Evolution is the gradual change in the inherited characteristics of a population over many generations. The theory of evolution by natural selection was proposed by Charles Darwin and Alfred Russel Wallace, who reached the same idea independently. Darwin set it out in detail in his book On the Origin of Species, published in 1859.Darwin based his theory on observations, including those made on his voyage on HMS Beagle, such as the finches of the Galapagos Islands, which differed in beak shape from island to island.Observations:
• organisms produce far more offspring than can survive
• population sizes stay roughly constant over time
• individuals of a species vary
• much of this variation is inherited by offspring.Deductions:
• there is a struggle for existence: individuals compete for limited resources such as food, mates and space, and many die
• individuals with characteristics better suited to the environment are more likely to survive and reproduce ('survival of the fittest')
• they pass on these advantageous characteristics to their offspring
• over many generations, the advantageous characteristics become more common, so the population changes. This is evolution.Given enough time, populations of one species in different environments can change so much that new species form.Darwin did not know how characteristics were inherited, because genes and DNA had not been discovered. His theory was later combined with genetics, as the next lesson explains.
• organisms produce far more offspring than can survive
• population sizes stay roughly constant over time
• individuals of a species vary
• much of this variation is inherited by offspring.Deductions:
• there is a struggle for existence: individuals compete for limited resources such as food, mates and space, and many die
• individuals with characteristics better suited to the environment are more likely to survive and reproduce ('survival of the fittest')
• they pass on these advantageous characteristics to their offspring
• over many generations, the advantageous characteristics become more common, so the population changes. This is evolution.Given enough time, populations of one species in different environments can change so much that new species form.Darwin did not know how characteristics were inherited, because genes and DNA had not been discovered. His theory was later combined with genetics, as the next lesson explains.