My own life has in some ways been a decades-long tour of the sibling experience. I have full sibs, I have half-sibs, and for a time I had step-sibs.

A close family member once offered his opinion that I exhibit the phone manners of a goat, then promptly withdrew the charge - out of fairness to goats.

Jellyfish serve as a model for bioengineers for the same reason yeast were once so valuable to geneticists: they're simple to deconstruct.

It's a deep and all but certain truth about narcissistic personalities that to meet them is to love them, but to know them well is to find them unbearable. Confidence quickly curdles into arrogance; smarts turn to smugness, charm turns to smarm.

Narcissism falls along the axis of what psychologists call personality disorders, one of a group that includes antisocial, dependent, histrionic, avoidant and borderline personalities. But by most measures, narcissism is one of the worst, if only because the narcissists themselves are so clueless.

Older siblings get more total-immersion mentoring with their parents before younger siblings come along. As a result, they get an IQ and linguistic advantage because they are the exclusive focus of their parents' attention.

Kids whose puberty begins too soon face not just psychological risks, but physical ones too, with an increased likelihood of cancer, as well as skeletal changes that could prevent them from attaining their full adult height.