by Michio Kaku
Evolutionary biologists point out that evolutionary pressure is placed on animals during their reproductive years. After an animal is past its reproductive years, it may in fact become a burden on the group and hence perhaps evolution has programmed it to die of old age. So perhaps we are programmed to die. But maybe we can reprogram ourselves to live longer.
Actually, if we look at mammals, for example, we find that the larger the mammal, the lower its metabolism rate, and the longer it lives. Mice, for example, burn up an enormous amount of food for their body weight, and live for only about four years. Elephants have a much slower metabolism rate and live to seventy. If metabolism corresponds to the buildup of errors, then this apparently agrees with the concept that you live longer if your metabolism rate is lower. (This may explain the expression “burning the candle at both ends.” I once read a short story about a genie who offered to grant a man any wish he wanted. He promptly asked to live 1,000 years. The genie granted him his wish and turned him into a tree.)
Evolutionary biologists try to explain life span in terms of how longevity may help a species survive in the wild. To them, a specific life span is determined genetically because it helps the species to survive and flourish. Mice live so briefly, in their view, because they are constantly being hunted by a variety of predators and often freeze to death in winter. The mice that pass on their genes to the next generation are the ones that have the most offspring, not the ones who live longer. (If this theory is correct, then we expect that mice that can somehow fly away from predators would live longer. Indeed, bats, which are the same size as mice, live 3.5 times longer.)
But one anomaly comes from the reptiles. Apparently, certain reptiles have no known life span. They might even live forever. Alligators and crocodiles simply get larger and larger, but remain as vigorous and energetic as ever. (Textbooks often claim that alligators live to be only seventy years of age. But this is perhaps because the zookeeper died at age seventy. Other textbooks are more honest and simply say that the life span of these creatures is greater than seventy but has never been carefully measured under laboratory conditions.) In reality, these animals are not immortal, because they die of accidents, starvation, disease, etc. But if left in a zoo, they have enormous life spans, almost seeming to live forever.
BIOLOGICAL CLOCK
Another intriguing clue comes from the telomeres of a cell, which act like a “biological clock.” Like the plastic tips at the ends of shoelaces, the telomeres are found at the ends of a chromosome. After every reproduction cycle, they get shorter and shorter. Eventually, after sixty or so reproductions (for skin cells), the telomeres unravel. The cell then enters senescence and ceases to perform properly. So the telomeres are like the fuse on a stick of dynamite. If the fuse gets shorter after each reproduction cycle, eventually the fuse disappears and the cell stops reproducing.
This is called the Hayflick limit, which seems to put an upper limit on the life cycle of certain cells. Cancer cells, for example, have no Hayflick limit and produce an enzyme called telomerase that prevents the telomeres from getting shorter and shorter.
The enzyme telomerase can be synthesized. When applied to skin cells, they apparently reproduce without limit. They become immortal.
However, there is a danger here. Cancer cells are also immortal, dividing without limit inside a tumor. In fact, that is why cancer cells are so lethal, because they reproduce without limit, until the body can no longer function. So the enzyme telomerase has to be analyzed carefully. Any therapy using telomerase to rewind the biological clock must be checked to make sure it does not cause cancer.
IMMORTALITY PLUS YOUTH
The prospect of extending the human life span is a source of joy for some and a horror for others, as we contemplate a population explosion and a society of decrepit elderly who will bankrupt the country.
A combination of biological, mechanical, and nanotechnological therapies may in fact not only increase our life span but also preserve our youth in the process. Robert A. Freitas Jr., who applies nanotechnology to medicine, has said, “Such interventions may become commonplace a few decades from today. Using annual checkups and cleanouts, and some occasional major repairs, your biological age could be restored once a year to the more or less constant physiological age that you select. You might still eventually die of accidental causes, but you’ll live at least ten times longer than you do now.”
In the future, extending the life span will not be a matter of drinking of the fabled Fountain of Youth. More likely, it will be a combination of several methods:
1. growing new organs as they wear out or become diseased, via tissue engineering and stem cells
2. ingesting a cocktail of proteins and enzymes that are designed to increase cell repair mechanisms, regulate metabolism, reset the biological clock, and reduce oxidation
3. using gene therapy to alter genes that may slow down the aging process
4. maintaining a healthy lifestyle (exercise and a good diet)
5. using nanosensors to detect diseases like cancer years before they become a problem
POPULATION, FOOD, AND POLLUTION
But one nagging question is: If life expectancy can be increased, then will we suffer from overpopulation? No one knows.
Delaying the aging process brings up a host of social implications. If we live longer, won’t we overpopulate the earth? But some point out that the bulk of life extension has already happened, with life expectancy exploding from forty-five to seventy to eighty in just one century. Instead of creating a population explosion, it has arguably done the reverse. As people are living longer, they are pursuing careers and delaying childbearing. In fact, the native European population is actually decreasing dramatically. So if people live longer and richer lives, they might space out their children accordingly, and have fewer of them. With many more decades to live, people will reset their time frames accordingly, and hence space out or delay their children.
