Aggression is likely related to the male hormone testosterone.

Aggression is likely related to the male hormone testosterone.

John Manning wrote in his first book ‘Digit Ratio’:

“Aggression may be viewed as hostile behavior motivated by fear and frustration … There is considerable uncertainty whether testosterone has a causal role in aggression, and other hormones such as cortisol may be equally or more important. In view of this uncertainty it may be instructive to examine whether the 2D:4D ratio or the lenght of the 4th digit adjusted for height are correlated with any forms of aggression including assertiveness, measures of status, verbal aggression, and physical aggression.”

In his first book John Manning presented research which indicates that in both men and women a low digit ratio is frequently accompagnied with: “More aggressive and assertive behaviour”. Since then various studies have confirmed the relationships between aggressive behavior, high levels of testosterone, and a low digit ratio:

An overview of some of the more recent scientific sources which have found a link between finger length and aggressive behavior:

* The presence of aggression cues inverts the relation between digit ratio (2D:4D) and prosocial behaviour in a dictator game. – 2008

* On the relation between 2D:4D and sex-dimorphic personality traits. – 2008

* Finger length ratio (2D:4D) correlates with physical aggression in men but not in women. – 2005

* Digit length ratios predict reactive aggression in women, but not in men. – 2004

Finger length & athletic ability.

digit ratio

A short history of major the developments in the concept of ‘digit ratio’:

  • In 1888 antropologist and biologist Dr. Frank Baker noticed that the index finger is usually short than the ring finger:
  • More than a hundred years ago, a very entertaining paper concerning various customs and superstitions associated with the hand – titled: Anthropological Notes on the Human Hand (1888) – was presented to the Antropological Society of Washington by Frank Baker, Professor of Anatomy at the University of Georgetown. Following some fascinating tales, and a debunking of palmistry, he concluded by discussing the comparative lengths of the digits, and noted that the second (index) finger is usually shorter than the fourth (ring) finger.

  • In 1930 antropologist Ruggles George noticed a sex difference in the index finger and the ring finger:
  • Some years later R. George described in a paper – titled: Human Finger types (1930) – a sex difference in the distribution of finger length ratios in that males are more likely to show the 2 < 4 pattern (i.e. a longer ring finger relative to the index finger), while females are more likely to show the opposite pattern (2 > 4).

  • In 1952 antropologist V.R. Phelps discovered that finger length is stable throughout life:
  • Two decades later the sex difference findings reported by George (1930) were confirmed in the work of V.R. Phelps – titled: Relative index finger length as a sex-influenced trait in man (1952) – noting that such differences were observed in foetuses, and then appeared to be stable throughout life.

    Psychologist Glenn Wilson

    Psychologist Glenn Wilson

    * In 1983 Psychologist Glenn Wilson introduced the word ‘digit ratio’:

    Dr Glenn Wilson of King’s College, London published a study – titled: ‘Finger length as an index of assertiveness in women‘ – which introduced the 2D/4D ‘digit ratio’ as a marker of exposure to prenatal testosterone + examining the correlation between assertiveness in women and their digit ratio. This was the first study to examine the correlation between digit ratio and a psychological trait within members of the same sex.

    Psychologist John T. Manning

    Psychologist John T. Manning

    * In 1998 Psychologist John T. Manning presented a link between ‘digit ratio’ and testosterone + sperm counts:

    This link was described by Manning in a study – titled: ‘The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone‘.

    'Digit ratio' - the book

    Digit Ratio - the book

    * In 2002 Psychologist John T. Manning presented the book ‘Digit ratio’:

    Psychologist John T. Manning presented his first book about the 2D:4D ratio – titled: ‘Digit ratio: A Pointer to Fertility, Behavior and Health‘.

    In this book Manning presents a first overview of the digit ratio research which has been presented uptill the year 2002.

    The finger book

    The finger book

    * In 2008 Psychologist John T. Manning presented the book ‘The finger book’:

    Psychologist John T. Manning presented his first book about the 2D:4D ratio – titled: ‘The finger book‘.

    Quote from New Scientist:

    “According to evolutionary psychologist John Manning, who has spent years researching the secrets they betray, your digits reveal all sorts of things, from your sexuality to whether you are socially disadvantaged or likely to suffer a heart attack. They even, as the legend goes, give away the size of a man’s penis.”