This morning I noticed a book in my office languishing under a pile of papers. I'd read most of it quite a while ago, except for a few pages at the end.
Having finally finished "Unique: The New Science of Human Individuality" by neuroscientist David J. Linden, I wanted to mark the occasion by sharing some excerpts on subjects that I found particularly interesting.
First up is the familiar "nature versus nurture" phrase that I remember from my schooling. The idea is that who we are is a function of just two things, heredity and upbringing. Linden makes clear that this way too simplistic. In fact, wrong.
The oppositional construction of "nature versus nurture" is just wrong. But the part of this horrid expression that really chaps my ass is "nurture." The word means how your parents raised you -- how they cared for and protected you (or failed to do so), when you were a child.
But of course, that's only one small part of the non-hereditary determination of traits. As we will explore in this chapter, a more correct term would be "experience," which I mean in the broadest sense.
Not just social experience and not just the experience of events that you have stored as memories, but rather every single factor that impinges upon you, from the moment that the sperm fertilizes the egg to your last breath.
These experiences start even before the embryo implants in the womb and encompass everything from the foods your mother ate while she was carrying you in utero to the waves of stress hormones you secreted on the first day of your first real job.
And there's another important factor that is neither heredity nor experience. That's the random nature of development, particularly the self-assembly of the brain and its five hundred trillion connections.
As I mentioned earlier, developmental randomness is a large part of what we measure in twin studies in the category of non-shared environment. This self-assembly is guided by the genome, but it is not precisely specified at the finest levels of anatomy and function.
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 genome doesn't say, "Hey you, glutamate-using neuron #12,345,763! Grow your axon in the dorsal direction for 123 microns and then make a sharp left turn to cross to the other side of the brain." Rather, the instruction is more like, "Hey, you bunch of glutamate-using neurons over there! Grow your axons in the dorsal direction for a bit and then about 50 percent of you make a sharp left to cross the midline to reach the other side of the brain. The rest of you, turn your axons to the right."
The key point is that the genetic instructions for development are not precise. In one growing identical twin, 40 percent of the axons in this area will make the left turn; in an another, 60 percent will. The example here is from the brain, but the principle applies to all the organs.
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." It's not nearly as fun to say but, unlike the former expression, it's true.
Then there's the question of how our memories are altered to some extent every time we recall them. Meaning, memories aren't like photographic images. They're more like Photoshop, which allows images to be edited, changed, altered. I've always thought this was a defect of human memory, but Linden says otherwise.
Another answer to the question of what memory is for is that the particular features of autobiographical memory are actually features rather than bugs. For memory to be useful, it must be updated and integrated with subsequent experience, even if it alters the memory of the original event.
In that way, it's helpful for recollection to render the memory of an event malleable, so that it may be integrated with the present.
In most situations, a generic memory compiled from many trips to the beach is more useful in guiding future decisions and behavior that fifty stand-alone, detailed, and accurate beach trip memories. The repetition-driven loss of detail allows for the efficient use of the brain's limited memory resources.
In other words, it's not surprising that our memories for events are often inaccurate, because the particular way in which memories are compromised is often useful. What's surprising is that we mostly fail to recognize this in our daily lives.
We humans all have an inborn tendency to create a plausible story out of memory fragments. Because of this ongoing narrative construction, we are often confident about the veracity of blurred memories and allow them to form the basis of our core beliefs about ourselves.
Free will fascinates me, for reasons outside of my control. Here's part of what Linden says about 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."
A habit is not just a behavioral routine that is formed and then performed at a subconscious level, it must become divorced from an ultimate goal. Your goal might be to stop off at the Thai restaurant for takeout after work, but instead you habitually drive straight home.
...As Haith writes, "Atop this massive conglomeration of habits sits a thin sliver of cognitive deliberation that steers only the highest-level decisions that we need to make." Without habits, our brain would be instantly overwhelmed with a multitude of tiny decisions better left to rapid, automatic processes.
The extent to which traits are inherited/genetic is a topic of great interest, since this gets at the extent to which we can control those traits (assuming we have free will).
Overall, adults in the United States are pretty good at estimating the heritable components of traits. In one recent online survey, most people guessed more or less correctly that, for example, political beliefs have a very small heritable component, height is strongly heritable, and musical talent falls in the middle.
There are a few traits for which people's estimates tend to be inaccurate. For example, most people think that variation in sexual orientation is about 60 percent heritable, whereas it's really only about 30 percent (about 40 percent in men and 20 percent in women).
On the other side, most people think that variation in BMI [Body Mass Index] is about 40 percent heritable, when it's really about 65 percent. It's interesting to imagine the ways in which cultural ideas inform these mismatches.
In the case of BMI, I imagine that many people want to believe that food consumption is more a matter of personal willpower than it really is. This is a frequent, if mysterious, theme.
In most cases -- from the accuracy of memory to the heritability of personality traits -- people imagine that they (and others) have a greater degree of autonomy and personal agency than they really do.