Hundredth monkey effect
The Hundredth monkey effect is a pseudoscientific anecdote claiming that a novel behavior—specifically, Japanese macaques washing sweet potatoes in seawater to remove sand—spread spontaneously across isolated populations once a critical threshold of adopters, symbolized as the "hundredth monkey," was reached, implying transmission through collective consciousness or a non-local field rather than physical contact or observation.[1]Popularized by South African author and naturalist Lyall Watson in his 1979 book Lifetide, the narrative extrapolates from mid-20th-century observations by Japanese primatologists studying a troop of macaques on Koshima Island, where researchers provisioned the monkeys with sandy sweet potatoes to encourage beach use.[2][1]
In reality, the behavior originated in 1952 when an 18-month-old female named Imo began washing potatoes, spreading gradually over years through imitation among juveniles, peers, and mothers via standard cultural transmission within the single Koshima troop, with older adult males largely resistant and no evidence of sudden group-wide adoption or diffusion to distant islands in 1958 or any other year.[2][3]
Watson later admitted embellishing details for dramatic effect, but the myth persists in New Age and self-help literature as a metaphor for tipping points in social change or paradigm shifts, despite refutations by the original researchers and skeptics highlighting its incompatibility with empirical data on animal behavior.[1][4][2]
Critics, including philosopher Ron Amundson, have noted that the tale exemplifies how anecdotal exaggeration can masquerade as evidence for untestable ideas like morphic resonance, underscoring the importance of verifying primary sources over popularized accounts.[1]