A. probably B. plant C. reasoning D. ability E. stage F. species G. mammal H. differ I. prehistoric J. period K. contact L. association M. definitely N. lies in O. distinguish The amazing success of man as a 1is the result of the evolutionary development of our brains which has led, among other things, to tool-using, tool-making, the ability to solve problems by logical 2, thoughtful cooperation, and language. One of the most striking ways in which chimpanzees biologically resemble humans 3 the structure of their brains. The chimpanzee, with his capacity for primitive reasoning, exhibits a type of intelligence more like that of humans than does any other 4 living today. The brain of the modern chimpanzee is 5 not too dissimilar to the brain that so many millions of years ago directed the behavior of the first ape man. For a long time, the fact that 6 man made tools was considered to be one of the major criteria to 7 them from other creatures. It is true that the chimpanzee does not fashion his tools to a regular and set pattern—but then, primitive man, before his development of stone tools, undoubtedly poked around with sticks and straws, at which 8 it seems unlikely that he made tools to a set pattern either. It is because of the close 9 in most people's minds of tools with man that 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 10, on its own, does not necessarily indicate any special intelligence in the creature concerned.