How to get from monkey to man

A Japanese group have a Japanese take on the evolution of primates (see citation) and their paper has some interesting aspects: a method to train and study macaques, a view of evolutionary selection, and a history of Japanese science in this area. All are interesting.


The macaques were trained to use tools but it was not easy. The training was done in baby steps with an intensive training period for each step, but eventually the monkeys seemed to get it. First the monkeys just retrieved food on a long spoon, then the spoon was replaced by a rake with food on near side, then the distance between rake and food was increased, then the food was put on the far side of the rake. Each step took several days of training, but at this stage there was a change and the monkeys began to learn quicker (they seemed to understand racks). Training continued with the rake and food behind a sight barrier but a video of the action on a monitor that the monkey could view. The monkeys were taught to retrieve food even when the size and position of the video image was changed. Finally they were taught to use a smaller rake to obtain a longer rake to use to retrieve food. This involves pre-planning and sequential combining of tools but the monkeys learned this last skill extremely quickly. Softly, softly, with patience – teach a monkey. This method was used on 50 macaques and all of them learned to use the rakes as tools and with facility.


During the training the brains of the monkeys were being followed for changes. In particular they looked at the body image of the hand through the activity of intraparietal bimodal neurons that respond both to tactile stimulation of the hand and visual stimuli presented in the same spatial vicinity as the hand – in other words, the image of the hand in space. At the point when training speeded up there was a change in these neurons.

When our rake-trained monkeys wielded the rake in order to retrieve food, these same neurons’ visual receptive fields extended outwards along the axis of the tool to include the rake’s head. In other words, it appeared that either the rake was being assimilated into the image of the hand or, alternatively, the image of the hand was extending to incorporate the tool. Whenever a monkey was not regarding the rake as a tool and just held it passively as an external object, the visual receptive field withdrew from the rake head and was again limited to the space around the hand.


When direct sight was replaced by the video on a monitor:

…we found that neurons with tactile receptive fields on the hand were now endowed with visual receptive fields around the image of the hand. Furthermore, these visual receptive fields could extend to the head of the video image of the rake…


The first 10-14 days of training (which could not be reduced) followed by much easier learning implied that there was not merely functional plasticity within the existing neural circuitry, but larger scale neuroplastic reorganization. They look for it and found it.

In the bank of the intraparietal sulcus, where the bimodal neurons described above reside, the expression of immediate early genes and the elevation of neurotrophic factors and their receptor was synchronized with the time course of the cognitive learning process…These training-induced genetic expressions turned out to be a part of morphological modification of the intraparietal neural circuitry.


Using tracers to see what was changed in the wiring of the monkeys’ brains – axons had extended beyond their former range into a new cortical area and made synapses there – a new interaction between the temporopariental junction and the intraparietal cortex.


Monkeys have latent abilities that can be triggered in a proper environment. In humans this is spontaneous and in monkeys requires artificial training. What does this say about human evolution? The author’s make a case for intentional niche construction. In a very simplified outline of types of selection and of environmental niches, I see the following:


First there may be genetic drift which does not involve selection of any kind but can result in evolutionary change. There is natural selection which is the archetypal selection. It preserves the genes of those best fitted to their niche. Sexual selection is an accepted type resulting in certain traits being selected by the mating preferences of the opposite sex (think peacock’s tails). Also accepted is kin selection where survival of related animals can be equivalent to one’s only survival in evolutionary terms. There is group selection which is not completely accepted. If an individual’s survival depends on the success of its group, then group selection would be expected to operate. All of these can operate with or without a change in the animal’s niche. Some animals create their own niches (think beavers); they have evolved to fit the niche but also evolved to create that niche. Take that a stage further to an animal that can intentionally change their behaviour to fit a new niche (think animals with some culture) and further still to an animal that can intentionally create a new niche (think human culture, communication and child rearing).


