We know that the intelligent species on Earth, that's us, are mammals and no other class of animals has ever done it, as far as we know. Would intelligent aliens have to be mammals as well, or originated from mammals before they started tinkering with their own genetics? Or are there certain attributes that mammals have which are needed for the development of intelligence, and on an alien world, other types of animals, other classes or even phylae, might become intelligent?
How are mammals unique in connection to intelligence? Intelligence requires a long, extensive learning period, and more freedom from instinctual behavior than non-intelligent creatures. Intelligence is almost synonymous with learning, and how do you induce learning? You have someone responsible for each new creatures learning, and this means parents in the usual case, so far here on Earth. Learning takes years to do, and during that time, someone has to be responsible for that learning, but also for provisioning, sheltering, and in general taking care of the young creature which is learning. How does it develop that the parents of humans put up with caring for youngsters for years and years? They develop a bonding with their young, and that bonding comes from, among other influences, breastfeeding.
No other class in the chordata phylum has such a long period of dependency. What happens in the evolution of mammals is that learning becomes less from genes and more from memes, if that is what you call what any mammal knows and teaches to the next generation. The mammalian class has plenty of species which demonstrate learning, usually by the young imitating their parents or even other elders in the species. Predator mammals teach their young to hunt, by allowing them to accompany the parents on a hunt after a certain level of maturity is reached. Herbivore mammals teach their young to evade predators, starting very young.
Nest building is common among many classes of animals, but little compares with the dams that beavers build. One generation of beavers demonstrates to the next one how to fell trees, now to transport them down to a river, how to block the river flow with a structure made of tree pieces and mud and rock from the river bottom, and how to build a lodge inside the dam with a underwater entrance.
Other nest building, such as with birds, is largely instinctual, but it is obviously not with mammals. With mammals, teaching by demonstration and imitation are the common mode of behavior. There are certainly strong instincts that push a parent to care for a child, but even in this linkage, there is imitation from generation to generation. One parent mammal can rear youngsters, who observe how it is done and this is added to their repertoire of behaviors when their time comes to rear youngsters.
Another aspect of mammals regards the nutrition of young mammals. In other classes, when parents of a species feeds their young, it is from hunted or gathered food. When breast milk is used, evolution has the option of optimizing the contents of the milk to further development in the very young mammal. Evolution has nothing to do with optimizing the nutritional value of whatever happened to be the caught prey or the found food that a parent in a non-mammalian class finds, and so it may be hit-or-miss. But mammals are optimized for this period.
The architecture of the brain of a mammal is different, in that there is very little written into the brain at birth, but there is a large write-space available for learning. During the initial period of a mammal's life, it learns to process sensory inputs, which takes time for repetition and experiment. The same holds for output from the brain for motion and other activities.
Would it be possible to have a different type of creature on a world far from Earth where the young had the ability to learn from imitation, observation, and experimentation for a long period? This is the mandatory requirement for the evolution of intelligence. There has to be some mechanism by which some creatures, likely parents, are involved with the young for a substantial percentage of their lifespan. The mechanism must somehow connect the youngsters with the parents, must make them provide an environment where nutrition, shelter, and learning are available. If it isn't based on the provision of nutrition, what can it be based on?
The brain of an animal which is hardwired to perform certain behaviors, which we usually call instinctual behaviors, has to be formed not of adaptive neural networks which learn by association in layers, but instead of circuits that are genetically programmed. In other words, the genome, when expressed in the brains of the non-mammalian animals, has to produce some associative layers before birth. Many non-mammalian animals are hardly able to learn at all. It would seem that it is an almost exclusive thing, instinctual patterns in the brain laid down by the genes or a largely blank slate of neurons which can record and transform themselves into something which can do the functions that an instinct can, but in many different variations.
Is this another puzzle posed by evolution? How did brains which were largely instinctual evolve into ones which were largely non-instinctual? Did the evolution of mammalian milk happen independently of the transformation of the type of brain circuits, or is it related? What is clear is that there is a strong connection between the parents teaching their young for extended periods and the development of the type of brain which can become intelligent. So the question is, does providing milk to young work somehow, via hormonal programming in the mother's brain, to promote long-term care and nurture, which somehow comes to include teaching by demonstration and imitation? Perhaps it is connected with the ability of a more associative and less pre-programmed brain to recognize individual youngsters, and to therefore bond with them in better ways. Perhaps there is a feedback loop, in that if parents have an associative neural network for their brain, the raising of young during the mammalian feeding period induces some patterns which still exist after that period is over, so the simple recognition of their own young creates a desire to nurture. This is, after all, how associative brains work.
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