The first use of the notion animal spirits is described by Descartes, Newton and other scientists on how the notion for the vitality of the body is used. These animal spirits are of an æthereal nature. In one of his letters about light, Newton wrote that the animated spirits very easily live in "the brain, nerves, and muscles, may become a convenient vessel to hold so subtil a spirit." The spirit Newton is talking about here are the animated spirits that have an ethereal nature. It relates to life in the body. Later it became a concept that acquired a psychological content but was always thought of in connection with the life processes of the body. Therefore, retained a lower overall animal status. William Safire explored origins of the phrase in his 2009 article "On Language: 'Animal Spirits'":
Thomas Hobbes used the phrase "animal spirits" to refer to passive emotions and instincts, as well as natural functions like breathing. Ralph Waldo Emerson in Society and Solitude wrote of "animal spirits" as prompting people to action, in a broader sense than Keynes's: In social science, Karl Marx refers to "animal spirits" in the 1887 English translation of Capital, Volume 1. Marx speaks of the animal spirits of the workers, which he believes a capitalist can impel by encouraging social interaction and competition within her factory or depress by adopting assembly-line work whereby the worker repeats a single task.
Earlier and contemporaneous English use
"Animal spirits" was a euphemistic late-Victorian and Edwardian phrase used by English public school boys such as P. G. Wodehouse who attended Dulwich College. Wodehouse and Arthur Conan Doyle were popular authors for public school boys in England before the Great War. Doyle himself used the phrase "animal spirits" in 1883, the year of Keynes's birth. Two examples of Wodehouse's use of the phrase are in the 1909 book Mike. "Animal spirits" denoted an adolescent attitude to authority that resulted in energetically and deliberately acting on advice, opinion, or exhortation to the point of stretching the letter of any regulations involved to the limit. The aim was to maximise short-term disruption of what was considered to be 'normal' behaviour. Restoring equilibrium subsequently required a firm sanction from those in authority and possibly also a re-casting of the regulation to prevent repeats of the actions undertaken. The slang term of the era for this was 'ragging'. Wodehouse uses antithesis in the latter example to make comedy out of Mr. Downing's astonishment; surely nobody could be less susceptible to "animal spirits" than the suave, debonaire Psmith? Psmith In The City was based on Wodehouse's own experiences in the 'square mile' and the theme is implicitly elaborated on in the financial environment of the New Asiatic Bank. John Coates of Cambridge University supports the popular English Edwardian public school intuition that qualities such as dynamism and leadership coexist with less constructive traits such as recklessness, heedlessness, and in-caution. Coates attributes this to fluctuations in hormonal balances; abnormally high levels of testosterone may create individual success but also collective excessive aggression, overconfidence, and herd behaviour, while too much cortisol can promote irrational pessimism and risk aversion. The author's remedy for this is to shift the employment balance in finance towards women and older men and monitor traders' biology.
Contemporary research
Recent research shows that the term 'animal spirits' was used in the works of a psychologist that Keynes had studied in 1905 and also suggests that Keynes implicitly drew upon an evolutionary understanding of human instinct. In 2009, economists Akerlof and Shiller advised in addition that:
