Bacterial biofilms and slime molds are among the most simply organized coalitions of individual organisms, although social insects are probably the most often-used example of clearcut organization above the level of what is traditionally considered an organism. Of course, human societies and hundreds of less elaborate animal social structures can be thought of in the same way.

From a darwinian point of view, of ever-present competition for reproductive gain, social organization should occur only if it confers a benefit that outweighs to the risks of group life (like potential exhaustion of food supplies). A major way this has been put is the need to explain the widespread occurrence of altruism, or how genes can evolve whose bearers sacrifice some or all of their own reproductive potential for that of others. This is an inflammatory dispute within biology, fought with ideological vigor. The argument is often engaged under the term "group selection." Strict genetic darwinism is individual-focused, strongly selectionistic, and will at most grudgingly accept sacrifice for the good of the group because of a lack of an obvious mechanism by which that can evolve. (Group selection was important in Wallace's view of evolution, however.)

The most common explanation for altruism is that its beneficiaries are close relatives who share similar genotypes with the individual making the sacrifice. Formally, in the general case, what an individual should be willing to sacrifice for another individual depends on the precise degree of relationship between them. As a general principle this seems reasonable, though it fails to account without contortions verging on implausibility for many of the social behaviors found in the world.

The individual cells in some bacterial biofilms are clones of each other, but many biofilms are aggregates of different kinds of bacteria. Why would different strains of bacteria be "willing" to enhance the survival of others? Is it that they are closely related enough? In Dictyostelium the slug forms from a collection of (former) individuals and it appears to be only a matter of chance which of them end up producing spores for the next generation. But to a considerable extent the issue is artificial. Most groups of organisms are collections of relatives to varying degrees, simply because individuals of most species do not disperse very widely from their place of birth or, if born into a horde or school, disperse as a reproductive group. Giving your all for the group usually means giving your all for your relatives in one way or another. Your peers are extensions of yourself. Precision in evaluating degrees of kinship before acting, or precise screening of individuals by selection in this regard, for the many reasons we have discussed, is neither required ¿a^ nor to be expected. J/%.

More interesting than the fine points of the altruism debate is a broader view of the nature of communities and the concept of community itself. An entire insect colony is produced by one or a few queens, and hence the entire progeny shares the half of the genome they inherit from her, with the other half coming from reproductive males. This means a peculiarly close kind of genetic kinship among members of the colony, as discussed in Chapter 8. This very close connection is why the term "superorganism" has been used to describe insect colonies.

But we can extend the concept. Even a cell can be viewed as a superorganism, of individual genes, and an individual organism a superorganism of cells. In each case, there is internal connectedness, communication via signaling and response elements, with associated specialization of function and coordination of action. The immediate life history as well as evolutionary fate of one is dependent on that of others. There is active and sometimes externally instructed self-sacrifice, as seen in the widespread apoptosis among the cells in the life of a complex organism (or controlled mRNA degradation within a cell). Gene inactivation is to a cell, and apoptosis to an organism, what altruism is to a member of a society.

These internal characteristics of organisms—genealogical connections among genes, signaling systems that alter gene expression, and responses by one component to conditions of another—also apply to relationships between members of the same species and, indeed even between members of different species. Social insects represent but one way in which this occurs; in fact, it is a phenomenon found from biofilms to ecosystems.

Organisms communicate and coordinate by pheromones, visual, auditory, tactile, olfactory, and other means of message transfer, reception, interpretation, and response. Even under the most classical of darwinian scenarios, flowers evolve odors that insects can smell and vice versa. Signal and ligand, reception and response. The genomes are intimately connected and literally interdependent.

As noted in Chapter 8, one distinction used in the definition of what we refer to as an "organism" is that its cells are connected together to form a single body, and derive from a common cellular ancestor. But this is a somewhat false distinction. Cells and other elements within an organism are not always physically attached (for example, circulating blood cells), whereas in many species distinct organisms are physically connected when they reproduce—usually an essential part of reproduction. And members of a population are clearly connected by their unbroken physical chain of shared cellular ancestry.

Social and ecological interactions affect the collective genome(s) involved, which of course is thus of direct evolutionary import. Like any other set of interacting factors, the relative frequency and spatiotemporal relationships among the factors depends on the dynamics of their interactions. Just as in development, they can generate gradients of location in space (such as microenvironments), wavelike oscillations (such as predator-prey cycles), or relatively stable frequencies (such as population size). These are "emergent" properties of communities in the same way that similar patterned traits within individual organisms are properties of interactions among signaling factors.

At the embryological, organismal, and ecological levels, the interacting system involves the partial sequestration of its modular components. Indeed, though we think of organisms as entirely different kinds of "being," their interactions, as in pheromone signaling or sepual reproduction, involve exactly the same molecular processes—even genes and types of genes—as found in developmental signaling. If biofilms are any indicator, it may be that interactions among single-celled organisms were exaptations for the evolution of multicellular organisms in the first place.

In this sense, it is rather arbitrary what we should call an "organism." For appropriate purposes, even the entire biosphere can be viewed, truly, as composed of comparable entities interacting in complex, hierarchically nested and networked ways, by related genes and common molecular mechanisms. The distinctions between kinds of biological entities blur because they are all interconnected, in similar ways, now and by common ancestry back through the entirety of life. This is the Great Chain of Beings.

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