Death is a New Invention
From the moment we're born, we begin to die. But death is actually a fairly new invention. Death has been around, as a natural way of life, for only a small percentage of the time that life has been on our planet!
Our planet is about 4.6 billion years old. (A Billion is 1,000 million.) Life began about 3.8 billion years ago - and for most of that 3.8 billion years, living creatures were effectively immortal, and did not die. From 3.8 billion years ago, to one billion years ago, each living creature was made up of a single cell. So a single-celled creature would grow to a certain size, and then split into two, and each of those two cells would then keep on growing until they divided and so forth. These single-celled creatures would never die of old age. They might die from being run over by a rolling stone, or by being eaten by another bigger single-celled creature - but apart from that they would not die.
But about 1 billion years ago, some of the single-celled beings evolved into creatures with many different types of cells. These new creatures had some cells for thinking, other cells for moving, other cells for digestion, and so on.
And at the same time, death was born. It seems odd, but there actually are a few advantages to dying - at least, as far as the species is concerned.
Firstly, an immortal species can't adapt to any changes in the environment - only their children, with a slightly different DNA, could. Another disadvantage of immortality is that the parents and their offspring would be fighting for the same amount of food. And thirdly, the DNA of these immortal creatures would constantly be damaged by radiation from space, and chemicals in the environment, leading to more defects in the eggs carried by the mother.
Now it might sound unbelievable, but we really don't know why we age, but we do have a lot of different theories.
The first one is the environmental theory. It looks at the environment that the cells inside living creatures survive in. For example, various chemicals may gradually build up in various parts of the body, giving the cells a less pleasant environment to survive in.
And yet another theory says that we are just plain programmed to die. There's a little genetic clock inside each cell, and once it has gone through a certain number of divisions, the cell dies.
The metabolic theory of aging is like a "wear and tear" theory. It basically says that we have a limited number of days of life, and the harder we work, the sooner we use up those days.
Another theory is the error theory. It says that as we age, we get more errors in the DNA, as it divides and divides with each successive generation of cells. For example we humans have 46 chromosomes in our cells. But in human females, the percentage of cells with the wrong number of chromosomes, increases from 3% in ten-year-old women, to 13% in 70-year-old women.
A third theory is the autoimmune theory, which says that when you're born, every cell in you is immunologically identical to every other cell in your body. But as time goes by, the immunological signature of some of your cells changes, and so your body's immune system starts attacking your own cells.
Now, as we get older, our bodies change. Our eyes can't focus as well. Our skin becomes less elastic, and our bones gradually lose calcium. Our lungs can't hold as much air as they used to. As we get older, our kidneys can't concentrate our urine so well. This means, that to dump out the same amount of waste, we need to add a greater volume of water.
But recent research shows that perhaps there is one surprisingly easy way to survive to a greater age, AND in a state of good health, and I'll tell you about that in our next episode, so long as I don't fall victim to my own pre-programmed immortality.
Published 26 July 2001
© 2015 Karl S. Kruszelnicki Pty Ltd