Battle of the Brains: Size Matters

Battle of the Brains: Size Matters

Sexual dimorphism, or gender differences in appearance and behavior, arose because selection pressure acts differently on males and females. It is surprising, then, that brain sizes typically do not differ between the sexes in the animal world. Yet, gender differences between selection pressures are common and the brain is one of the most adaptable and plastic organs. Recently, scientists discovered a dramatic difference in brain size among stickleback fish: the male brain is nearly 25% larger than the female, for the same body size and weight amongst fish living in two habitats (mud and lava) of Lake Mývatn in Iceland (see image).

Bigger is Better: Greater neural mass means greater information processing and superior cognitive power. In animals, larger brains have been shown to coincide with bower complexity in male bowerbirds and with single parenting by females in cichlids. Male sticklebacks build elaborate nests, perform elaborate courtship displays and care for their offspring alone. So guys, pay attention to the nursery if you want to be smarter!

Delusions of Gender: The costly gain in brain size usually comes with compensation you know where. Male bats trade testis mass against brain mass. Female sticklebacks invest heavily in egg production, which take up 40% of their body weight.  What about humans? Studies showing differences in male and female brains are highly controversial.


Ref: Extreme Sexual Brain Size Dimorphism in Sticklebacks: A Consequence of the Cognitive Challenges of Sex and Parenting? PLoS One. 2012; doi:  10.1371/journal.pone.0030055


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83 Responses to Battle of the Brains: Size Matters

  1. Jim Tipping says:

    “Male sticklebacks build elaborate nests, perform elaborate courtship displays and care for their offspring alone. So guys, pay attention to the nursery if you want to be smarter!”

    Hmm. Not sure that’ll do it. I lost a few IQ points while I was losing sleep on behalf of the little ones… 😛


  2. Chad Haney says:

    I don’t know about size but it matters if it’s grey or white.

  3. Rajini Rao says:

    Jim Tipping , even for 25% increase? Or perhaps you are worried about compensatory changes elsewhere? 😉

    Chad Haney , the link to the human studies does make a distinction between grey and white matter differences in human male and female brains.

  4. Chad Haney says:

    But it matters to mad hatters, like me.

  5. Chad Haney says:

    Exactly. Now you got me.

  6. Gayness seems to be another factor in the brain size and function;

    “The brains of lesbians and straight men were anatomically symmetrical while the brains of gay men and straight women had a larger right brain hemisphere.”

  7. Rajini Rao says:

    Akira Bergman , that study was published in PNAS, which is fairly reputable..I’ll check it out, thanks.

  8. Jim Tipping says:

    Rajini Rao No, no, I definitely lost brain capacity while the boys were growing up. Constantly being awakened in the middle of the night by sleepless babies will do that!

    The oldest now has a baby of his own. And that kid sleeps just fine! What goes around does not come around…


  9. Jim Carver says:

    I don’t think at least with Homo spp. it’s that much dependent on size, but how you use it. The arrangement of the different structures over time has seemed to play a more important role. No I don’t have a link because it’s from reading some things over the years.

  10. Rajini Rao says:

    Jim Tipping you reminded me of my second one, who terrorized us with his night terrors. After several sleepless weeks, when we were at our wits end, we took him to the pediatrician who said, casually, that he would grow out of it eventually…by the time he was 12 years old! He turned out to be quite correct, unfortunately. Fortunately, that kid turns 14 tomorrow.

  11. Rajini Rao says:

    Actually, that makes a lot of sense Jim Carver 🙂

  12. Jim Carver says:

    Rajini Rao I think it’s right according to anthropology experts. I would have to dig for references to substantiate this conjecture.

  13. Rajini Rao says:

    No need, I trust your memory. An analogy would be of longer muscles in natural sprinters, although they still have to train to win.

  14. Jim Carver says:

    Thanks, didn’t feel like doing that right now. Whew. haha. It still is tickling my brain cells though and I’m sure I’ll go re-check that a little later. Boy, that’s one complex subject and you surely do get differences of opinion also.

  15. Satyr Icon says:

    Generally speaking I don’t think a bigger brain necessarily means better cognitive powers, or even better survivability.

    The number of axons, neurons, synapses, and their activity, actual usage and efficiency should also matter.

