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In the first in a new series of programmes about hormones, Justin Rowlatt asks whether testosterone is responsible for causing stock market bubbles, and for offering false hope to American men of a certain age.

Neuroscientist and former Wall St trader John Coates explains why he thinks this chemical may be behind hubris, and particularly the irrational animal spirits of male traders.

Endocrinology professor Maralyn Druce of St Bartholomew's Hospital discusses how testosterone puts hair on your chest, and causes all her children - boys and girls - to act up at about the age of eight.

Plus researcher Adriane Fugh-Berman retells how she debunked the claims of some US pharmaceutical companies that ageing men could regain their youthful vigour by using testosterone gel.

Producer: Laurence Knight

(Picture: The word 'Manly' displayed on the trunks of a member of the Manly Surf Life Saving Club near Sydney, Australia; Credit: Greg Wood/AFP/Getty Images)