Humans have giant chimp brains

ResearchBlogging.orgHumans specialise in being smart. It wasn’t our sharp teeth that allowed us to rise to dominance chain but our brains. It provides us with the intelligence needed to build a metaphorical ladder to the top of the food chain. Yet what is it about our brains that makes us so smart? Is there something unique to the lump of organic matter in my head that distinguishes it from a chimp’s lump of organic matter or are they just variants of the same basic brain?

The most obvious difference between the two is brain size. Despite the fact that both Homo sapiens  and Pan troglodytes  have a very similar body size our brain is nearly thrice the size of a chimp brain. In other words our brain is bigger than would be expected given how big our body is. This is known as encephalisation and humans are indeed highly encephalised with our brains being over 7 times bigger than would be expected.

This increase in size is best explained by the social brain hypothesis, which postulates that it evolved larger to facilitate larger groups. This allowed them to better defend against predators, forage the landscape and so forth. Eventually the brain was sufficiently big that it could also be used for other things, like making fire, and these acted as additional benefits compounding the evolution of bigger brains.

So our brain is big, but is that that the key difference? If I were to magically make a chimp’s brain three times bigger (and also use my new found magic powers to make their skull appropriately bigger) could they develop the cognitive abilities of a human? Many have suggested that this would not be the case and our brain has many other unique components. According to these individuals a human brain is not simply a giant chimp brain.

As a test of what you’ve learnt on EvoAnth I challenge you to guess which one is human and which one is chimp!

Suggested differences between human brains and chimp brains have included everything from relative numbers of neurons (with humans, of course, having more) to the number of non-neuron cells(with humans, of course, having more of those too). And lets not forget the shape, with humans apparently having bits of their brain relatively bigger than would be expected if you just scaled up a monkey brain.

However, new research purports to disprove many of these differences between human and primate brains. Suzana Herculano-Houzel used a technique she created back in 2005 called the “isotropic fractionator.” Whilst I’m not familiar with the specifics it purports to offer a reliable way of counting the number of cells in a brain. And counting brain cells is what she’s been doing, documenting the number of cells in over 20 species.

Her results revealed that there is a relationship between the number of neurons and brain size. Which is kind of obvious. What’s less obvious (and thus more interesting) is that different groups of animals have differing relationships between the two. A rodent brain, for example, has less neurons than a similarly sized primate brain.

This relationship can be expanded and you can use it to predict the number of neurons in a hypothetically sized brain (or vice versa) of a particular type of animal. Returning to the rodent/primate example, if you increase the number of neurons in a rodent brain 10-fold you wind up with a brain that’s 35 times larger! Conversely increasing the number of neurons by the same amount would only get you a 10 times larger primate brain.

The relationship between brain size and number of neurons

The exponent between between brain size and number of neurons for different species. The larger the number the less dense the neurons (click for larger image, you’ll probably want to do that)

The data provided even more interesting information, hinted at in the above image: different parts of the brain had different rules governing the relationship between brain size and number of neurons. Of particular interest is the cerebral cortex since it is often associated with intelligence (and especially large in humans).

The number of neurons in the cortex compared to the number in the cerebellum (top) and the number of non-neurons compared to brain size (bottom). Note the realtionship between cortex and cerebellum and the linear relationship of non-neurons to structure size “H” and arrows mark humans. As always, click to enlarge

However, in primates the relationship between the number of neurons in the cerebral cortex and the size of that cortex were very similar to the relationship present in the rest of the brain. Increasing the number of neurons in the cerebral cortex 10 times increases the size of the cerebral cortex ~10 times. Compare that to a rodent where increasing the number of neurons in the cerebral cortex 10-fold increases its size 50-fold! Further, there was also a link between the size and the cerebral cortex and the size of the cerebellum.

Whilst neuron numbers varied across different groups of animals and in different areas of the brain, non-neuron numbers had a relatively stable relationship with brain size. Increase the brain size by x and the number of non-neuron cells also increase by x in a nice, linear fashion. This result is relevant given that, although they don’t get as much press as neurons, non-neuron cells also appear to be involved in intelligence.

