big buckles and dangling keys, and
always carried a knife.
That sounds like a lot of coincidence.
But maybe something about these
identical twins made them gravitate
toward similar experiences and types of
people in their environment. That’s why
I think that identical twins, even when
raised separately, have more similar
environments than other people —
because environments are partly of our
For example, who goes into
firefighting? Maybe vigilant people, with
an altruistic bent — you want to help
people. You’re also inclined toward risk-taking, and fires are dangerous. And
then maybe being a firefighter makes
you a little more vigilant, so you want
to always carry a knife. I’m not saying
this is right in all respects, but the story
makes you entertain ideas you wouldn’t
have thought of otherwise.
So the twins’ similar personalities
could lead to these seeming
coincidences? So for example,
if they’re both risk-takers and
vigilant, there’s a limited set of
careers that would appeal to you.
Fighter pilot, maybe …
Right, or hazmat team or EMT. All those
jobs have similar requirements. But these
twins happened to be firefighters.
What’s the significance of studies
like this for the vast majority of
us who don’t have an identical
Twin studies have two levels to them.
One is all about the twins themselves: all
the unique aspects of twinship, being a
twin, or parenting a twin.
But twin studies also have so
much to reveal about the genetic and
environmental aspects of behavior and
disease. That’s where these studies are
for everybody. For example, if you find
identical twin pairs in which one twin
has a disease and the other doesn’t —
they both have the predisposition for it,
but only one has it. So what triggered it?
If you can identify those environmental
triggers, then you can use that to
understand susceptibility in a non-twin
Right now you’re working on a
study of Chinese twins who have
been adopted by Western couples
and are being raised apart. How
does this work expand on the
Minnesota study, and what do
you hope to learn from it?
The Chinese twins study is tracking
them as they age, whereas the previous
reared-apart twins were found as adults.
We’re only at the beginning of the
study, but I’m hoping to be able to see
whether there are certain environmental
events that might trigger differences
between the two children. With respect
to their rearing, are they following
I’ve only published one study so far. It
looked at the mothers’ reports of the first
time the children met each other. The
mothers were impressed by the closeness
the children developed, so quickly. It was
What else are you working on?
I’m studying “virtual twins,” which are
same-age children raised together who
are not biologically related. It started
during my last years in Minnesota, when
a mother called me and said, ‘You would
love my children.’ And I said, “Tell me
why.” What happened was that she had
trouble conceiving, so she put in for
adoption. But then she got pregnant, and
the babies ended up being delivered just
a couple of days apart.
So these children are not biologically
related, but are being raised together in a
very twin-like situation.
I also have an online study of
identical twin adults and their
relationships with their nieces and
nephews. They are as genetically related
to them as to their own children because
they’re genetically the same as their
mother or father. And I compare their
relationships to fraternal twins, who
have the ordinary aunt-uncle/niece-nephew relationship. I have found that
the identical twins do have a closer
relationship with the children of their
I’m also studying unrelated
look-alikes — people who are
“doppelgangers.” They are not related
but, in some cases, look as similar
as identical twins. I find them just
fascinating. This research helps refute
the contention by critics of twin
studies that identical twins are more
alike simply because people treat them
the same because they look alike. My
reasoning is that if that’s the case, then
these unrelated look-alikes should be as
similar as identical twins raised apart.
And they’re not. And when they get
together they don’t form a close social
relationship because their interests are so
different. They have nothing in common
other than looks.
There are now more twins than
there used to be. Have you seen a
corresponding increase in interest
in your work?
Yes, there are more fraternal twins.
Two-thirds of the increase is due to
fertility treatments, and the other