An idea advanced in 1896 by US psychologist James Mark Baldwin (1861–1934) and others to explain the social evolution of traits that are learned during the lifetime of individuals. Originally called organic evolution by Baldwin, it proposes that acquired behavioural traits, such as a thrush learning to smash a snail against a rock, can be transmitted to subsequent generations without contradicting Darwin’s theory of natural selection in favour of Lamarckism. Essentially, the thrush that learns to smash snails improves its life chances and is more likely to breed successfully and produce fertile offspring. What the offspring inherit from their parent is not the snail-smashing behaviour itself but a propensity to acquire behaviours. Hence, there is an increased likelihood that the offspring will themselves acquire the behaviour, for example by imitating their parent, so increasing its frequency within the population. Over successive generations, the behaviour itself influences the evolution of the population as other genetically controlled traits are selected to enhance and consolidate the learned trait, which ultimately itself comes under genetic control as an instinctive behaviour. There is continuing controversy about the validity and biological significance of the Baldwin effect. Notably, it has been invoked to explain the rapid evolution of complex behaviours, cognitive skills, and language in primates, especially humans. Proponents argue (contentiously) that the emerging mind, through the dramatic advantage it confers in a social environment, effectively accelerates the evolution of the brain to accommodate it. See also phenotypic plasticity.