Cuvier MiraCosta Biology

Uploaded by MeerdesIrrtums on 11.01.2012

This topic introduces the evolutionary mechanism of Natural Selection, which is perhaps the
singlemost foundational principle in all of biology. But since we’ve been thinking about
the nature of science, I’d like this also to develop some of these bigger ideas, for
example exploring the boundaries between where knowledge is scientific and where it isn’t.
Rather than starting you off with the obvious lesson on Darwin and the development of his
explanation for evolutionary change via natural selection, I’m going to tell you about Georges
Cuvier, a Frenchman who was well-respected among academics of his time, though in the
end he really did not embody a way of thinking that could be called scientific.
Cuvier studied many things and he contributed to our growing body of knowledge in a way
that you might call “scientific—in the sense that they were based on careful observations
of the natural world. The time frame here was in the last part of the 1700s—Charles
Darwin was born in 1809 so this is well before Darwin’s time—and we were just getting
around to thinking carefully about fossils—they were mineral in composition but they certainly
bore a generic resemblance to living organisms, though often not matching up specifically
to any known living organism—it wasn’t clear how to interpret these differences.
Were fossils just some kind of inscrutable artifact produced during the act of creation,
or were they telling us that different kinds of life had existed in the past?
Cuvier did a lot of work with mammoth and Mastodon fossils established convincingly
that these were different from African or Indian elephants. The only explanation for
these fossils that he could offer was that they were indeed the remains of living organisms
from the past—organisms that were now extinct. Extinction is in fact a concept that comes
from Cuvier’s studies.
Cuvier also did work with a mining company that was active in the area around Paris,
and digging super-deep holes in the ground is an activity that is obviously going to
turn up a great number of fossils. By cataloguing and classifying the fossils and analyzing
the locations and depths of where they were found, Cuvier established that Paris had been
under the sea—not just once but at four separate times! His thinking works like this:
fossils of marine organisms were there in some of the deepest layers, so these would
have to have been the oldest—the sediments have to be deposited in order from bottom
to the top, right? So the deeper you go, the older the sediments. This is the basic rule
of Superposition, and Cuvier was the one to establish this rule.
So you have these marine fossils at the bottom in the area that is now Paris, and this tells
you that Paris was under the sea at the time those fossils were deposited a long, long
time ago. Then, on top of the marine fossils, you have a layer with a lot of fossils of
fresh water animals, and this tells you that after the saltwater fossils were deposited,
the area was above sea level, like at the bottom of a lake (Paris is in a large flat
basin, so it could have been a lake). And on top of the fresh water fossils there were
more marine fossils—telling us that the area was under the sea again, at a time after
it had been a fresh water lake. This sequence of alternating salt- and fresh-water fossils
was correctly interpreted by Cuvier as the area having a history of being alternately
under the sea and above the sea—a minimum of four times for the layers of sediments
that Cuvier had available. What’s more, changes in the early-to-late sequence showed
that extinction occurred between each event of submersion—the marine fossils in the
oldest layer were replaced by different marine fossils the second time Paris was under the
sea. The fresh-water fossils were similarly replaced by new life forms each time the area
was a lake bed.
If you’re hearing this and thinking that Cuvier’s findings suggest evolutionary change,
this was not lost on other naturalists—another Frenchman in particular, a guy named Jean
Baptiste de Lamarck presented an evolutionary explanation for this replacement of old life
with new life, and he did so publicly some 57 years before Darwin.
But realize that in the year 1802 the Bible was still considered as the authoritative
history of the universe, and it wasn’t cool to suggest things that weren’t there in
the holy book. As strange as this may seem, Cuvier—the guy who showed the world that
there were at least four massive-flood-like extinction events—was a strong proponent
of the Bible’s historical validity. Yes, the Bible only accounts for one flood—but
according to Cuvier, this is because it’s the only flood to occur since the creation
event of Genesis. Cuvier explained the Paris fossil data as well as mammoths and mastodons
by saying that there had been earlier creation events and extinction floods that simply pre-date
the events of Genesis. Cuvier’s model is called catastrophism, and in Cuvier’s mind
this was the best possible explanation for fossils without contradicting the Bible.
