The secret to how our brains grew may be hidden in our fingers before we are even born.
One of the defining features of human evolution is the steady expansion of our brains. New findings suggest this growth may be partly linked to higher levels of estrogen before birth. Surprisingly, a visible clue may lie in the relative length of a person’s fingers.
What the 2D:4D Digit Ratio Reveals
Professor John Manning of Swansea’s Applied Sports, Technology, Exercise and Medicine (A-STEM) research team specializes in the study of digit ratio. This measurement compares the length of the index finger to the ring finger and is known as the 2D:4D ratio. Research shows that this ratio reflects the balance of estrogen and testosterone to which a fetus is exposed during the first trimester of pregnancy.
People who experienced higher estrogen-to-testosterone ratios before birth tend to have longer index fingers (2D) than ring fingers (4D), resulting in a higher 2D:4D ratio.
Professor Manning recently collaborated with researchers from Istanbul University’s Department of Anthropology. Their study was published in the journal Early Human Development.
Newborn Head Size and Brain Development
Because head circumference in newborns is closely associated with brain size and later measures of IQ, the researchers examined both finger ratios and head measurements in 225 infants, including 100 boys and 125 girls.
The analysis found a clear association in boys. Higher 2D:4D values (indicating high prenatal estrogen) were linked to larger head circumference. The same pattern was not observed in girls.
Evolutionary Tradeoffs and the Estrogenized Ape Hypothesis
Professor Manning explained the broader implications of the findings. “This finding is relevant to human evolution because increases in brain size are found alongside feminization of the skeleton, what is known as the estrogenized ape hypothesis. High values of 2D:4D in males have been found to be related to elevated rates of heart problems, poor sperm counts, and predisposition to schizophrenia.
“However, increases in brain size may offset these problems. Thus, the evolutionary drive for larger brains in humans may inevitably be linked to reductions in male viability, including cardiovascular problems, infertility, and rates of schizophrenia.”
The research team says these results add to growing evidence that prenatal estrogen may have played a beneficial role in the evolutionary expansion of the human brain, even if that shift carried biological costs.
Broader Research on Digit Ratio
Professor Manning’s earlier studies have also explored how digit ratio connects to other traits and outcomes. His work has examined links to alcohol consumption, recovery after COVID-19 infection, and oxygen use in football players. Together, this body of research suggests that finger length may offer insight into the powerful hormonal influences that shape development before birth.
Reference: “Digit ratio (2D:4D) and neonatal head circumference: Evidence for oestrogenization in human brain evolution?” by Barış Özener, John T. Manning, Berna Ertuğrul and Fatih Aydık, 10 January 2026, Early Human Development.
DOI: 10.1016/j.earlhumdev.2026.106479
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59 Comments
The relative length of index/ring fingers depends on how a person holds their hand at the wrist. That may be a result of prenatal estrogen, but it might also be caused by environmental factors like Archery, playing Tennis, or blacksmithing. And of course those tendencies might also be a result of prenatal estrogen. IMHO it’s the same argument as did god or the big bang create the universe or did god cause the big bang or did the big bang cause god? More data needed.
Well yes definitely more data needed. If only because even a hundred babies is a small sample size. You have to be hitting the tens of thousands before your going to start getting results that are more reliable. It may come down to the families of the ones they studied, just having to be having one handstyle over the other…
However, it has nothing to do with wrist placement. Sure, the picture they have might be misleading. But you would measure the length of the bone from the first knuckle.
My guess they didn’t find any correlation with the female babies because they all have higher estrogen. So it would likely obscure any difference from the maternal estrogen.
Cranial size has nothing to do with intelligence or IQ. If this was true, men would be much more intelligent than women, and Asians would be some of the least intelligent people in the world.
Asian scientific advancement was literally held back by certain dynasties and royal decree. They invented gunpowder for example, centuries before the west, who literally imported the technology through their trade routes. You my dear boy just sound like a typical racist going on about white men invented when I doubt you, like most of us, has done sweet bugger all with that grey matter of yours, but like all racists you take the credit for other people’s achievements, Bravo.
They’re talking about head size in relation to body size.
After reading up on this.. it apesrs as reliable at predicting intelligence as phrenology..