    Therefore I would think in less sentient fauna the motor section size is probably more important than the memory and processing compartments size. And the motor section parts would be proportionally bigger with larger bodied animals, and animals that had more dynamic limbs. I’m guessing.

  16. Jim Carver says:

    Satyr Icon I think your guess is pretty good.

  17. Rajini Rao says:

    Well,  yes, Satyr Icon , I agree that the connections are very important. But, all those things things being equal, mass of brain tissue would matter. That’s essentially what this study tells us. At an individual level, a person with a smaller brain could use it more effectively than someone with a larger brain.  Over a population, though, on average, larger brains correlate with more cognitive power.

  18. Anyone compared the size of the brain of human beings by gender?

  19. Jim Carver says:

    In my simplistic mind I tend to think of it like a computer. Maybe we’re heading that way in making the computer more  like a brain. I’m sure we will.

    If you were to have a smaller hard drive with a very good processor, you have still a nice machine. etc. I don’t need to carry the analogy out any farther because you guys are smart.

  20. Rajini Rao says:

    Yes they have, Vasilina Orlova . The link is in the main post above. I mentioned that they are controversial, and the article discusses why.

  21. Rajini Rao says:

    No problem, it is buried in there 🙂

  22. Jim Carver says:

    We will get buried better. 🙂

  23. Rajini Rao But almost all the things so far in the nature I have seen is a balance between energy ( yes I mean food+process) needed to build and maintain that mass as against competitive advantage it gives.

    e.g. The large muscle mass takes energy and food away from other building processes and usage of the large muscle produces more toxins which in turn needs more work to excrete

    e.g. Large companies and countries fail eventually when maintaining the size undermines the advantage of the size.

    Also, to build large brain, it needs more resources and processes. It also takes a lot of oxygen to keep it going.

    Only in last few centuries, humans have enough food and safety to afford large body parts.

    So, dont you think that at some point the brain size increase will adversely affect survival?

  24. Rajini Rao says:

    mandar khadilkar , indeed the investment in size comes with an energy cost. That’s been noted in animal studies, and I alluded to compensations elsewhere in the body, in my post. But remember that evolution selects against unfavorable changes. If and when size adversely affects survival, then it will lose to smaller, more adaptable sizes (as mammals outwitted the dinosaurs eventually). That’s the beauty of nature, isn’t it?

  25. Rajini Rao Yes. You have described it very well.

  26. Rajini Rao says:

    How about behaving like a fathead? LOL.

  27. Feisal Kamil 🙂 May be it is because of over eating……just takes more energy to digest……

    Rajini Rao Dont you think that the evolutionary principles are more fundamental than living part of the world?

    You can apply it to organizations, countries and cultures. You can apply that to galaxies, planets and much more.

  28. Rajini Rao says:

    Very true, mandar khadilkar ! Evolutionary principles apply to other walks of life too. Have you heard of the infamous Darwin awards? It’s given to individuals whose foolishness takes them out of the gene pool 😉

  29. Rajini Rao says:

    Haha, Feisal Kamil , are you volunteering for the experiment testing food vs. energy?

  30. Rajini Rao says:

    Making breakfast = dressing your nest. If you were a stickleback, your brain would be bigger already 🙂

  31. Rajini Rao says:

    Which parts?

    LOL, don’t answer :O

  32. Feisal Kamil  Wish you happy breakfast!

  33. Rajini Rao darwinawards are funny. I drive motorcycle in US..hope I dont become part of the list before my time 🙂

  34. Jim Carver says:

    I think the evolutionary trend is to get perhaps somewhat smaller in many cases. A consolidation of effort seems to be quite evident as we see flower parts fuse in many later plants. The trend is more specialized and that worries me a bit as we appear to be entering a period of rapid change.

  35. Rajini Rao says:

    Inevitably, rapid change (~50 yrs) will trigger massive die-offs. The only consolation is that this has happened many times before, and more adapted life forms emerged. Unfortunately, those life forms may not be us the next time.

  36. Jim Carver says:

    Rajini Rao Sure, we live on the heels of the massive die off that happened 65 million years ago. And since we’ve only been around for about 2-3 million years. Hey, that’s not too much to ask. I think we did pretty well. To think that this would continue for another 1 million or even a thousand is, well, somewhat far fetched. The species will adapt or go out of existence. I don’t think you/we have to worry about the sun getting bigger.

