At present, the main argument against human cloning is that occasional difficulties observed in cloning other animals suggest that human clones would sometimes be born with medical abnormalities. This is a serious concern, but it doesn’t mean human cloning can never happen. In one plausible path to that end, veterinary scientists continue to get better at cloning agricultural mammals until the success rate is extremely high. When the chance of error in animal cloning becomes lower than the error rates of natural reproduction, human cloning trials could become socially and ethically acceptable or even recommended.
But even without cloning, life extension could be achieved. For instance, medical researchers might succeed in creating complex tissues and organs derived from patients’ own stem cells. These so-called pluripotent stem cells can be derived from a variety of adult cells and be guided into almost any other tissue type. Synthetic biocircuits made of DNA and encoded proteins could be inserted to detect and repair (or kill) cells with mutations known to cause cancer or aging.
In a related approach, new translational codes in the genome—which define how a cell uses DNA to construct proteins—could make organisms resistant to all viruses. Viruses do their damage by entering cells and using the cellular machinery to replicate themselves. They are able to do this because both the viruses and the host cells make use of the same genetic code. But if we changed the code of
the host cells, it would thwart the virus’s ability to replicate, and so make the host immune.
That may sound like science fiction, but the Church lab at Harvard has already changed portions of the genetic code of E. coli bacteria to repel viral attacks. Beyond this, we could take the DNA repair abilities from Polypedilum vanderplanki, a fly whose larvae can survive complete desiccation and extremes of heat and cold, and transplant them into human cells.
Ultimately, synthetic biology could free us from obsolete limits set by evolution. We could repair damaged tissue and direct the growth of new tissues to create built-in body and brain parts that could interface with electronic devices. For example, some cells could be engineered to light up and signal if a person is experiencing inflammation, unusual neuronal activity, etc., functioning as noninvasive diagnostic devices.
Globally, life expectancy and the onset of old-age symptoms have been steadily improving at a rate of three months per year. A nearly perfect straight line for the past 170 years! Impressive, but some biotechnologies are improving at up to a tenfold rate per year, meaning that a dramatic change in the slope of that line could happen soon.
The route to long-lived humans will arrive via milestones that we can only guess at. Genome engineering in clinical trials today may become routine by 2014. By 2016 we may have ways to rejuvenate neurons, such as by injecting them with fresh nuclei from engineered stem cells, to make them young again. Or we may have developed miniature electronic circuits capable of monitoring and stimulating neurons, which might be used to augment memory or maintain neural functions during the replacement of neuronal nuclei. Within a decade, we should be able to use these technologies to read and alter the state of neurons for an enormous fraction of the cells in human brains. (We can already do this for dozens of neurons in humans with
epilepsy.) This could lead to much longer life spans—semi-immortality, extending progressively toward an unknown limit—both for our cells and for our minds.
With such breakthroughs potentially less than a decade away, now is the time to consider what a world of semi-immortals would look like. One of the most commonly expressed objections to the prospect of human immortality is the unintended consequences of overpopulation, including the fear that long-lived individuals would take away jobs from younger people. Yet our resources have kept expanding.
Thomas Malthus died in 1834, worried about the survival of the world population, which then numbered 1 billion people and was growing by 5 million per year. Today the population stands at 7 billion and is growing by 75 million people per year. But instead of the global starvation and misery that Malthus envisioned, we have seen widespread rises in wealth, standards of living, health, and life expectancy. As economist Julian Simon once explained, “Resources come out of people’s minds more than out of the ground or air. Minds matter economically as much as or more than hands or mouths. Human beings create more than they use, on average. It had to be so, or we would be an extinct species.” Fertility rates tend to decrease with increasing life span even if the number of fertile years per person increases, which counters the trend toward population increase associated with increased life span.
The vision of a nearly immortal populace squelching the job prospects of youth is reminiscent of 19th-century Luddite concerns about machines’ taking over jobs from humans. The likelier scenario is a population implosion marked by increasing numbers of older, healthier citizens, and more women in positions of power, a situation that could be beneficial for child rearing, philanthropy, diplomacy, and other aspects of our civilized life. Look for our values to change: With children a rarer resource, educators may become among the highest-paid workers in the world. Instead of teachers, grammar school kids might be coached by personal tutors on the model of the British university system.
One thing that makes for a robust and long-lived species is diversity among the population. That is as true for Homo sapiens as for any other. Personalized tutorial education might yield the advantages of greater human diversity, allowing us to embrace larger spectra of personality types, perceptual and cognitive idiosyncrasies, and high-functioning autistics, bipolars, ADHDs, and hyperthymesiacs (who can recall autobiographical events in extraordinary detail). People with such traits occasionally succeed today, but in the future could do so more often.
Our new semi-immortals, people of indefinite and unknown longevity, would be a diverse population resistant to all viruses, known and unknown, all other pathogens, and all forms of cancer, autoimmune diseases, environmental toxins, and even radiation—that last attribute particularly handy for space travel. We can acquire such abilities by importing into the human genome the genetic sequences from other organisms that already possess such attributes. Think of it as genetic data mining. We could get radiation-resistance genes, for example, from the Bdelloid rotifer, a class of small invertebrates that live in freshwater pools and survive megadoses of ionizing radiation. We will acquire other life-span-
enhancing attributes by combining the best of all genomes of people who are comparatively youthful even though they are older than 100. The Church lab is currently analyzing the genomes of centenarians.
Semi-immortals could combine the best aspects of youthful dynamism with the wisdom of long experience. Such people in abundance would be of great benefit to society. If most of us expect to live possibly indefinitely in good health, there is a strong motivation to help protect humanity from long-term risks like extinction from a new pandemic, the exhaustion of key nonrenewable resources, global nuclear warfare—or a meteor strike. After all, the survival of Earth itself is a prerequisite for the survival of individuals, whether mortal or potentially immortal. One does not want to go to all the trouble of reaching for immortality only to be wiped out by a flying rock.
George Church is a professor of genetics at Harvard Medical School and director of the Center for Computational Genetics. Ed Regis is a science writer and author of seven popular science books. Adapted from Regenesis by George M. Church and Ed Regis. Available from Basic Books, an imprint of The Perseus Books Group. Copyright © 2012.