Emil Kirkegaard left a short commentary on John Skoyles’ 1999 paper Human Evolution Expanded Brains to Increase Expertise Capacity, not IQ, in which Emil writes in his article Evolution and imperfect mediators:
If we condense the argument, it becomes a little clearer:
John Skoyles (1999) [Condensed argument from Emil; paragraph 2] Brain expansion causes problems. Thus, whatever selected for increased brain size must have offered compensating benefits. People can have below average size brains yet exhibit normal intelligence. Thus, the compensating benefit offered by large brains is unlikely to be intelligence. Why should evolution have increased brain size with its associated problems for something smaller sized brains could have without expansion?
I merely edited out the unnecessary parts. Now try substituting some other trait, say fighting ability and some mediator of it.
Muscle size increases causes problems. Thus, whatever selected for increased muscle size must have offered compensating benefits. People can have below average size muscles yet exhibit normal fighting ability. Thus, the compensating benefit offered by large muscles is unlikely to be fighting ability. Why should evolution have increased muscle size with its associated problems for something smaller sized muscles could have without increase?
See the issue? This argument works for any imperfect physical underpinning of a trait, which is to say, basically all of them. Longer legs didn’t evolve for running well for some people with short legs run well. Bigger/stronger hears didn’t evolve for better cardio, because some people smaller/weaker hearts have good cardio. Longer arms didn’t evolve for fighting because some short armed people fight well. Darker skin didn’t evolve as a protection against sun exposure for some relative light skinned people don’t get skin cancer or sunburns. Larger eyes didn’t evolve for seeing better for some people with smaller eyes see well. Bigger ears… Bigger noses… Stronger hands… …
I don’t agree. Our brains sap about 20 percent of our daily energy needs while being 2 percent of our overall body mass whereas, in other primates, their brains cost about 9 percent of their daily energy needs (Fonseca-Azevedo and Herculano-Houzel, 2012).
In regards to Emil’s counterarguments, I’ll address them one by one:
Long legs: People with longer legs were better runners and could escape from predators and chase prey. People with shorter legs were killed.
Bigger/stronger hearts: Those with a larger heart (sans cardiomegaly) could run for longer distance (remember, we are distance runners; Carrier, 1984; Skoyles and Sagan, 2002; Bramble and Lieberman, 2004; Mattson, 2012) and so long legs and bigger/stronger hearts tie in with each other.
Long arms: This, again, goes back to our morphology in Africa. Long limbs are more conducive to heat dissipation (Lieberman, 2015). So those who had the right body plan for distance running could survive better during our evolutionary history.
Dark skin: A light-skinned person who spends enough time without protection in a tropical climate will develop skin cancer. (It is hypothesized that skin cancer is what caused the evolution of dark skin; Greaves, 2014, though this was contested by Jablonksi and Chaplin, 2014.)
Large eyes: Bigger eyes don’t mean better eyesight in comparison to smaller ones.
All in all, the brain size argument is 100 percent different from these arguments: large brains come with large problems. Further, there is evidence (which will be reviewed below) that people can live long, normal lives with half of their brain missing
The brain-size/IQ puzzle
The oft-repeated wisdom is that our brains evolved to such a large size so we could become more intelligent. And looking at when our brains began to increase (starting with erectus, which had to do with the advent of cooking/fire use), we can see that that’s when our modern body plan appeared. We can ascertain this by looking at Nariokotome boy, an erectus that lived about 1.6 mya.
Further, in regards to brain size, there was a man named Daniel Lyon. What was so extraordinary about this man is that, at the time of his death, had a brain that weighed 1.5 pounds (see Wilder, 1911)! Skoyles and Sagan (2002: 239) write:
Upon examination, anatomists could find no difference between it [Lyon’s brain] and other human brains apart from its size with one exception: The part of his brain attached to the brainstem, the cerebellum, was near normal size. Thus, the total size of Lyon’s cerebral hemisphere was smaller than would be suggested by a total brain weight of 1.5 lb. We do not know how bright he was—being a watchman is not particularly intellectually demanding—but he clearly was not retarded. A pound and a half brain may not be enough to manage a career as an attorney, a professor of theology, or a composer, but it was sufficient to let Lyon survive for 20 years in New York City.
