Let’s start by stating the obvious: It’s far easier and cheaper to fix the problems of this planet than to find a way to live off-Earth.

What are the challenges that might make us want to find a new home in space? The ultimate demise of Earth will occur in four billion years when the Sun runs out of its nuclear fuel. At that point, the Sun’s core will collapse and the star’s violent reconfiguration will eject a layer of gas that will engulf the Earth and cook the biosphere. But long before that, the Sun will start to burn hotter as it consumes its hydrogen; about half a billion years from now, the temperature on Earth will have risen enough to make the oceans boil.

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Those timescales are long enough that we might be forgiven for not getting too worried. The best metric for proximate danger is the Bulletin of the Atomic Scientists. Starting in 1947, a group of scientists and engineers created the Doomsday Clock to show how far we were from apocalypse. As the threat of nuclear holocaust receded, the proximity of the clock to midnight started to take into account the possibility that through climate change, biotechnology, and/or cyber-technology we could cause irrevocable harm to our way of life and the planet. The clock sat at two minutes to midnight in 1953, at the nadir of the Cold War. In 1991, it receded to seventeen minutes to midnight with the fall of the Soviet Union. In 2012, however, it read five minutes to midnight because of a surge of nuclear weapons in the hands of small, unstable countries, and the sense that climate change may have passed a tipping point.

Many voices have weighed in on the subject of leaving the Earth. Carl Sagan put it this way: “Since, in the long run, every planetary civilization will be endangered by impacts from space, every surviving civilization is obliged to become spacefaring—not from exploratory or romantic zeal, but for the most practical reason imaginable: staying alive.” Science fiction writer Larry Niven was more succinct: “The dinosaurs became extinct because they didn’t have a space program.” We may be able to fend off impacts from space, but physicist Stephen Hawking sounds the alarm about other threats: “It will be difficult enough to avoid disaster in the next hundred years, let alone the next thousand or million. Our only chance of long-term survival is not to remain inward-looking on planet Earth, but to spread out into space.”

A mass exodus from Earth is implausible. After all, it costs $50 billion just to send a dozen people to the Moon for a few days. Elon Musk may claim he’ll reduce the price of a trip to Mars to $500,000, which is a hundred thousand times less, but that seems unlikely at the moment. If the Earth becomes contaminated or inhospitable, we’ll have to live in bubble domes, fix it, or suffer through it. Nonetheless, in this century a first cohort of adventurous humans will probably cut the umbilical and live off-Earth. What issues will they face?

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Beyond survival, their first issue is their legal status. As we’ve seen, the 1967 Outer Space Treaty addresses ownership. According to Article II, “Outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.” That seems transparent, but it doesn’t mention the rights of individuals. Bas Lansdorp, the CEO of Mars One, said his legal experts looked into the treaty. He thinks that “what goes for governments also goes for individuals in those governments.” If Mars One achieves its goal, thirty people will settle the red planet by 2023; the gradually expanding settlement will use more and more Martian land. Lansdorp insists that their goal isn’t ownership. “It is allowed to use land, just not to say that you own it,” he says. “It is also allowed to use resources that you need for your mission. Don’t forget that a lot of these rules were made long ago, when a human mission to Mars was not within reach.”

Some space players claim altruistic motives, but none of them can succeed without revenue to fuel their dreams. What happens when profit is the only goal?

Large multinational corporations are bound by international trade law, but they could plausibly argue that they have the right to use, even to exhaust, the resources of an extraterrestrial body. A government that wanted to appropriate land on the Moon or Mars might withdraw from the Outer Space Treaty, and it’s unlikely it would suffer any serious -consequences. Even Mars One exists in a legal limbo. Bas Lansdorp needs to fund his $6 billion mission: “Imagine how many people would be interested in a grain of sand from the New World!”

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At some point, the debate will stop being hypothetical. The history of colonization of the Earth shows that a claim of ownership is irresistible. Each succeeding generation of settlers who are born and die beyond Earth will feel less connection to the home planet. They are likely to chafe at the rules and regulations imposed from afar. Tanja Masson-Zwaan, deputy director of the International Institute of Air and Space Law and a legal adviser to Mars One, says, “I assume at some point these settlers will become more detached from Earth, and will live by their own rules.”

