How our body measurements affect who we are
Top athletes have longer ring fingers – and women with larger hips have more intelligent children. Roger Dobson explains how the size and shape of body parts can speak volumes about our health, fertility, and even our personality traits
Tuesday, 27 January 2009
Forget good feet, it's the hands that are the mark of a good runner. Successful sprinters and endurance athletes are more likely to have long ring fingers than the also-rans, according to new research – based on the running speeds and times of young men.
Athletes with long ring fingers in relation to their index fingers also had superior aerobic capacity.
According to the researchers, it's all down to the ratio between the ring and index fingers being a marker of exposure to testosterone in the womb. The bigger the ring finger, the greater the amount of testosterone swishing around the womb during the first three months of the pregnancy.
And exposure to large amounts of the male hormone do much more than increase the chances of being a good runner. Long ring fingers have been linked to increased risk of autism and attention deficit hyperactivity disorder (ADHD), a lower risk of a heart attack at a young age, a reduced risk of early breast cancer in women, greater fertility and aggression in men, as well as depression and neuroticism.
But digit ratio is not the only dimension that has an effect on health. Research is showing that when it comes to health and longevity, size and body dimensions of all kinds matter.
Leg and trunk length have been linked to heart disease and diabetes, height with prostate and breast cancers, head circumference with intelligence, hips with fertility and attractiveness, and birth weight with depression, diabetes and high blood pressure. In some cases, the dimensions are markers of the kind of womb environment that the growing foetus was exposed to, while in others they are a visible sign of the early afterbirth environment, including nutrition and family wealth.
Some of the most intriguing research centres on the so-called digit ratio theory put forward by evolutionary psychologist Professor John Manning, now attached to Swansea and Southampton universities, and author of The Finger Ratio, due to be published shortly by Faber & Faber. The theory is that the finger ratio is a historical record of what went on in the womb at a time when the brain, heart, and other organs were growing. It's suggested that a relatively long ring finger is a sign that these organs were exposed to higher levels of testosterone, while a relatively long index finger points to lower level of the male hormone and higher levels of oestrogen.
Exactly how testosterone affects the foetal digit ratio is not clear. One theory is that for a certain time in foetal development, there are testosterone receptors on the fingers, and that the ring finger may have more of these receptors and therefore more likely to grow faster when exposed to higher levels of the hormone. "Testosterone affects a whole bunch of things," says Professor Manning. "There is evidence that these androgen receptors do appear on the fingers in foetal development. They seem to appear around week eight, but by week 14 they have gone. That is how testosterone has an effect on finger growth.
"It may be that there are more receptors on the ring finger than the index finger. It is interesting that if you look at the back of the fingers, people are more likely to have hairs on the middle part between the two joints of the ring finger than the index. Those hairs are dependent on testosterone and suggests that receptors have been on the ring finger rather than the index.''
Since the first research on digit ratio, more than 200 studies have found links between it and myriad diseases and personality traits. Exposure to hormones may impact on body and brain development and on future behaviour. In his latest study, Professor Manning found that young men with long ring fingers were faster at sprinting than boys with relatively long index fingers. One theory is that higher testosterone exposure in the womb may also have an influence on the developing vascular and respiratory systems, improving the aerobic capacity of the body and to a lesser extent increasing strength.
Several disease risks have been linked to the digit ratio, including breast cancer, which has been associated with high foetal oestrogen exposure, and heart disease. Autism and ADHD, both conditions that affect more boys than girls, have also been associated with male digit ratios. Schizophrenia is another condition that shows a gender bias. Researchers working at the University of Florida found that patients were likely to have a more feminine digit ratio with a smaller ring finger.
Other research has suggested higher testosterone levels might lead to a more masculine brain that is more adept at maths and navigation, more prone to aggression, and lacking social skills and agreeableness.
Research at Edmonton University, Alberta has found a link between finger length and depression, with men with a more feminine finger ratio scoring higher on a test for depression, while a study at Groningen University, The Netherlands, found that a masculine ratio was associated with low verbal intelligence, high numerical intelligence, and low agreeableness – all considered to be typical male traits.
Researchers at Cambridge University looked at the finger ratio in a group of male traders in the City of London. The results show that the earnings of men with relatively long ring finger were up to six times higher than those of their colleagues. More controversially, researchers have also suggested a link between both male and female homosexuality and digit ratio, but other research has found no effect.
Physical aggression, too, has been linked to longer ring fingers, especially in men. It had been thought that it was not a marker for aggression in women, until researchers at the University of Central Lancashire looked at other types of aggression. Their findings suggest that a quick premarital glance at the ring finger may be in order for assessing the likelihood of non-physical aggression in women. They looked at so-called indirect, social or relational aggression and found that women with a more masculine ratio showed higher levels.
They say that women with long ring fingers tend to be more aggressive to colleagues and partners and more likely to pen aggressive letters and to slam the phone down. They are also more prone to spreading rumours and sulking.