Others claim that people will reject this technology because it is unnatural and may violate their religious beliefs. Indeed, informal polls taken of the general population show that most people think that death is quite natural and helps to give life meaning. (However, most of the people interviewed in these polls are young to middle-aged. If you go to a nursing home, where people are wasting away, living with constant pain, and waiting to die and ask the same question, you might get an entirely different answer.)
As UCLA’s Greg Stock says, “Gradually, our agonizing about playing God and our worries about longer life spans would give way to a new chorus: ‘When can I get a pill?’ ”
In 2002, with the best demographic data, scientists estimated that 6 percent of all humans who have ever walked the face of the earth are still alive today. This is because the human population hovered at around 1 million for most of human history. Foraging for meager supplies of food kept the human population down. Even during the height of the Roman Empire, its population was estimated to be only 55 million.
But within the last 300 years, there has been a dramatic spike in world population coincident with the rise of modern medicine and the Industrial Revolution, which produced a bounty of food and supplies. And in the twentieth century, the world population soared to new heights, more than doubling from 1950 to 1992: from 2.5 billion to 5.5 billion. It now stands at 6.7 billion. Every year, 79 million people join the human race, which is more than the entire population of France.
As a result, many predictions of doomsday have been made, yet so far humanity has been able to dodge the bullet. Back in 1798, Thomas Malthus warned us what would happen when the population exceeded the food supply. Famines, food riots, the collapse of governments, and mass starvation could ensue until a new equilibrium is found between population and resources. Since the food supply expands only linearly with time, while the population grows exponentially, it seemed inevitable that at some point the world would hit the breaking point. Malthus predicted mass famines by the mid-1800s.
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nbsp; But in the 1800s, the world population was only in the early stages of major expansion, and because of the discovery of new land, the founding of colonies, increases in the food supply, etc., the disasters Malthus predicted never took place.
In the 1960s, another Malthusian prediction was made, stating that a population bomb would soon hit the earth, with global collapse by the year 2000. The prediction was wrong. The green revolution successfully expanded the food supply. The data show that the increase in food supply exceeded the growth in the world population, thereby temporarily defeating the logic of Malthus. From 1950 to 1984, grain production increased by more than 250 percent, mainly due to new fertilizers and new farming technologies.
Once again, we were able to dodge the bullet. But now the population expansion is in full swing, and some say we are reaching the limit of the earth’s ability to create food supplies.
Ominously, food production is beginning to flatten out, both in world grain production and in food harvested from the oceans. The UK government’s chief scientist warned of a perfect storm of exploding population and falling food and energy supplies by 2030. The world will have to produce 70 percent more food by 2050 to feed an extra 2.3 billion people, the UN’s Food and Agriculture Organization has said, or else face disaster.
These projections may underestimate the true scope of the problem. With hundreds of millions of people from China and India entering the middle class, they will want to enjoy the same luxuries that they have seen in Hollywood movies—such as two cars, spacious suburban homes, hamburgers and French fries, etc.—and may strain the world’s resources. In fact, Lester Brown, one of the world’s leading environmentalists and founder of the World Watch Institute in Washington, D.C., confided to me that the world may not be able to handle the strain of providing a middle-class lifestyle to so many hundreds of millions of people.
SOME HOPE FOR WORLD POPULATION
There are some glimmers of hope, however. Birth control, once a taboo topic, has taken hold in the developed world and is making inroads in the developing world.
In Europe and Japan, we see the implosion, not the explosion, of the population. The birthrate is as low as 1.2 to 1.4 children per family in some European nations, far below the replacement level of 2.1. Japan is being hit with a triple whammy. One, it has the fastest-aging population on earth. Japanese women, for example, have held the record for more than twenty years for having the longest life expectancy of any group. Two, Japan has a plunging birthrate. And three, the government keeps immigration extremely low. These three demographic forces are creating a train wreck in slow motion. And Europe is not far behind.
One lesson here is that the world’s greatest contraceptive is prosperity. In the past, peasants without retirement plans or social security tried to have as many children as possible to toil in the fields and care for them when they got old, doing a simple calculation: each new child in the family means more hands to work, more income, and more people to nurse you in old age. But when a peasant enters the middle class, complete with retirement benefits and a comfortable lifestyle, the equation flips the other way: each child reduces income and quality of life.
In the third world, you have the opposite problem—a rapidly expanding population, where much of the population is below the age of twenty. Even where the population explosion is expected to be the largest, in Asia and sub-Saharan Africa, the birthrate has been falling, for several reasons.
First, you have the rapid urbanization of the peasant population, as farmers leave their ancestral lands to try their luck in the megacities. In 1800, only 3 percent of the population lived in cities. By the end of the twentieth century, that figure rose to 47 percent, and it is expected to soar above that in the coming decades. The expense of child rearing in the city drastically reduces the number of children in a family. With rents, food, and expenses being so high, workers in the slums of the megacities perform the same calculus and conclude that each child reduces their wealth.
