The "Murderer's Thumb": From Palmists' Warning to Genetic Trait

Hold out your hands, thumbs up, and compare the tips. For a small share of people, up to a few in every hundred in some populations, one or both thumbs end in a short, wide pad with a nail that is broader than it is long. A century ago, a palmist who saw that thumb might have paused before saying anything. In the manuals of the period it had a name with a chill to it: the “murderer’s thumb.”¹

The name survives today mainly as a curiosity, listed among the informal labels for a common inherited bone difference that clinicians call brachydactyly type D.²³ How a harmless variation of the skeleton came to carry that label is a story about Victorian hand reading, the criminal science that grew up beside it, and the slow replacement of both by genetics.

The thumb as the seat of will

Modern palmistry in the English-speaking world drew heavily on two French writers, Casimir d’Arpentigny and Adolphe Desbarrolles. A. R. Craig’s popular Your Luck’s in Your Hand, which presented their systems to British readers, calls d’Arpentigny the “high priest” of the modern art and describes him as a French captain whose interest, in the story Craig tells, began with a palm reading on a road in Andalusia during the Spanish wars.⁴

In this tradition the thumb was the most important digit. Craig’s chapter on it treats the thumb as the sign of reasoning will, logic and decision, the faculties that separate people from other animals, and sums up the idea in one line: “The superior animal is in the hand, the man is in the thumb.” A small thumb, the same chapter says, announces an irresolute disposition.⁴ Later manuals assigned a meaning to each joint. In Benham’s system the tip, or first phalanx, stood for will and determination and the second for reason and logic; a will phalanx longer than the logic phalanx marked someone who acts first and thinks afterward.¹

Once the thumb tip was read as the measure of will, a thumb with a tip that was short, thick and blunt invited a darker reading: will without refinement, force without restraint. That is the reasoning the later manuals made explicit.

Benham and Cheiro on the “clubbed thumb”

The fullest treatment came from William G. Benham, an American palmist whose The Laws of Scientific Hand Reading carries an introduction signed in Columbus, Ohio, in December 1900. Benham presented palmistry as a science with fixed laws, and illustrated his book with photographs, prints and casts of hands he had collected over many years.¹

In his chapter on the thumb he describes a will phalanx that is thick and rounded, or broad and thick, with a coarse, short nail. He is careful to say that this is not the “consumptive” form of nail and fingertip (consumption being the old name for tuberculosis); it is found, he writes, on healthy people. Because of its shape it “has been called the Clubbed thumb,” and because of the obstinacy it supposedly reveals, it “has been designated the ‘murderer’s thumb.’”¹ The phrasing suggests that the nickname was already in use before Benham, though this article could not trace an earlier printed source.

Benham’s account is full of hedges. He warns readers that the name “should, by no means, lead you to conclude that the owner either has or necessarily will commit murder,” and adds that such thumbs are “found on very mild-mannered people.”¹ Yet he also insists that the danger is always present: “a mine lies underneath, and it will only take a match properly applied to explode it.”¹ Whether the mine ever goes off depends, in his system, on the person’s surroundings and on the rest of the hand: its consistency, color, flexibility, the size of the Mount of Venus, the shape of the fingers and the depth of the lines. Elsewhere he assigns the clubbed thumb most properly to his “Martian” type, the fighting hand.¹

He also had an explanation for where these thumbs came from. They were “largely hereditary,” he says, and could be traced back to a parent; when they appeared on gentle people, their presence was “due to something occurring at conception, or during the gestation of the subject.”¹ In other words, Benham noticed correctly that the trait runs in families, then folded that observation into a moral reading it did not support.

The celebrity palmist known as Cheiro, who styled himself “Count de Hamong” on his title page, went further. In a chapter of Cheiro’s Language of the Hand titled “Propensities for Murder,” he divides murderers by their hands into three classes. The first, those who kill in passion or rage, have a low-set thumb whose first phalange is “the clubbed thumb,” which he describes as “very short, broad, and square,” and which he claims “is found almost without exception in such types.”⁵ Cheiro offers no count of hands examined and no comparison with people who had not committed violence.

A parallel in criminal anthropology

Palmists were not the only people reading criminality into the shape of the hand. In Italy, Cesare Lombroso built a school of “criminal anthropology” on the claim that many offenders carried physical marks of an earlier stage of human evolution. The English summary of his system prepared by his daughter and collaborator, Gina Lombroso-Ferrero, and published in 1911, lists features of the palm and fingers among these supposed signs and states: “Those guilty of crimes against the person have short, clumsy fingers and especially short thumbs.”⁶

The overlap with the palmists is striking: short thumbs, violent crime, and a body that supposedly announces a nature in advance. The two traditions differed in prestige but shared a method, which was to look at people already labeled as criminal, note features that seemed to fit, and generalize. Lombroso’s strictly biological account of crime was criticized early, for example by Charles Ellwood in 1912, for paying too little attention to psychological and social causes.⁷

Benham’s own book shows why such a system was hard to refute from within. In his introduction he tells students that if a reading fails to match the person, “The fault is not with the science but with your application of it.”¹ A thumb that belonged to a gentle person could be explained by the rest of the hand, or by events in the womb. No observation could count against the rule.

