Human intelligence is not only difficult to measure; it's also difficult to define. Most researchers, these days, will tell you that our intelligence is a combination of what we know (our knowledge), our skills and our ability to understand and reason -- and that our cognitive abilities continue to grow throughout our lives, rather than being set at birth. The basis of intelligence is likely a combination of several factors. For example, are you biologically destined to be only as smart as your parents? Biology, though important, is only part of the intelligence package. Other factors, including everything from what we eat to where we live, can also affect our intelligence. But first, let's look at what's in our genes.