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Archive for the tag “palaeontology”

The time-averaging thing…

The palaeontologists that taught classes in the university I attended (UPMC, Paris VI), always told us we should be cautious while studying any fossil assemblage because it is important to take “time-averaging”* into consideration. It is very important, they told us, and I thought that I had understood it (as did my classmates). This until last week when I found an article by Michal Kowalewski (1996) on the subject, and I found out that the theory of the matter is very complicated.
I am not going to discuss the details, but what I wanted to put forward is the concept and theoretical work that had to be done in order to establish the notion of time-averaging and how it works. It is indeed quite complicated and shows that it is necessary to work on what I’d call theoretical geology.

 

*time-averaging: the fossils contained in a single sedimentological layer haven’t died and fossilised synchronously. Also, the different organisms that are found fossilised, don’t have the same fossilisation potential. This can create various problems while studying the assemblages, and the studies that have been carried out concern all the aspects of this phenomenon.

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George Gaylord Simpson.

G. G. Simpson is one of the greatest and most influential palaeontologists of the 20th century for several reasons: the evolution of horses is a very well known example of his work, as well as his contribution on the modern evolutionary synthesis.

I remember though, during palaeontology and/or evolution classes, the professors telling us repeatedly that we had to know and remember Simpson, but without ever telling us precisely why. It was only after a while that I came across one of his books in a little naturalistic bookstore right beside the University of Jussieu. It was an old book, published in French in 1951: “The meaning of evolution”, it was originally published in English in 1949.

First of all it is quite curious and pleasant to see that so shortly after the end of the Second World War the interest in palaeontology and evolution was such that this book was translated and published.

More importantly, while reading it, I realized that almost all of its content was the bigger part of everything that is taught in palaeontology classes (the principle of vicarience, speciation, migrations, the orientation of evolution and its trends, radiations, evolutionary factors and their impacts, …) . Only then did I understand his contribution to modern palaeontology, the importance of his life’s work, and how he established all the bases in the paleontological studies.

Evolutionary Epigenetism: why do we still mention it?

I was at the lab (UOA) looking for bibliography on the Pliocene of Greece, when  I found a copy of a rather old book on Evolutionary Paleontology (“Paléontologie Evolutive” of Jean Roger, 1976). It caught my attention, not only because it is one of my favorite subjects, but also because from what I’ve seen, Evolutionary Paleontology is and has been taught in different ways.

In the summary I found a lot of things that I’ve learned in relevant lectures, but there was one or two things that really got my attention. So here is my question: why do we still talk about evolutionary epigenetics?

Yes, in genetics classes we’ve learned that there are modifications of the genes after they’re transcripted into mRNA, and we’ve been told that this is one epigenetic mechanism. But, what is the relation between this and the evolutionary theories of epigenetics?

The book enlightened one first point, in the chapter on the mechanisms of evolution there is one part about the epigenetic theory. The author quotes P.P. Grassié: “an evolutionary necessity is the acquisition of new genes”. And later on we find another quote by S. Ohno (1970): “natural selection, much like a “policeman” is extremely conservative; if evolution depended only on this, from Bacteria could be obtained only many other forms of Bacteria. The creation of Metazoans, Fish, Mammals would be almost impossible without the creation of new genes.” No further explanation by the author. This is epigenetic evolution. The lack of further knowledge on genetics, genes duplication, the fact that natural selection is able to produce new genes, horizontal transfer etc. generated this idea that there are other mechanisms that produce diversity, independent from Darwin’s evolutionary theory. It does seem a little like an ensemble of speculations, because there is no specific proposition of a precise epigenetic mechanism. Also, and very wisely, the author does not take any sides, and waits for further research for an answer on the importance and the existance of such processes.

Modern epigenetics do not have the same evolutionary dimension.

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