The historical example of Manifest Destiny is misleading in the context of space colonization. Countries have grown and gained resources on Earth by seizing territory and displacing or subjugating the original inhabitants. Even in the twenty-first century, the stains of this brutal history persist. Space is a new resource. The people who leave Earth won’t be taking land from anyone. Eventually, they’ll have to make everything they need to survive and prosper. They will create their own wealth. It will be hard to hold them to any Earth-centric legal framework if they want to be independent.

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Colonization implies replacement and growth. A Mars colony can be augmented by new arrivals, but a healthy, normal culture centers on the family unit. There will be sex and there will be babies.

Sex in space hasn’t progressed beyond snickering and titillation. It’s the stuff of urban, orbital legend. Every couple of years, NASA and its Russian counterpart wearily deny that astronauts have had sex. The astronauts themselves stay tight-lipped. Official policy forbids it. Zero-​gravity sex is tricky for several reasons. Blood flow doesn’t work as well as on Earth, so men will have trouble getting erections. Sweat piles up in layers, making intimacy less pleasant. Physics is also an obstacle: The slightest push sets an object in motion. NASA astronaut Karen Nyberg once demonstrated this by using a single strand of her hair to propel herself across the cabin. Straps and harnesses would also have to be used. Given human ingenuity and desire, though, it’s possible that intercourse has taken place in some quiet, dark corner of the International Space Station. But it’s not written in any mission log.

Martian sex presents fewer obstacles. The 40 percent gravity would require minor adjustments. To finesse the issue of procreation, if not coupling, all-male or all-female crews have been proposed. More controversially, voluntary sterilization has been suggested for the first colonists. Mars One plans to arm its colonists with contraceptives, but it’s not known how well they would work on Mars. Norbert Kraft, the medical director of the project, isn’t entirely reassuring when he says they will “make colonists aware of the risks associated with having sex.” The first waves of Mars colonists will die there, and they know that the medical facilities will be rudimentary; they’re unlikely to want babies. But as colonies get established, the dictates of biology and human culture will prevail.

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Even if we discount Mars One’s plans as fantastical and hopelessly ambitious, colonization is likely eventually because there are enough pioneers with financial backing to make it happen.

When a small group of humans branch out from the root of the tree, who will they become?

Evolutionary Divergence

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Imagine when the first baby is born off-Earth. That event will be an extraordinary milestone, resetting the clock of human existence. In Arthur C. Clarke’s short story “Out of the Cradle, Endlessly Orbiting,” an engineer at a Moon base is preparing to relocate to Mars when his wife goes into labor. The baby’s first, plangent cry shakes him to his core, resonating more than the roar of any rocket ship.

How many people does it take to start over? In conservation biology and ecology, there’s a term called minimum viable population. This is the lower boundary on the population of a species in the wild such that it can survive natural disasters and demographic and genetic variations. In animal population studies, about 500 adults are required to avoid inbreeding, and 5,000 adults are required to allow a species to pursue a typical evolutionary lifespan from origination to extinction of one to ten million years. These are rough estimates, used in biology to estimate the probability of extinction; in the United States, models of minimum viable population trigger protection by the 1973 Endangered Species Act.

For humans, the minimum number can be relevant during a dramatic population bottleneck. If a species population is reduced by environmental catastrophe, the genetic diversity in the remaining individuals is also reduced, and it can only grow slowly by random mutations. The robustness of the remaining population is weakened, making them more vulnerable to another adverse event. This is true even though the survivors may have been the fittest individuals. Also, inbreeding is more likely, with offspring having an increased chance of recessive or deleterious traits.

When geneticists sequenced the DNA of chimps and humans, they made the staggering discovery that a single band of thirty to eighty chimps can have more genetic diversity than all seven billion humans alive today. We have very little genetic diversity, even though it could have developed since we diverged from chimps six million years ago. Research on mankind’s restricted gene variation indicates that humans migrated out of Africa about 60,000 years ago, and at some stage before that our numbers may have dwindled to as low as two thousand. Some geneticists hypothesize that this bottleneck was caused by the explosion of the Toba supervolcano in Indonesia and resulting major environmental change. Regardless of the cause, our genetic makeup hints at the fact that we were once in a perilous state, at the edge of extinction.

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More recent human history gives better examples of how to define the viable size of a space colony. When a new population is established by a small number of individuals from a larger population, it’s subject to the founder effect, first described by evolutionary biologist Ernst Mayr. The founder effect leads to both loss of genetic variation and genetic divergence from the original population.

