A far better explanation of Selfish Gene Theory can be found at www.world-of-dawkins.com.
This may seem wrong for humans, who have free will and are not mere programmable automaton, but in fact humans make logical decisions to satisfy their emotions, and human emotions are as murky and as illogical as any of those found in their animal counterparts.
Many of Charles Darwin's thoughts and opinions were strongly influenced by religion, and also the lack of understanding of DNA molecules, and of the process of information replication. We think of Darwin as being the creator of modern evolutionary theory, but in fact in retrospect he was confused about the subject, and a fuller understanding came much later, with the recognition of work by Gregor Mendel, and James Watson and Francis Crick's elucidation of the DNA molecule. Darwin was simply the first to publish suggestions that evolution occurred by a process of survival of the fittest.
The purpose of evolution is not, as Darwin suggested, survival of the species, it is simply the survival of the information in the genes of the individual. The individual is almost irrelevant to the genes - they are useful containers of the genetic code, but are in the final analysis expendable, and can be cast away if doing so can cause a greater reproduction elsewhere.
Life and evolution is pattern reproducing for no other reason than this: patterns which are good at reproducing tend to reproduce themselves - other patterns do not. The behavior we see in living things is simply behavior which has a history of causing replicating the patterns. The genetic code dictates behavior, and behavior changes the success of the replication process. The genetic codes which cause behavior which causes a more replication of the pattern becomes more prevalent.
This is what we call survival of the fittest. We talk about purpose of reproduction or the purpose of evolution because it helps to explain behavior and to focus on the process, but in fact it has no more purpose than a group of random numbers. We might say that evolution has created leaves which are green so that they can photo-synthesize, but in fact the process of evolution has merely selected for DNA patterns which generate green leaves because they were better at reproducing themselves than other forms of DNA.
We are used to things moving in a certain direction because they have a purpose - a wild animal goes hunting because it is hungry, for the purpose of finding food. Evolution too appears directed. Animals develop fur for the purpose of keeping warm and so on, but this does not mean that there truly a purpose behind it - just a mechanism which makes it happen.
Selfish Gene Theory regards the visible organism (the cat, human, flower, amoeba or whatever) as the host. It is like a big lumbering robot whose purpose is to replicate the genes it carries in its cells.
This is the essence of selfish gene theory. All common characteristics of living things have their roots in this phenomenon, including humans.