Philosophy of Genetics

Common Sense and Bias

According to Judith Rich Harris, researchers tend to seek out evidence that confirms their biases, and downplay (or attack) any evidence to the contrary.  Furthermore, according to Christopher Chabris "people often react most defensively when challenged not on their firmly held beliefs but on beliefs they wish were true but suspect at some level to be false." 

For example, psychologists often assert that a child’s personality can be guided and shaped by his or her parents.  This implies that well-adjusted children must have had good parents, and fearful children must have been overprotected by their (bad) parents.

This common sense view completely overlooks the possibility that children who are born with a genetic predisposition to be anxious or fearful are more likely to be reared by anxious, fearful parents, because children get their gene variants from their parents as well as their environment.

When asked to consider this, researchers have backtracked, and now claim it’s not parental over-protectiveness that makes all children fearful, it’s the child’s "high-reactive" temperament.  So overprotecting some children makes them fearful, and overprotecting other children does not... Which begs the question -- how can you predict who react which way?

Another example of bad research shows that “mothers who improved in their child-rearing methods (through interventions) are more likely to have children who behave well in school”.  Due to their biases, researchers overlooked the fact that “compliance depends on certain personality traits that may also be associated with the outcome event”. 

In other words, “people who comply with interventions are likely to differ in personality and intelligence from those who do not comply. Because these characteristics are heritable [innate], parents who respond well to the demands of an intervention are more likely to have children who respond well to the demands of school.”  Again, children share their parents' gene variants, not just their environment.

Why do identical twins differ?

Why do identical twins (who possess the same genes) differ from each other?  New studies show that:

Human cells have tens of thousands of genes in them, each with its own job, such as producing energy. But only certain genes are active at any given time or in any cell type while the rest are appropriately dormant — a grand orchestration that adds up to a smooth-running life.

The new research, led by Mario Fraga and Manel Esteller of the Spanish National Cancer Center in Madrid, focused on two biological mechanisms that influence gene activity. In one, called DNA methylation, enzymes inside a cell attach a minuscule molecular decoration to a gene, deactivating that gene. In the other, called histone acetylation, a dormant gene is made active again.

These altered genetic settings can last a lifetime and can be important if, say, the gene turned off is one that protects against cancer.

In the new work, described in the current issue of Proceedings of the National Academy of Sciences, researchers measured the extent to which twins of various ages, from 3 to 74, differed in the number and variety of genes that had been either turned on or shut down by epigenetic processes. They found young twins had almost identical epigenetic profiles but that with age their profiles became more and more divergent.

In a finding that scientists said was particularly groundbreaking, the epigenetic profiles of twins who had been raised apart or had especially different life experiences — including nutritional habits, history of illness, physical activity, and use of tobacco, alcohol and drugs — differed more than those who had lived together longer or shared similar environments and experiences.

Small epigenetic events before birth probably account for many of the minor distinguishing differences in the appearance, personality and general health of young twins, Esteller said, and a lifetime of further epigenetic changes gradually increases individuality.