    Oh say btw, sorry for off topic but the sriracha is in the jar and fermenting nicely. 🙂

  37. Adam Dray says:

    That chart is shit. The y-axis value starts at like 1.31 or something, and that exaggerates the 25% difference.

  38. Jim Carver says:

    Adam Dray Do you think she would put up a bad chart? Man you need your head examined. You are not understanding this.

  39. Rajini Rao says:

    I knew someone would bring that up 🙂

    You are correct, most of us would not choose to depict data like that. However, the axis is clearly labeled, and if one did not note the scale and mistakenly assumed that it started at 0, then difference would have been huge, at least 300%! I looked at the scale, and noted the numbers they cited which matched the 25% (to be precise 23%) difference in the text. So I had no problem with it (other than expecting someone to point this out!). 😀

  40. Or create a log scale on the y axis that would make more real life visualization. Most of our senses tend to work log scale….

  41. Rajini Rao says:

    Hehe, the chart is simply figure 1 in the linked article. The brain images are figure 2. I added the fish and the notes (colored font! coordinated!). 

  42. Feisal Kamil i was about to suggest color and other things…….well color is much better because then we can have real debate about what color makes more sense 🙂

    Once we ignore small things as real science and information, we will have lot time debating more important things like scale, color and don’t forget font.

    Now we will talking….

  43. Rajini Rao says:

    Do I get any credit for finding the right fish? 

    There is even a scale bar on the fish. And three spines, if one cannot count 😛

  44. Jim Carver says:

    mandar khadilkar I don’t understand what you are talking about most of the time, so bear with me.

    I don’t know what you refer to as the color and other things and even a debate about that and if it makes sense.

    Makes no sense to me.

    Colors are just the different wavelengths and frequencies of electromagnetic radiation. What are you debating? I don’t get it.

  45. Chad Haney says:

    You get credit if you catch one while fishing with me and Peter Lindelauf Don’t worry you don’t have to eat it.

  46. Rajini Rao says:

    Okay, you guys are having way too much fun with this post. Next time, no colors for you.

  47. Rajini Rao says:

    Pictures, or I’m not giving you credit Chad Haney .

  48. Lol.

    Now I suddenly don’t feel bad about my previous project review where we spent half the time about debating “cancel” “ok” or “ok” “cancel”

  49. Chad Haney says:

    No you have to catch one and I’ll take a picture of you fishing.

  50. Jim Carver says:

    Rajini Rao Yep, told ya. 🙂

  51. NEY MELLO says:

    Hi  Rajini Rao An interesting fact is that superior cognitive power  is not associated with wisdom….. And wisdom is what matters for human survival : the rest is in the end insignificant unless appropriated by actual wisdom, which most of humanity including some of it’s brightest minds is entirely devoid of as in….Genius French mathematicians losing their precious lives in a pistol duel over some hot chick  …or Nazi scientists misapplying  their genius against humanity..etc…and the list is as long as known history… 😀 😀

  52. Jim Carver says:

    HEY Ney, I think you have something to say!

    If I can get past the annoying syntax.

  53. Rajini Rao says:

    Excellent point, wise too NEY MELLO ! Thank you. 

    To be fair, from a scientist’s perspective, some forms of cognitive ability are easier to score than others..wisdom would be hard to quantify.

  54. Feisal Kamil UX is important. No doubt. And most of the Engineers have no clue what is good for users….

  55. Rajini Rao says:

    Brain size does correlate with cognitive animals, it is defined by the complexity of behavior, skills in building next and so on. There is a lot of literature on this. Wisdom, is more nuanced isn’t it? One applies experience and makes judgement calls..more than a computational task.

  56. Isn’t cognitive word too vague? Wikipedia says:

    In science, cognition is a group of mental processes that includes attention, memory, producing and understanding language, learning, reasoning, problem solving, and decision making. Various disciplines, such as psychology, philosophy, linguistics, science, and computer science all study cognition. However, the term’s usage varies across disciplines; for example, in psychology and cognitive science, “cognition” usually refers to an information processing view of an individual’s psychological functions. It is also used in a branch of social psychology called social cognition to explain attitudes, attribution, and groups dynamics.[citation needed]

    That is too much for my small brain!

