As a description of biology, Kropotkin's perspective is consistent with contemporary understanding. Stephen Jay Gould admired Kropotkin's observations, noting that cooperation, if it increases individual survival, is not ruled out by natural selection, and is in fact encouraged.[6] Kropotkin's ideas anticipate the now recognized importance of mutualism (a beneficial relationship between two different species) and altruism (when one member of a species aids another) in biology.