Final answer:
Charles Darwin and Alfred Russel Wallace independently developed the theory of natural selection, which explains the evolution of species through inheritable advantageous traits. The integration of Mendel's genetic principles with this theory led to the modern synthesis, which provides a comprehensive explanation of adaptive evolution.
Step-by-step explanation:
The theory of natural selection, the cornerstone of evolutionary psychology, was postulated by Charles Darwin and Alfred Russel Wallace. These scientists observed patterns of variation within organisms that gave certain individuals an advantage in survival and reproduction over others. These advantageous traits would then be more likely to be passed down to future generations, leading to a population evolving over time. The concept that supported these observations were that traits are heritable, there is competition for resources due to excessive population growth, and that there is variation in traits which affects survival and reproductive success. These principles are fundamental to the theory of natural selection, where only the fittest individuals for the environment will survive and reproduce, spreading their traits in the population.
Darwin and Wallace presented their ideas in 1858 and Darwin's seminal work, On the Origin of Species, was published in 1859 detailing this theory. However, they were not aware of Gregor Mendel's work in genetics, which later provided the understanding of how traits are passed down through generations. The integration of genetics with the theory of evolution resulted in what is known as the modern synthesis, combining the ideas of natural selection and genetic inheritance to explain adaptive evolution.