A Study of the Results of Scientific Research in Relation to the Unity or Plurality of Worlds. With 8 diagrams in the text and 2 charts at the end. First published in 1903 and reprinted from the third edition of 1904. This work was the first serious attempt by a biologist to evaluate the likelihood of life on other planets, which drew the conclusion that Earth was the only planet in the solar system that could possibly support life mainly because it was the only one in which water could exist in the liquid phase. Wallace (1823-1913) was a British naturalist, explorer, geographer, anthropologist and biologist. He is best known for conceiving the theory of evolution through natural selection - his paper on the subject being jointly published with some of Charles Darwin's wrtings in 1858. He was the 19th century's leading expert on the geographical distribution of animal species and his interest in natural history resulted in his being one of the first prominent scientists to raise concerns over the environmentall impact of human activity. Aside from his scientific work he was a social activist who was critical of what he saw as an unjust social and economical system, and he was a prolific writer on both scientific and social issues.