Modern Evolutionary Theory
and Patterns of Attachment
It is not uncommon to read in child and human development textbooks (Bee, 1995; Cole & Cole, 1989; Harris & Liebert, 1992; Hetherington & Parke, 1993; Sigelman & Shaffer, 1995; Turner & Helms, 1995) and in scholarly publications that attachment behavior evolved because it protected infants from predators, and in so doing promoted the survival of the species. From the perspective of modern evolutionary biology, it is clear that such arguments, as far as they go, are insufficient to account for the evolution of attachment behavior (or any other, for that matter), for two reasons (see Simpson, Chapter 6, this volume). First, evolution works at the levels of the gene and the individual, not the species; second, evolution is about differential reproduction, not just survival.
Genetic replication is the goal of (all) life, and thus the ultimate target of natural selection. That is, simple survival is not selected for. Only if survival fosters the reproduction of the surviving individual’s genes (via his or her own survival and/or that of kin, including descendants), rather than those of the species, does natural selection operate on a behavior or behavior system—perhaps like attachment—that fosters survival. In fact, the goals of reproductive success and survival are often in conflict; when such conflict occurs, the genes and behavior that enhance reproductive success are selected for, not the genes and behavior that promote survival. This can be seen clearly in many species, including birds and monkeys, in which individual organisms that make loud calls to warn others of the presence of predators reduce their own survival prospects by drawing the predators’ attention to themselves.
Why should any individual engage in such potentially selfdestructive behavior? That is, why has behavior that is so clearly a threat to individual survival evolved? The answer to this question is founded on the fact that those most likely to benefit from the warning call are relatives of the caller and thus possess some of the very same genes as the caller does (i.e., inclusive fitness). Because the benefactors of the warning call have the potential to collectively replicate the caller’s genes (through their own reproduction), more than would be the case were no call given, calling behavior that ends up enhancing the reproductive fitness of the caller while simultaneously reducing the caller’s probability of survival evolves.
What this analysis should make clear is that attachment behavior would not have evolved if it had only functioned to protect the child and thereby to promote survival, because survival per se is clearly not the goal of natural selection. Thus, unless survival enhanced the reproductive prospects and especially the reproductive fitness of ancestral human infants, there would have been insufficient evolutionary pressure for attachment behavior to evolve. To the extent, then, that evolution had anything to do with human attachment—as Bowlby believed it did, and as the theory he promulgated presumes—it is because the protection and survival it promoted fostered successful reproduction of those individuals