Tuesday, 5 July 2011

Brain Storms - 3 - Evolutionary factors starting on the African Plains

Image the plains of Africa three or four million years ago – populated by a range of medium to large sized mammals which (for verbal convenience) we will describe in terms of modern species. There will be herds of antelope and zebras grazing on the ground plants, and animals such as giraffe who can eat foliage from high in the trees. Other herbivores will include elephant and rhinoceros. Wart hogs will have a more varied diet, and there would be the carnivores and carrion feeders such as lions and hyaenas. All have basically the same body plan, biochemistry, and genetic coding mechanisms – which have been modified by evolutionary pressures in different ways in different species. It is reasonable to assume – at least in a brain storm such as this – that the basic body plan includes the processes that allow the brain to store and process information.

Some of the variations in the plan are quite spectacular – such as the elephant's trunk, which will be associated with extra nerves and work for the brain to do. In other cases parts have been lost from disuse – as in the case of the zebra, where the five digits per limb have been reduced to one. However evolutionary changes to the basic plan need to be possible in small incremental steps, with all intermediate stages being viable. The problem is illustrated by the giraffe's neck. It not only retains the seven vertebrae of the basic plan, very elongated, but one nerve runs all the way down the neck and up again, some 15 feet further than optimal. The reason is that there are some things in the basic plan which cannot be changed incrementally – such as suddenly acquiring extra neck vertebra or radically re-routing a nerve.

What can we expect in terms of differences in the development of the brain in different species within the basic model? We can expect these to parallel other changes in the basic model. If a particular species needs particularly good eyesight to survive the relevant section of the brain can be expected to become larger, If the sense of smell is little used we can expect the appropriate section of the brain to be comparatively small.

There is one section of the brain of particular interest here. This is basically the overall “control centre” - which is used for planning actions – and which stores each individual animal's conceptual map of the environment in which it lives. What we are trying to determine is the plan for the processes within the basic model and what types of variation are possible. Initially I will be assuming that changes in size and operational efficiency can vary incrementally, but the basic brain mechanisms are like the vertebrae in the giraffe's neck – and radical change by many small incremental steps is difficult.

As human beings (who are not disinterested observers in this process) we are likely to jump to the conclusion that the more “control centre” type brain the better – and we may also tend to assume that the human brain has something significant beyond beyond the “standard model”. However you have only to look at the bones in a giraffe's neck to realise that under some circumstances the basic model can be stretched a long way while retaining the same underlying structure and function. 

In fact more brain power is not always better on the African plains. There are costs in running the brain's control centre and it has to compete with resources with other parts of the animal in the attempts to maximise survival. A bigger control centre means more weight, more demands for food and oxygen, and more heat generated in an environment where keeping cool can sometime be a problem. In addition the control centre needs to learn about the local environment (such as the best route to the nearest water hole) which cannot be pre-programmed in the genes – and the bigger the control centre the more time and energy that will have to be dedicated to learning activities. Finally, when an animal dies all the knowledge that had been built up, at significant expense, is lost.

On the African plains one economical approach is shown by herd animals such as antelopes. Food is plentiful (as long as the herd keeps moving to new areas) and almost all you need to know to get along as a young animal is to follow the herd and run as fast as you can if you have been singled out and are being chased by a predator. As individual animals get older they will become aware of the herd moving to new areas due to seasonal changes. Effectively the intelligence needed for survival is distributed throughout the herd – with multiple eyes on guard for predator activity - and older animals have knowledge of what happened in earlier years. There is comparatively little social interaction within the herd and the more animals in the herd the better – even if they are of different species. In such circumstances there is little pressure to develop a significant control centre.

At the other extreme there are the family groups of carnivores, with high levels of social interaction. This allows then to develop hunting strategies – such as splitting into groups with one group driving potential prey towards an ambush. There is also a well developed learning stage for the young, involving play and imitation of the adults. Such an approach will only work effectively is there is effective communication between individuals which some taking a more dominant “leader” role. Such species will obviously require a far more active brain control centre than the herbivores.

In this thought experiment we will introduce some large apes (early man) and look at the evolutionary pressures on them. At first sight they are not very well adapted for the open plains. They cannot run fast enough to catch the antelopes for food, or to outrun the carnivores such as lions. They do not have the zebra's kick or the buffalo’s horns to defend themselves, or the dagger-like claws or teeth of the carnivores. However they have clasping hands and (like other primates) they have somewhat bigger brains for their body size, perhaps to allow them to make better use of their hands. They are social animals, who can interact with others in the group with body movements and facial gestures and I will assume they have the communication and tool-making skills that have been observed in other modern large primates – such as chimpanzees and orangutans. In this context it is worth pointing out that chimpanzees have been known to make a spear, sharpening one end to a point with their teeth, and using it to kill small mammals.

What we know some 3 million years later is that one large ape has evolved to have a larger brain, and changes to the larynx and tongue which allow it to produce a very wide variety of sounds. We are also piecing together some of the history of the changes in its tool-making capacity over time.

The evidence suggests that until about 75 to 100,000 years ago the Homo line remained hunter gatherers with a comparatively simple tool kit (at least in terms of what is preserved in the geological record), although getting a little more sophisticated over the millennia. Round about 75,000 years or so things started to change. One line, Homo sapiens, expanded in Africa and started to move across the rest of the world, for instance reaching Australia about 40,000 years ago. At about the same time the tool kit started to expand significantly and the rate of expansion has increased exponentially as the present day is approached. It is quite clear that at least the later stages of this expansion are cultural. The big question is what was happening some 75 thousand years ago, and how far is language involved.

The fossil evidence does not show any major changes at this particular time slot and it would appear that the size of the brain and the almost certainly the changes of the vocal tract happened gradually over the 3 million or so years. Could this be that in developing better hunting techniques mankind used an increasingly varied series of “hunting” calls – possibly imitating other animals. For instance the hoot of an owl is a far better “I am ready in the ambush position” call than an obviously human call which the prey might learn to know indicated danger. What happened in Africa seems to have been a race between the new hunter and the hunted. This is unlike America and Australia – where skilled human hunters rapidly pushed most of the larger animals towards extinction

One possibility explanation of the apparent change is that the development of language beyond some critical point suddenly altered the way information could be transferred between adults and their children. When an individual died their key memories were not all lost because language had advanced to the stage that important survival information could be transferred to children by word of mouth – rather than by demonstration by example. For example a child could learn how to make a new tool, or better hunting techniques, or the danger round the bend in the river, simply by verbal instruction.

The key question is whether, for this to happen, there has to be a major evolutionary change in the human brain “control centre” or whether the basic mammal control centre architecture can be stretched sufficiently far that it can control a spoken language. If the later possibility is true the most significant biological differences between the human and other ape brains may be the effective capacity for processing thoughts rather than any genetically controlled novel process.

We cannot begin to answer this question until we have a better understanding of the mammal basic control centre processes – and how far it can be stretched. The next Brain Storm will start looking at a possible target model of these control centre processes, while the following posts will start to look at a possible working model which will show that a quite simple model is actually capable of demonstrating a very useful level of "mind power",

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