. Insects are cheap, short lived and there are many billions of them. Rats are a little more expensive and live a bit longer and there are billions of them. Elephants are expensive, long lived and there aren’t very many of them.

Ah, but hang on! There are billions of humans now and we are not that much cheaper than elephants. Well, yes, that is true. We cheated. By developing intelligence, we have changed to numbers in our favour. By cooperation, we have almost eliminated predation. We build shelters against the sun. We wear clothes against the cold. We plant crops so that there is food in the lean times. In evolutionary terms, this happened an eyeblink ago and we still have the same design at cellular level that we always did have. We are slow breeders, not repairers.

Actually, there is an interesting little wrinkle with humans. Human females live longer than males, well past reproductive age. This sounds like a glitch but it isn’t. Evolution works on groups as well. Intelligence and experience can help a group survive. Groups where there were still older females around did better and so passed on their genes. Why older females rather than older males? Well, because males were more exposed to danger and so were less likely to grow old. In species terms, this makes sense as well. Human gestation is 9 months. Single births are the most common case. One woman can bear one child at a time but a man can be the father of multiple children by different mothers at any one time. If anyone is expendable, it is the men, not the women. Of course, it is handy if the man is around to do his share of looking after junior but in a cooperative society, the offspring will probably survive anyway. So, men were preferentially exposed to danger and older men were more likely to get trampled/gored/eaten than the younger men.

So, that is where we are. In the next entry, let us continue and have a close look at cellular biology.