This subject can no longer be avoided by anyone interested in anything.
Here is the best brief overview of this subject I have ever seen: 10 Replicants in Search of Fame.
The author, James Thomson, has very capably summarized a longer paper: Top 10 Replicated Findings From Behavioral Genetics.
Both papers are worth reading, but Thomson’s is the better place to start for most people. Here is a sample:
Rather than asking whether a monolithic factor like parental control is primarily responsible for non-shared (unique) effects, it might be necessary to consider many seemingly inconsequential experiences that are tipping points in children’s lives. The gloomy prospect is that these could be idiosyncratic stochastic experiences. However, the basic finding that most environmental effects are not shared by children growing up in the same family remains one of the most far-reaching findings from behavioral genetics. It is important to reiterate that the message is not that family experiences are unimportant, but rather that the salient experiences that affect children’s development are specific to each child in the family, not general to all children in the family.
Here is another:
More than 100 twin studies have addressed the key question of co-morbidity in psychopathology (having more than one diagnosed disorder), and this body of research also consistently shows substantial genetic overlap between common disorders in children and in adults. For example, a review of 23 twin studies and 12 family studies confirmed that anxiety and depression are correlated entirely for genetic reasons. In other words, the same genes affect both disorders, meaning that from a genetic perspective they are the same disorder.