Image: Photograph by Adam Voorhes
In Brief
- Human intelligence may be close to its evolutionary limit. Various lines of research suggest that most of the tweaks that could make us smarter would hit limits set by the laws of physics.
- Brain size, for instance, helps up to a point but carries diminishing returns: brains become energy-hungry and slow. Better “wiring” across the brain also would consume energy and take up a disproportionate amount of space.
- Making wires thinner would hit thermodynamic limitations similar to those that affect transistors in computer chips: communication would get noisy.
- Humans, however, might still achieve higher intelligence collectively. And technology, from writing to the Internet, enables us to expand our mind outside the confines of our body.
More In This Article
Santiago Ramón y Cajal, the Spanish Nobel-winning biologist who mapped the neural anatomy of insects in the decades before World War I, likened the minute circuitry of their vision-processing neurons to an exquisite pocket watch. He likened that of mammals, by comparison, to a hollow-chested grandfather clock. Indeed, it is humbling to think that a honeybee, with its milligram-size brain, can perform tasks such as navigating mazes and landscapes on a par with mammals. A honeybee may be limited by having comparatively few neurons, but it surely seems to squeeze everything it can out of them.
At the other extreme, an elephant, with its five-million-fold larger brain, suffers the inefficiencies of a sprawling Mesopotamian empire. Signals take more than 100 times longer to travel between opposite sides of its brain—and also from its brain to its foot, forcing the beast to rely less on reflexes, to move more slowly, and to squander precious brain resources on planning each step.
This article was originally published with the title The Limits of Intelligence.
Already a Digital subscriber? Sign-in Now
If your institution has site license access, enter here.
Rights & Permissions
See what we're tweeting about
28 Comments
Add CommentThe fact that all of us aren't yet running around with genius IQ's suggests it might be a little "early" to say that the human brain's evolution has "maxed-out"!
Reply | Report Abuse | Link to thisWell if everyone could be as smart as the smartest humans ever (whether Mozart style or Einstein style) that would be a huge change from the current average... and would be a change we at least know is physically possible.
Reply | Report Abuse | Link to thisOh Please. The first two commentators are absolutely correct. Add the old saw about us using only 10%, or Einstein's 5%, of our brains and we've got a long, long way to go. BTW, what do you mean by intelligence, anyway? I didn't get the memo that it had been adequately defined.
Reply | Report Abuse | Link to thisSince we know that some colony lifeforms use optical connections to communicate, rather than electrical or chemical, it follows that the limits imposed by electrical and chemical connections are merely hard limits for the brain as it stands, it is not a hard limit for biological systems.
Reply | Report Abuse | Link to thisBTW, there's an interesting theory that Autism may actually be a throwback to our Neanderthal ancestors. It's a condition that’s hugely "over-represented" in Northern European & Eurasian populations, and one of the primary symptoms is the absence of empathy & social intelligence, located in modern humans in the pre-frontal cortex, the newest evolutionary part of the brain. It's thought that acquiring this more sophisticated capacity for social connections (and all the useful organizations along with them), is why modern humans eventually overtook the Neanderthals, who otherwise had very comparable intelligence and tool-making abilities. Even today, hi-functioning autistics (aka "Asperger's) often have very high IQ's, but are also extremely literal, along with very poor social skills. In other words, evolution ain't just about "higher IQ's" and "processing speed"!
Reply | Report Abuse | Link to thishttp://www.rdos.net/eng/asperger.htm
I saw a program on tv several years ago about a young girl in England who was 12 when the documentary was made. When she was younger, two I think, she had a severe case of hydrocephalus. She was saved with a ventricular catheter but left her brain deformed. At the time they did the documentary, it was compressed to about a three-quarter inch layer around the skull. The interior was hollow and filled with cerebrospinal fluid. Yet she had developed fairly normally. She was doing well in school and was a fairly talented pianist. It's amazing how adaptable the brain can be.
Reply | Report Abuse | Link to thisThe limits of intelligence may indeed be finite, but to some of us there are still goals not yet achieved and room to grow. Unfortunately for some of the politicians running this country they have long ago reached their limits and are now regressing.
Reply | Report Abuse | Link to thisWhat about possibility that the brain, cells or consciousness may have the capabilities of a quantum computer?
Reply | Report Abuse | Link to thisWhat about the observations that all living cells (when healthy) emit coherent, laser-like light, indicating macroscopic quantum states throughout an organism?
What about the possibility (still under fierce debate) that the microtubule structures of neurons allow for quantum computing?
Quantum computing may allow a person, consciousness, cells, or neurons to be super-supercomputers!
Read my book, The Quantum Shield.