Skoyles and Sagan (2002) review numerous lines of evidence of individuals with small brains/people with severe TBI living full lives, even having IQs in the average/above average range. They write (pg 238):
You would think that cutting out one-half of people’s brains would kill them, or at least leave them vegetables needing care for the rest of their lives. But it does not. Consider this striking story. A boy starts having seizures at 10 years of age when his right cerebral hemisphere atrophies. By the time he is 12, the left side of his body is paralyzed. When he is 19, surgeons decide to operate and remove the right side of his brain, as it is causing gits in his intact left one. You might think this would lower his IQ or leave him severely retarded, but no. His IQ shoots up 14 points, to 142! The mystery is not so great when you realize that the operation has gotten rid of the source of his fits, which had previously hampered his intelligence. When doctors saw him 15 years later, they described him as “having obtained a university doploma . . . [and now holding] a responsible administrative position with a local authority.” (18)
They also write about the story of an Argentinian boy who had a right hemispherectomy when he was 3-years-old who was notable for “the richness of his vocabulary and syntax” and also “attends English classes at school, in which he attains a high level of success (20; quote from Skoyles and Sagan, 2002: 238).
It is also a “medical myth that microcephaly (having a head smaller than two standard deviations (SD) below average circumference) is invariably linked to retardation.” (Skoyles and Sagan, 2002: 239).
There are some important things to be noted in regards to the study of Nariokotome boy’s skeleton and skull size. Skoyles and Sagan (2002: 240) write (emphasis mine):
So how well equipped was Homo erectus? To throw some figures at you (calculations shown in the notes), easily well enough. Of Nariokotome boy’s 673 cc of cortex, 164 cc would have been prefrontal cortex, roughly the same as half-brained people. Nariokotome boy did not need the mental competence required by cotemporary hunter-gatherers. … Compared to that of our distant ancestors, Upper Paleolithic technology is high tech. And the organizational skills used in hunts greatly improved 400,000 years ago to 20,000 years ago. These skills, in terms of our species, are recent, occurring by some estimates in less than the last 1 percent of our 2.5 million year existence as people. Before then, hunting skills would have required less brain power, as they were less mentally demanding. If you do not make detailed forward plans, then you do not need as much mental planning abilities as those who do. This suggests that the brains of Homo erectus did not arise for reasons of survival. For what they did, they could have gotten away with much smaller, Daniel Lyon-sized brains.
Lastly, I will touch on the fact that since we are running apes, that we need a narrow pelvis. As I stated above, our modern body plan came to be around 1.6 mya with the advent of erectus, which could be inferred from footprints (Steudel-Numbers, 2006; Bennett et al, 2009). Now the picture is beginning to become clearer: if people with brains the size of erectus could have intelligence in the modern range, and if our modern body plans evolved 1.6 mya (which is when our brains began to really increase in size due to metabolic constraints being unlocked due to erectus’ cooking ability), then you can see that it’d be perfectly possible for modern Homo sapiens to have brains the size of erectus while still having an IQ in the normal range.
Lastly, Skoyles and Sagan (2002: 245) write (emphasis mine):
Kanzi seems to do remarkably well with a chimp-sized brain. And while we tend to link retardation with small brains, we have seen that people can live completely normal lives while missing pieces of their brains. Brain size may enhance intelligence, but it seems we can get away without 3 pounders. Kanzi shows there is much potential in even 13 oz.
So Skoyles and Sagan do concede that brain size may enhance intelligence, however, as they have argued (and as Skoyles does in his 1999 paper), it is perfectly possible to live a normal life with half a brain, as well as have an average/above average IQ (as reviewed in Skoyles, 1999). So if people with erectus-sized brains can have IQs in the normal range and live normal lives, then brains must have increased for another reason, which Skoyles has argued is expertise capacity.
