Final answer:
Charles Darwin(3) is the author who argued that living things have changed over time due to the struggle for limited resources in 'The Origin of Species'.
Step-by-step explanation:
The author who argued in The Origin of Species that living things have changed over time because of the struggle for limited resources was Charles Darwin(3). Darwin's theory of evolution by natural selection was influenced by his understanding that populations could potentially increase faster than the available resources, leading to competition and a 'struggle for existence'. His observations during the voyage of the HMS Beagle, as well as the writings of Thomas Malthus and Charles Lyell, contributed to his development of evolutionary theory.