I love science. So I love scientific books.
Since I'm also fascinated by what makes us into the person that we are, David Linden's "Unique: The New Science of Human Individuality" hits the sweet spot for me of reading pleasure.
Linden is a professor of neuroscience at the Johns Hopkins University School of Medicine and the Kavli Neuroscience Discovery Institute.
Impressive credentials. Plus, Linden is an excellent writer with a sense of humor.
Here's some excerpts from the three-fourths of the book that I've read so far. These will give you a flavor of the fascinating facts that Linden shares on every page.
Heritability of human traits. One main conclusion of MISTRA [Minnesota Study of Twins Reared Apart] and related studies was that most human traits, regardless of whether they are physical or behavioral, have a significant heritable component, usually ranging from 30 to 80 percent.
...For decades, the dominant thinking in the field of psychology, and in society at large, was that the most important determinant of one's adult personality was the influence of immediate family, particularly the parents.
This idea came from the twentieth-century psychological movement called behaviorism, which held that humans come into the world as blank slates, ready to be molded by social experience.
As a result, it was quite a shock when the MISTRA experiments showed significantly higher correlations in personality measures in identical twin pairs than in fraternal ones. The main result was that about 50 percent of the variation in personality can be accounted for by heritability.
...Importantly, while one's likelihood of having religious beliefs is influenced by both heredity and shared environment, the specific religion you choose has no hereditary component.
Your genes might contribute to making you religious, but they will not specify a Hindu or Wiccan or Roman Catholic faith -- that's mostly a family and community affair.
Human genome. On average, considering the entire DNA sequence (both the genes and the stretches of other DNA between them), each human is about 99.8 percent similar to any other human, 98 percent similar to a chimpanzee, and 50 percent similar to a fruit fly.
This is because, if you go back far enough in evolutionary time, about eight hundred million years, humans, chimps, and fruit flies al share a common ancestor.
If only a 2 percent difference separates us from chimps, then it follows that small differences in the DNA sequence have a big effect on traits.
...The genome is not a detailed cell-by-cell blueprint for the development of the body and brain, but rather a vague recipe jotted down on the back of an envelope.
...The key point is that the genetic instructions for development are not precise.
...That's the main reason why identical twins, who share the same DNA sequence and nearly the same uterine environment, are not born with wholly identical bodies, brains, or temperaments.
This means that your individuality is not a matter of "nature versus nurture" but rather "heredity interacting with experience, filtered through the inherent randomness of development."
Free will. We like to imagine that we are fundamentally creatures of free will. We reliably call certain facts, events, and concepts to mind. We make conscious decisions and act volitionally. Our individuality is inextricably bound up with a deep sense of agency and autonomy.
To a large degree, this is a trick our brain plays on us. Most of our behavior is subconscious and automatic. In the words of neuroscientist Adrian Haith: "Almost everything you do is a habit."
...Almost all of our instincts about memory are wrong. We feel like creatures of free will, with detailed and unlimited recall of those events that have helped to form us as individuals.
In reality, most of our behavior is composed of learned, subconscious habits and skills with only a thin veneer of decision-making at the surface.
Our recollection of specific events is unreliable and subject to further distortion every time we recall them. Our memories of facts and concepts are only marginally better. When asked about how confident we are about the veracity of a particular memory, our estimation bears no relationship to the truth.
We feel like we can learn more and more with no limit, yet intensive training in one type of memory seems to degrade our ability to store some other forms of memory.
Our memories are suboptimal, and yet we hold them close. They feel true and important. They are central to our sense of individuality and agency. The mismatch between how we revere our memories and how often they fail is striking.
Why we should feel more agency than we really have is an interesting and open question. I tend to see it as more of a feature than a bug.
When we feel that we are in charge of our behavior, that we are making decisions based on accurate recollection, this allows for more rapid decision-making in those cases of the "thin sliver of cognitive deliberation" where it is truly required.
In other words, when we don't have to stop and second-guess whether we are in charge, we can be decisive when it really matters.
Sexual orientation. There have now been several large-scale anonymous surveys of sexual orientation performed using random sampling in the United States and Europe.
They indicate that approximately 3 percent of men and 1 percent of women identify as consistently homosexual, about 0.5 percent of men and 1 percent of women as bisexual, and the remainder heterosexual.
...Ask a straight man, "When did you decide to be straight?" and he'll likely answer that it didn't feel like a decision at all, but rather like a deep compulsion that became evident around puberty or before.
Gay and bi men will give the same answer: in one survey in the United States, only about 4 percent of all gay and bi men reported that they chose their sexual orientation -- the rest felt that they were "born that way."
...If sexual orientation had no heritable component, we'd expect that the percentage of twin pairs where both are gay would be roughly the same for fraternal and identical twins.
Conversely, if sexual orientation were entirely determined by genes, then every gay identical twin would have a gay twin sibling.
The best estimates to date, from a population of 3,826 randomly selected twin pairs in Sweden, indicate that about 20 percent of the variance in sexual orientation in women is determined by genes; in men, it's about 40 percent.
...The conclusion is that genetic variation is one factor in determining sexual orientation, but it is far from the whole story and it is a somewhat stronger effect in men than in women.
As always, it's important to remind ourselves that these estimates of heritability are measures for populations, not individuals.
It may be that there are some individual women and men who carry gene variants such that their sexual orientation is entirely genetically determined, and others for whom their sexual orientation has no genetic contribution whatsoever.
As with all behavioral traits, there is no single gene that determines human sexual orientation. Rather, many different genes each appear to make a small contribution, and at present we do not have a useful list of these genes.