cooperative breeding

The vast majority of the 10,000+ living species of birds are passerines, and the vast majority of those have a similar system of breeding: Mom and dad bird make a nest and share parental responsibilities roughly equally, if not identically. There are variations on that theme, of course. Even the non-passerines often follow this pattern. So, when we find a pattern that is different it is reasonable to try to explain this in adaptive terms; what features of this variant pattern provide enhanced fitness, and what ecological or social factors underly it? There are two patterns that are fairly…

You could argue that life is all about cheating death and having enough sex to pass on your genes to the next generation, as many times as possible. From this dispassionate viewpoint, human reproduction is very perplexing for our reproductive potential has an early expiry date.  At an average age of 38, women start becoming rapidly less fertile only to permanently lose the ability to have children some 10 years later during menopause. From an evolutionary point of view, this decline is bizarre. Other long-lived animals stay fertile until close to the end of their lives, with elephants…