All of this suggests two key things. Firstly that primates have evolved a much more efficient neuron set-up than other animals, being able to pack many more neurons into a much smaller area. This explains why a non-primate with a brain the same size as a primate is often not as intelligent. Secondly, non-neuron cells are much more restricted in how they can evolve. The lack of variation in their relationship with brain size indicates that any such variation is detrimental and so being organised how they currently are is either necessary for the brain to work or optimal.

Some of the species examined in this study, along with their brains. Again, click for the larger image

As well as these two general points about the brain the researcher was also able to make more specific statements about the primate brain. They then looked humans to see if our brain also followed the same rules. In other words, if you would get a human brain by simply scaling up a primate brain. She found:

  • Primates have ~1:1 ratio between neurons and non-neuron cells. Humans also have this, with 85 billion neurons and 86 billion non-neurons in our brain
  • The size of the primate cerebellum increases linearly with number of neurons in it (i.e. increase the size by 10-fold and you increase the number of neurons in it 10-fold). Humans also follow this trend
  • The size of the primate cerebral cortex increases linearly with number of neurons in it. Humans also follow this trend.
  • The size of the primate cerebral cortex is related to the size of their cerebellum. The same is true of humans.

So essentially humans have giant chimp brains. It turns we aren’t as unique as many have suggested we are. However, if that’s got you feeling down, remember that we still have a large brain. Combined with our high density of neurons this means that we probably have the most neurons of any species!

More true than you know

That said, I have two major qualms with the study. The first is that I couldn’t find a description of the “isotropic fractionator” either in this paper or her citation for it. As such I don’t know how reliable it is. The second is the small sample size, with only 7 non-human primate species being examined and only 1-3 members of each species being studied.

However, the “isotropic fractionator” (which is sounding more like an evil geniuses super-weapon the more I say it) has been employed by other scientists so there are clearly a number of individuals who have deemed it to be reliable. And at the rate Suzana Herculano-Houzel is measuring brains the small sample size will soon be rectified but until then the conclusion should be taken with a grain of salt.

A bigger concern I have (and did not list earlier, what a twist!) is that other research is revealing other changes to the human brain that would not be picked up by just counting cells. SRGAP2 mutations, for example, seem to have changed the very cells themselves! As such there may well be “hidden” differences between humans and primates.

So where does that leave us? Well this study shows that many of the alleged differences between human and chimp brains are non-existent. Relatively speaking we have the same number of neurons, non-neurons and all the various bits are the same size. However, this doesn’t show that the human brain is essentially a giant chimp brain but it does make us a lot less special. As a result its evolution isn’t necessarily that special either.

Suzana Herculano-Houzel, Christine E. Collins, Peiyan Wong, Jon H. Kaas (2007). Cellular scaling rules for primate brains Proceedings of the National Academy of Sciences, 104 (9), 3562-3567 DOI: 10.1073/pnas.0611396104
Suzana Herculano-Houzel (2012). The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1201895109

I didn’t post last week because I was on holiday. I would apologise for this except I’m not really sorry as I had a very nice time.

19 thoughts on “Humans have giant chimp brains

  1. Adam you are very thorough and explain scientific matters in an easily understandable language (increased neurons?). I find your posts fascinating and your rebuttal on my blog interesting which I intend to refute point by point in the future.

    Let’s agree that a neuron is a nerve cell that is the basic building block of the nervous system. Neurons are similar to other cells in the human body in a number of ways, but there is one key difference between neurons and other cells. Neurons are specialized to transmit information throughout the body. So we can identify the mechanism of the transmission of data and the more “highly evolved” human have more of these neurons which would logically lead anybody to believe that more information is transmitted in humans.

