Darwin’s Aeolian Dust
(In which we escape Covid-19 for 1831)
We need a break from Covid-19, that miserable virus. There was science before it and there will be science after it, but for now, a scientific voyage at sea is just the escapism, we, or at least I, am after. So let’s join Charles Darwin and Captain Robert FitzRoy on HMS Beagle.
The Beagle, a ten-gun bark, was to sail from Devonport on December 27, 1831, with Admiralty orders to sample the flora and fauna of Tierra del Fuego and Patagonia, to survey the West Coast of South America and the Galapagos and then sail home across the Pacific and westward. The voyage was to last five years and Captain FitzRoy thought a naturalist was essential for a full examination of these regions.
Captain Francis Beaufort, creator of the Beaufort scale of wind force, was charged with finding a naturalist and through connections he found Charles Darwin, a recent graduate of Cambridge University. Charles was eager to see the watery parts of the world and signed on. He was educated, wealthy, and had the social status to dine with the austere Captain FitzRoy. When the Beagle sailed into the English Channel, Charles Darwin was 24.
On January 16, 1832, the Beagle anchored off Porto Praya, the largest of the Cape Verde Islands. Looking at the desolate island as it rose from the sea, Darwin noted a cliff, with a white band about 45 feet above the water. He found that it was full of shells which were identical to living mollusks in the sea below. Science begins with people who ask: How did those marine shells get 45 feet above the sea? And when did it happen? The rock below the shells was igneous and formed from volcanic activity of which there was no recent evidence. He reasoned that the shells had been lifted from the sea a long time earlier. Later, in the Andes, he found marine shells imbedded in rock thousands of feet above sea level. Darwin was a collector of odd observations that later in life, he synthesized into the fundamental theory of biology. The theory of evolution requires immense time, great diversity in a population, and natural selection of heritable advantageous characters. The shells were one of many observations that convinced Darwin and others that the world was old and had dramatically changed over time.
While still at sea, not far from Porto Praya, Darwin noted that the Beagle’s sails were coated with fine dust. That also seemed odd; it was a known phenomenon, but odd, nonetheless. Such dust was called aeolian, carried on the wind, from the Sahara, we now know. Darwin scraped some dust into a glass tube, which he sealed and sent to Christian Gottfried Ehrenberg at the Prussian Academy of Sciences in Berlin. Ehrenberg’s collection of aeolian dusts has survived wars and devastation. It is now housed in the Museum of Natural History in Berlin, including the tube that Darwin sent.
Museum curators do not hand this stuff out easily, but molecular microbiology only needs a few milligrams to learn if there were any living organisms trapped in the Beagle’s dust. There were many forms and they had been dormant since 1831; Darwin called them infusoria, a generic and somewhat archaic term for small organisms. Whether fungi or bacteria, they all formed spores with thick coats that had evolved to resist high temperatures and dry climates. Given moisture and nutrients, the spores awake from their slumber and cells emerge and grow. The ability to form a spore when life gets tough is a handy trick for a cell to have. Darwin was interested in how organisms survive and are distributed.
The finches and tortoises in the Galapagos had evolved specializations because they lived isolated on separate islands. The reason that life is organized into species is that useful combinations of genes, say the ones that control beak shape, are kept together. Hence, the finches each had beak unique to their own island and food supply. The isolation provided by islands was key to Darwin’s thoughts on the evolution of species.
When The Origin of Species was published in 1859, then Admiral FitzRoy, believed that the world was a Biblical 6000 years old. Darwin, whom he had ferried around the world, had forced a retreat from the idea of a young world with static land masses and species that do not change. The clash led to a debate in 1860, that still roils the world. Darwin’s position was argued by Thomas Huxley and the case for a young divinely created earth and its unchanging species was argued by Anglican Bishop Samuel Wilberforce. Others participated, including Admiral FitzRoy, who declared that he should never have taken Darwin on the Beagle. Too late.