Genetic engineering requires neither nuclear bombs nor mirrors the size of a solar system. Its results can be seen within a few years, given the generation time of most terrestrial species, compared with the millennia of terraforming. Also, whereas terraforming is a linear, one-shot deal, genetic engineering resembles parallel processing in that several lines of inquiry can be pursued concurrently.

Last but decidedly not least, genetic engineering may well turn out to be economical. Species not so good for one world may well thrive on another. The hubris involved in genetic engineering is several orders of magnitude smaller than that involved in terraforming. At least we’re good at the former, as the variety and quality of our foodstuffs and pharmaceuticals attest. Nor would we be condemning entire worlds or species to destruction. Terraforming is a battering ram, genetic engineering is a scalpel. Which one would you prefer for a delicate, complex operation — whether this is repairing a watch, performing a heart bypass or fine-tuning a new world?

Among its consequences, genetic engineering may also reverse a problematic human trend towards biological homogenization which is as dull and dangerous as its cultural equivalent. By eventually recognizing that we are one species and interbreeding enthusiastically to celebrate that fact, we have stopped our further evolution by extinguishing isolated breeding pools. We have overtaken earth, first by being adaptable, then by dint of our technology. From a jaundiced ecological viewpoint, the recent explosion of humanity has been likened to a lemming population boom or a moth infestation. Such booms are invariably followed by busts — and in our case, a crash would also mean irreversible loss of technology.

From our very beginnings, we tended to consider ourselves the jewel in the crown of creation. We believed that at least some of us had been created in the image of the local deity. Yet by considering our germ line sacrosanct, we have painted ourselves in a biological corner. Each terrestrial species has a finite lifespan. Moreover, most successful species branch, whereas we humans are down from a half dozen relatives to a single representative — Homo Sapiens sapiens. If we insist in remaining unchanged, without evolving or radiating, we may degenerate and disappear without intervention of a great catastrophe either from something home-brewed like war or from a random event, such as the impact of a rogue comet. We’ll blink out not with a bang, but with a whimper.

In that respect, our absolute dominance in our current configuration has not served us well for the next step. Deeply embedded in all our plans and ideas is the not-so-hidden assumption that we will fundamentally remain as we are. But the difference between living on Earth and anywhere else is qualitatively different from living in New York versus living in the Arctic. Almost certainly, if we really wish to go into space as long-term explorers, rather than as tourists, we will have to accept radical change — and with it the disquieting possibility that we will not be the crowning spire of the next cycle, but its foundation.

Interestingly enough, we actually seem to be designed for rapid speciation. The successive branchings of the humanoid group have come at ever shorter intervals: the genus Homo arose 5 million years ago; Sapiens, 0.5 million years ago; Sapiens sapiens, 0.05 million years ago. If you put 1,000 people in a row, the first in the line would be the very first Cro-Magnon, the last in line one of us. Our species is actually very young, and almost certainly in biological flux — except for our insistence that we are the perfected end product.

Settling on other planets will speciate humanity even if we forego genetic engineering, because it will create relatively isolated breeding pools in circumstances radically different from those on earth. Human groups also developed characteristics specific to their terrestrial environment — the Mongolian epicanthic fold, the heat-efficient Inuit compactness, the heat-dissipating Tutsi lankiness, the enlarged heart of the Nepalese and Ecuadorians; last but not least melanin, whose dosage increased where appropriate to provide shelter from sunburn, unwittingly causing humanity endless woes. Genetic alleles that are anathema today spread quickly and widely through populations for very good reasons in the past: a mutant hemoglobin made carriers resistance to malaria, while killing homozygotes with sickle cell anemia; a mutant ion transporter did the same for cholera, but killed homozygotes with cystic fibrosis. Between the expense of interstellar travel and the discomfort from different gravity, pressure and other planetary specifics, we will see differentiation much faster.

Speciation means this, in practical terms: At some point, the pools will no longer be able to interbreed. Our colonials will not just have different accents. They won’t be Brazilian Portuguese, or Egyptiot Greeks — or even those real aliens, Australians. They will no longer be humans as we define the term. To put in succinctly, they will not be someone that we can easily love either in the fundamental biological sense or in the equally influential cultural one — and in the end, that is the commonality that binds us.

In that respect, TV science fiction has served us poorly, by depicting humanoid aliens as ersatz samurai like the Klingons or fake Tibetans like the Bajorans. Written science fiction has done much better in presenting visions of such offshoots of humanity — for example, Kingsbury’s Courtship Rite and Cherryh’s Forty Thousand in Gehenna. In effect, by sending out long-term planetary expeditions, we will create aliens more surely than by leaving picnic trash on an uninhabited planet. Our first alien encounter, beyond earth just as it was on earth, will be with ourselves as seen through the distorting mirror of divergent evolution.

The differentiation of humans into truly separate branches will force us to face our hard-wired fear of anyone who is almost like us, but not quite. The last true such encounter was roughly 40,000 years ago, between the Neanderthals and the Cro-Magnon, though it has been replayed in countless first contact situations between cultures ever since (not to mention the exchanges between the sexes). Ever since humans became sapient, they enhanced their self-esteem and justified their raids by insisting that those beyond the next hill (or for that matter, those cleaning their latrines and/or bearing their children) were subhuman, despite the indisputable and well-known fact that all aliens were fully human by the sole criterion that is biologically relevant; namely, production of offspring.

Such xenophobia was once a survival mechanism, but now it’s as useful as our appendix and wisdom teeth. And despite our other strengths, embracing the alien is decidedly not high on our list of attributes. Certain segments of the scientific and space aficionado communities have been cheerfully discussing how to interact with Little Green Women and Men. Well, the armchair philosophers will get the chance to practice their theory when humanity splits into groups of cousins who won’t look like the usual Hollywood brands of benevolent aliens — not like angels, not like human newborns and not like snuggly, cuddly Ewoks.

This prospect is one of the scariest aspects of venturing into space, yet at the same time one of the most exciting. It’s also a development that will guarantee the survival if not of our species, then certainly of our legacy. It has taken us a long time to reach a fragile and imperfect unity, cemented by the understanding that we are all really one large family. To go to the next stage, we must voluntarily renounce that unity and relax our iron grip on the evolution that we have arrested. After all, don’t forget that if not for sudden jumps in speciation, most of them caused by environmental pressures — an asteroid hit here, an Ice Age there — we wouldn’t be here. Planetary settlement helped along by judicious application of genetic engineering is merely the continuation of this trend, except that some of the process will be under our control. Stasis ends in death not only culturally but also biologically. If we don’t go into the next stage, our descendants won’t just lead lives devoid of meaning, doomed to repeat outworn patterns in the confines of a worn out planet. They will also peter out, dead branches of a dried-up tree.

If we allow ourselves to grow up and give rise to other sapients, it’s quite possible that our descendants will be as kind to us as we were to our ancestral species. However, whether we like each other or not, I hope that they inherit our curiosity, because that’s the one indispensable ingredient for success. And despite all the caveats I listed, I think we will venture to the stars — for knowledge, for glory, but above all, because we thirst to know what is behind the next bend in the path. Compared to the oceans that we and our inheritors will navigate, our efforts until now are like the launching of paper boats in a bird fountain.