Why shouldn't aliens look like us?
There are good scientific reasons to believe that extraterrestrial life forms might resemble human beings
Monday August 9, 2004
Would extraterrestrials look like us? Why not? In sci-fi movies, aliens are often basically humanoid in size and shape, like the Klingons in Star Trek, or various characters in the Star Wars films. Even the robots are built on anthropomorphic lines, because there's an actor inside that suit, whether it's furry, scaly or metallic.
The advent of computer-generated imagery means this limitation might be left aside, but alien monsters still tend to be given broad similarities to our own form: bilateral symmetry, and something that looks like a head. Arms and legs may outnumber our own, but they tend to be in pairs and terminate in hands, claws or feet.
For the purposes of enjoyment we suspend critical judgment, although if you thought about it you'd probably conclude that ET, if he exists, would be quite different from us, not at all like his depiction in the eponymous movie. But would he? Actually, an argument can be made that extraterrestrial technological (radio-communicating, space-faring) lifeforms might be similar to us.
Statements regarding the possibility of extraterrestrial organisms are often qualified with the glib phrase "life as we know it". But life as we know it, here on Earth, can also tell us a lot.
For 3bn years Earth-life was restricted to monocellular forms; in short, slime. Then, sometime around 600m years ago, the first polycellular life - the first animals - evolved. This step came after an extended era during which our planet was completely covered by ice, with intermittent thaws. Palaeo climatologists call this "Snowball Earth". Climatic shocks, coupled with a build up in the oceans and atmosphere of oxygen released by algae, may have made possible the emergence of the first marine creatures. Some appeared similar to jellyfish, others to sponges and segmented worms, while many were unlike anything seen today.
These are termed the Ediacaran fauna, after the Ediacara Hills, just west of the Flinders Ranges in South Australia, where peculiar fossils were found in the 1940s. Later it was realised that examples had been reported earlier on other continents.
Geologists have just agreed to define the Ediacaran as a new geological period, the first such declaration since the 19th century, after 14 years of wrangling. The Ediacaran stretches from the end of the Snowball Earth era through to the start of the Cambrian period 543m years ago.
The relevance of the Ediacaran to the search for extraterrestrial life is clear. All we can hope for on Mars is microbes, but elsewhere in the solar system conditions similar to Snowball Earth may exist. Beneath the icy crust of Jupiter's moon Europa, an ocean has been suggested, perhaps making complex life feasible there. Nasa plans a probe to Europa. The Ediacaran fauna give us the best concept of what to look for.
When it comes to searching for ET, though, microbes or jellyfish are of limited interest to the passengers on the Clapham omnibus. They want little green men, or benign Klingons: technological beings able to beam messages to us from elsewhere in the galaxy, telling us we are not alone. Simply intelligent life is not enough: dogs and frogs can build neither radio dishes nor spaceships.
The Cambrian itself is delineated by an explosion in life's diversity. Palaeontologists count at least 35 distinct body plans in fossils from that period, giving rise to evolutionary lines reaching down through the ages. Some have died out, while others have continued to the present.
Evolutionists sometimes talk of the dead ends as being experiments in life that did not work. Well, what about the ones that did work?
A finite number of solutions exist for any physical problem. The laws of hydrodynamics, for example, govern efficient movement through water, and as a result dolphins, sharks and ichthyosaurs assumed the same shape, despite mammals, fish and reptiles having diverged many millions of years ago. This is termed convergent evolution. Similarly, humans and octopuses have eyes with the same basic architecture, because there are only so many ways to focus and detect light.
Life elsewhere might be based on a different set of 20 amino acids to that on Earth, but we don't know that, so we can only use our experience. The number of ways DNA can be mixed to produce different viable lifeforms is huge, but it is finite. What if the only solutions to the problem of producing an organism capable of interstellar communication were in the DNA combinations resulting in bilateral symmetry, four limbs, opposable thumbs and brains more proficient than is required for the health and reproduction of the species? We could extend that list, but you get the picture.
Since the Copernican revolution in the 16th century, indicating that the Earth is not the centre of the universe, we have been conditioned to reject the anthropocentric viewpoint. In interpreting observations, scientists try to exclude human values. But we shouldn't be afraid of imagining the simplest solution: that ET might be just like us.
· Duncan Steel is a space researcher based in Adelaide, Australia