different could life have been?"
including several in this group, are fond of asking, What if the
universe had been different? Are the fundamental constants just
numbers we accept as given, but which could have been different? Or
is there some deeper rationale, which we shall eventually discover,
that renders them unfree to change? Is our universe the way universes
have to be? Or is it one of a huge ensemble of universes? Given present
company, I would not aspire to this question, fascinating as it is.
Mine is its biological little brother. Is the life that we observe the
way life has to be? Or could we imagine other kinds of life? Long the
stock in trade of science fiction, I want to move it closer to sciences
domain. Unfortunately the question is one for a chemist which
I am not. My hope is that chemists will listen, and work on it.
Life as we know it is far more uniform than superficially appears. The
differences between an elephant and an amoeba are superficial. Biochemically
speaking, we are all playing most of the same tricks. At this level,
most of the variation in life is to be found among the bacteria. We
large animals and plants have just specialised in a few of the tricks
that bacterial R & D developed in the Precambrian.
But all living things, bacteria included, practise the same fundamental
tricks. Using the universal DNA code, the one-dimensional sequence of
DNA codons specifies the one-dimensional sequence of amino acids in
proteins. This determines the proteins three-dimensional coiling,
which specifies their enzymatic activity, and this, in turn specifies
almost everything else. So, Im not talking about whether living
things on other planets will look like us, or will have television aerials
sticking on their heads. It is easy to predict that heavy planets with
high gravitational fields will breed elephants the size of flies (or
flies built like elephants); light planets will grow elephant-sized
flies with spindly legs. It is easy to predict that, where there is
light, there will be eyes. This is not what I am talking about. I want
the answer to a more fundamental question.
My question, which is for chemists, is this. Can you devise a fundamentally
different, alternative biochemistry? Given that, as I firmly believe,
life all over the universe must have evolved by the differential survival
of something corresponding to genes self-replicating codes whose
nature influences their own long-term survival do they have to
be strung along polynucleotides? The genetic code itself almost certainly
didnt have to be the one we actually have plenty of other
codes would have done the job. Ours is a frozen accident which, once
crystallised, could not change. But can you think of a completely different
kind of molecule, not a polynucleotide at all, perhaps not even organic,
which could do the coding? Does it have to be digital like the DNA/RNA
code, or could some kind of analogue code be accurate and stable enough
to mediate evolution? Does it even have to be a one-dimensional code?
And is there any other class of molecules that could step into the shoes
Biochemists, please stop focusing exclusively on the way life actually
is. Think about how life might have been. Or how life could be on other
worlds. Channel your creativity to devising a complete, alternative
biochemistry, whose components are radically different from the ones
we know, but are at the same time mutually compatible participants
in a wholly consistent system which your chemical calculations show
could actually work.
Why should we want this? I wanted to ask the question, Is there
life on other worlds, and how similar is it to the life we know?
But there is no immediate prospect of our receiving direct answers to
these questions, and I am pessimistic of our ever doing so. Life has
probably arisen more than once, but on islands in space too widely scattered
to make a meeting likely. Theoretical calculations may be our best hope,
and are certainly our most immediate hope, of at least estimating the
probabilities. Theres also the point, which hardly needs making
on Edge, that to seek the unfamiliar is a good way to illuminate oneself.
Reply to Paul Daviess response to John
Davies notes that some night-migrating birds navigate by the stars,
and asks whether avian DNA contains a map of the sky. Could a
scientist in principle sequence the DNA and reconstruct the constellations?
Stephen Emlen, of Cornell University, researched the matter in 1975.
He placed Indigo Buntings in a circular cage in the centre of a planetarium,
and measured their fluttering against different sides of the cage as
an indicator of their preferred migratory direction. By manipulating
the star patterns in the planetarium, blotting out patches of sky and
so on, Emlen showed that the buntings did indeed use Polaris as their
North, and they recognized it by the surrounding pattern of constellations.
So far so good. Now comes the interesting part. Is the pattern of stars
built into the birds DNA, or is there some other, more general
way to define the north (or south) pole of the heavens? Put it like
that, and the point jumps out at you: the polar position in the sky
can be defined as the centre of rotation! It is the hub that stays still,
while the rest of the heavens turn. Did the birds use this as a rule
Emlen reared young buntings in the planetarium, giving them experience
of different artificial night skies. Half of them, the controls,
experienced a night sky that rotated about Polaris, as usual. The other
half, the experimental birds, experienced a night sky in which the centre
of rotation was Betelgeuse. The control birds ended up steering by Polaris,
as usual. But the experimental birds, mirabile dictu, came to treat
Betelgeuse as though it was due north. Clever, or what?
Dawkins is an evolutionary biologist and the Charles
Simonyi Professor For The Understanding Of Science at Oxford University.
He is the author of Unweaving the Rainbow.