For 21st-century renaissance science, look no ­further than the stars. Closer to home, the Royal Society, as part of its 350th anniversary celebrations, this week brought together some dizzying intellects to ponder the ­emergent field of astrobiology, and ask: "Are we alone in the universe?"

Meanwhile, the space telescope Kepler silently orbits above, its continuing mission to seek out Earth-like planets. Kepler's eye focuses on what we fondly refer to as "Goldilocks zones": areas of space close enough to a sun that planets therein are neither too hot nor too cold, but just right. There, we think, we might find Earth-like life.

Present at the Royal Society meeting in London was Frank Drake, the godfather of the scientific pursuit of ET; 50 years ago he founded the Search for Extra Terrestrial Intelligence (Seti), and designed a formula that predicts the number of civilisations capable of making contact with us. Then not one planet was known outside of our solar system. Today, with only an infinitesimal wedge of the sky incompletely explored, we have found more than 420. Every day evidence mounts that life beyond our planet seems almost inevitable.

What would aliens look like? Our psychological set-up is so egocentric that we find it hard to relate to creatures that don't resemble ourselves: the common octopus rarely stands alongside monkeys in animal rights campaigns despite similar sentience. Not only do we look for Earth-like planets, we think of aliens in humanesque form. The "grey" alien of science fiction, with its frail body and enlarged head and eyes, plays to our evolution away from animal ancestry and towards our cerebral tendencies.

There's no reason to think that an alien would stand on two feet, have two eyes or breathe air. The subtlest shift in circumstance might render intelligent life entirely different to our anthropocentric obsession. Some evidence suggests that our upright stance is connected with our ability to endurance-run: on the plains, our ancestors couldn't outsprint a fleet-footed meal, so perhaps we stalked our food to death. But imagine if our ancestors were mountain-dwellers: running would have had no currency, and no selective advantage. Change the geography of the cradle of humanity, and humankind becomes something unimaginable.

It's impossible to know, but fun to speculate. This game presupposes that Darwinian natural selection is a universal truth. Fine by me: it occurs in all known species, and there have been no credible challenges to the theory of evolution. It's hard to imagine the evolution of life via a different scientific route.

Life on Earth is encoded in DNA, the universal language on which natural selection acts. Many scientists believe that the precursors of life began not with DNA, but its cousin, RNA – still a vital tool in all living things. In 1969 a meteorite crashed into the Australian backwater of Murchison. In 2008, Zita Martins at Imperial College showed that it harboured an essential component of RNA that was extraterrestrial in origin. While this does not say that life exists or began in space, it does say that the complex components of life are present in the universe. When we return to Mars in the next few years, it will be these hallmarks we are looking for.

Frank Drake is a visionary, a man who quite rationally wants to find our place in the universe. In 50 years of watching the skies, the Seti team has not found extraterrestrial life among the stars. Either intelligent life is extraordinarily rare or its civilisations are short-lived, snuffed out by cataclysms, perhaps of their own making. While we continue to explore our vast universe, we should remind ourselves that even if it is ­buzzing with life, our own existence is far from guaranteed.