Ivan Ivanovich Schmalhausen (Russian: ???´? ???´????? ???????´????; April 23, 1884 – October 7, 1963) was a Russian and Soviet zoologist and evolutionary biologist of German descent.
He developed the theory of stabilizing selection, and took part in the development of the modern evolutionary synthesis.He is remembered, among other things, for Schmalhausen's law, which states that a population at its limit of tolerance in one aspect is vulnerable to small differences in any other aspect.