In 1790, Fletcher Christian and eight other mutineers from HMS Bounty were joined by twelve Polynesian women to settle on Pitcairn Island, a windswept volcanic outcrop in the South Pacific. The fifty current residents of the island are all descended from these few “founders.” In 1814, fifteen British voyagers settled the remote island of Tristan da Cunha, located in the Atlantic midway between South Africa and South America. The population had grown to 300 by 1961, when a volcano erupted and everyone was evacuated to England. These small populations left the inhabitants subject to genetic abnormalities. On Pitcairn Island, Fletcher Christian spread a gene that contributes to Parkinson’s disease, while the current inhabitants of Tristan da Cunha have ten times the normal incidence of a degenerative eye condition that leads to blindness.

But you don’t have to be stuck on an island or Mars to suffer genetic isolation. The 18,000 Old Order Amish of Lancaster, Pennsylvania, are descended from a few dozen individuals who emigrated from Germany in the early 1700s. It’s tragic that babies born into this community have a high incidence of an extremely rare and fatal genetic disorder called microcephaly.

The sweet spot for a space colony may be the size of a small village. John Moore, an anthropologist from the University of Florida, developed simulation software for analyzing the viability of small groups. He suggests that the optimum number for a viable long-term colony is 160. This number could be reduced with judicious genetic selection to minimize the probability of inbreeding.

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If space colonists don’t get “new blood” from the home planet, their gene pool will experience genetic drift—the change in frequency of gene variants or alleles due to random sampling. The effect is larger in smaller populations, and it acts to reduce genetic variation, which in turn reduces a population’s ability to respond to new selective pressures. This may sound bad, but genetic drift and the founder effect on Earth are major drivers of evolution. They lead to the formation of new species.

Over generations, the colonists will evolve. We can imagine some of the changes that will take place. The lower gravity on Mars will alter the cardiovascular system and reduce the cross-sectional area of load-​-bearing bones and tendons. There will be accelerated trends in human evolution on Earth—toward being taller and having less body hair, weaker muscles, and smaller teeth. The lack of a varied natural environment will probably lead to weaker immune systems. An additional challenge will be to maintain sensory stimulation as well as intellectual stimulation, to keep the brain sharp.

A new species will have evolved if off-Earth humans can no longer mate and produce viable offspring with those who never left Earth. We know this will take a long time, because a small group of people went on a one-way trip to the Americas about 14,000 years ago, and when Europeans encountered them 500 years ago, they were still the same species. Some groups in Australia and Papua New Guinea have been mostly isolated for 30,000 years and speciation didn’t occur. But for colonists on the Moon or Mars, the process will be accelerated by the different physical environment and the higher incidence of mutations due to cosmic rays.

Finally, after hundreds of thousands of years and thousands of generations, when the first off-Earth baby’s cry is no more than an ancestral memory, the colonists will have come of age. They will no longer be us. Imagine that the colonists live in total isolation and one day we encounter the ancestors of the people who left our planet. They’ll speak their own language, have their own culture, and resemble us only partly. For each side, it will be like looking in an eerily distorted mirror.

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Our Cyborg Future

It’s one of the classic scenes in movie science fiction. In the cult film Blade Runner, the replicant Roy Batty saves “blade runner” Rick Deckard from slipping off the edge of a tall building. With superhuman strength, Batty tosses Deckard onto the roof. He then sits cross-legged and waits for his preprogrammed four-year lifespan to expire. He says to Deckard: “I’ve seen things you people wouldn’t believe. . . . ​Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tannhäuser gate. All those moments will be lost in time . . . ​like tears in rain. Time . . . ​to die.”

Roy Batty is a cyborg, as originally imagined by Philip K. Dick in his novel Do Androids Dream of Electric Sheep? The term cyborg—short for cybernetic organism—was coined by Manfred Clynes and Nathan Kline in 1960. Clynes was a gifted pianist and inventor who worked as a chief research scientist at Rockland State Hospital in Orangeburg, New York; his boss was Kline, a medical researcher with more than 500 publications. They envisaged that an intimate relationship between humans and machines might help explore the new frontier of space: “Altering man’s bodily functions to meet the requirements of extraterrestrial environments would be more logical than providing an Earthly environment for him in space. . . . ​Artifact-organism systems which would extend man’s unconscious, self-regulatory controls are one possibility.”

Although cyborgs are the stuff of dystopian science fiction, we creep ever closer to the merger of flesh and machine.