It seems that big dinosaurs had enlargements in their spinal cord at the level of limbs, that acted as some kind of a secondary brain to have a faster control of movements. In mankind,the big difficulty may be that brain circuits do support several functions at once, if a function is purposedly damaged, such in psychosurgery or after some kinds of psychotherapy, a lot of functions besides the ill one that is intended to be supressed will suffer, and some kind of loss of function may even be passed to the offspring, as education involves a lot of brain modulation, and lacking a function in the parents makes extremely difficult to shape it in their children. It's good being extremely conservative when educating or treating people; as Ernst Jung said, some therapies produce severe mutilations
Reply | Report Abuse | Link to thisHuman evolution to a more powerful thinking machine will not be possible by much more simple reasons. Natural selection based on IQ is not allowed anymore and high IQ people don't want kids. Even a mutation that leads to an ultra powerful thinking machine will be lost in a generation or two.
Reply | Report Abuse | Link to thisThank God or nature which had given us limited intelligence otherwise What Neapolitan or Hitler did ? they may destroy whole world.Man may be extremely arrogant.Limit of intelligent teach man be humble take care of nature.I don't want extraordinary intelligence.If God is there I request to him please give me limited intelligence from help of it I can create pure joy and self-satisfaction in my life.I don't more
Reply | Report Abuse | Link to thisJose53 said: "Human evolution to a more powerful thinking machine will not be possible by much more simple reasons. Natural selection based on IQ is not allowed anymore and high IQ people don't want kids. Even a mutation that leads to an ultra powerful thinking machine will be lost in a generation or two."
Reply | Report Abuse | Link to thisThere are a couple of things that come to mind. First, you seem to be underestimating how much evolution is happening when people with very limited resources and education are thrown into a dangerous environment. Just being able to survive or escape would help the evolution of mental capacities. Of course, they don't make headlines with amazing scientific discoveries, but their contribution may be much greater than those who do.
Another thing is that sheer brain power is not all that advantageous in evolution. Emotional Intelligence, including the ability to get along with people, to communicate ideas, to be admired and respected, is at least as important as the ability to come up with novel inventions and theories. A popular person who makes people comfortable, does not make enemies, does not inspire envy, loves people and is loved in return, gets married to a similarly popular spouse, raises similarly popular children, and dies happy, is solving multivariate equations orders of magnitude more complicated than any problems dealt with by science. And doing it unconsciously.
Children can do science. It takes real intelligence to do life.
Curious you see only the evil potential in higher intelligence, and not any of the good. Or don't "average IQ" folks commit evil too?
Reply | Report Abuse | Link to thisActually, it sounds like all you're basically saying is that "ignorance is bliss. Although I hope you don't mind if some of us are unwilling to "take your word for it".
Our species-specific brain size is ultimately determined by the narrowness of our human birth canal ( unless we want all our future babies be delivered by Caesarian section that is..)
Reply | Report Abuse | Link to thisMy hunch is that this dilemma might have caused the decline of the last Neanderthals, what with their heavier-than-thou brains....
Their brain 'hypertrophy' would have been caused by their abundant meat-eating during the last, rather severe Ice Age, when not much else food was available; therefore, vitamin deficiencies would also have been a big survival problem.
Funny though that we super-savvy human moderners still can't get it right when it comes to our own species-specific nutrition! Otherwise we would not be over- or- underweight by the billion.
Might it just be that we have reached the limits of our chimp-de-luxe' s braininess because we cannot rein in our rampant phantasizing super-sized me-brains, especially when it comes to food & lifestyle? Youthevity.com
Exactly what I wanted to say. When we consider the almost unimaginable capabilities of some of our geniuses, or even our idiot savants, or when we someone with a huge portion of his cerebral cortex destroyed by congenital hydrocephalus yet able to gain a masters degree, then we know that mankind has a way to go before we max out the limits of human cognitive capabilities.
Reply | Report Abuse | Link to thisWho and where are the physical laws that limit the working of the brain?
Reply | Report Abuse | Link to thisThe 3/4 exponent power law relating brain size to body size, with some fluctuations for individual species, is related to Klieber's allometric scaling laws in biology. A theoretical explanation for such scaling laws can be found in the work of West, Brown and Enquist based on optimizing metabolism in fractal networks. According to the article, humans have a factor of 7 enhancement over this law. I would appreciate a discussion of the 3/4 power law, specifically focused on brain size.
Reply | Report Abuse | Link to thisNo one here has asked the basic question: Why is there a "range" of human intelligence? A good working hypothesis might be that, as a species, we don't need to have our entire population supplied with 200 IQ capability. So there's probably a genetic reason for the existence of this range and therefore, it's most probable that a majority simply will never have "top level" intelligence.
Reply | Report Abuse | Link to thisNotice too that we differ from all related species by our prodigious population. No other monkeys or apes have ever achieved populations of even a few millions world wide. Finally,notice our current preoccupation with communications technology. We, I think, may be evolving into a hive-mind species. I also think that we may find superior extraterrestrial species to be "like us" in brain size but far more evolved in the direction of hive-mindedness.
interesting...I thought homo sapiens have only been around for 200k years not 2.5 million years...
Reply | Report Abuse | Link to thisWonder what old D'Arcy Wentworth Thompson, author of the great morphological classic On Growth and Form (1917, 1942), might say about all this? Or Julian Huxley, whose thoughts on the size of organisms even made it into the now-comparatively Promethean Reader's Digest of the early 1930s?
