Thursday, February 12, 2009

Darwin in Context

I've been trying to figure out what to write about for my Blog for Darwin entry. I've been reading Origin, but I haven't finished it yet (the last few chapters are not nearly as interesting as the first few). Even so, as I've been reading, I haven't really been struck with any brilliant insights or profound thoughts. One thing that has occurred to me a lot, however, is just how much we've learned since Darwin's time. So, I thought that for my BfD contribution, I would outline what was going on in science while Darwin was doing his thing. I'm hoping it might give some insight into what Darwin did and didn't know, and how his ideas may have been influenced by what was going on around him.

Disclaimer: I am not a historian; the summary below is not intended to be exhaustive. I'm mainly going to focus on the big ideas and events; if you're interested in the gory details, there are a plethora of excellent books out there to satisfy you, I'm sure. Also, please note that I've done my best to verify all of the information below, but I'm not an expert in this stuff. Any errors are solely my responsibility. If you find any, please let me know!

By the 1800s, the study of chemistry was becoming modernized. In the 1600s and 1700s, naturalists began to discover general laws that govern natural processes. Both Boyle's law and Charles's law (on the properties of gases) had been discovered by the early 1800s; a number of gaseous elements and compounds (including oxygen, nitrogen, and nitrous oxide) had been isolated and described.

John Dalton proposed his atomic theory in the early 1800s; although his concept of the atom (i.e., hard, solid, indivisible sphere) has since been replaced, his work on the conservation of mass and the law of definite proportions still underlies much of modern chemistry. His law describing the partial pressures of gases in a mixture is still used today.

The early 1800s also saw the publication of Avogadro's hypothesis (i.e., that equal volumes of gases at the same temperature and pressure contain the same number of molecules).

In the mid 1800s, Lord Kelvin proposed the idea of absolute zero and an absolute temperature scale.

What Darwin didn't know: Most elements were not identified or isolated until after the 1860s. Electrons were not discovered until the late 1800s; the concept of the atom as we know it today (i.e., nucleus of protons and neutrons surrounded by electrons) was not developed until the twentieth century. The nature of chemical bonding was also unknown in Darwin's time, as was the periodic table and the notion of periodic properties.

Electricity and magnetism were the order of the day in eighteenth and early nineteenth century physics. Franklin "discovered" electricity in the late 1700s; Ohm's law was proposed in the 1820s; Oersted discovered evidence of a magnetic field around a current-carrying wire in 1820; Faraday discovered electromagnetic induction in the 1830s; Joule and Helmholtz proposed the law of conservation of energy in the 1840s.

Newtonian mechanics were well established by the 1800s.

What Darwin didn't know: Radioactivity, quantum physics, relativity, and nuclear physics were decades to centuries away in Darwin's time.

As Origin does a pretty decent job of summarizing what was going on in evolutionary biology (such as it was) at the time it was written, I won't spend space on that here. In the mid-1800s, the idea that all living things are made of cells was just beginning to take hold; spontaneous generation was beginning to be discredited. Taxonomy was becoming more rigorous. Paleontology was starting to become a well-established field; most naturalists accepted that the majority of the fossils being unearthed around the world represented organisms that no longer exist.

What Darwin didn't know: Genetics and the theories of inheritance had not been discovered when Darwin did his work; a story I've heard (which I have not verified) is that Darwin had Mendel's papers on his desk when he died. Molecular biology, most of microbiology, and, of course, genomics were completely unknown. The germ theory was still a few years off, as was the discovery of many disease-causing microorganisms.

Earth Science
Naturalists were just beginning to come to grips with Earth's immense age during the late 1700s and early 1800s. The best consensus was that Earth was a few hundred million years old at most; these estimates were based on rates of physical processes (such as sedimentation and cooling). Radioactivity was unknown, so both a method for accurate dating and a mechanism for keeping Earth "warm" for long periods of time were lacking.

However, the principle of uniformitarianism was pretty well accepted, having been proposed in the late 1700s. As I mentioned above, paleontology was becoming more rigorous and "scientific," although some of the interpretations of fossils--especially dinosaurs--were rather interesting.

The idea of a global geologic column or time scale was becoming increasingly popular. Indeed, Darwin makes many references to the accepted contemporary time scale (although the time scale of the mid-nineteenth century bears little resemblance to our modern one).

What Darwin didn't know: The theory of plate tectonics was still about a century away. Radiometric dating (and an understanding of how radioactive decay has heated the planet) wouldn't be developed for quite a while, so Earth's true age was unknown to Darwin. In addition, research into the fossils and strata of the planet was generally restricted to Europe and North America, so Darwin's (and everyone else's) ideas about geologic history (and paleontology) were accordingly limited.

Well, there you have it: the two-bit tour of the state of science in the 1860s. I hope this is helpful to someone. If I had time, I'd go into more detail...yet another item to add to my "things to do when I win the lottery" list!


Tony Wildish said...

This is a very interesting post, thank you. Knowing the context is so important for understanding the process behind the science, which in turn is important for understanding the science itself.

I recently read Darwin's book on Coral Reefs, and not knowing how much he understood about plate tectonics or the true age & history of the earth made it harder to assess it.

NewtonsOcean said...

Hi Kate - thanks for giving Darwin and Origin some nice context in terms of the state of scientific knowledge in the first half of the nineteenth century. It must have been a fascinating time to live in, with fields like chemistry and geology only really taking on a solid foundation around then. Re my earlier suggestion of swapping ideas to get a bigger science crowd visiting - so far this Blog for Darwin gig hasn't done much for me but I guess one keeps plugging away! Anyway, I'll start visiting you regularly and will update my blog list soon...

Kate Porter said...

Thanks! I'm glad you both found it interesting. I would have liked to have spent a bit more time on it and gone into more detail, but the time just wasn't there.

Tony, I'm having similar problems with Origin--I keep having to remind myself of what he did and did not know. The thing that's throwing me most is the geologic time scale. The names and terminology used back then were very different from those used today.

Newton--well, I got one new commenter out of it, anyway! (Thanks, Tony!) I think the only way to get on is just to keep writing.