Chapter One
Human Nature?
The Great DNA Crap Game
Does your DNA determine your destiny? It used to be that scientists believed our genes were responsible for a select number of our physical features, and that was about it. We began almost as blank slates and our behavior was determined largely by our environment, molded over the years through stimulus and response.
It was an overly simplistic view. A better understanding of human genetics eventually showed that we don't have nearly as much control over who we are and how we behave as we think we do, even though that sounds insane. A few years ago, a look at the newly mapped human genome showed that there were genes that could help determine whether a person grew up to be fat, an alcoholic, or a thrill-seeking hang glider. There is even a shyness gene.
Suddenly, it seemed that the truth of the matter was somewhere in the middle: many of our traits are both inherited and environmentally responsive. It's not nature versus nurture, but nurture complementing nature. Our genes set us on a path at birth and guide us, but ultimately our past experiences lead us to decide how far we go and where we stop along the way.
That being said, it is human nature to wonder to what extent our genes control the course of our lives, and how. Part of it is that we want to know what makes us tick and why we are who we are. Another factor is our desire to gain some inkling of our fate. If someone told you he could let you in on the time and the date of your death, as the old saying goes, wouldn't you want to know?
Does Cutting Your Hair Make It Grow Back Thicker?
For some reason, people of all ages consider this question of haircutting one of biblical import, more urgent than questions about diseases and more pressing than the fear-inducing old wives' tales that mothers have been spreading for centuries.
Part of the reason might be that cutting or trimming hair on various body parts is something we all have to deal with at some point—sometimes hair we wanted to be thick and sometimes, unfortunately, hair we really didn't want at all. And almost all of us grew up convinced that the claim was true. I have to confess that I was one of those kids who would occasionally steal his father's shaving cream and razor, slip into the bathroom, and shave away nonexistent facial hair, hoping it would turn into a thick Tom Selleck mustache. For my sisters and other women, on the other hand, the notion that hair grows back darker and thicker is a nuisance, a reason to spend money on waxes and trips to the salon.
But despite what millions of people think, trimming or waxing hair on any part of your body isn't going to speed its rate of growth, make it thicker, or change its texture. When this myth was born is not exactly clear, but it's been around in the scientific literature for well over half a century. The first studies to show that cutting hair isn't going to stimulate growth were performed in the 1920s, and many more have been carried out since then. All had the same results: the length, texture, and coarseness of your hair are determined by genetics and hormone levels, not by how often you shave, pluck, or Nair it away.
But according to dermatologists, there are several reasons why trimming your hair on a regular basis creates the illusion that it's growing back faster and thicker.
Many people—myself included—start shaving at an early age, while their hair is still lightly colored or not growing at the rate it's destined to reach. Since hair is darker and rougher at its roots, removing the tips gives the appearance of coarser hair. The bristly stubble that emerges after shaving is also more noticeable than the same amount of growth in hair that's already long. Plus, many people don't realize that the hair we see above the surface of the scalp is already dead, which means there's no way that cutting it can affect the living section that we don't see below the scalp. No matter how often you trim your hair, it will always grow back at a rate of about half an inch each month.
So, men and boys who shave their faces won't speed up the growth of their eagerly awaited lumberjack beard, and—fortunately for them—women who get peach fuzz removed from their faces won't sprout real mustaches.
Is Male-Pattern Baldness Inherited From Your Mother's Side of the Family Tree?
Before we answer this question, we should probably take a look at what seems like the much bigger issue here: Why do bald men get such a bad rap?
Ever since the Middle Ages, people have considered baldness a disease, like bad skin or leprosy. Hundreds of years ago, baldness was seen as a sign of mental illness; the thinking was that a frail mind couldn't support a full head of hair, much like dry soil can't support a plant. Then there were those who blamed a thin head of hair on sexual frustration, a belief that stems from observations of eunuchs, who have no desire for sex. People who have no testicles, it seems, never seem to go bald.
All these ugly connotations have driven men to go to extraordinary and sometimes ridiculous lengths to hold on to their hair, spending millions of dollars on pills, creams, and other dubious cures. Remember the "blood flow" craze of the 1980s, when thousands of men who feared going bald were driven to literally stand on their heads, all because of a bogus theory that thinning hair was caused by reduced blood flow to the scalp?
It was only five decades ago that researchers came up with a credible theory: that baldness has something to do with the X chromosome, which men inherit from their mothers. That prompted hordes of men who noticed their hair vanishing prematurely to lay the blame squarely on their mothers—or, more specifically, on their mother's father.
Most scientists, meanwhile, said that it couldn't be true. All this blame and resentment that maternal grandfathers have been getting from their balding grandsons was misplaced, they said, because baldness is caused by high levels of testosterone, hence the tendency for castrated men (and women in general) to avoid going bald.