Yep, similar to phrenology. It also comes with an ethnic bias. A test created by European academics (IQ) *happens* to be one they’re good at. A trait that Europeans happen to have (high 2D:4D ratio) is linked to high IQ performance. I wonder how they account for different finger ratios by ethnicity? My ethnicity (and finger ratio) suggests a low IQ, which I don’t believe is accurate.
I am an extreme counterexample to this article. I am male. My pointer finger is significantly shorter than my ring finger (on both hands, my index finger ends where the nail of my ring finger begins). However, my head size is much larger than average – only the largest of hats and glasses fit me, and my IPD is so wide thst no VR or smart glasses are wide enough for me to see the outer edges of their screens. My IQ is ~160 (genius level). I may be an anomoly – had I been born this millenia, I likely would have been diagnosed with Asperger’s or other high-function autism disorder, but this correlation is simply not true in any way for me.
Similar case here (female). As well as my husband, and my son. In fact we were sent to an endocrinologist when my son was born because apparently our large sized craniums were concerning our pediatrician. Our index fingers are all longer than the pointer. The only reason I was inclined to read this article was my expectations that the results would be thr opposite.
Says nothing about pointer fingers.
I also have a significantly longer ring finger to index on both hands. I tend to have a high level of intellect and stand out from most people I know, I am also a quick/ adaptive learne, If you will.. I am highly curious as to the validity of these claims in relation to finger length and so on… the article photo seems to be misleading as it only points out(no pun intended) the longer index to ring finger ratio.. I’d like to know more about studies involving the former. If anyone has information relating to the opposite and,/or any studies on the matter id appreciate if you could point me in the right direction. (Pun intended that time) 🙂 thank you
Naaaa,, i’m happy as it is ,, don’t need to put more complicated equetions in My head
I’m interested in the opposite as well. I happen to have a ring finger that is considerably longer than my index finger (and middle) finger. As a 63 year-old male I have often wondered if this related to an estrogen mimic from the early ’60’s and the plastics in use in that era.
It’s having your hands look feminine. The shorter index finger is the man’s hand. We see the problem so we need a solution. The very short pinky is feminine.
Likewise. 58 yrs old, XL hat size that most are still too small. Same range quotient, ring finger considerably longer than index on both hands (my index stops at base of middle fingernail, ring half way through same nail).
Recently clinically diagnosed an extreme example of Asperger’s.
Since when did large heads automatically mean someone is smarter? They say we only use 10% of our brain anyways so increased intelligence wouldn’t demand for a larger head… honestly I’m always thought ppl associated big heads have an extra chromosome, down syndrome or something, the opposite of a savant…
That 10% brain power thing is a myth
It is that they only know what 10% of our brains are used for , not only using 10%.
My index is short and despite what people say, I was put in honors calculus at GT for a reason having nothing to do with my exceptional good looks, my tremendously strong body, nor my long, long list of neuroses. I lived to hot a baseball. Loved football except got hurt too much. Said screw this nonsense.
I figure I have neanderthal in my DNA.
Also, one last tidbit, okay 2. My sperm could row a battleship. I am meek & mild.
Also. I hate freaking dictators with a cold fury. Love is the answer.
Im a stud and chick’s love me. The end.
You got it back-wards smarty pants. 😉
My ring finger is also a nail’s length longer than my index finger but I measure around average in hat size. I test in the 148 to 153 range on IQ, depending on which test is used.
I also know some big headed folks whose opinions I don’t value very much.
Same here
So nothing for me with a longer ring finger? Lol
Something may be there but… Why do articles like this always end up on my main page. 🤦
A few years ago a similar “study” said a shorter index finger than ring finger predicted a greater probability of being gay. Haven’t heard anything about that lately. I have a feeling the current study will become a passing thought as well.
I did not see how holding your hand changes the ratio in a study.
That is why you standardize measurements.
Hold up your hand looking at the back, you can tip your fingers to the left or right. one side raises the ring finger relative to the index, tip to the other side raises the index. My mom read palms when she was in school. Palm readers look for hand posture to reveal psychological traits. Long index fingers indicate assertiveness, long ring fingers indicate compliance and agreeability. Those are traditional male/female characteristics (in 1930 ok, please don’t beat me up).
Right?
