Parenting isn't a one-way street. A child's inherent temperament (e.g., ADHD, agreeableness) actively shapes parental reactions. This creates powerful feedback loops where, for instance, a difficult child elicits stricter parenting, which in turn affects development. The outcome is often misattributed solely to the parenting style.

Personality stability isn't just one concept. 'Rank order' stability measures if the most extraverted person in a group remains the most extraverted over time. 'Mean level' stability tracks how the average trait level for an entire population changes with age, such as dips in conscientiousness during adolescence.

Countering the idea that parenting has little effect on outcomes, a twin study found that the twin receiving slightly more maternal affection between ages 5-10 grew up to be more open, conscientious, and agreeable. This suggests that small, differential parenting choices have measurable long-term consequences for personality.

People tend to marry and befriend those who are genetically similar, a process that amplifies genetic inequality in the next generation. This is compounded by geographic sorting, where individuals with genetic propensities for success migrate away from disadvantaged areas, leaving them 'doubly disadvantaged, genetically and environmentally.'

It's a myth that all cells are a 50/50 blend of parental DNA. Neuroscientist Catherine Dulac's work shows that entire brain areas can be genetically identical to either the mother or the father. This explains why certain behaviors and traits are so strongly inherited from one parent.

Your outcomes are influenced not just by your own DNA but by the genes of those in your social environment, a concept called 'genetic nurture.' A spouse’s genes can affect your likelihood of depression, and a child's genes can evoke specific parenting behaviors, showing that the effect of genes doesn't stop at our own skin.

We age because natural selection favors genes that provide benefits early in life (e.g., faster growth, stronger immune response), even if those same genes cause deterioration later. Aging is the price we pay for traits that maximize reproductive success in our youth, not a fundamental law of biology.

Citing research, Sam Harris finds it humbling how little control parents have over their children's character. He states that for most psychological traits, the breakdown is roughly 50% genetic and 50% environmental, but the environmental component is driven by peers and culture, not direct parenting.

Trying to determine which traits you inherited from your parents is clouded by the 'noise' of shared environment and complex psychological relationships. For a more accurate assessment, skip a generation and analyze your four grandparents. The generational remove provides a cleaner, less biased signal of your genetic predispositions.