The Darwin of 20th century is Ernst Mayr.

Ernst Mayr was a German-American biologist and ornithologist who is considered as the "Darwin of 20th century" due to his significant contributions to the field of evolutionary biology. He was born in 1904 in Kempten, Germany and died in 2005 in Bedford, Massachusetts, United States.

Contributions to Evolutionary Biology:

1. Biological Species Concept: Mayr introduced the Biological Species Concept which defined a species as a group of individuals that can interbreed and produce viable offspring. This concept is widely accepted in the field of evolutionary biology.

2. Evolutionary Synthesis: Mayr played a crucial role in the development of the Evolutionary Synthesis, which was a unification of genetics and evolutionary biology. He proposed that the evolution of new species occurred due to the accumulation of genetic changes over time.

3. Geographic Speciation: Mayr proposed the theory of geographic speciation, which suggests that the formation of new species occurs when a population is geographically isolated from the parent population.

4. Ornithology: Mayr was also an accomplished ornithologist and contributed significantly to the study of bird species. He proposed the theory of allopatric speciation in birds, which suggests that the formation of new bird species occurs due to geographic isolation.

5. Systematics: Mayr made significant contributions to the field of systematics, which is the study of the classification of living organisms. He proposed the concept of "cladistics", which is a method of classification that groups organisms based on their evolutionary history.

Conclusion:

Ernst Mayr's contributions to the field of evolutionary biology have had a significant impact on our understanding of the process of evolution. His work has helped to shape the field of evolutionary biology and has influenced generations of biologists. Therefore, it is justified to consider him as the "Darwin of 20th century".