The author’s envisage a particular kind of human evolution:

The evolutionary path that led from the monkey brain to the human brain must have proceeded through a continuous, incremental process of natural selection. Nothing completely new should have been added to the primate brain. Evolution has limited the means for reoganizing so complex a structure; these means mainly involve tinkering with size and developmental timetables. One of our main claims here is that the precursors of the mental functions that allowed the human intellect achieve a cultural snowball effect are present, even if only in latent or inchoate forms, in our primitive primate ancestors. A corollary claim is that certain forms of training can produce incremental but functionally significant changes in the non-human primate brain that mimic, perhaps even recapitulate, some of the key neurogenetic changes our ancestors underwent during their long march towards becoming us.


The author’s also discuss whether the Japanese culture and relationship with monkeys, makes these ideas more natural and acceptable to Japanese scientists. I am not going to comment on that part of the paper. The discussion of Japanese science is also not mentioned in the abstract.


Here is the abstract:

We trained Japanese macaque monkeys to use tools, an advanced cognitive function monkeys do not exhibit in the wild, and then examined their brains for signs of modification. Following tool-use training, we observed neurophysiological, molecular genetic and morphological changes within the monkey brain. Despite being ‘artificially’ induced, these novel behaviours and neural connectivity patterns reveal overlap with those of humans. Thus, they may provide us with a novel experimental platform for studying the mechanisms of human intelligence, for revealing the evolutionary path that created these mechanisms from the ‘raw material’ of the non-human primate brain, and for deepening our understanding of what cognitive abilities are and of those that are not uniquely human. On these bases, we propose a theory of ‘intentional niche construction’ as an extension of natural selection in order to reveal the evolutionary mechanisms that forged the uniquely intelligent human brain.

Iriki, A., & Sakura, O. (2008). The neuroscience of primate intellectual evolution: natural selection and passive and intentional niche construction Philosophical Transactions of the Royal Society B: Biological Sciences, 363 (1500), 2229-2241 DOI: 10.1098/rstb.2008.2274

4 thoughts on “How to get from monkey to man

  1. This made me think of Susan Savage-Rumbaugh’s article in On the Human, “Human Language – Human consciousness”
    – which argued that second-generation bonobos raised by parents familiar with language showed some distinctly human patterns of attention or cognition. The discussion and objections are also interesting.

    JK: Thanks for the link. It is indeed a very interesting article and the discussion is even more interesting to me. I am currently in the middle of a series on embodiment and had planned to write the second last on language – some of the comments are making me think again about some aspects of language. Thanks again for the link. Janet

  2. Thanks for this. A mere layman here, but this goes into my reference pile on hominoid evolution.

    As an aside, I racked my brain over the described tool use here until I hit the phrase “use a smaller rack to obtain a longer rack”. Then realized I should instead have raked it for tools. =D

    As for the biology, layman ponderings, but I don’t see how the latent plasticity supports as much as detracts from coevolution of niche construction since there is no presentation of differential plasticity. (I presume it can facilitate niche construction though.) Ironically the authors use their unsupported model as a tool in an unsuccessful attempt to resurrect a japanese evolutionist in his abandoned niche.

    Which gets me to group selection. I’m as of yet a mere observer of that area of biology and have no intention of entering it.

    But my impression is that group selection isn’t as much as “not completely accepted” but nearly unanimously rejected by evolutionary biologists. Quoting <a href=”” rel=”nofollow”>Jerry Coyne on this</a>:

    “West concludes that while NGS is not usually wrong, it’s not useful, and, anyway, it’s not really new, since its mathematics were already worked out several decades ago. While advocates of NGS claim that they’re ignored (and, at worst, persecuted), West implies that the theory is simply irrelevant. His conclusion:

    [presenting a slide of West presentation] Summary … However, selection is always on the level of inclusive fitness.”

    My understanding is that this isn’t a mere semantic question (i.e. that “group selection” is actually embedded in inclusive fitness theory. But that:

    “1. The old idea of selection among groups leading to the evolution of group-level traits works only under very special circumstances.

    2. The “new” view of group selection (NGS)—the one espoused by D. S. Wilson et al.—gives results that are either wrong or, when they’re right, essentially equivalent to those derived from the simpler and less confusing inclusive-fitness theory (IFT), pioneered by Price and Hamilton and developed in the 1980s.”

