Basically highlights all the flaws in the famous Minnesota Twins study that "race realists" (i.e. alt-right racists), centrist libs, and even a leftist (https://www.madinamerica.com/2021/02/left-wing-behavioral-genetics/) like to point to to say that some people are just dumber/lower-IQ than others. (They basically say that genetically identical twins have similar outcomes even if they grew up in different environments, i.e. reared apart, and that this proves that genetics are way more important than environmental factors).

Articles includes links to the full and abridged PDFs. The abridged one is worth skimming. Here are some of key flaws in the twins study:

• Many twin pairs experienced late separation, and many pairs were reared together in the same home for several years
• Most twin pairs grew up in similar socioeconomic and cultural environments
• MZA correlations were inflated by non-genetic cohort effects, based on common age, common sex, and other factors
• Twins share a common pre-natal (intrauterine) environment, and the MZA pre-natal environment is more similar than the DZA pre-natal environment
• TRA study findings might not be (or are not) generalizable to the non-twin population
• In studies based on volunteer twins, a bias was introduced because pairs had to have known of each other’s existence to be able to participate in the study
• MZA samples were biased in favor of more similar pairs, meaning that studied MZA pairs are not representative of MZAs as a population
• The similar physical appearance and level of attractiveness of MZAs will elicit more similar behavior-influencing treatment by their social environments
• Twins sometimes had financial and other types of incentives to exaggerate or lie about their degree of separation and behavioral similarity, and their accounts are not always reliable
• There were several questionable or false assumptions underlying the statistical procedures used in the studies
• MZA pairs were not assigned to random environments There was researcher bias in favor of genetic interpretations of the data
• There were problems with the IQ and personality tests used
• The validity of concepts such as IQ, personality, and heritability are questionable
• In cases where evaluations and testing were performed by the same person, there was a potential for experimenter bias in favor of twin similarity

And on and on. Worth checking out to show how sometimes what is purported to be "science" can be full of bias.