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The following is based on part 12 of Jacob Bronowski’s BBC series on the history of science and invention, “The Ascent of Man” (1973). This one is about genetics:

Gregor Mendel was a farm boy who became monk. He joined the Augustinian order in Brno, the second largest city in what is now the Czech Republic. They sent him to the university of Vienna to get a teaching degree. The university said he “lacks insight and the requisite clarity of knowledge” and failed him in 1853.

A few years later he began to do experiments on pea plants. People assumed that if you cross a tall pea plant with a short one you get pea plants of middling height. Instead of assuming Mendel tried it: he found that you get nothing but tall pea plants! And if in turn you cross those tall pea plants you get 75% tall pea plants and 25% short ones.

Why? Mendel said it was because each plant gets a height particle – what we now call a gene – from each parent. In the first generation of his experiment, each plant had a tall gene and a short gene, so all of them were tall. But in the second generation one fourth received two short genes and so they were short.

He had discovered the gene, one of the greatest discoveries in the history of science. It sank like a rock. Mendel was a nobody: the important science journals in France and Britain did not print it. In 1866 he had it printed in a Brno science journal and there it sat unknown to the top people in science till 1900.

The next big discovery was printed in Nature in 1953, so it was known instantly worldwide: DNA and how it works. DNA is what genes are made of. James Watson and Francis Crick beat out Linus Pauling in discovering how it works.

DNA is a double molecule, each half the mirror image of the other half. When the molecule splits in two, each half can create its missing half. But there is more: it is a long molecule that contains smaller molecules called bases: adenine, guanine, cytosine and thymine. These become in effect the four letters – A, G, C and T – of the language that genes are written in, containing the instructions of how to build everything in the body.

But genes and DNA are not enough to account for life as we know it. You also need:

  1. Sex, which mixes genes in new ways. Till sex came along life did not progress beyond the level of pond scum.
  2. Human sexual selection, which speeds it up even faster: humans, compared to other animals, put far more thought into choosing who they have children with. They also have taboos against incest which prevents a few older males from getting all the females and lowering the rate at which genes mix.

As John Donne said:

Love’s mysteries in souls do grow
But yet the body is his book.

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