What medicine calls it

Clinical genetics describes the same thumb in different terms. In the classification of short fingers drawn up by Bell in 1951, it is brachydactyly type D: the last bone of the thumb, the distal phalanx, is shorter than usual and wider at the base, which gives the tip its broad look and makes the nail short and wide.²⁸ It can affect one thumb or both.⁸ A research paper on the trait lists “stub thumb” and “murderer’s thumb” as its common names, and a Washington University hand surgeon’s page adds “club thumb,” while noting that it should not be confused with the separate medical condition called clubbing.²³

The trait is common. Reported frequencies range from 0.41 to 4 percent depending on the population studied, with high figures reported among Japanese and Israeli Arab populations.⁸ In a study of 2,130 members of the Jirel community in eastern Nepal, whose hand X-rays had been collected for research on growth, 3.55 percent had it.² In Japan it has its own everyday names, less sinister than the English one: Mamushi-yubi, after the viper, whose shape the thumb tip is said to resemble when seen from the side, and Shamoji-yubi, after the flat paddle used to serve rice.⁸

Isolated brachydactyly type D is not a disease. A hand surgeon at Washington University writes that “Treatment is rarely if ever indicated,” describing it as mainly a difference in appearance with function usually normal, though some people report trouble with tasks that need a lot of bending at the thumb’s end joint.³ A short distal thumb bone can also occur as one feature of certain rare syndromes, so a physician may look for other signs; in most people with nothing else unusual, it is an isolated finding.⁸

Inheritance: what Benham got right, and what is still open

Benham was right that the thumb runs in families. The earliest published study of the trait, cited by later researchers, followed it through five generations of one family in 1923 and suggested dominant inheritance, meaning a single copy of a variant can be enough.² Many later family reports agree but note “incomplete penetrance”: some people who carry the variant show no short thumb, so the trait can seem to skip a generation.⁸² Researchers have also noted that the mode of transmission has been disputed, partly because the trait overlaps with another type of short-digit pattern, type E. In the large Nepalese study, the pattern in families fitted a complex trait with incomplete penetrance better than simple dominant inheritance.²

The genes involved are only partly known. In 2003 a team working with patients from a plastic surgery department in Oxford described two missense changes in HOXD13, a gene that helps pattern the developing limb, associated with short-digit patterns that overlapped types D and E.⁹ But other studies point elsewhere. A 1999 study of one four-generation family found no linkage to six candidate regions of the genome, and the Nepalese study found linkage to a region of chromosome 7 whose candidate genes include the HOXA cluster.¹⁰² The most cautious summary is that several genetic routes can lead to a short, broad thumb tip, and that the trait is strongly heritable in at least one large population studied.²

None of this research has found any connection between the shape of the thumb and personality, temper or crime, and none of these studies set out to look for one, because nothing in the biology suggests it. The genes in question shape bones in the embryonic limb.⁹

Why the name lasted

The “murderer’s thumb” survived because it was vivid, because the trait is easy to spot, and because it rested on a real observation: the thumb does run in families. Benham built on that observation, and Cheiro on bare assertion, a theory of character that never had evidence behind it; Benham protected his with rules that explained away every exception. Lombroso’s criminal anthropology made a similar move with the authority of medicine.

Today the label turns up in scientific papers and clinic pages as an informal nickname, alongside the gentler stub thumb, viper finger and rice paddle.²⁸ For the millions of people who have the trait, it marks a family resemblance and nothing more.

Footnotes

1. Benham 1900 (title page 1901), Introduction pp. viii-ix and ch. on the thumb, pp. 146, 152-156, 170-172, 295. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

2. Williams et al. 2013, introduction and results. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

3. Goldfarb 2022, Washington University congenital hand page. ↩ ↩² ↩³

4. Craig, Your Luck’s in Your Hand, ch. III and ch. V (“The Thumb”). ↩ ↩²

5. Cheiro 1898, “Propensities for Murder,” pp. 149-151. ↩

6. Lombroso-Ferrero 1911, part I, ch. I. ↩

7. Munthe and Radovic 2015, introduction. ↩

8. Saraya et al. 2013, BMJ Case Reports. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

9. Johnson et al. 2003, abstract and introduction. ↩ ↩²

10. Robin et al. 1999, abstract. ↩