On the spiritual theory, man consists essentially of a spiritual nature or mind intimately associated with a spiritual body or soul, both of which are developed in and by means of a material organism.

Darwin emphasised competition between individuals of the same species to survive and reproduce whereas Wallace emphasised environmental pressures on varieties and species forcing them to become adapted to their local environment. Although Lyell could not agree he urged Darwin to publish to establish priority. The cybernetician and anthropologist Gregory Bateson would observe in the 1970s that though writing it only as an example Wallace had "probably said the most powerful thing that'd been said in the 19th Century".

He is best known for independently conceiving the theory of evolution through natural selection which prompted Charles Darwin to publish his own ideas in On the Origin of Species. Wallace was a prolific author who wrote on both scientific and social issues; his account of his adventures and observations during his explorations in Singapore Indonesia and Malaysia The Malay Archipelago is regarded as probably the best of all journals of scientific exploration publiAlfred Russel Wallaced during the 19th century. Wallace was strongly attracted to unconventional ideas.