    The “isotropic fractionator” , which I , too, am not versed in but given the size of a brain correlates the numbers of neutrons in the brain we will accept as true. Please allow me to paste an article from Scientific American (Jan 15, 2008 06:04 PM):

    If the whale brain is so much bigger than the human brain, does this mean it has more neurons? Logically, brain function and intelligence must relate to the number of neurons. Intelligence resides in the neocortex (the thin, convuluted “rind” of the brain) rather than in other, underlying areas devoted to controlling vital housekeeping functions for the body, so Eriksen and Pakkenberg focused their investigation there. The frontal lobes of the dolphin brain are comparatively smaller than in other mammals, but the researchers found that the neocortex of the Minke whale was surprisingly thick. The whale neocortex is thicker than that of other mammals and roughly equal to that of humans (2.63 mm). However, the layered structure of the whale neocortex is known to be simpler than that of humans and most other mammals. In particular, whales lack cortical layer IV, and thus have five neocortical layers to humankind’s six. This means that the wiring of connections into and out of the neocortex is much different in whales than in other mammals. The researchers’ cellular census revealed that the total number of neocortical neurons in the Minke whale was 12.8 billion. This is 13 times that of the rhesus monkey and 500 times more than rats, but only 2/3 that of the human neocortex. What can account for the fact that whales have bigger brains — and similarly thick neocortexes — but fewer neurons? Eriksen and Pakkenberg found that there were 98.2 billion non-neuronal cells, called glia, in the Minke whale neocortex. This is the highest number of glial cells in neocortex seen in any mammal studied to date. The ratio of neocortical glial cells to neocortical neurons is 7.7 to 1 in Minke whales and only 1.4 to 1 in humans. This finding may indicate a tendency for larger glia/neuron ratios as brain mass increases to support the growing neurons. But when one considers other recent research revealing that glia play an important role in information processing (see “The Other Half of the Brain,” fromn Sci. Am. April 2004), one is left to wonder. Is the whale brain intellectually weaker than the human brain, or just different? They have fewer neurons but more glia, and in traditional views of the glia, the neurons count for much more. But if glia process information too, does the different ratio in Minke whales mean they think not more weakly but just much differently? We’re now wondering, essentially, what goes on in a whale’s head — and why, if it’s supposedly so smart, it doesn’t have great works to show for it. (

    Excuse me for the long reference to the article but I believe it arrives at the reliability using the number of neutrons in animal to determine the intelligence of that animal.

    Let’s say we did evolve from other animals through the billion of years supposed by evolutionists. We will use the classic man evolved from hominids (or “great apes). If this be true mutations must have been beneficial and added information. Can mutation create new information? Yes, depending on what you mean by ‘information’. Also, ‘new’ does not necessarily imply ‘better’ or even ‘good’. When evolutionists cite examples of ‘new’ information, they are almost invariably citing evidence of new traits, but these traits are caused by the corruption of existing information. Mutations can create new varieties of old genes, as can be seen in white-coated lab mice, tailless cats, and blue-eyed people. But damaging mutations cannot be used to vindicate molecules-to-people evolution. Breaking things does not lead to higher function (and presupposes a pre-existing function that can be broken). Also, not all new traits are caused by mutation! Some come about by unscrambling pre-existing information, some from decompressing packed information, some from turning on and off certain genes.

    In all the examples I have seen used to argue against creation, evolution is not helped. There are no known examples of the types of information-gaining mutations necessary for large-scale evolutionary processes. In fact, it looks like all examples of gain-of-function mutations, put in light of the long-term needs of upward evolutionary progress, are exceptions to what is needed, because every example I have seen involves something breaking.

    Lastly where did the information from the evolving creature into the human being come from? Evolutionary science is based on a materialism (that the universe exist of of only two entities: matter & energy). Therefore if a third entity can be shown to exist, then materialism and all philosophies based on it must also be false. Information is this third entity. The UDI (Universal Definition of Information) defines it as having:

    1) Code (syntax)-a set of symbols and rules for using letters, words, phrases or symbols to represent something else.

    2)Meaning (expression): Meaning enables communications by representing real objects or concepts with specific symbols, words, or phrases.

    3) Expected Action (pragmatics): expected action conveys an implicit or expilicit request or command to perform a given task.

