The Surprising Gene Shared By Criminals - Kathryn Paige Harden

Is there a difference in heritability

of antisocial behavior that's sexed? Do

men

>> Yeah.

>> inherit more

uh accurately more is is is the

heritability greater effect on boys than

it is on girls?

>> Generally, no. But there's one exception

that I want to come back to. So what we

see is that the genes that are

associated with antisocial behavior in

boys also affect girls. If you have a

fraternal twin, if you're female and you

have a fraternal twin that's a male

sibling, then his antisocial behavior

predicts your likelihood of manifesting

it. Um that the same liabilities are

uh reflected in the same way. So the

same genetic liabilities make you more

likely to be physically aggressive. They

make you more likely to be relationally

aggressive. They make you more likely to

be substance using. They make you more

likely to be risk-taking.

>> It's just for everything the mean for

men, the average for men is shifted up.

>> Mhm.

>> So

>> Oh, so the same impact would have a

sorry the the same raw materials would

have a greater impact in real life.

Yeah. Yeah. Yeah. Yeah. Yeah. The same

way as women commit suicide. Sorry.

Women attempt suicide more than men, but

men commit suicide more than women. It's

their ability to enact

>> violence, antisocial stuff tends to be

greater. So, it's magnified. Right.

Interesting.

>> And so, you know, part of that is around

social opportunity. Like for many years,

you know, women were very discouraged

from drinking, very different were

discouraged from smoking. So, you saw a

big sex difference in smoking and

drinking. Now, it's more socially

acceptable for women to smoke and drink.

And so that average difference has

narrowed and it's the same genes that

seem to be involved in both. The

exception there is that most of our

current studies have focused on what are

called the autotosomes. So we have 23

pairs of chromosomes. One pair is the

sex chromosomes XY or XX and typically

developing children and then the other

22 pair are the same across sexes. And

nearly all of our contemporary studies

have focused just on those 22 pairs of

autotosomes for kind of boring technical

reasons that I'm not going to get into.

We're just now really diving in to the X

chromosome to see is there something

about the X chromosome that might have

specific effects on antisocial behavior.

And the reason why that's interesting is

because men only have one X whereas

women have two. And so men are much more

vulnerable to the effects of a genetic

variant that's XL linked because they

don't have another copy to compensate.

>> Oh, that's so cool.

>> So that's why color blindness for

instance is much more prevalent in men

versus women because it's a sex link.

It's an X chromosome linked um genetic.

>> That is so sick. So the reason why we

think the X chromosome might be

important

um is

and again just to back up a second most

of what we study in our lab is what we

would call common genetic variation. So

these are genetic differences between

people that exist in at least 5%

sometimes people say at least 1% of the

population.

The thing about common genetic variants

is that um they're common which means

that they are likely to have a

relatively small effect in isolation

because if they had a big effect

evolution would make them not common

would weed them out very very quickly.

So you have this trade-off between how

common is a genetic variant and how big

of an effect how powerful it is. Um, so

what we're looking at is lots of common

genetic variants, each of which have a

tiny effect, but if you add them all up,

then you get an appreciable effect of

one one that's meaningful. But there are

studies of rare genetic variants. And

there's one very famous study that was

done in the 1990s where they looked at a

rare variant on um a gene on the X

chromosome and that gene was called

MAOA. So um your monoamines are how your

neurons are talking to each other. It's

like serotonin is a monoamine, dopamine

is a monoamine. So mono monoamine

oxidase is an enzyme that basically is

like a Pac-Man eating the

neurotransmitter in your brain. And if

it doesn't work well, then you get this

incredible buildup of the signals that

your brain ordinarily uses to

communicate with each other. Okay, so

why is that important? In this one

family where they found this genetic

variant on the X chromosome,

it made the MAOA

enzyme not work and all the men in that

family suffered from extremely serious

antisocial behavior problems. Whereas

their sisters were completely

>> wow

>> typically functioning. So the men, one

raped his sister, one committed arson,

one stabbed his boss with a pitchfork.

Huge levels of antisocial violence in

this family. And the their sisters and

their moms were like, "What the [ __ ] is

going on here?" Like, why why do my sons

and my brothers keep doing this and we

don't have this problem? And it's

because they have two exes. And so if

they inherited the mutation, it didn't

matter because there was another

functioning version of

>> to regress them back toward the mean

>> to to to kind of dosage like they could

compensate for it. Whereas if if you're

a man and you have 1x and you got this,

you know, 50-50 shot, which of your

mom's exes are you getting? It's a 50-50

shot whether or not you were going to be

antisocial.

>> So that's a rare variant.

You know, the vast majority of people

who are deeply antisocial do not have

this MAOA problem.

>> Don't use the MAOA excuse.

>> They can't use the MAOA excuse. But I I

think it's important for two reasons.

And one is that we think of our moral

faculties as our ability to not go

around stabbing our boss every time

we're mad at him in moral terms, in

spiritual terms or in cognitive terms.

And it turns out that it's very

vulnerable to disruption. You can change

one letter of your genome that changes

one gene which changes one enzyme and

that capacity is really

if not destroyed very very impaired. And

so the extent to which our morality is a

biological faculty I think is very much

supported by the fact that we can so

profoundly disrupt it by this one change

in our genome. And the other thing that

I find so interesting about this case

study is that um these men were in the

criminal legal system in the Netherlands

and no one was like, "Oh, this must be a

genetic problem. They weren't not guilty

by reason of insanity. They weren't, you

know, lacking capacity to stay on trial.

They were indistinguishable

from the rest of the offending

population based just on their behavior.

And the only reason we know that their

behavior was due to this genetic cause

is because of the familial data that

made the pattern of transmission so

clear.

And I think that really brings up the

question, how many other people who are

persistently violent in families that

are persistently violent? There might be

some

um genetic or neurobiological

explanation that we just haven't

discovered yet. Like we just don't know

that. In the 80s, they would have

considered it ridiculous. Like this

persistently violent family, it's you're

telling me it's because they have a

>> one gene that's wrong. like would have