Everyone has intelligence because we are born with it. It's how you apply it that makes the difference. Parents help in this regard as they can easily direct a young child with chances to learn and be ahead of the pack. In this age we see young kids reading and writing before they even start school. Some are so smart they can do amazing things like Mozart, for example, who played music in concert halls in Europe at the age of 6, although he was an exception.
Intelligence is not just being smart it's about solving problems. Every animal can do that in regards to their safety, requirements, and reproduction. Some animals are much smarter than their counterparts and they become teachers for their pack. That is how they adapt to new things and even new environments.
Improving your brain power is not always the result of education. Some people can't even read and write but they know how to survive and even how to run a business. In recent years we have seen people who could not complete high school invent systems that are now household items, such as the Internet.
Reading is a big part of modern learning and it is an escape route for many who get absorbed into books that take them on mental journeys into the unknown. An appreciation of books starts when young and through an interest generated when they are read out.
Adults, however, have set minds and that means it is harder to take on new tasks and succeed, but it can be done. It has nothing to do with your intelligence but a lot to do with control and will power. Old folk are learning computer skills, for instance, and enjoying the thrills of communicating with the world at the click of a mouse.
Looking after the brain is important and something I was aware of from a very young age. It is damaged through knocks, accidents, alcohol, drugs, and other forms of abuse. Overloading it with horror stories and fiction can result in nightmares caused when it tries to expel things that it cannot relate to. Those who are addicted to television programs of that type or to movies may find they are slipping backwards on the intelligence scale.
The brain is an organ that controls and protects the entire body. If it is fed with the right food it will result in improved skills and awareness. If it is abused and impacted with non-intellectual stuff then it will not perform well. One of my favourite adages is: "what you eat today walks and talks tomorrow."