Replacing body parts such as hearts and arms and legs has been routine for years, but cyborgs imply enhanced capabilities not present in the original human. Conventional medicine is already exploring this -terrain—robotic limbs can be more powerful and flexible than the original limb, and cochlear implants can perceive sounds inaudible to a normal person. (We’ve already met a modern-day cyborg in the form of Tony Stark, aka Elon Musk.) Brain-computer interfaces give direct communication from the brain to an external device. They are being used to restore sight to blind people and mobility to people who are paralyzed. NASA has developed the X1 Robotic Exoskeleton to enhance the capabilities of astronauts—Iron Man is becoming a reality (Figure 47).

Neil Harbisson is a British artist born without the ability to sense color. In 2004, he started wearing a head-mounted “eyeborg,” a device that converts colors into vibrations that Harbisson hears through the bones in his head. The eyeborg is referred to in his passport, making him the first government-sanctioned cyborg. The camera extends his senses by letting him hear infrasound and ultrasound, and see infrared and ultraviolet colors beyond the range of normal human vision. He wants to have the device surgically and permanently attached to his skull, and he’s described how the software and his brain united to give him an extra sense.

Cyborgs resonate in modern culture, embodying the tension between free will and mechanical determinism. They’re reminiscent of Mary Shelley’s dark vision of Frankenstein, animated by electricity and overpowering its creator.

The acceptable face of cyborg research is represented by Kevin Warwick, a professor of cybernetics at the University of Reading in England. He was one of the first to experiment with implants, having an RFID chip put into his arm in 1998. Four years later, he had an array of a hundred electrodes grafted onto the nerves of his arm. This allows him to extend his nervous system over the Internet and control a robotic hand at a remote location. Warwick’s wife also had a cybernetic implant, and when someone grasped her hand, he was able to feel the same sensation in his hand on the other side of the Atlantic—a bizarre form of cybernetic telepathy. “Jamming stuff into your body, merging machines with nerves and your brain, it’s brand new,” according to Warwick. “It’s like this last, unexplored continent staring us in the face.”

Cyborg technology can be found in research labs but it’s also gone underground. When Warwick gets an implant, he employs a team of trained surgeons; Lepht Anonym settles for a potato peeler and a bottle of vodka. She’s one of a growing number of biohackers, also called grinders, who do their own implants. As she puts it, “I’m sort of inured to pain at this point. Anesthetic is illegal for people like me, so we learn to live without it.” Her YouTube videos establish her as the young face of the biohacking movement. To the underground cyberhackers, computers are hardware, apps are software, and humans are wetware. One popular starting point is to have a powerful rare-earth magnet inserted into the fingertip. This lets someone sense a variety of electromagnetic fields, in addition to subways passing underground and power lines hanging overhead. Once they learn how to miniaturize them, biohackers will implant themselves with medical sensors that can talk to a smartphone and a device that will let fingers “see” by echolocation. This goes beyond sensory extension to the creation of entirely new senses.

The philosophical movement that forms an umbrella for cybernetics and cyborgs is called transhumanism. Transhumanism is a worldwide cultural and intellectual movement that seeks to use technology to improve the human condition. Radical life extension is one aspect, as is the enhancement of physical and mental capabilities. Two prominent transhumanists are Nick Bostrom, a University of Oxford philosopher who has assessed various risks to the long-term survival of humanity, and Ray Kurzweil, the engineer and inventor who popularized the idea of the singularity, a time in the not-too-distant future when technology will enable us to transcend our physical limitations. This isn’t a prospect that leaves people apathetic. Author Francis Fukuyama called transhumanism “among the world’s most dangerous ideas,” while author Ronald Bailey said it’s a “movement that epitomizes the most daring, courageous, imaginative, and idealistic aspirations of humanity.” Kevin Warwick is committed to the cause of transhumanism: “There is no way I want to stay a mere human.”

Transhumanism could revolutionize space exploration. If we follow the route of nanotechnology, space probes will be miniaturized and the lower costs of manufacture and propulsion will allow us to explore a broad new range of venues in the Solar System. Alternatively, we can use robots as proxies while we’re comfy in a control room on Earth. More radically, we might embrace the future seen in Blade Runner, where cyborgs are sent out to explore and toil. They’re imbued with artificial intelligence and superhuman powers, and they have a “kill switch” in case something goes wrong. Cyborgs could be our metaphorical children—the descendants of our species—spreading out into the cosmos long after we cease to exist.

Excerpted from "Beyond: Our Future In Space" by Chris Impey. Published by W.W. Norton and Co. Copyright 2015 by Chris Impey. Reprinted with permission of the publisher. All rights reserved.