Thursday, June 13, 2013

Benjamin Franklin And Erasmus Darwin: Musings About Geology and Evolution

I am reading When You Were A Tadpole and I Was A Fish  by Martin Gardner. It is a collection of essays on science and culture. There is a really good one on the complex personality of Isaac Newton, another one on Ann Coulter's rants against evolution and quite a bit of writing on debunking paranormal claims. I haven't yet finished the entire book with some chapters on literature and religion still unread. I am not sure they will hold my interest as there is more critical dissection of literary figures like Chesterton and a long explanation on why he (Mr. Gardner) is not an atheist than I care to read about.

In one of the chapters Mr. Gardner gives a list of anticipations made by famous figures about how the world works which have turned out to be right, although not in all details. The larger point he is making throughout the book is the lack of evidence for clairvoyance. People are making predictions all the time. Most of them turn out to be wrong. We however tend to remember and wonder only at the tiny fraction that turn out to be correct.

He off course does not categorize Benjamin Franklin and Erasmus Darwin as people making loose predictions. They were both far better thinkers than your run of the mill soothsayers and fortune tellers. Their musings were serious attempts to understand natural processes and were not just opportunistic attention grabbing stunts.

This is Benjamin Franklin in a letter to Abbe Soulaive, September 22, 1782:

"Such changes in the superficial parts of the globe seemed to be unlikely to happen if the Earth was solid to the centre. I therefore imagined that the internal parts might be a fluid more dense, and of greater specific gravity than any of the solids we are acquainted with; which therefore swim in or upon that fluid. Thus the surface of the globe would be a shell, capable of being broken and disordered by the violent movements of the fluid on which it rested."


In current plate tectonic thinking, the shell are the rigid plates made up of the crust and the upper part of the mantle, and the internal parts are the mantle asthenosphere. We know today that the interior of the earth (asthenosphere) is not a fluid but a solid that behaves like a very viscous fluid, in that it deforms and convects in a viscous manner. The superficial parts of the globe i.e. the rigid tectonic plates move and jostle atop this viscous solid.

And a passage from Zoonomia written in 1794 by Erasmus Darwin, Charles Darwin's grandfather:

"Would it be too bold to imagine that, in the great length of time since the world began to exist, perhaps millions of ages before the commencement of the history of mankind-- would it be too bold to imagine that all warm-blooded animals have arisen from one living filament, which the great First Cause imbued with animality, with the power of acquiring new parts, attended with propensities, directed by irritations, sensations, volitions, and associations, and thus possessing the faculty of containing to improve by its own inherent activity and of delivering down these improvements  by generation to its posterity, world without end?"

Erasmus Darwin appears to flirt with common descent by imagining that all warm-blooded animals have arisen from one living filament or ancestor. He was wrong about the mechanism of evolution though. Inheritance of acquired characters is not how evolution works. Why organisms vary and how those variations are inherited was not understood then. Most of the non-mystical explanations converged on the idea that organisms changed by interacting with the surroundings, with features that were used more becoming prominent and then strongly inherited, while those in disuse slowing dying away. Jean Baptiste Lamarck made this idea of use and disuse and inheritance of acquired features popular, although Erasmus Darwin also seems to be thinking along similar lines and his thoughts appeared a good 15 years or so before Lamarck published his ideas on evolution in Philosophie Zoologique in 1809.

The title of the book is taken from a poem entitled Evolution by the journalist Landon Smith whose career spanned the late 1800's to early 1900's. Mr. Gardner has paid a long tribute to him. I will reproduce only the first few lines of his poem:

When you were a tadpole and I was a fish,
In the Paleozoic time,
And side by side on the ebbing tide
We sprawled through the ooze and slime,
Or skittered with many a caudal flip
Through the depths of Cambrian fen,
My heart was rife with the joy of life,
For I loved you even then.

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