While those things may influence the shape of a person’s hand/fingers, I don’t think a newborn has had enough time for that to happen
Or a pinched nerve/that literally reshape the body over time like me for the second time after I fixed it once before. Not only do my fingers show different lengths but my toes elongated and curled up. My hands and feet are more narrow. Despite the same relative calorie intake and weights at the gym I’m skinnier. I have a pelvic tilt. And my jawline is more narrow and my cheekbones are less prominent. My forehead narrow and slopes before it was wide and curved outward. There are many reasons your body grows the way it does. And not to mention iq and head size I thought that was proven to be bs
Am I mistaken? Did I just hear that the future is female?
Feminized skeleton structure, not exclusively female (lest we go extinct). Interestingly enough, it’s not unlike the images we often see of depictions of technologically advanced alien beings- large oversized/overdeveloped heads and very petite/underdeveloped feminized bodies.
So you’ve personally seen these aliens right in order to be making such a claim? So you are actually justifying this article as being correct and your proof is: Alien bodies. You’re not very bright are you little buddy?
That’s what I heard
That is not what was said. Please dont bring ideology into science.
Yes, you’re mistaken.
What happens if it’s not the same on both hands? lol
so basically this is saying every one is different and there are indicators on our own bodies like height ,pigment ,and many other things that agree in our wonderfully and fearfully created bodies . Regardless of finger size, IQ ,or any other test .every individual is exception to “limitations ” because we have free will and choice .which exceeds any limitations. I would love to see more uplifting posts that motivate and stimulate ,rather than have the reader focus on( 2D-4D ) but on the other hand the article did hold my attention to finish reading ,which is not easy with ADHD .S o great job, fun read ,i hope anyone that reads my post will be Encouraged by it and not see the many flaws I still haven’t overcome yet.im a work in progress. have a great day everyone.
I also have a significantly longer ring finger to index on both hands. I tend to have a high level of intellect and stand out from most people I know, I am also a quick/ adaptive learne, If you will.. I am highly curious as to the validity of these claims in relation to finger length and so on… the article photo seems to be misleading as it only points out(no pun intended) the longer index to ring finger ratio.. I’d like to know more about studies involving the former. If anyone has information relating to the opposite and,/or any studies on the matter id appreciate if you could point me in the right direction. (Pun intended that time) 🙂 thank you
Why didn’t they use actual pictures of hands from the study?
Since when did large heads automatically mean someone is smarter? They say we only use 10% of our brain anyways so increased intelligence wouldn’t demand for a larger head… honestly I’m always thought ppl associated big heads have an extra chromosome, down syndrome or something, the opposite of a savant…
Mine is also alot bigger then all my other fingers.
And my iq is pretty high too.
Intresting article.
Fascinating
Huh. My left hand shows my index finger shorter than my ring finger by 3 millimeters. My right hand shows my index finger and ring finger to be of equal length. I guess I’ll just give this study the finger.
I love how the majority of the comments from the people with SuPeR hIgH iQs have spelling and grammar mistakes, lol.
I think the 2D:4D ratio has been mostly debunked. Some journals don’t even accept publications that use it.
A 145 IQ this side. Longer ring finger.
The article specifically states ‘head size AT BIRTH’. Stop grabbing your tapes and measuring your heads!! O.o
I’m interested in the opposite as well. I happen to have a ring finger that is considerably longer than my index finger (and middle) finger. As a 63 year-old male I have often wondered if this related to an estrogen mimic from the early ’60’s and the plastics in use in that era.
2d:4d ratio is pseudoscience. Very little strong or replicable evidence that it correlates in any meaningful or significant way w prenatal T or E. It is dimorphic (ie, men on average tend to have shorter index fingers relative to ring finger) but it’s not universal and has zero use-value in predicting complex behaviors and social outcomes.
This research is clearly nonsense. 225 subjects? Please its not even a weekly political poll.
also, It was also conducted on only ASD
The scientist: “U got big pointer finger u gay af.”
The studies were only conducted on those with autism spectrum disorder
You really shouldn’t be telling people who’s smart when you write like that. You cannot even form a coherent argument. If youre the common denominator in those conversations, it may not be the Asian people who are the issue.
Google images of Einstein, Newton, Capernicus, DaVinci and other notable luminaries, and their hands, suggest this study is popycock. But what do I know.
Welcome back, Phrenology.
Read an study years ago that related the length of the ring finger to the size of another part of the body entirely.