Large brains are, clearly, not needed for high IQs.
(Also search for this paper: Reiss, A. L., Abrams, M. T., Singer, H. S., Ross, J. L. & Denckla, M. B. (1996). Brain development, gender and IQ in children: A volumetric imaging study. Brain, 119, 1763-1774. where they show that there is a plateau, and a decrease in IQ in the largest brains; see table 2. I also reviewed some studies on TBI and IQ and how even those with severe TBI can have IQs in the normal range (Bigler, 1995; Wood and Rutterford, 2006; Crowe et al, 2012). Yet more evidence that people with half of their brains missing can lead normal lives and have IQs in the modern range.)
Increased brain size is a result of higher selection for circuit redundancy and an increase in absolute number of neurons. In this “model” Neuronal density can be increased as a more economically viable solution than absolute brain size which is partly an after effect of increased diet breadth, which subsequently increases body size. Social bonding as a countermeasure against within group social competition is hypothesized to account for the exceptionally high neuron to synapse ratio found in birds and primates. Following anatomical changes(bipedalism, proposed increase in cortical complexity) in Australopithecus and homo habilis Humans transitioned to a more predatory lifestyle, this in turn encouraged a higher dependency on tool culture, Which would catalyze a need for social learning. Language, bodily and vocally along with this “father to son” communicative model are proposed to to replace parasitic grooming as a new form of social bonding, making the cons of group living null. These new forms of social bonding would put pressure on plasticity, specifically neural plasticity. Essentially the human brain has achieved it’s size solely so that it could be damaged and still function “properly” So that it could learn and improve itself. The added Neurons add extra heat and energy which of course contributes to intellectual output but in this model brain size is not the end goal of cognitive evolution within humans. In fact in this thesis, High EQ itself is a Neotenous trait.
Also do you have a source on daniel lyon that isn’t from over a century ago?
You know I agree and that I am a huge proponent of Herculano-Houzel’s work.
I agree. Though—as can be gleaned from my piece—I believe that our extra brain mass is irrelevant to our ‘intelligence’. I also like the social learning hypothesis—but hate how the Neo-Darwinists use it for evidence for ‘cultural evolution’. One more point on a predatory lifestyle/hunting: it increased cooperation as well, which of course aided in social learning.
I agree with this (the origins of language is something I’m currently reading into and I will write something on it). I have told you before that I am taking to the social brain hypothesis (SBH) since I’ve done a lot more reading into our evolutionary history.
What are your views on how neural plasticity shaped our evolution?
I agree with this as well (‘damaged and still function “properly”‘), I cited an article on this but I can’t find it at the moment, I’ll link it later.
You know my views on EQ, which I’ve touched on a bit in my articles on Herculano-Houzel’s work (I will write something on it eventually).
Yes, through symbols, learning and tools, our brains learned how to ‘shape themselves’, so to speak. Neural plasticity is a very interesting field.
No I do not. I did a bit of digging, couldn’t find anything.
I think Skoyles and Sagan make a good case that (at least some—maybe most) of the extra brain mass we have in comparison to erectus is due to the need for increased expertise capacity, since larger brains hold more cortical columns (and neurons, which are needed for learning how to use/make tools and become an expert tool maker).
I’m also in the process of compiling as much information about individuals that suffered severe TBI, hemispherectomy, etc to write a nice piece on it.
People like Daniel Lyon and others prove that it is very possible to live a normal life with half of your brain. There is also a minimal IQ hit when the PFC is removed (will cite sources later). So I do believe that most of our extra brain mass after erectus (early erectus) is not needed for higher ‘intelligence’—but for expertise capacity, as I have argued.
“I believe that our extra brain mass is irrelevant to our ‘intelligence”
I don’t believe it’s irrelevant. It obviously has an effect but only because the size of the cranium would correlate with absolute number of neurons.
