Partnerwahl: Von Promiskuität zu festen Bindungen

In einem interessanten Artikel zur Partnerwahl wird dargestellt unter welchen Bedingungen feste, (verhältnismäßig) monogame Bindungen entstanden sein könnten.

A crucial step in recent theories of human origins is the emergence of strong pair-bonding between males and females accompanied by a dramatic reduction in the male-to-male conflict over mating and an increased investment in offspring. How such a transition from promiscuity to pair-bonding could be achieved is puzzling. Many species would, indeed, be much better off evolutionarily if the effort spent on male competition over mating was redirected to increasing female fertility or survivorship of offspring. Males, however, are locked in a “social dilemma,” where shifting one’s effort from “appropriation” to “production” would give an advantage to free-riding competitors and therefore, should not happen. Here, I first consider simple models for four prominent scenarios of the human transition to pair-bonding: communal care, mate guarding, food for mating, and mate provisioning. I show that the transition is not feasible under biologically relevant conditions in any of these models. Then, I show that the transition can happen if one accounts for male heterogeneity, assortative pair formation, and evolution of female choice and faithfulness. This process is started when low-ranked males begin using an alternative strategy of female provisioning. At the end, except for the top-ranked individuals, males invest exclusively in provisioning females who have evolved very high fidelity to their mates. My results point to the crucial importance of female choice and emphasize the need for incorporating between-individual variation in theoretical and empirical studies of social dilemmas and behaviors.

Quelle: Human origins and the transition from promiscuity to pair-bonding

Aus der Diskussion dort:

I have shown that, under biologically realistic conditions (e.g., when the group size is not too small, competition between males is strong, and the effects of male provisioning and care are not too large), the population is not able to escape the low fitness state at which males invest exclusively into competition for mating. This conclusion is not changed qualitatively, even if one accounts for an elevated genetic relatedness between males arising from their philopatry. Note that communal care provided by females, the importance of which has been stressed in a number of recent publications (4, 6–8), is even less likely to become established because of low relatedness between females who disperse to different groups on maturity. Moreover, females may benefit from multiple matings (46–48), which implies additional selection against pair-bonding. The power and implications of the male’s dilemma discussed above have not been generally acknowledged in the discussions of human transition to pair-bonding (10). The solution of the male’s dilemma proposed here builds on the idea of mate provisioning augmented by the explicit consideration of (i) females’ evolutionary response to provisioning and (ii) the role of males’ dominance ranks in determining their preferred actions. Mate provisioning has double benefits, one of which (mating) is immediate and another (increased fertility and decreased between-birth interval) is delayed. These benefits are most pronounced for low-ranked males who have a low chance of winning a mate in competition with top-ranked males. One, therefore, should expect that it is low-ranked males who will attempt to buy mating by provisioning. Note that, if there are more males at the bottom than at the top of the hierarchy, selection benefiting the “masses” may become stronger than selection benefiting the “elite”. Top-ranked males can easily beat out or chase away the low-ranked males and steal the paternity, making the investment of low-ranked males in production wasteful. However, after females start developing preferences for being provisioned, the low-ranked males’ investments start to pay off. In the model presented here, male provisioning and female faithfulness coevolve in a self-reinforcing manner. At the end, except for a very small proportion of the top-ranked individuals, males invest exclusively in provisioning females who have evolved very high fidelity to their mates. Overall, females are not predicted to become completely faithful, but rather, the level of their faithfulness is expected to be controlled by a balance between selection for better genes (potentially supplied by top-ranked males) and better access for food and care (provided largely by low-ranked males).

Hier wird auch aufgezeigt, dass Verhalten nicht einfach losgelöst von anderen Umständen ist. Ein biologischer Impuls seinen Nachwuchs als Vater zu versorgen kann sich biologisch nicht umfassend neben weiblicher Promiskuität entwickeln, weil sich der Impuls dann nicht mehr lohnt. Im Gegenzug ist Treue erst dann lohnenswert, wenn der andere etwas beisteuert. Es sind im Endeffekt spieletheoretische Modelle, bei denen man erkennen kann, dass eine Evolution nicht vollkommen frei ist, weil bestimmte Selektiondrücke bestimmte Kombinationen begünstigen. Allerdings wird auch hierbei deutlich, dass Verhalten und Umwelt interagieren. Ein niedrigrangiges Männchen in einer Horde sehr starker Männchen mag eher auf Bindung setzen, dass gleiche Männchen in eine Gruppe mit noch viel schwächeren Männchen versetzt könnte hingegen eine andere Strategie fahren und weniger auf Versorgung setzen.

Die Folgen für unsere Entwicklung könnten enorm gewesen sein:

The transition to strong pair-bonding opened a path to intensified male parental investment, which was a breakthrough adaptation with multiple anatomical, behavioral, and physiological consequences for early hominids and all of their descendants (4–6). The establishment of pair-bonding shifted competition between males for mates, which was potentially destructive for the group, to a new dimension which is beneficial for the group — competition to be a better provider to get better mates (64). Pairbonding provided a foundation for the later emergence of the institution of modern family (65) as an outcome of additional processes, such as wealth accumulation and inheritance (66). Pairbonding also made possible the recognition of male kin, dramatically expanding the efficiency of kin selection and helping by grandparents, leading to stronger within-group coalitions and alliances (67, 68), and allowing for subsequent evolution of widespread cooperation in general (6, 69).

Hier hat sich also ein Weg ergeben, der uns friedlicher macht, der uns erlaubt eher zusammenzuarbeiten und Allianzen einzugehen und gleichzeitig Besitz und Reichtum interessant gemacht hat, ebenso wie die Vererbung von Besitz an unsere Verwandten, da wir damit im Wege der Verwandtenselektion die Weitergabe unserer Gene fördern.

Zu Vätern und Evolution, Gruppenbildung, Versorgung durch den Mann etc vergleiche auch: