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"Wonderful Life" - repeated.
I hope I'm not too late on this, but a couple of weeks ago
on this list a writer solicited advice on (something like) the
likelihood of there being a Cretaceous on an alternate planet.
Mickey Rowe told him (rather peremptorily I thought) that this
was unlikely and referred him to S.J. Gould's _Wonderful Life_.
Gould wrote, in his book about the fossils of the Burgess
shale, that if you could rewind the "tape" of evolutionary
history, erase it and start re-recording, that you would have a
very different result on the second "recording".
But he makes phylogenetic history out to be more whimsical
than it is. I believe there are in biology, as in physics and
chemistry, some absolute, if emergent, rules. And I believe this
relates to dinosaur extinction. But first I want to poke some
holes in Gould's thesis of non-repeatable history.
On pp. 310 he says: "Surely, the mitochondrion that first
entered another cell was not thinking about the future benefits
of cooperation and integration; it was merely trying to make its
own living in a tough Darwinian world. Accordingly, this
fundamental step in the evolution of multicellular life arose for
an immediate reason quite unrelated to its eventual effect upon
organic complexity. This scenario seems to portray fortunate
contingency rather than predictable cause and effect."
I don't see why mutual symbiosis between these cells would
not be predicted. Cells had surely been invading or engulfing
each other before this fortunate contingency occured. Symbiosis
is _everywhere_ in nature. My own favorite example of the range
and _inevitability_ of these relationships are the lichen. Some
fungi engulf algae and digest them, some set up relationships
with them. And there are a number of lichen on a continuum
between these two extremes. Gould suggests endosymbiosis was a
fluke. But the frequency of these relationships is demonstrable.
Then Gould says: "And if you wish nevertheless to view the
origin of organelles and the transition from symbiosis to
integration as predictable in some orderly fashion, then tell me
why more than half the history of life passed before the process
These events were not predictable in an "orderly fashion".
But they _were_ predictable. The completetion of organelle
attainment and integration took a lot of time because eukaryotic
cells are tremendously complex. Maybe the most magical trick in
all of nature is the replication of a eukaryote's genome. And
then there is the endoplasmic reticulum, Golgi body, etc. etc.
These complex evolutionary feats took time.
For me, the point is not how "orderly" the sequence of
events was, or even how much time they took, but whether the
acquisition of a nucleus, a mitochonrion, or a chloroplast was in
some sense inevitable. If the mechanism for acquisition was
there and things were present which were worth acquiring (even
Gould doesn't argue about the inevitability of prokaryotic
metabolic diversity), and the advantages were telling enough
(they were) then the development of a euk. cell was predictable.
On page 317 and 318 Gould seems to be saying it was a
miracle that vertebrates made it onto land. Wind back the tape,
he says, and "expunge the rhipidistians by extinction, and our
lands become the unchallenged domain of insects and flowers."
By saying that only the lobe-finned fish were capable of
developing walking appendages he is truly a slave to his thesis.
Nearly every other group put representatives on land: arthropods,
molluscs, worms. It takes a prohibitive leap of faith to argue
that vertebrates would be denied. Though it might take time in a
replaying of the tape, vertebrates were destined to come ashore!
Gould's trivial use of chaos obscures a deeper truth, a
biological absolute: a niche was available, vertebrates, too,
must exploit it, no matter what, unless there were _a priori_
reasons why this could not have happened (he suggests none).
Vertebrates have a proven record of adapting to new media. Birds
can be fish (penguins); fish can be birds (sort of--flying fish),
mammals can be birds (bats), fish (whales), and so on.
You could argue that mine is just one person's opinion
against another's, and, without such a phylogenetic tape machine,
I must admit that is true. But Gould is so sure he is right
about unknowable things. As a scientist he lacks humility! This
is especially true with his version of dinosaur extinction:
"(dinosaurs) probably became extinct only as a quirky result
of the most unpredictable of all events--a mass dying triggered
by extraterrestrial impact." And: "Since dinosaurs were not
moving towards markedly larger brains...we must assume that
consciousness would not have evolved on our planet if a cosmic
catastrophe had not claimed the dinosaurs as victims. In an
entirely literal sense, we owe our existence, as large and
reasoning mammals, to our lucky stars."
There are at least two things wrong with this view:
1. There is no EVIDENCE tying dinosaur extinction to anything.
2. Primates were arboreal and ultimately may well have been able
to outcompete dinosaurs in this medium.
But, busy promulgating his thesis, Gould puts a heavy spin
on his version of mammalian attributes, a spin that veers toward
"...dinosaurs remained in unchallenged possession of all
environments for large-bodied terrestrial creatures. Mammals
made no substantial moves toward domination, larger brains, or
even greater size."
First of all, Gould cannot know how challenged the dinosaurs
were toward the end of the Cretaceous. Their diversity was
decreasing, and something was driving an unhealthy arms race--the
trend towards bigness. And challenges don't come only from
things bigger. Often the biggest challenges come from the
smallest things--bacteria and viruses come to mind. For all we
(and Gould) know mammals, birds, lizards, crocs, and other
dinosaurs could have been plenty challenging to all dinosaurs.
Secondly, mammals _were_ achieving bigger brains over the
Mesozoic. John McLoughlin says, in _Synapsida_, "The smell-
illuminated inner space was so important to our Mesozoic
forebears that its organ gradually increased in volume to handle
its increased capabilities. At first merely a little fold of
tissue at the front of the cerebral hemisphere, the neopallium
bloated out across the entire brain, permitting ever finer tuning
of the inner awareness of the outer reality."
Gould would, I suppose, argue that this brain growth was not
"substantial". McLaughlin, though, clearly feels that this
degree of brain development was a watershed event: "Symbolic
thought was born in the terrible Mezozoic night, and what was to
become the human spirit arose in the (neopallium)."
Finally, I would of course claim that dinosaur extinction
was inevitable. They were violating an absolute rule: laying
eggs in plain view is a strategy which is susceptible to
exploitation. Whether or not they were done in by adhering to
this strategy, and whether or not it was the birds, mammals,
lizards, crocs, and other dinos which did them in, I cannot know.
What I do know for sure is this: non-stealthy egg laying is
today, by and large, an unsuccessful strategy. This is because
there are creatures around which can exploit it. My _opinion_
remains that their were also such creatures around towards the
end of the Cretaceous.