Given that con­fi­dence and risk tol­er­ance are cor­re­lated with high lev­els of pre-natal testos­terone, John Coates—Wall Street trad­ing floor man­ager turned academic—wondered if the behav­iour of high-frequency, suc­cess­ful traders is sim­i­larly influ­enced, and thus innate. Unsur­pris­ingly it was; but it was the extent to which it was found to be true that was sur­pris­ing:

Coates, Gur­nell and Rus­ti­chini found what they were expect­ing: that high-testosterone foe­tuses grew up to be excel­lent high-frequency traders. What was sur­pris­ing was the huge size of the effect. Traders with a low 2D:4D ratio made six times as much money as those with high 2D:4D ratios. In an envi­ron­ment when the best traders earned more than £4m a year, this is hardly a triv­ial discovery.