Estonian astronomer Ernst Öpik postulates that long-period comets originate in an orbiting cloud (the Öpik–Oort cloud) at the outermost edge of the Solar System. Biology  English geneticist C. D. Darlington publishes Recent Advances in Cytology, describing the mechanics of chromosomal crossover and its role in evolutionary science. English geneticist J. B. S. Haldane publishes The Causes of Evolution, unifying the findings of Mendelian genetics with those of evolutionary science. American physiologist Walter Bradford Cannon publishes The Wisdom of the Body, developing and popularising the concept of homeostasis. A flock of Soay sheep is translocated from Soay to Hirta (also in the depopulated archipelago of St Kilda, Scotland) by conservationist John Crichton-Stuart, 4th Marquess of Bute. The heath hen becomes extinct in North America. Earth sciences  Braggite is first described, the first mineral discovered with the assistance of X rays. Mathematics  Menger-Nöbeling theorem. John von Neumann makes foundational contributions to ergodic theory in a series of papers.
Estonian astronomer Ernst Epic postulates that long-period comets originate in an orbiting cloud (the Epic–Port cloud) at the outermost edge of the Solar System. Biology
 English geneticist C. D. Darlington publishes Recent Advances in Cytology, describing the mechanics of chromosomal crossover and its role in evolutionary science. English geneticist J. B. S. Haldane publishes The Causes of Evolution, unifying the findings of Mend Elian genetics with those of evolutionary science. American physiologist Walter Bradford Cannon publishes The Wisdom of the Body, developing and popularizing the concept of homeostasis. A flock of Soya sheep is translocate from Soya to Heart (also in the depopulated archipelago of St Kilda, Scotland) by conservationist John Crichton-Stuart, 4th Mia of Butte. The heath hen becomes extinct in North America. Earth sciences
 Brigitte is first described, the first mineral discovered with the assistance of X rays. Mathematics
 Menger-Nöbeling theorem. John von Neumann makes foundational contributions to erotic theory in a series of papers.