Have you ever heard that you can accurately know a man's penis size by looking at his extended thumb and middle finger? Purportedly, the distance between the two is the precise base-to-tip length. If that sounds totally unrealistic to you, then you have great instincts. Truth is, the only real way to know the size of any man's erect penis is to see it first-hand (failing a photo with a ruler included or something in the foreground for scale). So what can we tell about a man from his fingers? As it turns out, some researchers have been looking into this, and have come up with some interesting data.

Oxford Study Measures Faithfulness by Fingers

A study from Oxford University suggests that finger length can be an indicator of whether a man is more prone to monogamy or promiscuity. The study concluded that 57% of men and 47% of women are more inclined to be promiscuous rather than content with one partner. But one thing all the promiscuous people tended to have in common was a shorter index finger in relation to the ring finger. Faithfulness versus unfettered giggity based on finger length? Really? Wouldn't that negate a whole world of life lessons, role-modeling, media influence, personal experience, and intimate feelings? Probably.


So, what is this discovery based on? Oxford scientists were trying to understand why human sexuality differs markedly from the rest of mammals, which are either monogamous or not, depending on their species. Orcas, for example, mate for life. Bears find new mates every season while lions stay within their own pride. Tigers play the proverbial field. With humans though, it's anyone's guess whether a particular male or female person is faithful to one partner for life, serially monogamous, or never actually settles down with one mate.

The researchers arrived at their conclusions via a combination of finger measuring and questionnaires on sexual behavior. I'm instantly suspicious of this type of self-reported data. This is because even the most honest people are reticent to be completely forthcoming about their sexual habits. I think we all know people who inflate or diminish their number of reported sexual partners out of a fear of judgment. The study focused on Caucasian males between 18-60 years of age. The average age was 25. Why only white guys? The study doesn't say.

The 2D : 4D Ratio

The correlation between finger length and monogamy begins with something called the 2D : 4D ratio. The 2D stands for "second digit." The 4D stands for "fourth digit." Arriving at this figure involves dividing the length of the index finger by the length of the ring finger of the right hand (no word on whether or not this changes for left-handed fellas). If the index finger is longer, the ratio is more than one. A longer ring finger results in a less-than-one ratio. This data was compared to responses in the sexuality questionnaire. Finally, the results were interpreted.


According to Oxford scientists, the shorter the ring finger is compared to the index finger, the more testosterone the fetus was exposed to in the womb. A longer ring finger also received more testosterone. More testosterone, in their mind, equals a greater statistical likelihood of promiscuity. Really? Obviously, statistical likelihoods are not hard facts. If your current man hasn't given you a reason to doubt his loyalty, learning of an unfavorable 2D : 4D ratio shouldn't lead to an immediate breakup.

The Problems with the 2D : 4D Ratio Results

The 2D : 4D ratio study has taken a few giant leaps to reach this conclusion. First, it's all about correlation (showing a statistical relationship between two things). This is not the same as causation (showing that one condition or event caused another). Second, even if high testosterone was a precursor to promiscuity, this would merely indicate a propensity and not a certainty. It's just as likely that high testosterone leads to a man aggressively protecting his life mate and offspring. Finally, it divides humans into two groups: monogamous and promiscuous. It does not give any controls for sexual preference, maturity, or the ability to consciously modify one's behavior.


Oxford University professor Robin Dunbar points out a need for caution when interpreting the results of the study. "Human behavior is influenced by many factors, such as the environment and life experience. What happens in the womb might only have a very minor effect on something as complex as sexual relationships." You don't say!

Evolutionarily speaking, promiscuity increases the likelihood of having many offspring, thus carrying on one's genetic line. However, a lifetime relationship with one mate and one litter of children (as it were) increase the chance that the offspring will survive and thrive. If people can really be separated into "monogamous" and "promiscuous" varieties, and I'm not sure that they can, we probably need both kinds to keep the world an interesting and a sexually satisfying place.