Susan Greenhalgh's history credits Song Jian — a missile-guidance control theorist — with engineering China's one-child policy from a 'Sinified cybernetics of population'

Song Jian (b. 1931) was the chief control-systems designer of China's submarine-launched ballistic missile, trained in Soviet cybernetics and optimal control theory — the same mid-century mathematical tradition that produced Lev Pontryagin's maximum principle (claim-pontryagin-worked-blind-via-mothers-spoken-symbol-glosses) and, on the American side, the Kelley–Bryson gradient methods the vault charts as a precursor to backpropagation (claim-kelley-bryson-optimal-control-precursor, moc-backpropagation-origins). In Susan Greenhalgh's peer-reviewed history Missile Science, Population Science (China Quarterly, 2005, Tier 1), that defence-science expertise is the engine of a demographic policy: she argues that "during 1978–80 the resources of defence science and the self-confidence of the elite scientist enabled him boldly and arbitrarily to modify the work of the Club of Rome and use that Sinified cybernetics of population to redefine the nation's population problem, create a radical one-child-for-all solution to it, and persuade China's leaders that his 'scientific' solution was the only way out." The claimed trigger, per uncontested biography (Tier 4, Wikipedia), was Song's 1978 encounter at the IFAC World Congress in Helsinki with the cybernetic, Club-of-Rome-associated approach to population control — a modelling wave whose method (Jay Forrester's system dynamics) originated with a computer engineer, not a demographer.

The cross-domain bridge is the point: optimal-control mathematics built to steer a rocket to a target was turned on a nation's fertility rate. Greenhalgh frames Song as one case of Cold War-era "elite scientist/engineer" policy capture out of the defence-science world — a milieu the vault also touches at claim-soviet-scientists-immigration-act-1992-exceptional-ability-waiver.

The causal thesis is contested. Other historians — Liang Zhongtang most directly — reportedly argue Greenhalgh overstates Song's personal role relative to a Party leadership already inclined toward strict population control. That refutation has been seen only via secondary summary here: [unverified-historical — Liang refutation seen only via secondary summary, needs primary], routed at question-verify-greenhalgh-song-one-child-policy-causal-role. Song's own self-attribution is recorded separately at claim-song-jian-self-credited-1980-projections-triggered-one-child-policy.