  57. Rajini Rao says:

    That was quite a mouthful, thank you mandar khadilkar 🙂

    My brain is under assault, and being past midnight, I’ll have to cogitate on that in the morning 😛

  58. Jim Carver says:

    I think he should eat more cheese, Feisal Kamil .

    and relax. Really, take my advice.

  59. Jim Carver Cheese for brain! That is a new one for me. Must be some survey with size of two showing the link…. 🙂

  60. Jim Carver says:

    Well I guess it’s all ATP no matter how you get it. Longer molecules can do more, but shorter molecules are quicker.

    GN 🙂

  61. NEY MELLO says:

    Rajini Rao ..Indeed, it would be hard to qualify wisdom as you so sagaciously put it…It would be even harder to actually find some to even attempt to qualify it! 😀 :D… It would require extra grant funding just to find some, with absolutely no guarantees of any valid  results… 😀 😀

  62. Jim Carver says:

    NEY MELLO I find your style and tone less than pleasing. It reminds me of a neotaxian I met on Beta4. I’m sure you have seen the episode since it has been in syndication for some time now.

    I believe that it would be futile to continue your ill advised attempt on trying to discredit  Rajini Rao. As they would say in the vernacular: You are barking up a tree that is too big for you.

  63. Adam Dray says:

    Hey, Rajini Rao! I didn’t realize you’d created the chart. I thought it was something you linked, or I’d have, um, been less of an asshole. Sorry about that. 

    I attended a Tufte seminar 15 years ago and have been a chart snob every since.

    The content of  the article was great, even if I didn’t like your y-axis. Thanks for sharing, and again, sorry to be a jerk.

  64. Rajini Rao says:

    No worries, Adam Dray . If you sum up a chart do’s and don’ts, it would be a great share. As Feisal says, I didn’t make the graph..I just combined their original figures and added some legends. (and the fish!).

    There are some occasions when it makes sense to have axes not start from zero. If you recall the recent election coverage, Obama and Romney were only a percentage point or two apart in the last few months. Although statistically significant, and as it turns out, accurately predictive, we would never have seen the difference if the y-axis scale was not focused on a very narrow range. What’s important is whether the authors mean to mislead or simply present data in a more legible way. In this case, the researchers were quite clear with their findings, and did not try to pass them off as more significant than they already were (25% is huge!).

  65. Chad Haney says:

    You are very generous Rajini Rao 

  66. Rajini Rao your last comment to the Adam’s post is a classic, balanced and reasoned note.

    This is so factual, very well and still simply put.

    It demonstrated respect and shown ability to address issue with wise head on the shoulders.

    A lot to learn from Mam Scientist…keep on posting good stuff for us to read.

  67. Rajini Rao says:

    Awww, thank you mandar khadilkar . I suspect you are all being too generous 🙂

  68. this is a very interesting topic…thanks!

  69. Rajini Rao

    “… pay attention to the nursery if you want to be smarter!”

    I know you were being tongue-in-cheek, but that statement has the causality backwards. Being smarter is what causes the attention to the nursery in those species.

    It would be more proper to say “pay attention to the nursery if you want to appear smarter!”

  70. Rajini Rao says:

    Andreas Geisler , the authors of the study would not agree with you. To quote, they “speculate over the evolutionary reasons for the reported brain size dimorphism, but we propose that this brain size dimorphism is likely driven by the high cognitive demands of mate attraction and parental care in males.” In other words, evolutionary pressure arising from their nursery care selected for larger brain size. So my tongue-in-cheek advise to guys is that baby sitting may help their brains “evolve” to larger sizes too 😉  

  71. Rajini Rao That’s still got the mechanic of selection backwards. Selection functions the other way around.

    The ones with the brains focus on caretaking tend to have more surviving offspring. That’s how brain size and selection are connected in the described situation.

    “Faking it” will have no impact on the brain of the faker or on the brain sizes of their offspring. On the contrary, it will cause the faking one’s normal-brained offspring to have (some of) the same advantages as the big-brained one’s offspring.

  72. Andreas Geisler you are right. The evolutionary forces make no difference if you either fake the care or do really care. It only will make the difference if you actually take care.

    Here is why- (historically)

    If you take care of the young, then you either have more females accepting and then can engage in more contacts or raising your offsprings batter for survival.

    In both cases you increase you chances of passing your genes to next generation.

