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