Final answer:
Social monogamy involves long-term pair bonds with one partner, where both may provide parental care. Polygyny entails a male having multiple female partners, often leading females to largely handle offspring care. Polyandry, where a female has multiple male partners, is rarer, usually because of the greater energy females invest in offspring production.
Step-by-step explanation:
To compare and contrast social monogamy with polygyny and polyandry, we need to look at the mating systems each term refers to. Social monogamy is a system where individuals form long-term pair bonds with a single partner. This is observed in many bird species where both males and females provide parental care for their offspring. Polygyny, on the other hand, involves a situation where males have multiple female partners. In a polygynous system, one male mates with several females, which often results in the female being largely responsible for offspring care, as seen in the harem mating structures of elephant seals. Polyandry is much rarer and involves a mating system where females have multiple male partners, as suggested by the word's Greek roots meaning 'many' and 'man'.
An advantage of a monogamous relationship might include the mate-guarding hypothesis where male parental investment can increase offspring survival. Polygynous mating, such as resource-based polygyny and harem mating structures, maximizes labor force and resource sharing within a family, creating strong kinship ties and sometimes conferring higher social status.
Polyandrous mating systems are rare, partly because females usually devote more energy to offspring production and development, which provides them with less opportunity for multiple mating compared to males. These systems tend to arise when there is an ecological or demographic rationale for such arrangements.