A few comments about genetics
Older Studies:
Many traits examined in genetics, such as athletic ability or psychiatric symptoms, exist along a smooth continuum rather than in clear categories.
In contrast, earlier genetic research often compared groups using broad labels like “has a condition” versus “does not,” which ignored this continuum and drew artificial lines between normal and abnormal.
These studies depended on assumptions that have been widely questioned and can bias the results, such as the equal environment assumption.
Because of these limitations, many researchers view results from those older approaches more cautiously than modern studies that measure genetic differences directly.
Newer Studies: What GWAS Shows, and What It Cannot Show
Modern studies often use genome-wide association studies (GWAS), which look for genetic variants that are statistically associated with a trait.
GWAS results point to many small influences, not single genes for complex traits. For traits like intelligence, personality, psychiatric diagnoses, and athletic performance, it finds many genetic differences, each one associated with only a very small difference in the trait.
A GWAS association does not prove a genetic cause. It can reflect ancestry or environment rather than a biological effect.
GWAS depends on how the trait is defined and measured. If a diagnosis contains many different underlying problems, or if a trait is measured loosely, the results become harder to interpret. The study can find associations while still leaving the real causes unclear.
Bottom line. GWAS supports the idea that genetics can contribute to complex traits, but it also shows that the effects are spread across many variants and are hard to translate into clear biological explanations or practical predictions. These limits leave plenty of room for large effects from childhood experience and for large differences in adult outcomes that are not locked in by DNA.
Furthermore, genetic studies measure differences between people in their current environments, not what people could become under the best developmental conditions.