The longer and wider the head, the greater the IQ, according to some research. In one study, a head with a capacity of around 1,359cc has an IQ of 110, while 1,600cc was linked to an IQ of 125. In another study, larger head volume and circumference were also linked to higher IQ. "It is widely asserted that there is no relationship between head size and intelligence. This assertion is false,'' say a report in the journal Personality and Individual Differences.
Weight at birth has been shown to have a key impact on later health. As well as cardiovascular diseases, low birth weight has been linked to an increased risk of diabetes, depression, chronic pain, obesity, intelligence and longevity. Findings from the US Nurses' Health Studies based on studying 160,000 women aged 30 to 55, show that those born weighing less than five pounds were later 39 per cent more likely to develop high blood pressure.
A study at Keele University of adults aged 18 to 25, found that those who had a low birth weight were 2.8 times more likely to suffer with depression, while research on more than 20,000 male health professionals showed that those weighing less than 2.5kg at birth were 75 per cent more likely to develop diabetes in later life than those born weighing 3.2kg or more.
A Swedish study based on 14,611 people shows that for each two-pound increase in weight, the risk of stroke in adulthood drops by between 21 and 55 per cent. A study at the National Public Health Institute, Finland, found that high cholesterol in middle age may be linked in part to birth weight.
A number of studies have linked increasing height with a lower risk of heart disease and an increased risk of prostate cancer. According to a Bristol University report, there are a number of possible explanations for the heart disease link, which remains even after taking into account social class and smoking. It could be, they say, be because height is, at least in part, a marker for diet, infections, or psychological stress during childhood. It may be because coronary vessel diameter increases with height, or it could be that growth factors are involved. A study at the same university found that height is positively associated with prostate cancer. A 10-centimetre increase in height was linked to 6 per cent increases in the likelihood of cancer, and a 12 per cent higher risk of aggressive cancers.
A study based in the West of Scotland shows that longer legs, but not trunks, are associated with lower blood pressure, and more favourable levels of cholesterol and body mass index than trunk length. A study reported in the British Medical Journal showed that the risk of breast and prostate cancers increases with height.
Women with small waists and larger hips – a low waist to hip ratio – and their children perform better in intelligence tests, according one study. Fatty acids stored in the fat around the hips which are vital for the development of the brain, are thought to be responsible for both mothers and their offspring, say the researchers, who suggest that may be why men prefer such dimensions. "Women with lower waist to hip ratios and their children have significantly higher test scores.
"Our findings support the idea that waist to hip ratio reflects the availability of neurodevelopment resources and offers a new explanation for men's preference for a low ratio,'' say the researchers in the journal Evolution and Human Behavior.
A waist-hip ratio of 0.7 – a waist circumference that is 70 per cent of the hip circumference has been shown to be the most attractive to men.
Researchers investigating what makes a super-attractive woman stand out from the rest found that thigh girth was a vital element. The academics from the University of Gdansk studied 19 vital statistics and 20 body features of 24 finalists in the Miss Poland competition and of 115 other women.
Results show that the super-attractive woman has a thigh to height index some 12 per cent lower than the other women, giving them a more slender look. Findings also show that the average super-attractive height was 175cms and that waists were 76 per cent of the size of their chests, and 70 per cent of the size of the hips. Bust size was 49.3 per cent of their height, and shoulder width was 20.9 per cent of height.
The researchers say the findings back up evolutionary psychology theories that a woman's sexual attractiveness is based on signs of health and reproductive potential. They say the results for super-attractive women show that their body mass index at 18:5 is close to that associated with the lowest mortality rate, while the average waist to hip ratio corresponds to high fertility.
Folklore has it that the size of a man's foot is indicative of a somewhat more discreet measurement. Not so, according to research at the Naval and Veterans Hospital in Athens, based on men aged under 40. They looked at a wide range of body measurements to see if there were any links, and the only significant association they found was with the length of the index finger – so don't bother checking his shoe size.
Finger size: What the measurements mean
Measuring your finger ratio
Divide the index finger length by the ring finger length, which gives you the ratio. If these fingers are the same length, the ratio is one, which is an average female ratio. If the ring finger is longer, the ratio is less than one, which is typically male. A ratio of 0.97 is about the average for males, but in elite runners, the ratio can be down to 0.9. In some men, the ring finger can be up as much as a centimetre longer than the index finger.
Traits more associated with having a female hand (long index finger relative to ring finger):
Low levels of assertiveness
Vulnerability to early breast cancer, cervical cancer, and polycystic ovary syndrome
Low risk taking
Women with masculine ratio
More likely to report side-effects of birth pill
Vulnerable to osteoarthritis
Greater pain tolerance
High risk takers
Traits more associated with a male hand (long ring finger compared with index finger):
Good at football, rugby, basketball, fencing, skiing
Prone to osteoarthritis
Reduced chance of heart disease
Autism and Asperger's syndrome
Low verbal fluency
Good maths skills
Tendency towards left-handedness
Men with feminine ratio
Good social and verbal skills
Poor at football
Reduced chance of osteoarthritis
Prone to heart disease
Tendency towards right- handedness
Tendency towards schizophrenia