But actually, Bob and Rob are completely identical in every way, no incident in their past did anything to separate them, and Bob just ended up working for a crappy CEO.
In this scenario, inherent predisposition to earning money is exactly the same in both twins, they just have different amounts of luck at it. The genome can’t encode the location of every cell in the body.
In this world, scientists might conclude that about 80% of IQ is genetic and 20% is environmental.
But in fact in terms of real, stable IQ differences, 100% would be genetic and 0% environmental.
Two identical twins take an IQ test, one makes some lucky guesses, the other is tired, and they end up with a score difference of 5 points.
Then some random unrelated people take the test and they get the 5 point difference plus an extra 20 point difference from genuinely having different IQs.
Obviously amount of variability attributable to environment (shared and non-shared) increases as the variability in environments in the sample increases] The “nature vs.
Identical Twin A becomes a small-time cocaine dealer in a back alley in West Philly, sells to an undercover cop, and ends up in jail.
Identical Twin B becomes a small-time cocaine dealer in a back alley in East Philly, doesn’t run into any undercover cops, and so avoids conviction.
Riemann and Kandler obsessively collect every possible measurement of personality – self-report, other-report, multiple different tests – and average them out to get an unusually accurate and low-noise estimate of the personality of the twins in their study.
They find that variation in personality is about 85% genetic, 15% non-shared environmental. Bob becomes a junior advertising executive at Coca-Cola, where he designs a new ad targeting young female consumers.