Exploration Insights Great Geos ebook | Page 51

Great Geologists | 51 Darwin’s explanation of the formation of coral atolls. Top figure: lower solid line, stage 1, a fringing reef (AB) abuts the shoreline. Island sinks (because of subsidence) to upper dotted line, stage 2, barrier reef (A’) separated from sinking island by lagoon (C). Bottom figure: lower solid line, stage 2 barrier reef (as for upper figure). Island sinks further to upper dotted line, stage 3, an atoll (A’’), enlarged lagoon (C’) marks previous location of sunken island. From The Structure and Distribution of Coral Reefs (1842). returning home, Darwin started a new notebook dedicated to capturing his developing ideas on evolution, by 1842, a ‘first-sketch’ of the natural selection theory was complete. An important development was Darwin’s reading of Thomas Malthus’ work on population expansion, an intellectual concern in the 19th Century. In his autobiography, Darwin notes, “In October 1838 … I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence that everywhere goes on from the long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances, favourable variations would tend to be preserved and unfavourable ones to be destroyed. The result of this would be the formation of new species”. This is the essence of natural selection! In a given ecological niche, competition to survive would favour any characteristic that would confer an advantage on offspring. Over time, these characteristics would increase, resulting in a form that was distinctly different from its remote ancestors. Using his documentation from the Beagle’s expedition, Darwin established himself in scientific society in London with the publication of Journal of Researches (1839). In 1842, needing peace and privacy in which to work and suffering from progressively ill health, Darwin and his wife Emma Wedgwood (his first cousin) moved to Down House in Kent. There, surrounded by a growing family (ten children, seven of whom survived to adulthood), he worked for just two or three hours each day in isolation from the normal cares of the world, but in correspondence with scientists from across the globe on a huge range of topics. Despite this limited work schedule, his output was immense.