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| Stephen Jay Gould |
One of the most spectacular controversies to have arisen in biology at the end of the 20th century was that between two famous biologists: the American Stephen Jay Gould and the British Simon Conway Morris. The controversy began with the former's book, published in 1989, Wonderful Life: The Burgess Shale and the Nature of History, to which Conway Morris responded in 1997 with another book, The Crucible of Creation. As the subtitle of Gould's book indicates, both biologists based their work on the discoveries of the Cambrian fauna of the Burgess Shale (Canada), which I referred to in another post, and which was discovered and studied precisely by Conway Morris.
In his study, Stephen Jay Gould focuses in particular on the surprising and abrupt diversification that took place 550 million years ago and left its mark on the Burgess Shale fauna to argue that evolution is dominated by the effects of chance, so that, if we rewound the history of life and repeated the evolutionary process, the results would not resemble anything we have now. As a corollary, if there is animal life on other worlds, around other stars, it won’t resemble anything on Earth. And if there is intelligent life outside Earth, their physical appearance will not resemble ours.
In contrast, Simon Conway Morris focuses primarily
on the phenomenon of convergent evolution, which causes living beings of very
different lineage to be very much alike [1], to claim that, if evolution were
repeated, the results would be very similar to those we have now, and
therefore, that life on other worlds would probably give rise to beings very
similar to those on Earth, including, of course, hypothetical intelligent
beings, which would probably resemble us.
Curiously, in 1989, the same year that Gould
published his book, Ingrid Inickelgren, in a popular article published inScience News, entitled Bioengineers see physics as a lever that acts on evolution, defined the problem quite reasonably with these
words:
Looking at
the natural world in the form of individual molecules, especially genes, makes
biological variation seem boundless. But watch diverse forms of foliage fold or
wildlife walk, wiggle or hang from trees, sharing the same techniques to tackle
the physical world. And notice: While round and cylindrical organisms abound, there
are almost no square ones, no organism's skeleton is made of metal and very few
use any kind of wheel for transport. Why not? It’s elementary, my dear Watson:
physics.
Where she agrees with Conway Morris, by stating
that the reason why the form of living beings tends to converge is the set of
restrictions imposed by physics. And to support this idea she quotes the
American biologist Steven Vogel, who says: Every organism has mechanical things to
worry about, however good its reproductive capabilities might be. In other words, it is all very well to talk about
chance in evolution, but that chance is restricted by natural selection, which
will never allow living beings to adopt forms incompatible with physical
restrictions.
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| Simon Conway Morris |
In this context, it would be useful to quote some
sentences from chapter 4 of the book by Conway Morris The Runes of
Evolution (2015), coincidentally
titled The Inevitability of Form:
[W]hen one
looks at either the functionality of biological solutions or the roads taken,
then the choices are restricted, if not inevitable… at whatever level of
biology one considers there will be loci of persistent biological stability
that will act as irresistible attractors… Yes, evolution is divergent, but at
each and every step it will be accompanied by convergence.
As ever
with convergent evolution it is not how you got there, but how it works that
matters.
[C]onvergence
opens new ways of looking at evolution, fresh possibilities that may yet
transcend the oxymoronic triumphal aridity of the ultra-Darwinists who continue
to rejoice in both the complete meaningless of the universe while taking a
special, if not gleeful, pleasure in perversely magnifying our utter cosmic
insignificance.
There are many examples of evolutionary
convergence, as well as many examples of evolutionary diversification and
branching. Both sides of the debate have their arguments, and the difference
comes from where each side focuses their attention. But the conclusions drawn about
life on other worlds will not be contrasted soon. Traveling to other stars, or
even sending automatic capsules that will send us photographs, is so far away
that I am sure none of the human beings currently present on Earth will be able
to be a witness.
[1] See Convergent evolution
in Wikipedia.
Thematic Thread on Evolution: Previous Next
Manuel Alfonseca
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