How did Herbert Spencer’s theory of evolution differ from Charles Darwin’s early theory?

Herbert Spencer’s early theory of evolution differed significantly from the views held by Charles Darwin and Alfred Russel Wallace. While Darwin and Wallace identified natural selection as the primary mechanism for biological evolution, Spencer initially attributed evolutionary change to the inheritance of acquired characteristics.1

Spencer’s approach was also fundamentally different in methodology. He favored a deductive, philosophical style of reasoning to explain development across cosmic and biological realms, whereas Darwin relied on an empirical, scientific framework supported by extensive evidence. Spencer’s broader "synthetic philosophy" sought to unify knowledge under a "law of the multiplication of effects," viewing evolution as a process of increasing variety arising from homogeneous states.12

Although Spencer later accepted natural selection as a contributing factor in biological evolution, his earlier focus on acquired traits and his speculative, deductive approach remained distinct from Darwin’s rigorous scientific method. Furthermore, Spencer is famously associated with the term "survival of the fittest," which he applied to social and economic spheres, a concept that Darwin later incorporated into his own work.123