2.3: The organization of organisms

Some organisms consist of a single cell, some of many, often of distinct "types". Cells can be highly specialized, yet they all appear related, sharing many molecular and structural details. So why do we consider the organism rather than the cell to be the basic unit of life? The distinction is a matter of reality versus abstraction. It is organisms, whether single- or multi-cellular, that produce new organisms. A single cell within a multicellular organism normally cannot survive outside the organism nor can it produce a new organism – reproduction depends upon cooperation between the cells of the organism. A multicellular organism is a cooperative, highly integrated social system.

In a typical multicellular organism most cells have given up their ability to reproduce a new organism; their future depends upon the reproductive success of the organism as a whole. Within the organism the cells that give rise to the next generation are known as germ cells; cells that do not give rise to new organisms are known as somatic cells. All organisms arise from a pre-existing organism or through the cooperation of two sexually reproducing organisms. We will also see that breakdowns in social systems can lead to the death of the organism or the disruption of a social system. Cancer is the most obvious example of an anti-social cellular behavior. In the short term, cancerous behavior maybe "rewarded" (more copies of the cancer cell are produced) but ultimately it leads to the death of the organism and the extinction of the cancer cells.^[51] Evolutionary mechanisms involve cost-benefit “calculations” based on in terms of reproductive success.

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