He was born in Moscow. He had two brothers Vasily (1904) and Andrei (1911) and a sister Tatyana (1908) (two born sisters died in infancy). His father (Nikolai Vasilyevich Nesmeyanov), graduated with excellence Vladimir Gymnasium, and then the Faculty of Law of Moscow University. He became interested in enlightenment and was working as a public teacher in the village of Bushov (Tula province) for 10 years. He had married in 1898 and worked at the Moscow city government, then he was a director Bakhrushinsky orphanage in Moscow (1901 – 1917). Alexander's mother, Lyudmila Danilovna (1878 – 1958), was a multi-talented teacher. At ten years Alexander became a vegetarian, and in 1913 he stopped eating fish. It was not easy to follow this conviction, especially in the famine years of 1918 – 1921, when roach and herring were an essential food product. He had become interested in various branches of biology: entomology, hydrobiology, ornithology and from the age of thirteen became interested in chemistry.