“but hate how the Neo-Darwinists use it for evidence for ‘cultural evolution”
What do you mean?
“What are your views on how neural plasticity shaped our evolution?”
Neural plasticity would correlate with our increased neoteny. Better parenting skills would have been preferred to high fecundity especially in scenarios with high risk failure. There are studies on baboons that indicate this unfortunately I am having trouble finding the study. If the CIH is correct we should see a step like increase in tool complexity, which seems to be the case. It should be noted that in this instance redundancy is not to denote a sense of uselessness.
Secondly, we should of course see anatomical correlates of social function which is indeed the case. Spindle neurons, believed to help regulated emotion Are found only in the most social of animals like Great apes and Cetaceans
“Their restriction (among the primates) to great apes leads to the hypothesis that they developed no earlier than 15-20 million years ago, prior to the divergence of orangutans from the African great apes. The discovery of spindle neurons in diverse whale species has led to the suggestion that they are “a possible obligatory neuronal adaptation in very large brains, permitting fast information processing and transfer along highly specific projections and that evolved in relation to emerging social behaviors.”Their presence in the brains of these species supports this theory, pointing towards the existence of these specialized neurons only in highly intelligent mammals, and may be an example of convergent evolution”
Plus there has been the recent discovery of social and asocial neurons.
“During the experiment, some of these neurons were only strongly activated in the presence of a conspecific. They have thus been dubbed social neurons. On the other hand, the activity levels of other, asocial neurons only spiked in the absence of a fellow monkey. Even more surprisingly, the greater the intensity of social neuron activity in the presence of a conspecific, the better the subject performed the task. Social neurons are hence at the root of social facilitation. Likewise, the greater the activity of asocial neurons in the absence of conspecifics, the better the subject performed the task—though not as well as in the presence of another, when social neurons are stimulated. The researchers also demonstrated that in the other, rare permutations—activation of social neurons in the absence of conspecifics, or of asocial neurons in their presence—the monkeys did not perform as well.”
Also in regards to that 2017 Dunbar paper you showed me, even though it cleared up a lot of misconceptions that even I had about the SBH it has still coem under scathing criticism lately.
“We agree with Dunbar & Shultz (43) that, in principle, comparative analysis should differentiate between selection pressures and constraints, but it remains unclear how this can be achieved in practice. While path analysis has been suggested as a possible solution it is essentially a protocol for arranging a set of regression coefficients according to some causal hypotheses; it cannot be used to discover causality from correlational data, it cannot solve the problem of instability across datasets, and it is as vulnerable to underlying issues with the data as are the regression analyses on which it is based. In summary,
while it remains plausible that sociality is related to cognitive evolution in primates, we suggest that this can no longer be claimed on the basis of a strong or robust correlation between brain size and group size that remains after controlling for other variables.”
The study found that Home range size was the best predictor of Primate brain size however, the Authors note that almost all data on this subject is far too inconsistent for a perfect rendition, using what limited reference materials we have.
This actually boosts my version of the SBH I had always assumed that group size would only have a moderate effect after a certain extent, i think it’s a sufficient explanation for the increase cellular density in birds and primates and possibly cetaceans, but beyond that I think it’s the actual interactions that determines increased selection on higher cognitive functions.
Interesting I found that mid sized groups had the largest home range size, according to my theory the high correlation with brain size is due to two major factors 1) Home range size correlates significantly with Diet breadth and 2) A larger territory size means a higher cognitive demand to defend it from other humans and successfully hunt on it.
Click to access 14882.full.pdf
“is not needed for higher ‘intelligence’—but for expertise capacity”
What is the difference?
” Compared with men born with appropriate birth weight for gestational age, men born light for gestational age suffered an increased risk of low intellectual performance after adjustment for maternal and socioeconomic factors. The increase in risk of low intellectual performance related to a decrease in birth weight for gestational age was similar between families and within families.”
It’s an very short read RR. Only like 7 pages of big text!
Click to access bergvall2006.pdf