    In one case having more offsprings as you get more mating and statistically increasing chances in passing genes overcoming mortality.

    In other case, your care increases survival directly.

    In either cases the gene which made you take care is also passed. It does not matter if you genuinely cared or just did it to increase your chances to mate.

    You were smart in both cases. This is the brilliancy of evolutionary forces.

    In several cases evolutionary forces are very very basic and obvious.

    Would be interesting to read what Rajini Rao has to say…

  73. Rajini Rao says:

    Andreas Geisler , the question is, how did the male stickleback brains get so large? A random mutation could not do that..but evolutionary selection of small changes over a long period of time would. What would select for larger brains? Successful mating and survival of offspring with those characteristics. What would ensure successful mating and survival of one’s progeny? Complex behavior such as nest making and caring. All the authors are saying is that complex nursing behavior drives the selection of larger brains, given the fact that complex behavior does require more neurons and connections (your point, which I agree with!).

    So it’s a chicken and egg argument, really. More sophisticated wiring and brain function is required for complex tasks, which in turn drives further selection of highly developed brains.

    As mandar khadilkar says, it does not matter whether one fakes the nurturing or does it sincerely, as long as the job gets done 🙂

  74. The most interesting to me is that the physical demands on the female prevents them from having the same brains.

    However, I wonder if the females’ brains have the same kinds of differences as are observed in humans.

    In the females the pressures would favor having as efficient a brain for the size.

    The males can grow their brains big. The females might have to optimize the function of the brain, getting the most out of the limited amount they can have.

  75. Rajini Rao The most unresolved issue in evolution would be-

    Is there is any mechanism that makes statistically more useful changes which are self driven as against a large set of random changes only to be sustained or eliminated.

    The current agreed thinking is that it is the latter. A similar argument exist in astrophysics today. The fundamental values of various constants are just mathematically coherent for us to exist.

    For either evolution or universe to produce how we are (large brain, limbs are particular proportion and location, location of other parts and all social behavior. The same is true for gravity, forces in nature, location of earth etc) all the probabilities need to be tried and then whatever is suitable will lead to how things are.

    My view is that we will never know if there is intrinsic built in mechanism to select a specific mutation. We are at ‘present’ of a ‘successful past’.

    We will never know if a small brain would survive or not.

    Assume that we had smaller brain. We would never build modern society and kill our environment. We can not decide if future is better for primitive life form without big brain or people like us with who can virtually change the face of earth.

    Only time will tell…..

  76. mandar khadilkar You forget the relevant scopes involved!

    An individual carries the genetics it carries, be they novel mutations or one of the myriad combinations of the many subtypes already in existence in the gene pool.

    So there is no selection within the individual at all.

    The “selection” only comes into account when the individual breeds.

    If a mutation is not passed on, it’s like it never existed.

    So the only relevant forces that could perform a genetic arbitration like what you describe would be the in the minds of the breeding partners available … and we know that exterior variables can affect breeding choices – however, we do not have reason to suspect that detailed genetic analysis is involved. Among other things, we don’t know what organs various life forms would use to perform such an analysis.

    Even if there were such an organ, there’s going to be a lot of chance involved. Proliferation depends on a lot of factors.

  77. Rajini Rao says:

    I just came across this fascinating study in which guppies were artificially bred to have larger brains. This made the females “smarter” but it came with a cost of smaller gut size and fewer offspring. The authors make a good point: why does every animal not have a large brain? The answer seems to be that there is a downside in cost (energy use and other body parts), so in the end it is a trade off between cost and benefit.

  78. Rajini Rao that was the discussion we had previously on trade offs. I read somewhere that brain consumes very large quantity of oxygen and needs a lot of sugars if I remember correctly. I also vaguely remember that large muscles are very expensive and put a lot of stress on lever so when body thinks that it does not need muscles, it decreases muscle mass fast.

    Obviously my info is pure layman knowledge.

  79. Rajini Rao and mandar khadilkar  Weren’t Neanderthals supposed to have had bigger brains than we do?

    The same cost/benefit problems could be true even for hominids. If nothing else, it consumes a lot of energy, and that makes the species vulnerable to ecological changes.

    Even our smaller brains consumes 20% of our total energy consumption, and it doesn’t slow consumption no matter what we do, even sleeping it keeps consuming.

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