The actions that relate living beings to their environment can be grouped into two very broad categories that throw light on the genome- environment relationship. The first is incorporation-the process by which an individual internalizes parts of the environment in some way as part of the process of living. To paraphrase the famous physicist Richard Feynmann, yesterday's lentils are today's muscle tissues or sperm cells. The oxygen in the air when breathed in becomes part of hemoglobin in blood; carbon dioxide in the air turns to carbohydrates in grasses.

Incorporation is also part of the process of reproduction. For instance, reproduction by mitosis requires incorporation of nutrients. In sexual reproduction, sperm is incorporated into the oöcyte to form the cell that becomes the new individual. More broadly, incorporation also includes internalization of social structure needed for survival.

The obverse set of processes can be grouped under the term excorporation. Carbohydrates once used up inside the body become carbon dioxide and other unneeded molecules to be excreted. Excretion of bodily chemicals involves a variety of functions such as getting rid of toxins or attracting a mate. Giving birth is an act of excorporation. And "behavior" in all species having social structure can be understood as excorporation of internalized social structure.

The internal structure of the insect appears to the crocodile through excorporation of light, chemicals, and sounds by the insect. Similarly, the flight of the insect away from its predator is mediated by the ecosystem through excorporation by the crocodile. There must therefore be a systematic correspondence between the internal genomic structure of the prey and predator that allows their relationships to exist. In other words, in so far as the predator and prey are related, their internal genomic structures are two expressions of the same ecosystem structure. Of course, one is the prey and the other the predator, and there are also essential differences in their internal structures. In sum, incorporation and excorporation are approximately reciprocal sets of activities that are needed to perpetuate a species as such and the individuals within it. Genetic structure is, of course, but one aspect of the matter.

The acts of incorporation and excorporation, in their totality, constitute the fundamentals of living. They can even be used to define life. A living being, by its internal structure, needs to incorporate its environment and to excorporate into its environment so that it may go on existing as such. To put it more simply, living beings have needs that relate them to their environments; inanimate things do not. This is the central feature that distinguishes the living from the inanimate. One might modify the famous Cartesian claim "I think, therefore I am" and say instead: I eat therefore I am-and vice versa.

Such a construct is supported by genetic research. Genes that code for proteins directly associated with the vital functions of incorporation and excorporation tend to be conserved across species. But it is difficult to say what detailed inferences about entire genomes or specific genome sequences whose functions are not yet understood may be drawn from observations of their patterns of incorporation and excorporation, given that present ideas about genetic structure are the result mainly of the dissection of DNA.

Next: Chapter 3

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Posted November 2001

Endnotes

¹ This is similar to, but also somewhat different from, the autopoiesis description of Fritjof Capra (Capra 1996, Chapter 7). The definition of living being given here allows us to create a functional boundary between the living and non-living, though, as Lewis Thomas observed "we [human beings] are shared, rented, occupied" for instance by mitochondria, " and in a strict sense they are not ours." He concluded that "...I am grateful for differentiation and speciation, but I cannot feel as separate an entity as I did a few years ago...." Thomas 1974, pp. 4-5. J. Scott Turner has published an extensive analysis of this fuzziness of boundaries between living beings and their environment, providing examples such as the way a cricket uses a leaf to improve the efficiency of the sound it needs to produce for its mating call and the creation of burrows by earthworms as they ingest the soil to extract organic matter from it. Turner 2000, p. 165 and pp. 115-119.

^{2 This is evident if one focuses on what French people do, instead of on what their philosophers say. Once we have identified that which is common between humans and other living beings-they all have needs they must fulfill in order to go on existing as living beings-we can begin to identify what makes humans different. For instance, in growing from babies, human beings acquire the capacity to go on a hunger strike-that is, negate a biological need-in order to secure what is precious. How such a notion of freedom can be elaborated so as to throw light on human nature is beyond the scope of this essay. (These ideas were printed in a letter to the editor on May 17, 1997, sent to the New York Times by the author as a comment on the essential differences between Deep Blue, a chess playing computer, and human beings.

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