After all, if resources are scarce, it’s better that the strongest offspring survive and that their potential efforts go to ensuring that happens. (It’s the old story of genetic replication again: Surviving offspring are more likely to have the strongest genes, and they are the ones that have the best chance of reproducing later and passing those genes on.) Forbes thinks that such extreme jealous reactions are not common in the human species, but “the more modest forms of sibling rivalry that are ubiquitous in species with extensive parental care—the scrambles for food and begging competitions—resemble more closely the dynamics that occur in human families.”
Perhaps this fundamental link is why sibling jealousy is such a common theme in life and letters. Forbes paints it out as a normal, natural, and largely unperturbing force in human life, but some of our oldest stories point to its violence. The most famous of all is the murder of Abel by Cain. If you believe the book of Genesis, this was the first jealous murder in human history—the first to be born caused the first to die. According to the biblical story (Genesis 4:1-8), Cain murdered his brother out of jealousy. God was pleased with Abel’s offering of a lamb, but not with Cain’s offering of some leftover harvest and his selfish expectation of something in return—God’s love, or some special standing in his eyes. Cain is disappointed and enraged, and kills his brother in the field. There is the jealous triangle of Cain, Abel, and God, and Cain’s heightened emotional reaction when he feels the threat of losing God’s love to Abel. This particular type of jealous family conflict echoes in many other stories: Joseph and his brothers, Jacob and Esau, Thyestes and Atreus, Romulus and Remus.
The conflict between brothers sometimes stands as an emblem for civil war, including John Steinbeck’s rewriting of Cain and Abel in East of Eden. This great novel focuses on two families, each with biblical resonances. Charles Trask, a farmer, beats his younger brother Adam nearly to death after being rejected by their father, and Adam’s sons, Caleb and Aron, do not treat one another any better. In a climactic scene, Adam rejects Caleb’s gift of money, telling his eldest son that “I would have been so happy if you could have given me—well, what your brother has—pride in the thing he’s doing, gladness in his progress.” In a fit of jealousy, Caleb takes Aron to a brothel and reveals to him their mother, Cathy, who is a prostitute there, leading the disillusioned and disgusting Aron to enlist in the army. He’s killed in the last year of the First World War.
It is not only in literature that such vehement sibling jealousy is to be found. The legendary actor-sisters Joan Fontaine and Olivia de Havilland had a famously jealousy-ridden relationship. They admitted to loathing one another from childhood. At the apex of their jealousy triangle was their mother Lillian, who raised them alone after her husband’s many infidelities and eventual elopement with their Japanese housekeeper, and who flip-flopped in her affection for the girls for most of their lives. Joan, the younger of the sisters, said, “I regret that I remember not one act of kindness from her all through my childhood,” and she spoke in her autobiography of her sister’s unhappiness at having to share parental attention with the new baby. Lillian seems to have encouraged the rivalry between her girls. The fact that they both became Oscar-winning actresses, sometimes vying for the same roles, and one year even competing against each other for the Oscar for best actress (Joan won), was not surprising at all. But it hardly helped the family dynamic. Even Lillian revived her stage career once the “de Havilland” name was getting well-known.