Second, as countries industrialize, as in China and India, this creates a middle class that wants fewer children, as in the industrialized West. And third, the education of women, even in poor countries like Bangladesh, has created a class of women who want fewer children. Because of an extensive educational plan, the birthrate in Bangladesh has gone down from 7 to 2.7, even without large-scale urbanization or industrialization.
Given all these factors, the UN has continually revised its figures about future population growth. Estimates still vary, but the world population may hit 9 billion by 2040. Although the population will continue to increase, the rate of growth will eventually slow down and level off. Optimistically, it may even stabilize at around 11 billion by 2100.
Normally, one might consider this to be beyond the carrying capacity of the planet. But it depends on how one defines carrying capacity, because there might be another green revolution in the making.
One possible solution to some of these problems is biotechnology. In Europe, bioengineered foods have earned a bad reputation that may last for an entire generation. The biotech industry simultaneously marketed herbicides to farmers as well as herbicide-resistant crops. To the biotech industry, this meant more sales, but to the consumer, this meant more poisons in their food, and the market quickly imploded.
In the future, however, grains such as “super-rice” may enter the market, that is, crops specifically engineered to thrive in dry, hostile, and barren environments. On moral grounds, it would be difficult to oppose the introduction of crops that are safe and can feed hundreds of millions of people.
RESURRECTING EXTINCT LIFE-FORMS
But other scientists are not just interested in extending human life span and cheating death. They are interested in bringing back creatures from the dead.
In the movie Jurassic Park, scientists extract DNA from the dinosaurs, insert it into the eggs of reptiles, and bring dinosaurs back to life. Although usable DNA from dinosaurs has so far never been found, there are tantalizing hints that this dream is not totally far-fetched. By the end of this century, our zoos may be populated by creatures that ceased walking the surface of the earth thousands of years ago.
As we mentioned earlier, Robert Lanza took the first major step by cloning banteng, an endangered species. It would be a shame, he feels, if this rare ox dies out. So he is considering another possibility: creating a new cloned animal, but of the opposite sex. In mammals, the sex of an organism is determined by the X and Y chromosomes. By tinkering with these chromosomes, he is confident he can clone another animal from this carcass, except of the opposite sex. In this way, zoos around the world could enjoy watching animals from long-dead species have babies.
I once had dinner with Richard Dawkins of Oxford University and author of The Selfish Gene, who takes this a step further. He speculates that one day we might be able to resurrect a variety of life-forms that are not just endangered but also have been long extinct. He first notes that every twenty-seven months, the number of genes that have been sequenced doubles. Then he calculates that in the coming decades it will cost only $160 to fully sequence anyone’s genome. He envisions a time when biologists will carry a small kit with them and then, within minutes, be able to sequence the entire genome of any life-form they encounter.
But he goes further and theorizes that, by 2050, we will be able to construct the entire organism from its genome alone. He writes, “I believe that by 2050, we shall be able to read the language [of life]. We shall feed the genome of an unknown animal into a computer which will reconstruct not only the form of the animal but the detailed world in which its ancestors … lived, including their predators or prey, parasites or hosts, nesting sites, and even hopes and fears.” Quoting from the work of Sydney Brenner, Dawkins believes that we can reconstruct the genome of the “missing link” between humans and the apes.
This would be a truly remarkable breakthrough. Judging from the fossil and DNA evidence, we separated from the apes about 6 million years ago.
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bsp; Since our DNA differs from that of chimpanzees by only 1.5 percent, in the future a computer program should be able to analyze our DNA and the chimpanzee’s DNA and then mathematically approximate the DNA of the common ancestor who gave birth to both species. Once the hypothetical genome of our common ancestor is mathematically reconstructed, a computer program will then give us a visual reconstruction of what it looked like, as well as its characteristics. He calls this the Lucy Genome Project, named after the celebrated fossil of an Australopithecus.
He even theorizes that once the genome of the missing link has been mathematically recreated by a computer program, it might be possible to actually create the DNA of this organism, implant it into a human egg, and then insert the egg into a woman, who will then give birth to our ancestor.
Although this scenario would have been dismissed as preposterous just a few years ago, several developments indicate that it is not such a far-fetched dream.
First, the handful of key genes that separate us from the chimpanzees are now being analyzed in detail. One interesting candidate is the ASPM gene, which is responsible for controlling brain size. The human brain increased in size several million years ago, for reasons that are not understood. When this gene is mutated, it causes microcephaly, in which the skull is small and the brain reduced by 70 percent, about the size of our ancient ancestors’ millions of years ago. Intriguingly, it is possible using computers to analyze the history of this gene. Analyses show that it mutated fifteen times in the last 5 to 6 million years, since we separated from the chimpanzees, which coincides with the increase in our brain size. Compared to our primate cousins, humans have experienced the fastest rate of change in this key gene.
