Lamarck vs Darwin: Two Theories of Inheritance

Before Darwin, Jean-Baptiste Lamarck proposed that organisms pass on traits acquired during their own lifetime — a giraffe that stretches its neck to reach high leaves would have offspring born with a slightly longer neck. Darwin's natural selection instead says the variation was already present in the population before any environmental pressure acted, and the environment simply decides who survives to reproduce. This simulator runs both rules as real generational update equations over the same starting population of 40 animals with neck length drawn from a normal distribution, so you can watch — not just read — how the two mechanisms produce different population trajectories: Darwin filters existing variation through differential survival, while Lamarck grows every individual toward the target and inherits the acquired result directly, with no death at all.