|MadSci Network: Neuroscience|
David, this is a good question and touches on many subjects. First let me say that behaviors which are known at birth are generally called ‘instincts’. These are behaviors which are ‘hardwired’ into the brain and are not learned behaviors. Most, if not all, animals have certain instincts. These instincts help the animal to survive in one way or another. You may think that humans are not born with any instincts, but this is not the case. For example, a newborn baby will instinctively hold its breath if placed under water.
Of course, most animals are born with more instincts than humans, as you pointed out in your question. Generally, if we examine the instinctive behavior of all animals we will see a pattern immerge - as we move forward through evolutionary time, we see fewer and fewer instinctive behaviors. Teathered to this change in behaviors is the increasing size of the animals brain compared to its body size (brain/body ratio) and the increasing amount of time animals spend raising their young. If we look at fish, amphibians, and reptiles (which evolved well before mammals), most of their young, whether hatched from eggs or born alive, are completely able to live on their own without any aid from their parents. They instinctively know what to eat and how to find and capture their food and how to escape predators. Their brain sizes are small and not capable of much learning compared to mammals. Further, since their parents do not hang around to raise them, they do not have the time to learn how to survive. They must be born with these abilities. If we look at mammals, we see fewer instinctive behaviors and more learned behaviors. We also see an increased brain/body ratio and we see that most mammals spend some amount of time raising their young (rearing). During this time, the parents can help feed and protect their young. As the young grow, they learn skills needed to survive.
Even within mammals, general distinctions can be made between prey and predator species. In general, prey species, are born with more instincts such as knowing how to stand/walk/run. You can probably see how this is advantageous. If prey species couldn’t run, they wouldn’t survive long in the wild. Predators, on the other hand, generally are born with fewer instincts. Presumably this is because hunting is a more complex behavior than running and requires time to learn. Humans are born with the fewest instincts, we have the largest brain/body ratio of all animals and we have the longest rearing period. We also have the capacity to learn more than any other species.
You have to realize that things like brain size, instinctive behavior, and the length of postnatal rearing are all parts of the evolutionary balance, that is, they are all methods developed throughout evolution to help animals survive. There are a lot of fish, a lot of mammals, and a lot of humans in the world therefore you cannot say that one system of survival is better than another. Each has its own advantages and disadvantages.
At this point, you may be wondering what brain size has to do with this and asking, if humans have such large brains, then why can’t they have a lot of instincts and learn too. The answer to this is somewhat complex, but I will try to make it as simple as possible. Imagine the brain as a large circuit board with hundreds of thousands of connections. Instincts would be, as I said above, hardwired. That is to say, that they would consist of various connections which could not be altered. Learning consists of making new connections. To make new connections, you cannot use connections which are hardwired together. In order to maximize the amount of learning, you need to minimize the amount of hardwiring. Even though our brains are large and contain a vast amount of connections which can be rewired (the term ‘plastic’ is used in neuroscience), these plastic connections are required to handle the vast amount of learning that humans are capable of. This vast ability to learn is our greatest survival tool.
I hope that this answers your question.
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