The obvious ones are the need for resources to maintain the day-to-day activities necessary for basic survival and the need to locate and contend with available mates for reproduction. Within the context of reproduction, controls have evolved to ensure that equilibrium exists between the number of produced offspring and the number that will likely reach adulthood. This is an important element in the entire process since being too successful will increase interspecies competition and risk survival just as surely as inadequate reproduction would.
In biology there is always a balance, or tension that produces a kind of equilibrium. If an event tips the scales in any particular direction then the balance shifts and an alternate strategy can dominate. As an example, one can examine the population dynamics of any given species and see that there is invariably a balance between the number of offspring and the steady-state case of the population. If resources become depleted, then an increased number of deaths and fewer offspring may result. If resources are abundant then the number of healthy individuals will increase. Depending on the initial conditions, such variations are chaotic in nature and may oscillate from season to season with strikingly different results in different environments.
In addition, many species that are prey to others will often produce far more offspring than are expected to survive, so a change in the number of predators will also determine how many offspring remain viable.
This also brings about another problem, since the more offspring survive, then the greater the competition for resources in the originating species. Therefore it is beneficial if the species reproducing isn’t too prolific, lest it deplete the resources it depends on for the entire group. In this context, the concept of a group is not meant to suggest any social organization, but rather that the same species resides within a specific geographic locale. While there doesn’t have to be any tacit recognition of the group, or any social mechanisms that dictate behavior within the group, the mere fact of sexual reproduction requires a co-dependence on the group, since that is the source of all potential mates.
This does NOT imply some sort of “group selection”, but it simply indicates that group considerations are very much a part of self-interest.
This can be useful in explaining why apparent anomalies seem to occur, such as the subject of insect cannibalism that was briefly mentioned, and also the consideration of species that may even eat their own young.
As an example, let’s consider the practice of some female spiders that consume the males before, during, or after copulation. Perhaps a partial explanation may be that the female is literally responding to the availability of food (be it the male or offspring). If resources are plentiful, then the female may be less inclined to view them as food, whereas when resource shortages exist, then they may be candidates for being the meal. This would serve the purpose of ensuring that a new generation of competitors isn’t introduced into an environment that may be unable to support them and the original parent.
After all, reproduction may not be a one-time event, so the ability to control the number of offspring will be directly related to the viability of the parent’s long-term survival. Just to offer a bit speculation, a female spider that kills the male before he can breed may simply be exercising the spider’s equivalent of birth control. If resources are constrained enough so that the male’s value is better recognized as food than as a mate, then the failure to breed may be beneficial. If resources are adequate, then the killing of the male (after mating) may satisfy the food urge, but more significantly prevent him for breeding other females and thereby reducing the competition for resources. If resources are plentiful, then the male may survive and be free to be more prolific in breeding.
Similarly since it is often the size of the male that may determine the likelihood of being eaten, perhaps the size of the male is also an indication of resource availability; the large males tending to represent an environment replete with resources.
In animals that do not have large territorial ranges, it becomes increasingly important to not saturate an environment to where the primary competitive force occurs between members of the same “family”. As a result, it may make sense (as in the case of our spiders) to kill the male to avoid mating with other females.
While it is not my intent to deal with the issue of sexual selection, this is being pointed out to demonstrate that these are probably the most striking examples of what might be considered “selfish” behavior. Although even in these circumstances, the selfishness appears to be primarily one-sided (i.e. from the female) and not consistent.
The risk in describing any of these actions as being selfish or cooperative, is that it creates the impression that there is an intent behind these actions, rather than recognizing that they are all self-correcting adaptations and simply require each participant to act in their own self-interest. This is somewhat analogous to modern economic views, wherein each individual, acting in their own best interest, creates an environment where goods are produced and wealth accrues.
In summary we need to consider that biological success requires reproduction, but similarly, there appears to be a dynamic tension between species that has given rise to reproductive adaptations that try to maximize the chances of survival for the offspring, but not to be too successful and compromise the survival of the geographic group itself.
In the next post, we will address the basic issues and assumptions in regards to what is meant by competition.