Meanwhile, on the English front, a different perspective of the earth’s history was taking
shape. Charles Lyell, building upon earlier work by James Hutton was developing a model
of geologic change in which gradual forces like erosion, deposition, and uplift were
continually giving rise to canyons and mountains and other geologic features—this idea of
uniformitarianism is the exact opposite of Cuvier’s catastrophism, which runs more
along the lines of “animals get created and they stay that way” until… BAM! Flood
wipes everything out and we start over with the creation of somewhat different animals.
By this way of thinking, the mountains would have had to have been either created and canyons
eroded during those massive flood episodes. Two very different explanations for the existence
of mountains and canyons. The uniformitarian view says it’s the accumulation of the work
of gradual forces, catastrophism says it all happened in sudden events. So how do you decide
which one to believe?
Well, as we learned in an earlier lesson, the scientific way of dealing with this is
by experimentation and allowing observations from the natural world to support one or the
other model with evidence. Well guess what. Catastrophism is supported by exactly no evidence,
while the uniformitarian view is supported by lots. Okay, you saw that coming.
Now back to Lamarck—the French evolution guy who suggested evolutionary change sixty
years before Darwin. Nowadays, we don’t give any credit to Lamarck for being the father
of evolution, and this is because the mechanism that he proposed was just totally wrong—his
idea was that organisms somehow passed on whatever improvements they made on themselves
to their offspring. This doesn’t happen, although much later on when we talk about
the human brain, we’ll see how the spread of ideas by imitation and emulation gives
a dynamic that is very much like Lamarckian evolution. At the time, however, nobody knew
whether or not Lamarck had the right evolutionary mechanism. Cuvier attacked Lamarck for a totally
different reason. This is going to be a little deep, so put on your philosopher’s hat.
Both Lamarck and Cuvier knew that in order for evolution to be true, it would require
millions of years, whereas the Bible’s chronology puts the earth at around six to ten thousand
years old—this is simply not enough time for evolution to occur. Lamarck’s answer
was that the earth was actually much older than what the Bible said. This is where Cuvier
cries “foul”— Cuvier blasted Lamarck, saying that he was altering the earth’s
history with only the justification that he needed to accommodate the time requirements
for his theory of evolution. Lamarck was guilty of a posteriori reasoning. A posteriori means
“to the rear” and this is problematic because you’re supposed to let the facts
of the case drive the conclusion, right? You’re not allowed to start with your conclusion
and make up the facts in a way that will make your conclusion true.
[Never mind that this is exactly what Cuvier did with his catastrophism model. But this
isn’t what I want to stress here…]
Now if you paid careful enough attention in the scientific inquiry lesson, you should
realize that when you’re trying to explain something scientifically, there’s going
to be a little bit of a posterior reasoning, because that’s how the hypothesis gets made
in the first place. But then very quickly you get into activity that is not posterior—such
as designing an experiment and making predictions, and this is what makes science a legitimate
investigative enterprise. But Cuvier was stalwart in his opposition to Lamarck’s view that
the earth was old. Lamarck was actually right about the earth being older—not just millions
of years but as it turns out the earth is 4.6 billion years old. Cuvier’s judgment
of Lamarck was based on his not having the appropriate justification for making a claim
for the earth being older.
In the years following Cuvier’s attacks on Lamarck, this little shouting match became
a totally moot historical footnote. The uniformitarian model for geologic change became fully established,
and it became generally accepted—though never by Cuvier—that the earth is much,
much older than just a few thousand years. By the time Darwin proposed his evolutionary
model, this particular objection could not be raised—everyone knew that there was plenty
of time for evolutionary change to occur.
Darwin’s idea—that populations change by natural selection (and we’ll be addressing
this in the next couple of videos)—propelled him to the status of scientific immortality
for two basic reasons. One—it’s incredibly powerful. This simple mechanism provides a
naturalistic explanation for everything biological. As the great geneticist Theodosius Dobzhansky
said, “nothing in biology makes sense except in the light of evolution.” Two—Darwin
was right, in all the ways that Lamarck was wrong. Like uniformitarianism, evolution by
natural selection has a mountain of supporting evidence from observations and experimental
results—and this is how it got elevated to the level of a theory, which in science
is the highest level of establishment that a scientific model can gain—just short of
a natural law.
Cuvier has been at the center of this discussion, and in thinking about Cuvier now I’d like
you to consider how conflicted of a person he must have been. On one hand, he was highly
skilled at making observations from the natural world and interpreting them, and at the same
time he was never able to let go of his incorrect views in spite of a growing body of evidence
supporting the opposing point of view.
Science is about following the lead of evidence and not ideologies.