[Paleopsych] Guardian: Why shouldn't aliens look like us?

[Premise Checker]

Why shouldn't aliens look like us?
http://www.guardian.co.uk/print/0,3858,4988691-103677,00.html

    There are good scientific reasons to believe that extraterrestrial
    life forms might resemble human beings
    Duncan Steel
    4.8.9

    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
    duncansteel at fsmail.net