Multiplicity

articles
March 2 1997 3:30 AM

Multiplicity

Cloning, Nature, and Nurture.

(Continued from Page 1)

But what triggers the release of oxytocin in the rat brain when there's no researcher to inject the hormone? Warmth, touch, and friendly social interactions. So, does a hormone cause an action? Or does an action cause a hormone to be released? It seems to be a bit of both, especially in big-brained animals, like us, that have a lot of flexibility to their behavior. In primates, says Kim Wallen, a behaviorist at the Yerkes Regional Primate Center in Atlanta, hormones "act in concert with so many other factors. I think we might see these not as chemical signals that turn things on and off but as things that permit an organism to do certain things under certain circumstances."

Advertisement

The question of where characteristics come from also turns out to be too complicated to divide neatly into Nature or Nurture, according to Stephen Suomi, director of the Laboratory of Comparative Ethology at the National Institutes of Health. His research suggests that a rhesus monkey's sexual behavior, aggression, thinking, and responses to stress are affected by "prenatal stressing"--that the strains and pains to which the pregnant mother is subjected will have an immense impact on her infant long after it is born.

Not even DNA, that supposedly impregnable "digital" code, is viewed as platonically separate anymore. "DNA doesn't do anything," says James Shapiro, a cell biologist at the University of Chicago Medical School. A gene is an instruction for making a protein. Reading that instruction, following it, folding the protein into the shape it must have to do its job--all this is the job of the cell, and the cell is affected by its environment.

In twin studies, too, as Elizabeth Spitz, a researcher at the Université René Descartes in Paris, has noted, Nurture is nearly impossible to tease out. Identical twins, at the moment of birth, may have already had very different experiences during their nine months in the womb. This is because the number of membranes identical fetuses share depends on when exactly their single egg split into two embryos. If this divisional split occurred early (within four days after fertilization), then each twin grew to birth in its own little world. Each developed its own chorion, the outermost membrane, and its own amnion, the inner membrane that contains the amniotic fluid in which the fetus floats. If the cell division happened later (four to eight days after fertilization), each twin got its own amnion but shared a chorion. If the division happened later still (eight to 10 days after conception), the two fetuses shared both chorion and amnion.

How similar twins are depends in part on how many membranes they shared. That amazing story about how two separated twins both married red-headed engineers in the same year--the resemblance could be because they shared the same amnion, and not because of their genes. So it's a little premature to propose a genetic predisposition to divorce.

In fact, the standard laboratory procedure for sorting out one influence from another--controlling the genetics, the prenatal environment, and the rearing of the twins--turns out to be impossible. The point may seem abstruse now. But once all those millions of Dollies have been gamboling about for a few years, and it's plain that they don't all look and act alike, we'll have no choice but to get off Galton's seesaw.

David Berreby writes regularly about science and culture for Slate.

TODAY IN SLATE

Politics

Smash and Grab

Will competitive Senate contests in Kansas and South Dakota lead to more late-breaking races in future elections?

Stop Panicking. America Is Now in Very Good Shape to Respond to the Ebola Crisis.

The 2014 Kansas City Royals Show the Value of Building a Mediocre Baseball Team

The GOP Won’t Win Any Black Votes With Its New “Willie Horton” Ad

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?

Technocracy

Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

I Am 25. I Don’t Work at Facebook. My Doctors Want Me to Freeze My Eggs.

These Companies in Japan Are More Than 1,000 Years Old

  News & Politics
Politics
Oct. 20 2014 8:14 PM You Should Be Optimistic About Ebola Don’t panic. Here are all the signs that the U.S. is containing the disease.
  Business
Moneybox
Oct. 20 2014 7:23 PM Chipotle’s Magical Burrito Empire Keeps Growing, Might Be Slowing
  Life
Dear Prudence
Oct. 21 2014 9:18 AM Oh, Boy Prudie counsels a letter writer whose sister dresses her 4-year-old son in pink tutus.
  Double X
The XX Factor
Oct. 20 2014 6:17 PM I Am 25. I Don't Work at Facebook. My Doctors Want Me to Freeze My Eggs.
  Slate Plus
Tv Club
Oct. 20 2014 7:15 AM The Slate Doctor Who Podcast: Episode 9 A spoiler-filled discussion of "Flatline."
  Arts
Brow Beat
Oct. 21 2014 10:41 AM Taylor Swift Just Went to No. 1 on iTunes Canada With 8 Seconds of Static 
  Technology
Future Tense
Oct. 21 2014 10:43 AM Social Networking Didn’t Start at Harvard It really began at a girls’ reform school.
  Health & Science
Bad Astronomy
Oct. 21 2014 7:00 AM Watch the Moon Eat the Sun: The Partial Solar Eclipse on Thursday, Oct. 23
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.