History of Evolution: Historians of Science to the Rescue!

[Diane_]

Disclaimer: While I think I'm pretty well educated in math and the physical sciences, I'm pretty much a moron in biology. Be nice to me.

I read the following statement from one George Olshevsky, responding to a Creationist argument:

For example, the theory of evolution predicts that the fossil record will be progressive in time, because species changes build on one another. You cannot have a wing without first having an arm; you cannot have an arm without first having a front foot; and you cannot have a front foot without first having a fin. The theory of evolution predicts that fins will come before feet, and feet will come before arms, and arms will come before wings.

He was responding to the claim that evolution is not a "scientific" theory because one cannot directly observe the origin of life or the processes of evolution by stating that one can use the theory to make predictions which can be confirmed. He's right, of course, but in reading this, my first thought was that the theory of evolution did not make the particular prediction he cites but was rather crafted to explain the observed progression in the fossil record.

My smugness was quickly interrupted by my wondering if, in fact, that was the case. Was the fossil record well enough known when evolution was being developed that the fin/foot/arm/wing progression (to use a specific example) was a factor in its development, or was it developed to the point of making that prediction before that progression was observed?

Historians of science: to your marks!

 

[russ_watters]

No, the fossil record was not well enough known. Darwin's original formulation of the theory was based on birds in the Galapagos Islands.

And besides the fossil record, it now includes DNA.

 

[Diane_]

Thank you, Russ.

 

[pattylou]

The prediction is that evolution is progressive.The theory of evolution certainly predicts progression.

It is a feature of scientific theory, that one can make predictions and then perform tests to specifically address that particular prediction. (In this case, the test was "Can we find examples of progression in the fossil record.")

The fin-foot-arm-wing is an example that was found that validates that prediction. But of course "fin-foot-arm-wing " was not the specific prediction. Finding that progression in the fossil record, validates the *prediction* one can make with evolutionary 'theory' that it will be progressive.

-Patty

ps Origins of life is a separate, though related, topic.

 

[Phobos]

He was responding to the claim that evolution is not a "scientific" theory because one cannot directly observe the origin of life or the processes of evolution by stating that one can use the theory to make predictions which can be confirmed.

Note that direct observation is not a requirement for something to be "scientific". Deductions based on evidence are allowed.

He's right, of course, but in reading this, my first thought was that the theory of evolution did not make the particular prediction he cites but was rather crafted to explain the observed progression in the fossil record.

As previously noted, the theory does not make that specific prediction (fin-foot-arm-wing)*. The theory predicts change in species and that changes are built upon or from existing features.

* Plus, that lineage is not necessarily the case either. Flight has developed independently more than once. That lineage may be ok, generally speaking, for birds, but not necessarily other species. Check out...http://pharyngula.org/index/weblog/comments/flap_those_gills_and_fly/

In insects, we have an interesting origin explanation for wings: they're modified gills.

Was the fossil record well enough known when evolution was being developed that the fin/foot/arm/wing progression (to use a specific example) was a factor in its development, or was it developed to the point of making that prediction before that progression was observed?

As Russ noted, Darwin (and his predecessors & peers in the theory) did not know enough of the fossil record in detail for that specific lineage. But they did have several other lines of evidence upon which to build the theory, including observed changes in species in the fossil record (e.g., examples of extinct variations of modern species). Darwin's finches were an example of how a species can be modified to fit various environmental niches. Animal & plant breeding provided another example of how species could be modified. And so on.

 

[Diane_]

Perhaps I miscommunicated by using too specific an example. As I understand it, Darwin developed the theory after observing the variation in species arising from a physical separation - the whole Galapagos Islands thing. In that sense, evolution was crafted to explain how species come to vary, which would mean that one could not cite examples of species variation as successful predictions made by the theory. If it was designed to explain such variation, then using such an example to bolster the theory would be tautological.

However, if specifics from the fossil record were sparse at the time the theory was originally crafted, one could say that evolution predicts a particular sequence of variations as a consequence of the theory itself and the mechanisms proposed for its functioning. In that case, discovery of such a sequence could legitimately be used as evidence in favor of the theory. I would not expect to see a paper from 1860 predicting the whole "fin-foot-arm-wing" sequence. Rather, I would expect to see speculations regarding the kinds of sequences expected to be found, which could be confirmed or refuted by the evidence as it was obtained. Confirmatory findings would then constitute evidence in favor of the theory.

Mine was really an historical question concerning the information Darwin had at the time he proposed the theory. I am gathering that there was very little fossil evidence then, and he based it primarily on observing living things. In that case, evidence from the fossil record that "simpler" things became "more complex" things (and I really don't want to debate "simpler" verses "complex" right at the moment) would tend to confirm what he said.

My apologies for any confusion.

 

[Moonbear]

Right, Darwin based his theory on the range of variation in living organisms. Think of the Galapagos Island voyage as the "pilot experiment" where he observed something on a small scale among a few species and developed an hypothesis based on those findings of what has happened on the larger scale, worldwide, across all species, and since the beginning of life on Earth.

The real experiment is not just finding things that support the hypothesis- that wouldn't be sufficient for scientific criteria- but searching for examples that do not fit the hypothesis. This has been done repeatedly, and has failed to come up with anything to disprove evolution, so, thus far, all the evidence supports evolution as a correct theory. If someone went out on an archaeological dig next week and found fossilized remains completely resembling modern humans in a layer of Earth otherwise only containing Paleozoic era fossils with no indication of disturbances that could have mixed layers (volcanic eruptions or earthquakes, for example), then we'd have to toss out evolution and adopt a new theory. So far, no such example has been found.

 

[erok81]

Sorry to break off-topic a little, but are there any good books on human evolution or evolution in general?
We touched it for half of a class period in biology, but that's it. Since I am not a bio major, I doubt I'll be taking anymore classes on it.

While I do believe in evolution, I am by no means an expert. I can hold my own in arguments as long as it doesn't become to detailed. So I definitely need more education on it.

I'd love to learn more but am not sure where to start. I searched a bit, but didn't find much.

Thanks.

 

[Phobos]

but are there any good books on human evolution

From Lucy to Langauge by Donald Johanson & Blake Edgar

...and of course any of the popular books by S.J. Gould and R. Dawkins. Carl Zimmer's book "Evolution" has a good, non-technical overview with a lot of history mixed in.

 

[Phobos]

Right, Darwin based his theory on the range of variation in living organisms. Think of the Galapagos Island voyage as the "pilot experiment" where he observed something on a small scale among a few species and developed an hypothesis based on those findings of what has happened on the larger scale, worldwide, across all species, and since the beginning of life on Earth.

For what it's worth, Darwin also discovered many fossils of extinct animals (variations of modern species) during his voyage on the Beagle which helped him formulate the theory (perhaps not in mechanisms, but emphasizing the idea of slow changes in species over time...an idea that was starting to take seed in the outskirts of the scientific community). Darwin didn't realize the significance of the Galapagos finches until he returned to England and had the specimens examined by an anatomy expert.

 

[selfAdjoint]

An important datum for Darwin was the homology between living species. This has been mentioned above, but the basic mammalian five digit extremities were known to be present in a whale's flipper (embedded deep inside as residual bones) and the bat's wing. And perhaps most strikingly the condensation of the five digits into the horse's single hoof (essentially a toe) could be followed in successive embryonic stages of the unborn colt. Darwin saw that this identity of pattern in the case of different functions was a strong evidence of common causal origin.