The Voyage of
HMS Beagle
by Charles Darwin
***
As the Royal Navy’s HMS Beagle made its way around South
America in the mid-1830’s, frequently dropping off its on-board geologist,
Charles Darwin, to make inland excursions inland, Darwin had time to wonder
about the strange fossils he was collecting along river banks. What were they? And
what had happened to sweep them from the earth?
The sheer numbers of
fossils troubled him. He struggled to accommodate the huge quantities of bones,
seemingly produced by the catastrophic deaths of large numbers of animals, with
his enthusiasm for Scottish geologist Charles Lyell’s theory of gradual change
over time.
“The number of the remains
embedded in the grand estuary deposit which forms the Pampas and covers the
granitic rocks of Banda Oriental, must be extraordinarily great. . . Besides
those which I found during my short excursions, I heard of many others, and the
origin of such names as ‘the stream of the animal’, ‘the hill of the giant’, is
obvious,” he wrote in his journal of the voyage of the Beagle.
Darwin published his
records in two editions, in 1839 and 1845. The 1957 collectible edition I’m
working from is based on the 1845 edition, when Darwin was well on his way to
puzzling out his theory of evolution based on natural selection. Some of the
South American fossils, such as the extinct giant sloths, were obviously
related to still living relatives. But what to make of creatures such as the Macrauchenia, looking like a humpless
camel with a long snout, whose 1913 reconstruction illustrates this post? Or
the Toxodon, with a rhinocerous-like
body and rodent-like teeth, whose skull he bought for 18 pence, which when
found “was quite perfect; but the boys knocked out some of the teeth with
stones, and then set up the head as a mark to throw at.”
It would require 21st
century science to place the giant grazers in the family trees Darwin was
starting to create, Scientific American
magazine reported March 20, 2015, in “Mystery of Darwin’s ‘Strange Animals’Solved.”
Initially researchers trying
to place the animals’ relationships were stumped by a lack of DNA, which
degrades quickly in the South American climate. Instead, an international team
used a different tactic, extracting collagen protein, to at last give two of
Darwin’s mysterious mammals their place in the family tree of mammals.
“Part of a group of more
than 250 mammals known as the South American ungulates,” Scientific American reported, “the creatures lived on the continent
for around 60 million years before disappearing around 12,000 years ago.”
Purely on the basis of
their fossils’ physical appearance, some had been suspected them of being
related to elephants. Darwin himself suggested a possible link between the
camel-like Macrauchenia and surviving
llama-relatives, the wild guanacos of the pampas. But after sequencing proteins
from two museum specimens of Toxodon
and two of Macrauchenia, scientists
finally placed them in a group that includes horses, tapirs and rhinos.
And what caused their
disappearance after millions of years of survival? I’m going to suggest a
catastrophic cause undreamed of by Darwin – the arrival of humans on the South
American continent.
(Next Friday, Adventure
classics puts Darwin back on board ship, to continue an August of adventures at
sea.)
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