"What I am trying to do is to present a unified scientific view of life; that is, a view integrating life's biological, cognitive, and social dimensions. I have had many discussions with social scientists, cognitive scientists, physicists and biologist who question that task, who said that this would not be possible. They ask, why do I believe that I can do that? My belief is based largely on our knowledge of evolution. When you study evolution, you see that there was, first of all, evolution before the appearance of life, there was a molecular type of evolution where structures of greater and greater complexity evolved out of simple molecules. Biochemist who study that have made tremendous progress in understanding that process of molecular evolution. Then we had the appearance of the first cell which was a bacterium. Bacteria evolved for about 2 billion years and in doing so invented, if you want to use the term, or created most of the life processes that we know today. Biochemical processes like fermentation, oxygen breathing, photosynthesis, also rapid motion, were developed by bacteria in evolution. And what happened then was that bacteria combined with one another to produce larger cells — the so-called eukaryotic cells, which have a nucleus, chromosomes, organelles, and so on. This symbiosis that led to new forms is called symbiogenesis."