Sibling Rivalry

Here's to you, kids
By my mother-in-law's request.
"We must be a product of God's kid brother." -The Dead Milkmen (off the Soul Rotation album)

My wife and her sister live with me, and I am one of two siblings, as well, so this is good. This term makes me think of school rivalries, which coaches can really rev up to a fury, and assorted punks can make into after-game battles to "rival" the intensity on field/court. I remember my dad gave me a "I hate the Dodgers" T-shirt when I was a kid, when I went with him to see the Giants play L.A. I've had a basic antipathy toward Los Angeles ever since, I guess. I think of it as smoggy and superficial and too trafficked and gangy and filled with vampires, or something. I'm sure it's not really that bad (!) Anyway, about siblings:

From Wikipedia:
Sibling rivalry is a competition or animosity between brothers, sisters, or brother and sister, whether related or not.

David Levy introduced the term "sibling rivalry" in 1941, claiming that for an older sibling "the aggressive response to the new baby is so typical that it is safe to say it is a common feature of family life."

According to child psychologist Sylvia Rimm, sibling rivalry is particularly intense when children are very close in age and of the same gender, or where one child is intellectually gifted. Children with the closest relationships to their mothers show the most upset after the baby is born, while those with a close relationship to their father seem to adjust better. The child’s developmental stage may affect how well they can share their parents’ attention. Often two-year-olds have trouble adapting to a new baby, because they still have a great need for time and closeness from their parents.

82% of people in Western countries have at least one sibling, and siblings generally spend more time together during childhood than they do with parents. The sibling bond is often complicated and is influenced by factors such as parental treatment, birth order, personality, and people and experiences outside the family. There is an Arabic saying: "I against my brother; my brother and I against my cousin; I, my brother, and my cousin against the stranger."

Evolutionary theory explains everything, I seem to remember from my college days. S.R., too: Evolutionary psychologists explain sibling rivalry in terms of parental investment and kin selection. A parent shares 50% of her genes with each child, and is inclined to spread resources equally among all children in the family. However, a child shares 50% of his genes with a sibling but 100% with himself; so if the relationship follows Hamilton's rule, he should only share resources if the benefit to the sibling is greater than twice the benefit to himself (this is not a conscious calculation, but a genetic coding that unconsciously guides the behavior). So parents try to encourage their children to share, but often meet resistance. Children have motivation to feel both positively and negatively towards brothers and sisters, which may explain the mixed feelings that siblings sometimes have towards each other.

The natural world, such as insects and even plants, obey these rules.
Am I my brother's keeper?