The correct answer is Option (3) –Darwin

The theories of "struggle for existence" and "survival of the fittest" are associated with Charles Darwin.

Darwin, in his theory of evolution through natural selection, proposed that within a population, individuals with advantageous traits that better suit their environment tend to survive and reproduce more successfully than those with less favorable traits.The struggle for existence refers to the competition for resources and survival among individuals of a species.

Lamarck, another evolutionary theorist, proposed the theory of inheritance of acquired characteristics, suggesting that an organism can pass on characteristics that it acquired during its lifetime to its offspring. However, Lamarck's ideas differ significantly from Darwin's theory of natural selection.

Alfred Russel Wallace, a contemporary of Darwin, independently arrived at similar conclusions about natural selection and the mechanism of evolution. He co-published a joint paper with Darwin on the subject. While Wallace made significant contributions to evolutionary theory, the concepts of the struggle for existence and survival of the fittest are more commonly associated with Darwin's work.