Reply | Report Abuse | Link to thisHuman evolution which is based upon the survival of the fitest no longer applies nor should it in a compassionate society. A more relevant concept is sustainability for us and our fellow creatures.
Reply | Report Abuse | Link to thisInteresting article. I've just written blog post about it on Psychology Today, in case anyone is interested:
Reply | Report Abuse | Link to thishttp://www.psychologytoday.com/blog/after-phrenology/201107/is-our-brain-good-it-gets
Stop making fun of the TeaParty.
Reply | Report Abuse | Link to thisI am a little rusty on neuro so correct me if any of this is wrong:
Reply | Report Abuse | Link to thisI understand that planning out motor functions (the problem that was illustrated in elephants) is taken out at the pre frontal area of the cortex and essentially 'tweaked' for lack of a better word at the cerebellum in real time to alter existing movements. However this is by no means what the majority of people would consider to be intelligence.
So my questions is can areas strictly involved in intelligence such as integration of, say, mathematical problems or comprehension of complex worded problems (if such structures exist), rather than relatively simple motor planning, be encumbered by the inherent growth of body size?
In any case, how is the rise in body size relevant to being more intelligent, as it causes so many inherent problems (according to the article). Is the potential to gain intelligence more likely to be from a loss vestigial/non-essential areas of the brain to make room for more cortical matter without running into the need to decrease neuronal conduction speed?
We'll have plug-in expansion modules long before we make any evolutionary advances.
Reply | Report Abuse | Link to thisThere is a very basic evolutionary reason for a limit on the increase intelligence.
Reply | Report Abuse | Link to thisEvolution is determined by both individual and species survival. While intelligence is usually measured as a function of the ability to handle information in a logical methodology, logic is only as valid and useful as the assumptions upon which it is based.
As a result (and unfortunately) any information system reaches a threshold point where the availability of additional information diminishes the utility of that information and the processing of that information is more dependent upon the assumptions on which it is based than the information itself.
Or as Giordano Bruno (the Patron Saint of Geeks) discovered, smarter is not always better.
I found the article quite interesting however it left me hanging a bit because it does not really address one side of the equation, so to speak, which is the problem of defining and measuring intelligence across species. It is mentioned briefly in the article and I would have liked a much deeper discussion, because it is fundamental to the whole argument. Humans assessing the intelligence of another species can be likened, almost equated, to that species demonstrating its intelligence, i.e. "here's what we can do". That of course will be within that species frame of reference: to show off what THEY perceive is particularly advanced. But let's look at it the other way: do humans really make an impression on other species? Let's imagine lab rats and two scientists in the animal house, the latter discussing the latest experiments and models in their field or even putting the said rats through their paces in some fancy new paradigm. Is there any chance that the rats are impressed by this??? Can the rats perceive the 'superior' intelligence they are dealing with? Let's say, 'no'. The next question is, why should the situation be asymmetric? How can humans know what is clever rat or whale behaviour? Also, can stupid behaviour (e.g. that leads to self-destruction) be defined and identified more easily across species than cleverness? There seems to be me to be no guarantee that humans have the capability to recognise what is particularly clever in another species. In summary, I would have liked to read more about the intelligence side of the equation. Signed: not an animal 'rights' activist.
Reply | Report Abuse | Link to thisThe article is interesting enough so long as one can make a working definition of intelligence suitable for the article. Thinking quickly and thinking well are two different things, the former being more suitable for academic IQ tests or puzzle-type pattern recognition IQ tests (which if I am correct would include Raven's matrices).
Reply | Report Abuse | Link to thisSuitability of cognitive problem solving skills to particular environments may not be critical at all, given the relatively long maturation period that humans have compared to other primates. Scoring high on academic and clinical IQ tests would probably not predict success or failure in an environment of which the individual being tested has no knowledge, say some environment occupied by our ancestors 100,000 years ago, including limits of accessibility to food and shelter and saftey from predators.
Other things being held equal, the quicker thinker in many situations is going to have an advantage only where speed of cognition and action are essential factors in long-term survival (long enough to reproduce). There are other things to consider as far as survival and reproduction go, however. Human behavior has seldom been driven overall by rational problem solving or quick thinking.
I think the ability to cognize relatively longer lists of relationships has been the difference in human's intelligence and that of other vertebrates. That comes almost certainly from having relatively more neurons.
This is of more interest to comparative psychology than to IQ in any case. The note that a whale also has relatively larger neurons is of interest, but I understand that a certain sea snail is favored for research because it too has relatively large neurons.
I think most human beings have ample opportunity to learn both maladaptive and adaptive behaviors. Some of the maladaptive behaviors have no effect on survival and reproduction as far as is defined by clinical psychologists. What we need to look at is a measure of cognitive skill in a natural environment, and in our case that can probably only be inferred by patterns of evolution and adaptation over very long periods of time (like 200,000 years, minus the most recent 10,000 years).