Map of life expectancy at birth from Global Education Project.

Tuesday, May 20, 2008

Why death?

But first, a brief digression to note that Her Majesty's Parliament has approved research using cells created by transfer of nuclei from human somatic cells into non-human ova. The media report, as usual, is scientifically inaccurate, calling these "animal-human embryos." They aren't really. As I have discussed previously, the nuclear DNA is 100% human. Only the mitochondria are from other mammals.

The mitochondria -- descendants of ancient archaea that became endosymbionts in eukaryotic cells some billion years ago -- reproduce exclusively asexually, cannot exchange genes with counterparts of other lineages, and live exclusively in the comparatively homogeneous environment of the eukaryotic cell. Hence, while they experience some genetic drift, they do not really evolve. Rabbit mitochondria are very similar to human mitochondria, and it isn't clear that these cells are any different from human cells in any practical way. Nevertheless, as the AP report tells us, "opponents warn that an easing of laws on creating the embryos could lead to the genetic engineering of human beings." As I said before, I really don't see how this is a meaningful step in that direction. This technique is not envisioned for reproductive purposes, but for stem cell research. Conceivably it could be used to produce therapeutic stem cells some day. But it does not contribute to modification of human nuclear DNA, which is what genetic enhancement is all about.

As Kathleen points out in a comment on the previous post, there are enormous practical difficulties with trying to genetically modify humans. The organism is incomprehensibly complex, and pulling on the wrong thread could unravel the whole cloth. Changing genes to try to give someone greater intelligence or some other capability could have unforeseen ill effects; and how could we ever ethically do the experiments to find out? This is a valid observation, certainly, for the present. But we are already doing experiments with animals, to create livestock with commercial advantages; and we are also very close to genetically modifying human embryos in order to correct some of those rare, but real, genetic disorders caused by an identifiable single abnormal gene, such as cystic fibrosis and sickle cell anemia. As this sort of research proceeds, along with research into patterns of genes associated with various characteristics, I would not rule out that we'll learn enough that somebody, somewhere, some day will decide to try enhancing a human genome. But I agree it is not an imminent problem.

So anyway (whoof), let's talk about a non-genetic treatment to delay the aging process, such as a pill. Why do we get old and die in the first place? Because evolution compels it. Evolution is not, as we are often mistaught, driven by "survival of the fittest." This is quite obvious because no organism survives. Natural selection does not concern survival, but reproduction. Genes are preserved that are associated with more successful reproduction, and not just for a single generation but into the future, generation after generation. That requires not only reproduction, but continual evolution, because the environment changes and new challenges arise as other organisms evolve and the earth also changes.

Shorter generations advantageous because they allow an organism to evolve faster, although there is a balance for complex organisms that require time to develop. It may also be advantageous to reproduce multiple times, and then there are mammals and some other creatures that benefit from sticking around to invest in their offspring. So there are factors that may favor a longer lifespan as well. Nevertheless, sooner or later, you have to get out of the way, because you are competing with your offspring for limited resources. In order for them to succeed, and for their offspring to succeed in turn, you must die. You are programmed to do so because evolution has produced that result.

Presumably our lifespan is more or less optimal, from an evolutionary standpoint, for the way our ancestors lived some time ago. That doesn't create any ethical imperative for us to honor it today. We can live longer if we want to, but is that wise? Suppose we could take a pill that would enable us to live to be 120, without necessarily experiencing degenerative diseases, disability, or severe mental decline. What would be the implications for our children and grandchildren? What would our own superannuated lives be like? I don't expect we could draw Social Security for 50 years, we'd have to keep working. And, obviously, this would cost money. Presumably the pills would be patented for the first 15 years or so, and cost thousands of dollars a year. Some people would have access to them, but most would not.

So how would that scenario play out? I doubt that many people who had the chance to take the magic pill would turn it down, but what would be the social consequences? Think about it.

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