Greg Detre
Thursday, July 04, 2002
Franklin lived for 84 years and, except in popular legends and myths, no one has ever lived twice that long. According to the estimates of Roy Walford, professor of pathology at UCLA Medical School, the average human life span was about 22 years in ancient Rome; about 50 in the developed countries in 1900, and today stands at about 75. Still, each of those curves seems to terminate sharply near 115 years. Centuries of improvements in health care have had no effect on that maximum
Why are our life spans so limited? The answer is simple: Natural selection favors the genes of those with the most descendants. Those numbers tend to grow exponentially with the number of generations--and so this favors the genes of those who reproduce at earlier ages. Evolution does not usually favor genes that lengthen lives beyond that amount adults need to care for their young. Indeed, it may even favor offspring who do not have to compete with living parents. Such competition could promote the accumulation of genes that cause death.
For example, after spawning, the Mediterranean octopus (O. Hummelincki) promptly stops eating and starves to death. If we remove a certain gland though, the octopus continues to eat, and lives twice as long. Many other animals are programmed to die soon after they cease reproducing. Exceptions to this include those long-lived animals, like ourselves and the elephants, whose progeny learn so much from the social transmission of accumulated knowledge.
certain species (including some varieties of fish, tortoises, and lobsters) do not appear to show any systematic increase of mortality rate with age. These animals seem to die mainly from external causes, such as predators or a lack of food. Still, we have no records of animals that have lived for as long as 200 years
Walford and many others believe that a carefully designed diet, one seriously restricted in calories, can significantly increase a human�s life span--but cannot prevent our ultimate death.
biological wearing out would still be a problem
are merely clever pumps. Muscles and bones are motors and beams. Digestive systems are chemical reactors
When we consider replacing a brain though, a transplant will not work
we might be able to replace certain worn out parts of brains by transplanting tissue-cultured fetal cells. This procedure would not restore lost knowledge --but that might not matter as much as it seems. We probably store each fragment of knowledge in several different places, in different forms. New parts of the brain could be retrained and reintegrated with the rest -- and some of that might even happen spontaneously
The brain, like other finite things, must reach some limits to what it can learn. We don't know what those limits are; perhaps our brains could keep learning for several more centuries. Ultimately, though, we will need to increase their capacity
Does this mean that machines will replace us? I don't feel that it makes much sense to think in terms of "us" and "them." I much prefer the attitude of Hans Moravec of Carnegie-Mellon University, who suggests that we think of those future intelligent machines as our own "mind- children.�
Fortunately, we would not need to know every minute detail. If that were so, our brains wouldn't work in the first place. In biological organisms, generally each system has evolved to be insensitive to most details of what goes on in the smaller subsystems on which it depends. Therefore, to copy a functional brain, it should suffice to replicate just enough of the function of each part to produce its important effects on other parts.
Suppose that we wanted to copy a machine, such as a brain, that contained a trillion components. Today we could not do such a thing (even were we equipped with the necessary knowledge) if we had to build each component separately. However, if we had a million construction machines that could each build a thousand parts per second, our task would take only minutes
In none of these situations were people able to learn, and later remember, more than about 2 bits per second, for any extended period. If you could maintain that rate for twelve hours every day for 100 years, the total would be about three billion bits -- less than what we can store today on a regular 5-inch Compact Disk
Despite those popular legends about people with 'photographic memories,' no one seems to have mastered, word for word, the contents of as few as one hundred books--or of a single major encyclopedia. The complete works of Shakespeare come to about 130 million bits. Landauer's limit implies that a person would need at least four years to memorize them. We have no well-founded estimates of how much information we require to perform skills such as painting or skiing, but I don't see any reason why these activities shouldn't be similarly limited
The brain is believed to contain the order of a hundred trillion synapses
Hence, we could design our "mind-children" to think a million times faster than we do. To such a being, half a minute might seem as long as one of our years, and each hour as long as an entire human lifetime.
But could such beings really exist? Many thinkers firmly maintain that machines will never have thoughts like ours, because no matter how we build them, they'll always lack some vital ingredient. They call this essence by various names--like sentience, consciousness, spirit, or soul. Philosophers write entire books to prove that, because of this deficiency, machines can never feel or understand the sorts of things that people do. However, every proof in each of those books is flawed by assuming, in one way or another, the thing that it purports to prove--the existence of some magical spark that has no detectable properties.
Many philosophers have declared that understanding (or meaning, or consciousness) must be a basic, elemental ability that only a living mind can possess. To me, this claim appears to be a symptom of "physics envy"--that is, they are jealous of how well physical science has explained so much in terms of so few principles.
"If you understand something in only one way, then you don't really understand it at all. This is because, if something goes wrong, you get stuck with a thought that just sits in your mind with nowhere to go. The secret of what anything means to us depends on how we've connected it to all the other things we know. This is why, when someone learns 'by rote,' we say that they don't really understand. However, if you have several different representations then, when one approach fails you can try another. Of course, making too many indiscriminate connections will turn a mind to mush. But well-connected representations let you turn ideas around in your mind, to envision things from many perspectives until you find one that works for you. And that's what we mean by thinking!"
In order to think effectively, you need multiple processes to help you describe, predict, explain, abstract, and plan what your mind should do next. The reason we can think so well is not because we house mysterious spark-like talents and gifts, but because we employ societies of agencies that work in concert to keep us from getting stuck. When we discover how these societies work, we can put them to inside computers too. Then if one procedure in a program gets stuck, another might suggest an alternative approach. If you saw a machine do things like that, you'd certainly think it was conscious
I was amazed to find that at least three quarters of the audience seemed to feel that our life spans were already too long. "Why would anyone want to live for five hundred years? Wouldn't it be boring? What if you outlived all your friends? What would you do with all that time?" they asked. It seemed as though they secretly feared that they did not deserve to live so long. I find it rather worrisome that so many people are resigned to die. Might not such people be dangerous, who feel that they do not have much to lose?
My scientist friends showed few such concerns. "There are countless things that I want to find out, and so many problems I want to solve, that I could use many centuries," they said. Certainly, immortality would seem unattractive if it meant endless infirmity, debility, and dependency upon others--but we're assuming a state of perfect health. Some people expressed a sounder concern--that the old ones must die because young ones are needed to weed out their worn-out ideas. However, if it's true, as I fear, that we are approaching our intellectual limits, then that response is not a good answer. We'd still be cut off from the larger ideas in those oceans of wisdom beyond our grasp.
Will robots inherit the earth? Yes, but they will be our children. We owe our minds to the deaths and lives of all the creatures that were ever engaged in the struggle called Evolution. Our job is to see that all this work shall not end up in meaningless waste.
�Many computers maintain unused copies of their most critical "system" programs, and routinely check their integrity. � The trouble is that error correction then would stop mutation--which would ultimately slow the rate of evolution of an animal's descendants so much that they would be unable to adapt to changes in their environments.�
I don�t think this is a strong argument. but the only better one I can think of is simply that it�s too expensive and not worth it, or that such an animal would probably die anyway while healing or something. hmm.