    4)Intended Purpose (apobetics): Intended purpose is the anticipated goal that can be achieved by the performance of the expected action(s).

    To summarize information it is to be an encoded, symbolically represented message conveying expected action and has an intended purpose.

    A Bible, newspaper do contain Information (UDI).
    Physical stars, random sequence of letters do NOT contain information (UDI).

    There exists two fundamental laws regarding information.

    Fundamental Law 1 (FL1)
    A purely material entity, such as physiological processes, cannot create NON-MATERIAL. (Something material cannot create something material.)

    Fundamental Law 2 (FL2)
    Informational is a non-material fundamental entity and not a property of matter.

    Let me give you an example. Let’s say you have a very accurate analytic balance scale that can read to 10^-6. You weigh a blank cd and record weight. You fill it up with music, movies, whatever strikes your fancy. You weigh it again and the weight is the same. Likewise erasing information on the CD has no effect on the weight. This means that the information is independent of the material source. A material source is required to store information, but the information is not part of the material object.

    So where did this increase in information come from? Since information is a non-material entity and cannot originate from purely material quantities, and since information originates from man we conclude man’s nature must have a non-material component (spirit). Man has a spirit. The presuppositions of materialism has been shown scientifically to be false3.

    My challenge to you if you disagree with these laws and conclusions I have made must be to falsify them by demonstrating the initial origin of information from purely material sources.

    • The paper did not analyse any whale brains, although from the sound of things the researcher is trying to get her hands on one. As such their remains the possibility that future analysis of whale brains may buck the linear relationship between brain size and non-neuron cells this paper identified. However, even if this were the case and our models of general trends had to be altered this would not change the fact that humans have more neurons than any known animal (which may go some way to explaining our intelligence) and still fit nicely within the primate brain structure.

      Which, in a somewhat roundabout way, leads me onto your second point regarding mutations altering existing functions. We are modified apes, still sharing every feature which unites that group. Almost every bone and muscle we have has an analogues structure in chimps and the features we don’t share aren’t exactly novel – every feature has some kind of antecedent. Be it a gene that has been modified, mixed-up, conserved or duplicated and altered to produce a new function there is always some kind of origin. That last source is particularly important as it can result in more functions than you started with allowing for new “information” to be introduced by only altering what already exists. As such the fact you see mutations altering existing function is what you’d expect given we are an altered ape and so no real problem for evolution.

      Further natural selection adapts an organism to that particular environment, often sacrificing abilities that aren’t useful there. We developed fine motor control in our hands but in doing so lost a lot of the strength needed to climb trees. Our feet are now sturdy and well suited for walking but now lack the prehensile ability of most other primates. Changing to become better in one way normally results in losing something but that doesn’t matter provided that on balance the change is beneficial. So again, the fact that most mutations involve “corruption” are no problem for evolution provided the corrupted product is better suited to an organisms environment.

      Finally I reject essentially everything your saying regarding information on the grounds you haven’t shown that it is non-material. Whilst adding music to a CD might not change its mass it does still physical alter it, with various bumps at pits being created to record the data. There is a real and physical basis for the information being stored. Since you’re making the positive claims the burden of proof lies with you rather than me and so I ask that you provide evidence that information is non-material.

      • Information is non-material Adam. A team of researchers from various fields* set forth to apply a definition to the term “information”; Universal Definition of Information (UDI). They agreed that there are four essential attributes that define it:
        Code (syntax): Information within all communications systems contains a code. A code contains a set of symbols and rules for using letters, words, phrases, or symbols to represent something else. One reason for coding is to enable communication. Examples of codes would be the English alphabet, words, and syntax; hieroglyphics; or codes used in computers (for example, C, Fortran, or Cobol).