    “Here West checks off which of the two theories has better helped us understand various biological phenomena (in the slide below, “GS” is group selection and “IF” is inclusive fitness theory). It’s a slam dunk for IF.”

    So presumably it should be avoided at all cost and be replaced by IF theory instead.

    Thank you for your comment.
    (1) I have corrected the ‘racks’ to ‘rakes’ and appreciate you pointing out the error. I am dyslexic and do not always see such errors – I try to catch and correct them but they sometimes slip through.
    (2) I have nothing to say about the Japanese scientist mentioned in the paper. I know nothing about his work and the author’s defense of him seems off the subject of the research they are reporting and out of place in the paper.
    (3) There is a famous example of niche creation (although I think some narratives of it are exaggerations). Here is one that I think is accurate:
    “In 1952, on the island of Koshima, scientists were providing monkeys with sweet potatoes dropped in the sand. The monkey liked the taste of the raw sweet potatoes, but they found the dirt unpleasant.
    An 18-month-old female named Imo found she could solve the problem by washing the potatoes in a nearby stream. She taught this trick to her mother. Her playmates also learned this new way and they taught their mothers too…
    By March, 1958, 15 of the 19 young monkeys (aged two to seven years} and 2 of the 11 adults were washing sweet potatoes. Up to this time, the propagation of the innovative behavior was on an individual basis, along family lines and playmate relationships. Most of the young monkeys began to wash the potatoes when they were one to two and a half years old. Males older than 4 years, who had little contact with the young monkeys, did not acquire the behavior.
    By 1959, the sweet potato washing was no longer a new behavior to the group. Monkeys that had acquired the behavior as juveniles were growing up and having their own babies. This new generation of babies learned sweet potato washing behavior through the normal cultural pattern of the young imitating their mothers. By January, 1962, almost all the monkeys in the Koshima troop, excepting those adults born before 1950, were observed to be washing their sweet potatoes. If an individual monkey had not started to wash sweet potatoes by the time he was an adult, he was unlikely to learn it later, regardless of how widespread it became among the younger members of the troop…
    By using the water in connection with their food, the Koshima monkeys began to exploit the sea as a resource in their environment. Sweet potato washing led to wheat washing, and then to bathing behavior and swimming, and the utilization of sea plants and animals for food. “Therefore, provisioned monkeys suffered changes in their attitude and value system and were given foundations on which pre-cultural phenomena developed.” (M Kawai, Primates, Vol 6, #1, 1965).”
    This is the clearest example I know of where a new source of food resulted in a new niche for a group of animals. It appears that the monkeys’ had enough behavioural flexibility for young individuals to create a difference in ‘culture’ to exploit a shift in niche. We do not know to what extent this was due to plasticity in brain connections. I would suspect that the extent of the ‘cultural’ change was so large, involving eventually several new foods and swimming, that some non-genetic differences in connectivity were necessary in the monkey brains as they learned the new ways. Whether or not that is true – now that the monkeys are living in the new niche, they would come under selective pressure to genetically evolve to be more fit to that niche. All that the current paper shows is that such non-genetic differences in connectivity are possible through artificial training regimes.
    (4) I am a look-for-the-evidence sort of person and do not have a conviction for or against group selection. Usefullness does not seem to enter into it. Either it has happened or it has not. If it happened only once then it is a form of selection, and if that once was something significant then it is a significant form of selection. If it can be reduced to ordinary selection mathematically then people have a choice of how they describe instances and the question becomes one of personal taste – I do not know if this is the case. As far as I know that has not been a documented case of evolution that can only be explained by group selection. Nor has there been logical proof that group selection cannot produce evolutionary change. The idea seems to go in and out of fashion since Darwin’s day and the discussions are often more philosophical then just hard experimental science.

  3. I don’t know much about the evolution but I have been interested in science and physics and since graduating I have really started to read more about the beginnings and how we evolved into humans, and if we indeed started as monkeys. It definitely is something I like pondering and I think of every time I get to check out the apes at the zoo. Thanks for the article as well as the links, I have some more reading to get to!

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