We finally know that both sides were right. With sophisticated genetic testing, in 2005 scientists were able to pinpoint a gene variation that turns up frequently in bald men. It was identified in a study in the American Journal of Human Genetics that looked at balding men from ninety-five different families, each of which had at least two brothers with early hair loss. The culprit, a variant of the androgen receptor gene, sits on the X chromosome, which men get from their mothers (Y comes from the father). It turns out that this variant increases the effects of testosterone and other male hormones, called androgens, which have been linked to baldness for ages. Scientists say this gene variant may be the "cardinal prerequisite" for premature balding in a lot of men, but it's also possible that a number of genes and factors could be involved to a lesser extent, including genes that cause premature hair loss on a father's side.
All of which means at least two things. If you're a guy and your grandfather on your mother's side has little or no hair, start preparing yourself for the likelihood that you may go bald. Number two, if you're already bald and you're reading this while you're standing on your head, you can stand up now.
Do Babies Tend to Look More Like Their Fathers?
It's one of the first questions that cross a new parent's mind: Does the baby look like me? Any proud parent wants to see his or her own features in a child's face, but Dad really does have a stronger claim on the newest family nose. For new fathers, there may have been a time when seeing a familiar feature in that face was more a matter of necessity than vanity. A new mother can always be sure that a child belongs to her; that much we know. But long before the advent of paternity tests and The Maury Povich Show, a new father could never be certain that a child was actually his. If the basic goal of reproduction is to pass on genes, then why from an evolutionary standpoint would a male invest the time, energy, and resources needed to raise a child of dubious paternity when he could easily move on and father a new one?
Scientists have argued for years that evolutionary pressures would have made it beneficial for a child to resemble his or her father. In the event that a father believed that a child was not his, the likelihood of him abandoning it or even killing it outright would be terrifyingly great. Look no further than the fact that infanticide is widely prevalent among chimpanzees and others in the animal kingdom for some evidence. In addition, scientists who support this theory also point out that even among humans today, children are far more likely to be abused or killed by stepparents than natural parents.
But there is also reason to suspect that the reverse theory might be true: Couldn't it also be in a child's interest to conceal his or her identity? If a child unambiguously resembled his or her father, then a prospective father could be certain not only when a child was his, but also when a child was not. For the child, bearing a strong resemblance to one particular man could heighten the odds of being abandoned almost as much as being accepted.
Yet studies have tended to find the opposite. One from 1995 in the journal Nature, for example, put the question to the test by having 122 people try to match pictures of children they didn't know—at one year, ten years, and twenty years—with photos of their mothers and fathers. The group members correctly paired about half of the infants with their fathers, but their success rate was much lower matching the infants with their mothers. And matching the twenty-year-olds with either parent proved to be just as tough.
Another paper from 2003 echoed those findings, although this time the team that carried out the study took a more unusual approach. The researchers took head shots of a group of people and morphed them with photos of baby faces without the subjects' knowledge. When they presented the group with the digitally created faces, the men were more likely to indicate that they would adopt or spend time with the babies—male and female—who had been rendered with more of their facial characteristics. The women in the study meanwhile showed no preference at all for the children with their features.
As with most evolutionary theories, the case is not closed, perhaps because there are too many holes. Think back thousands of years ago, before there were mirrors, windows, and cameras. How would our predecessors have even known what they looked like?
So even if a baby did slightly resemble its father, how would he know?
No one can say for sure. But at least now we have daytime television to clear up cases of paternity uncertainty.
Don't Identical Twins Have Identical Fingerprints?
They share personality traits, interests, and habits. They come from the same fertilized egg and share the same genetic blueprint.
To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell identical twins apart: despite what most people think, they do not have matching fingerprints.
Like physical appearance and personality, fingerprints are shaped by a person's DNA and by a variety of environmental forces. Genetics help determine the general patterns on a fingertip—arches, loops, whorls. An individual finger can have just one of these patterns or a mix of them.
But there are plenty of other factors that play unique roles too. While a fetus is developing, the ridges along the patterns on the fingers are altered by bone growth, pressures within the womb, and contact with amniotic fluid. This, said Gary W. Jones, a former fingerprint specialist with the Federal Bureau of Investigation, is what causes the unique ridge characteristics in every person's fingers.
Identical twins will often have similar arrangements of patterns because of their identical genes. But they never have the same minute details. "It's impossible for people to have identical fingerprints," said Jones, who now works as a private consultant in Summerfield, Florida. "The study of fingerprints has been around for about a hundred years, and in all that time, two people have never been found to have the same prints."
The patterns on a person's fingers, palms, and feet are fully formed by roughly the fifth month of pregnancy. Barring any changes brought on by severe mutilation or a skin disease, the patterns stay the same for life. But even with severe traumatic damage, they change very little.
John Dillinger, the notorious Depression-era bank robber, famously tried to elude the authorities by altering his face and obliterating the skin on his fingertips with acid. It turned out to be his very last mistake. After the legendary gangster was killed, experts discerned a few of his remaining ridge patterns and had no trouble identifying him.
Copyright © 2007 by Anahad O'Connor. All rights reserved.