        Meaning (semantics): Meaning enables communication by representing real objects or concepts with specific symbols, words, or phrases. For example, the word chair is not the physical chair but represents it. Likewise, the name “Bob” is not the physical person but represents the real person. When words are associated with real objects or concepts, it gives the word meaning.
        For example, aichr and Bbo do not have meaning because they do not represent any real object or concept. However, if in the future one of these character strings were to represent a real object or concept, it would have meaning. Prior to the computer Internet age, the word blog had no meaning; today it is associated with a web page that serves as a personal log (derived from web log) of thoughts or activities. It can also mean a discussion community about personal issues. Another new word with meaning is simplistic. New words are continually being designated with meaning.

        Expected Action (pragmatics): Expected action conveys an implicit or explicit request or command to perform a given task. For example, in the statement, “Go to the grocery store and buy some chocolate chips,” the expected action is that someone will go to the store. This does not mean the action will actually happen, but it is expected to happen.

        Intended Purpose (apobetics): Intended purpose is the anticipated goal that can be achieved by the performance of the expected action(s). For example, in the statement, “Go to the grocery store and buy some chocolate chips,” the intended purpose might be to bake and eat chocolate chip cookies.
        These four essential attributes specify the definition domain for information. A definition of information (Universal Definition of Information) was formulated by using these four attributes:

        An encoded, symbolically represented message conveying expected action and intended purpose.

        If we apply the laws governing UDI (Universal Definition of Information) to DNA information, we can make logically sound arguments (conclusions).
        Since the DNA code of all life-forms is clearly within the UDI definition domain of information, we conclude there must be a sender (LI 1, 2).

        Since the density and complexity of the DNA encoded information is billions of times greater than man’s present technology, we conclude the sender must be supremely intelligent (LI 2, plus corollaries).

        Since the sender must have encoded (stored) the information into the DNA molecules constructed the molecular biomachines required for the encoding, decoding, and synthesizing processes designed all the features for the original life-forms we conclude the sender must be purposeful and supremely powerful (LM 1, plus corollary).

        Since information is a nonmaterial fundamental entity and cannot originate from purely material quantities, we conclude the sender must have a nonmaterial component (Spirit). God is Spirit (FL1, 2; LI 2, plus corollaries)!

        Since information is a nonmaterial fundamental entity and cannot originate from purely material quantities, and since information also originates from man, we conclude man’s nature must have a nonmaterial component (spirit). Man has a spirit (FL 1, 2; LI 2, plus corollaries)!

        Since information is nonmaterial and the third fundamental entity, we conclude that the assumption “the universe is composed solely of mass and energy” is false (FL 1, 2).

        The philosophy of materialism is false!
        Since all theories of chemical and biological evolution require that information must originate solely from mass and energy alone (no sender), we conclude all theories of chemical and biological evolution are false (Fl 1, 2; LI 1, 2, plus corollaries).

        The evolution of life is false!
        Therefore, the scientific laws governing the UDI domain have
        1) Refuted the presupposition of atheism, humanism, and the like, including the theories of chemical and biological evolution.
        2) Confirmed the existence of an eternal, all-knowing, all-powerful being (God).

        Adam if you disagree with these conclusions YOU must falsify them by demonstrating the initial origin of information from purely material sources. But why would we trust your answer since thought is materialistic and generated by random chance and undirected processes?

        *Team members included Werner Gitt, PhD, engineering/information; Jason Lisle, PhD, astrophysics; John Sanford, PhD, genetics; Bob Compton, PhD, physiology, DVM; Georgia Purdom, PhD, molecular genetics; Royal Truman, PhD, chemistry; Kevin Anderson, PhD, microbiology; John Oller, PhD, linguistics; Andy McIntosh, PhD, combustion theory/thermodynamics; Mike Riddle, BS, mathematics/ MA, education; Dave Mateer, BS, mathematics and computer science.

        • You’re not providing any support for your original premise, just restating it. Further, whilst I’m no information scientists, I do know that alternate definitions of information exist. So I’ll ask the additional question: what makes this “universal” definition one that should be accepted over alternate definitions?

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  3. “Relatively speaking we have the same number of neurons, non-neurons and all the various bits are the same size. However, this doesn’t show that the human brain is essentially a giant chimp brain but it does make us a lot less special”

    Similar size, shape, neuron count etc, just as much points to a common designer.

