Contents Updated: Tuesday, August 24, 1999
"Naught may endure save mutability."
There have been conflicting views about how easily intelligence evolves. The age old view supported by religious dogmata was that man is unique in all of creation and therefore intelligence is very rare indeed. In contrast, not many years ago a curious equation was bandied about which purported to prove that we are surrounded by life wherever we look in the universe. A proportion of this is bound to become intelligent and so intelligence exists in every direction you look into space.
The view expounded here is that intelligence corresponds with certain troughs in the evolutionary hyperspace, lakes in the evolutionary landscape. They might be very difficult to get to, perhaps via a small number of tortuous narrow valleys, but any species that finds itself evolving into one such valley is likely, sooner or later, to develop intelligence. Intelligence could be unique at the present time, if only man has so far reached one of the lakes, but in principle other species could get there.
H.J.Jerison has introduced the idea of the EQ, the encephalisation quotient. The EQ takes the ratio of the brain weight to the body weight of an animal, and relates it to the average such ratio for a group of comparable animals.
An EQ of 1 means that the animal's brain weight to body weight ratio is typical of the group of comparable animals. If its EQ were bigger than 1, it would have a greater weight of brain than an animal typical of its size in the comparison group.
EQ is not the same as IQ. Intelligence depends upon other factors besides the relative mass of the brain, such as the speed of transmission of nerve impulses and their shape. But EQ does indicate potential for IQ: the brain power is there if the evolution of the animal is able to find ways of using it. It is a useful proxy for intelligence.
EQ depends upon the ecological niche occupied by the animal. The three dimensional environment of squirrels give them a higher EQ than their rodent relatives, the rats. Insect eating monkeys have a higher EQ than their fruit eating cousins and the latter, in turn, have a higher EQ than leaf eating monkeys. Animals surrounded by food, the leaf eaters, need little brain power to seek it. The fruit eaters have to hunt for their food and need intelligence to find it. Insect eaters have to develop intelligent strategies to capture their prey which itself has the sense to try to escape. In general carnivores have a higher EQ than the herbivores upon which they prey.
For fossil animals fairly reliable estimates of EQ can be made from cranial casts and the size of the whole skeleton. They show that brain size tends to get bigger over time in accordance with Marsh's Law. There are well established explanations for this.
One is that intelligence of response is one aspect of the competition between the predator and its prey. Another is sexual selection. This particularly can give rise to exponential—explosive—evolution via positive feedback loops! Consider the two mechanisms in turn.
Other things being equal, a marginally more intelligent predator will be more successful than its dimmer peers in capturing its prey. The prey caught will be those that are marginally less intelligent than their peers. In the fullness of time, the results in the populations of predator and prey are that intelligence will increase: the predator's through the animal passing on its characteristic intelligence more successfully; the prey's because the less intelligent were less likely to pass on their lack of intelligence. Later generations of herbivores and carnivores are both more intelligent. There is still a balance of power but at a slightly higher level.
An evolutionary arms race is taking place with intelligence the superpower weapon. Predator and prey both finish up with a stronger armory but the balance of power is maintained. Of course intelligence need not be the only weapon. Similar arms races occur in respect of other weapons.
An obvious example is provided by tyrannosaurus rex and the ceratopsians both evolving in response to the other as each improved its weaponry. One developed more and more elaborate defences, heavy bony neck frills and long horns, while the other developed more and more sophisticated jaws and teeth for attack. Both also developed quite large brains by popular standards for dinosaurs.
Thus a predator-prey arms race should result in selection for increasing intelligence in both predator and prey and one might expect technological levels of intelligence to emerge quite naturally, even commonly.
That the tendency is there is unequivocal but that high intelligence develops commonly might not be true. The answer again lies in the phrase, other things being equal. They are not equal. And often they interfere with the competitive progress described above. At the extreme one could not imagine two separate intelligent species evolving in mutual contact. Whichever was the more advanced would rapidly eliminate the other. It seems this happened in the evolution of mankind... possibly several times.
Nevertheless, there is a tendency towards selection for intelligence in all predator-prey interactions. Any such tendency, once established, can be powerfully reinforced by sexual selection.