W1: Well, come on. Obviously, it can’t all be in the genes. I mean, we have free will.
W2: But then again, I don’t really see how it could be all environment
either. I mean, look at those twins you always hear about --- you
know --- they’re separated at birth and grow up in completely
different environments, but then they turn out to have a lot in
M: I’m glad you brought that up, Ellen. Twins can tell us a lot about
our genes. Think about it. Identical twins share 100% of their
genes. In the womb, the egg splits in two after it has been fertilized
by the father’s sperm. Because the split happens after conception,
the genes are the same. The twins come from the same egg and
the same sperm, so they have the exact same set of genes. That’s
why they look exactly the same.
Fraternal twins, on the other hand, have a different set of genes.
In this case, two eggs are released, before conception. Then, the
two eggs are fertilized by two different sperm. Fraternal twins
are no more alike, genetically, than any other pair of siblings.
Normally, they share about 50% of their genes. So, by comparing
the similarities and differences we see in identical twins with
those in fraternal twins, we can learn about the influence that
genes have on human behavior.
Think about intelligence. Some believe that people are born with
a predisposition for intelligence. Others think that environmental
factors influence how smart a child will grow up to be. So,
researchers conducted a study that compared the intelligence
of fraternal twins with that of identical twins. Now, all of these
twins were from wealthy families, so we can assume that they
had similar environmental advantages --- good schools, good
educational resources, etc. Now, they found that genetic
predispositions accounted for most differences in intelligence.
In other words, the studies found that with regards to intelligence,
identical twins were more alike than fraternal twins. That means
that genes do play a role.
W1: So, you’re saying that it is more common for identical twins to
have similar IQs than it is for fraternal twins to have similar IQs?
M: According to this study, yes.
W2: OK, but come on. Intelligence can’t all be in the genes. Think
about the implications. Surely there are studies that support the
M: Indeed there are. Researchers looked at the IQs of both fraternal
twins and identical twins who were raised in adequate conditions
with those of twins raised in poor conditions. What they found was
that when poverty is considered, environment is more important
W1: Wait a minute! How did they figure that?
M: Well, twins raised in adequate conditions have less intellectual
variation than those raised in poor conditions. Remember the first
study when the environment was controlled, or kept the same?
Identical twins were more alike than fraternal twins. All of these
twins had the same educational advantages. What the next study
found was that identical twins without educational advantages
were not as similar as those who had them. Understand?
W1: I think so.
M: So, as you can see, nature and nurture are not mutually exclusive.
Human behaviors are a result of an interaction between genetics
and the environment. Of course, nobody believes that human
behaviors are entirely genetic, but research such as twin studies
suggests that there is probably a role for the genes in shaping
the people we become.
Everyone knows that the giant squid is, well, giant. It’s extremely