    What is your best evidence for evolution?

    • Similar features are not just as much evidence for common ancestry as they are for common design because a piece of evidence offers more support for an idea if it is tested against a prediction than if it is incorporated post-hoc. And it is only a post-hoc justification of design.

      Science does not work by having a single excellent observation resulting in acceptance of a claim. To get to the stage of acceptance and certainty evolution has requires that a large body of top quality evidence be gathered in support of the idea. As such picking out a “best” evidence is rather difficult (and arguably pointless, given science doesn’t work that way). Ultimately I will have to plump with what I am most familiar with – human evolution. Had I done work into octupi I might claim they’re the best.

  4. Okay, your picture above states that ape-like to human evolution is “More true than you know.” So my question again is what is your best evidence or ANY piece of evidence for that matter, that humans evolved?

    • There is a large quantity of evidence for human evolution. Broadly speaking it can be broken down into three areas, although there are others I will omit.

      1. Anatomical/Palaeoanthropological: humans look a lot like other apes. The differences between us and these apes emerge in the fossil record, showing how we went from being the typical ape to the atypical ape.

      2. Genetic: humans are genetically very similar to other apes. Various calculations reveal the differences between us and the other apes accumulated over the same period of time our anatomical differences arose. Two lines of evidence converging on the same conclusion.

      3. Archaeological: archaeology shows the increasing complexity of human cognition, allowing behavioural changes between us and other apes to be tracked. It also provides a method for testing the other two ways of knowing, increasing with complexity as our brains get bigger and migrating across the world when genetics says we did.

      • “There is a large quantity of evidence for human evolution.”

        I asked you for your best evidence for evolution.

        You replied that Science does not work off of best evidences.

        So, I said, “Okay, then give my ANY piece of evidence for evolution.

        And you come back with similarities between apes and humans.

        Similarity does not prove evolution.

        Similarity just as much demonstrates a common designer designed both.

        If you want to BELIEVE that humans evolved from ape-like ancestors that is your business, but please don’t call that science.

        • I agree with R.K. Different makes of cars have similar features but it doesn’t indicate one evolved into another. It does indicate, however, that there is a common design. Homology as “proof” for evolution has long been discredited; especially with the Genome Project indicating similar building blocks used by a Great Designer (Francis Collins will even attest to that!). Do you realize how exact a protein needs to fold in an exact manner in order to be functional? And this happened by descent with modification by natural selection? Statistician would tell you the chance of that happening by evolution would be a number greater than the number of atoms in the universe! If you don’t believe me get some curdled milk (protein) and wait for it to “uncurdle” back to milk. Or maybe you don’t have the billions & billions of years to wait (it wouldn’t happen anyway).

        • well i hope god is more creative then just using the same base materials and tweaking it slightly each time. evolution makes perfect sense, end of discussion.

  5. can you please help me with my assignment. topic is ” evolution 0f human brain ( intelligence). i am supposed to tell how it basically evolved from chimpanzee but there is no as such material its just basic difference that they differ in size and number of neurones.. please help me with this

    • If I had to write such a thing I’d point out how many features of the human brain have analogues in the chimp brain. We both have the same lobes, even similar areas dedicated to communication (Wernicke & Broca’s area). The difference between the two brains is the relative size and complexity of these regions, not the presence/absence of the regions themselves.

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  8. Where do orang-utans and gorillas fit into the human/primate comparison? How much DNA do we share with them?
    Are evolution and creation necessarily opposed? Many modern theologians suppose that they are compatible,

    • The genetic differences between humans tends to be about 0.1%. The difference between humans and chimps is about 1%. Humans and gorillas is about 1.6% whilst humans and orangutans are around 3% different.

      Evolution and creation cannot be reconciled. They can be made to not directly contradict sure, but not reconciled because there’s nothing about evolution that needs outside intervention to work. It’s a self contained unit that can run all on its own, making god irrelevant.

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