who is the second mentioned person?
He was an evolutionary biologist,  taxonomist, tropical explorer, ornithologist, philosopher of biology, and historian of science.
Ernst Mayr
Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, philosopher of biology, and historian of science
when are organisms considered to belong to the same species When any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Some other ways of defining them include their karyotype, DNA sequence, morphology etc. how are they defined as? A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. was there any scientists who contributed to this classification? Some of the early ones include Linnaeus, Ernst Mayr, R. L. Mayden and John Wilkins.
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Ernst Mayr [SEP] Introduction
Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, philosopher of biology, and historian of science. His work contributed to the conceptual revolution that led to the modern evolutionary synthesis of Mendelian genetics, systematics, and Darwinian evolution, and to the development of the biological species concept. Although Charles Darwin and others posited that multiple species could evolve from a single common ancestor, the mechanism by which this occurred was not understood, creating the "species problem". Ernst Mayr approached the problem with a new definition for species.