20 November 2021 | New Scientist | 39>Why does
evolution
happen?
Why does time
only move
forwards?
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might someday design self-replicating
organisms. But that only gets you so
far, says Kershenbaum. “It’s definitely
a possibility we could find planets
covered in artificial life,” he says. “But
then you have to explain where the
designers, the original life, came from.”
And in that recursion, you hit
the nub of the matter. “Essentially,
the mechanism by which life arises
is accumulation of complexity,
and that complexity doesn’t come
from nowhere and it can’t arise
by chance,” says Kershenbaum.
Purely thermodynamically, it must
arise step by step.
The spontaneous, sustained
accumulation of complexity in a
system requires three things to be
present. There must be variation,
to give raw material for change in the
first place; there must be differences in
fitness, to give an advantage to change;
and there must be heritability, to
consolidate and pass on change over
time. These three things are nothing
more than the preconditions for
natural selection – and wherever theyE
VOLUTION is a fact of life, at
least of life as we know it. Here
on Earth, organisms that just
so happen to be better adapted, or
“fit”, for their environment, perhaps
by virtue of a fortuitous mutation,
tend to survive longer and leave
more offspring. The less fit leave
fewer descendants and the unfit
none at all. Whatever it was that made
the winners fit thus accumulates
in the next generation, a cruel and
random Squid Game called evolution
by natural selection.
As to why it happens, on one level
that’s simple. According to biologist
Richard Dawkins, evolution is simply
a change in gene frequencies in
populations. If a gene in a colony
of woodlice living under a dead log
becomes more or less common for
some reason, evolution has
happened.
But must it be like that? All life on
Earth that we know of comes from
the same origin and uses the same
biochemical operating system based
on DNA. Putative life on other planets,
or “shadow life” from an independent
origin on Earth, might conceivably
operate under very different rules.
Does life have to evolve – and if so,
does that have to be by natural
selection? “That’s a very interesting
and large question,” says Dawkins.
Arik Kershenbaum at the
University of Cambridge, author of
The Zoologist’s Guide to the Galaxy:
What animals on Earth reveal about
aliens – and ourselves, thinks the
alternatives are limited. One
might be to postulate an intelligent
designer, as perhaps we ourselves
come together, natural selection
inevitably follows.
The operating system itself matters
not a jot. “The biology is irrelevant,”
says Kershenbaum. “It doesn’t matter
what the biochemistry is, it doesn’t
matter if it’s silicon-based or methane-
based.” Even if a different type of life
got going, it is hard to see how it could
persist without mutation and selection
to make it fitter and provide resilience
to slate-wiping events in a world that
is itself dynamic and changing.
Kershenbaum proposes that evolution
is a law of nature, a bit like gravity.
Where there is life to ask the question,
there is evolution. Graham LawtonB
Y THE time you have finished reading
this, you will be a couple of minutes
older. Hopefully you won’t regret
those minutes, because you can’t get them
back. Time, as we all know, only moves in
one direction for us. The question of why,
however, doesn’t come with a simple answer.
Searching for time’s arrow in the underlying,
microscopic laws of physics certainly draws a
blank. They give us no reason to think atoms,
molecules and so on can’t move backwards as
well as forwards in time, much as they (and we)
move freely in three dimensions of space. The
laws don’t differentiate between past, present
and future, or between cause and effect.
“That distinction only becomes relevant in
the macroscopic world, where our incomplete
information about the precise physical
configuration of a system leads us to perceive
an arrow of time, and to put causes first and
effects after,” says physicist Sean Carroll at the