Ladies and Gentlemen:
The Evolutionary Biology Lecture of the Week for May 15, 2006 is now
available at:
http://aics-research.com/lotw/
The talks center primarily around evolutionary biology, in all of its
aspects: cosmology, astronomy, planetology, geology, astrobiology, ecology,
ethology,
biogeography, phylogenetics and evolutionary biology itself, and are
presented at a professional level, that of one scientist talking to another.
All of
the talks were recorded live at conferences.
This week's lecture is the third of three lectures that discuss whether or
not Darwinian evolutionary theory is sufficient to explain all of the phenomena
we see in nature.
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May 15, 2006
Part III: Is Evolution Sufficient?
A Planetary Perspective on Evolution
Andrew Knoll, Harvard
35 min.
What does paleontology contribute to evolutionary biology?
One answer is of course that paleontology provides a direct historical record
of evolution, one that includes organisms such as trilobites and dinosaurs,
organisms whose existence would not easily be inferred on the basis of
phylogeny alone.
But it does more than that. What paleontology really does is to inform us
about the nature of evolution on an active planetary surface.
Beginning in the 1970's, a number of paleontologists began to challenge the
notion that populational genetic processes are sufficient to completely explain
the evolution of life on earth, an idea most clearly spelled out by Steven
Stanley's dictum, "Macroevolution is decoupled from microevolution."
Evolution is not a process that operates only through time; there exists a
profound spatial component as well. As phyletic lineages increasingly better
learn their environments, they simultaneously become bound to those
environments.
Species diversification, the evolution of complexity and the evolution of
intelligence are all similar questions interwoven onto a biogeographic
tapestry,
governed greatly by a planet's obliquity, eccentricity, internal heat and
position in its solar system.
Evolutionary ecology has been slow to recognize the importance of those
geographic constraints on the evolution of life on Earth, but the last two
decades
have seen a fundamental shift in that regard with the recognition of a new
field of study, biogeography. Lomolino, Riddle and Brown write in their
excellent
book, Biogeography, 3rd Ed. (2006, p. 710):
"One of the esteemed founders of modern evolutionary theory - Theodosius
Dobzhansky (1973) - once told us that 'nothing in biology makes sense except
in the light of evolution.' We certainly take no issue with this, but instead
offer our own observation that is even more general and possibly more
strident. 'Little in ecology, evolution, and conservation biology makes sense
unless
viewed in a geographic context'."
But even this view is insufficient to fully understand the evolution of life
on this planet. An active planetary surface greatly influences evolution's
course, and many authors have recently argued variations of a central theme:
that
some degree of instability is necessary to induce episodic bursts of novelty
into the evolutionary process. Static worlds, although they may not be quite
"dead," would at best promote an early evolutionarily homeostasis and perhaps
never advance beyond a certain stage.
The introduction of episodic variation need not be catastrophic to be
significant. A striking example of the effect is found in a recently published
evolution of the cats in Science, where falling global sea levels during the
Late
Miocene and Late Pliocene/Pleistocene appears to have introduced bursts of
evolutionary invention into the Felidae. Correlations between lowered mean sea
level and the bursts of evolutionary novelty within the diversification of the
cats seem clear. It's during these epochs that previously isolated populations
were free to migrate into new environments, resulting in new adaptive
radiations.
While these recent changes in sea level have promoted a species diversity
pump, the evidence accumulated by Andy Knoll and colleagues, in a companion
paper
to this talk, strongly suggests that global catastrophes were essential in
creating an even more profound complexity pump.
Three events appear to have reset the course of life on Earth: the
Permo-Triassic and Cretaceous-Tertiary extinction events, and the "Snowball
Earth" epoch
just prior to onset of the Cambrian. The trends evident in their analysis
suggest that following each event, complex multicellular life on the surface of
the Earth became more mobile, more independent of its physical environment and
more predaceous, and thus more "intelligent."
Predators are by force of nature more analytical, more perceptive than their
prey. As seen in the graph to the left, the half-billion year trend for
complex life on this planet has been for life to become more predaceous,
punctuated
in that evolution by two great catastrophes, the End-Permian and
Cretaceous-Tertiary extinctions. It now appears that we owe at least a portion
of our
intelligence to these events.
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