The amazing success of humans as a【C1】______is the result of the evolutionary development of our brains which has led, among other things, to tool-using, tool-making, the【C2】______to solve problems by logical reasoning, thoughtful cooperation, and language. One of the most striking ways in which chimpanzees biologically【C3】______humans【C4】______in structure of their brains. The chimpanzee, with the capacity for【C5】______reasoning,【C6】______a type of intelligence more like that of humans than【C7】______any other mammal living today. The brain of the modern chimpanzee is probably not too dissimilar【C8】______the brain that so many millions of years ago【C9】______the behavior of the first ape man. For a long time, the fact that prehistoric people made【C10】______was considered to be one of the major【C11】______distinguishing them from other creatures.【C12】______pointed out earlier, I have watched chimpanzees【C13】______grass stems in order to use them to probe for termites. It is true that the chimpanzee does not【C14】______tools to ""a regular and set pattern"" —but then,【C15】______people, before their development of stone tools, undoubtedly poked around【C16】______sticks, and straws, at which stage it seems【C17】______that they made tools to a set pattern either. It is because of the close【C18】______in most people's minds of tools with humans【C19】______special attention has always been focused upon any animal able to use an object as a tool; but it is important to realize that this ability, on its own, does not necessarily indicate any special intelligence in the creature【C20】______."