Natural Selection – Evolutionary Mechanism of Biological Change. Darwin was not the first to understand that organisms evolve or change over time. His crucial contribution was in identifying the mechanism of change, natural selection.
Charles Darwin’s Voyage
The HMS Beagle
After graduating in 1831 with a respectable degree in theology from Cambridge, Charles Darwin went on to pursue his life-long interest in the natural world. Much to his father’s dismay, the 22-year old graduate joined a British Naval mapping expedition aboard the H.M.S. Beagle as an unpaid naturalist and companion for the aristocratic captain, Robert Fitzroy.
During this voyage, Darwin gained the knowledge that eventually led to his assertion that natural selection is the driving force of evolutionary change, and there were several key pieces of information that led him to this conclusion.
Charles Lyell & Uniformitarianism
The HMS Beagle was to sail around the world on what would ultimately become a five year long voyage. During this long passage, Darwin read the early books of Charles Lyell and became convinced that Lyell’s theory of uniformitarianism provided the correct interpretation of the earth’s geological history.
Lyell, an English lawyer and geologist, had carefully examined European geological deposits and concluded that geological transformation most commonly occurred through the accumulation of progressive changes over long periods of time rather than through sudden, catastrophic events.
Lyell documented the fact that the earth must be extremely old, and that throughout time, the planet has continually undergone processes that change and shape the land, including erosion, earthquakes, glacial movements, volcanoes, and even the decomposition of dead plants and animals.
Darwin’s readings and research on the voyage were critical factors that lead him to accept biological evolution, which was an idea that had already been proposed by others. But Darwin still wondered how exactly did evolution occur? What was the cause or driver of evolutionary change?
During the expedition, he spent 5 weeks in the Galápagos archipelago of the Eastern Pacific Ocean. On these isolated islands Darwin began to comprehend the factors that cause plants and animals to evolve over time, but apparently did not clearly formulate his views on the mechanism of biological change until after the voyage ended in 1836.
The Final Piece of the Puzzle
Thomas Malthus & Population
In 1798, Thomas Malthus, an English clergyman and economist, published Essay on the Principles of Population. In this paper he explained that human populations will double every 25 years unless population growth is kept in check by a limited food supply.
In 1838, Darwin read Malthus’ essay and came to realize that all plant and animal populations have this same potential to rapidly increase in number unless they are limited by biological and physical factors in the environment, such as predators, diseases, access to food and water, as well as other resources essential for survival.
Darwin’s readings on population dynamics were pivotal in spawning his discovery of natural selection as the mechanism for evolutionary change. Darwin realized that, in any given population, the individuals that are “most fit” (best adapted to a specific environment) are least likely to die of starvation and, therefore, most likely to pass on their traits to the next generation. In this way, over time, environmental factors can essentially mold the characteristics of a population.
Origin of Species
It wasn’t until 1858 that Charles Darwin and Alfred Wallace released a joint scientific paper introducing the concept of evolution by means of natural selection. This paper, along with Darwin’s subsequent publication, The Origin of Species, changed the way science and society explain the natural world.