neo-Darwinism is the modern synthesis of Charles Darwin's theory of 📝evolution by natural selection with Mendelian genetics and population biology, framing evolutionary change as gradual shifts in gene frequencies driven primarily by selection acting on random mutation.
The synthesis crystallized in the early-to-mid 20th century through the work of Fisher, Haldane, Wright, Dobzhansky, Mayr, and Huxley, and dominated evolutionary thought for the rest of the century. It treats the individual organism as the unit of selection and gradual mutation as the engine of variation, marginalizing mechanisms outside the gene-selection frame.
📝Lynn Margulis was among neo-Darwinism's sharpest critics, arguing that symbiosis and horizontal gene transfer — not just mutation — drive major evolutionary transitions. Her case is the spine of 📝Symbiotic Earth and a sustained counter-frame to the gene-centric orthodoxy.