FuturePundit: Humans Most Violent When Only 2 Years Old

April 25, 2004

Humans Most Violent When Only 2 Years Old

An excellent article by Erin Anderssen and Anne McIlroy in the Canadian Globe And Mail summarizes research on child development and human violence. They report that Richard Tremblay has found that 2 year old babies are more physically aggressive than teenagers or adults but fortunately too uncoordinated to do much damage to others.

Are human beings born pure, as Rousseau argued, and tainted by the world around them? Or do babies arrive bad, as St. Augustine wrote, and learn, for their own good, how to behave in society?
Richard Tremblay, an affable researcher at the University of Montreal who is considered one of the world leaders in aggression studies, sides with St. Augustine, whom he is fond of quoting.
Dr. Tremblay has thousands of research subjects, many studied over decades, to back him up: Aggressive behaviour, except in the rarest circumstances, is not acquired from life experience. It is a remnant of our evolutionary struggle to survive, a force we learn, with time and careful teaching, to master. And as if by some ideal plan, human beings are at their worst when they are at their weakest.

St. Augustine was obviously much closer to the truth.

What Dr. Tremblay and his colleagues around the world have now demonstrated is that the ability to feel rage exists the moment human beings take their first breaths. A four-month-old infant can show anger. And as they gain more control over their arms and legs, their mothers report increasing incidents of kicking and biting: They can also act in anger.

By the second year, aggressive behaviour peaks in temper tantrums, with slapping and pushing; according to Dr. Tremblay's work, a typical two-year-old, playing with others over the course of an hour, will commit one act of physical aggression for every four social interactions.

With teenagers, he says, researchers talk in terms of years or months or weeks between aggressive acts -- never hours -- though the incidents, obviously, are more severe. By their third birthdays, children have the motor skills to perform any of the acts of aggression an adult can. But at just that age, aggression begins to drop.

For almost everyone, it continues to drop for the rest of their lives. By Dr. Tremblay's calculation, only in about 5 per cent of men does the rate of aggression remain relatively stable into early adulthood. They are the most dangerous group to society.

The article tries to put what I consider to be an excessive environmental spin on the reason for the decline in physical aggression as children age. The fact that babies simultaneously become more physically coordinated and less violent at the same time strikes me as too much of a coincidence to be the result of teaching and discipline. Likely there is a genetically programmed stage of mental development that builds inhibiting neural circuits to control the physical outbursts.

The article vaguely refers to a study on the genetic and environmental factors that cause children to grow up to be antisocial. That is probably a reference to a New Zealand twins study which showed that a combination of a genetic variant for low level of expression of Mono-Amine Oxidase A (MAOA) and childhood abuse produces much higher rates of adolescent and adult criminal violence. However, contrary to Anderssen and McIlroy the study did not show that both the environmental and genetic factors studied had to be present to result in violence. It is just that those two factors made children far more prone to grow up to be violent. Some children who were not abused still grew up to be violent. Similarly, some children who expressed MAOA at a high level still grew up to be violent as well. There may be still more as yet unknown genetic variations, nutritional factors, toxins, social environmental factors, and other factors which contribute to higher probability of violent behavior.

The article also refers to Adrian Raine's work using positron emission tomography (PET) scans that showed differences in the glucose consumption rates in the brains of murderers.

For the Biological Psychiatry study, Dr. Raine directed scientists at USC and the University of California at Irvine as they used positron emission tomography (PET) to scan the brains of 41 murderers who had pleaded not guilty by reason of insanity. The scientists also scanned the brains of 41 control subjects matched for known mental disorders and for age and gender. Mental disorders among the subjects included schizophrenia, organic brain damage and a history of head injury.

PET scans measure the uptake of blood sugar (glucose) in various brain areas during the performance of simple, repetitive tasks. (Glucose is the basic fuel that powers most cell functions. The amount used is directly related to the amount of cell activity.)

On average, the murderers showed significantly lower rates of glucose uptake in three areas of the brain -- the prefrontal cortex, the corpus callosum and the posterior parietal cortex. Their rates were 4, 18 and 4 percentage points lower, respectively, than the rates measured in control subjects performing the same tasks.

When the researchers compared the brain's two hemispheres for glucose uptake rates, they found that murderers consistently showed weaker activity in the amygdala and the hippocampus of the brain's left -- or more rational -- hemisphere. These glucose uptake rates were each 4 percentage points lower than the rates measured in control subjects performing the same tasks.

But the murderers showed stronger activity in the thalamus, the amygdala, and the hippocampus of the right -- or more emotional -- hemisphere. These glucose uptake rates were 6, 6 and 3 percentage points higher, respectively, than the rates measured in control subjects performing the same tasks.

Raine has also shown that that psychopaths have distinct differences in the shapes of some parts of their brains and that violent criminals have less brain gray matter.

These discoveries add up to suggest that there are limits to how much violent tendencies can be reduced using environmental changes and different methods of teaching and disciplining children. It seems unlikely that methods of teaching and socialization can fully compensate for less grey matter in those who commit violent acts as adults or the larger corpus callosums and asymmetrical hypothalamuses found in psychopaths.

By Randall Parker at 2004 April 25 12:31 AM Brain Violence | TrackBack

Comments

Bob Badour said at April 25, 2004 08:14 AM:

It seems unlikely that methods of teaching and socialization can fully compensate for less grey matter in those who commit violent acts as adults or the larger corpus callosums and asymmetrical hypothalamuses found in psychopaths.

Unless, of course, teaching and socialization cause the differences in the first place. To determine or refute that, researchers would have to follow some cohort from birth and observe that differences existed prior to socialization or arose from other causes.

Deanne said at July 3, 2004 07:38 AM:

I have a brother who is mentally retarded. He is also diabetic. After eating
anything with high kilojoules he is prone to aggression, anger and shouting.
He comes back to normal after he has been coaxed to drink water, take a walk
and his metformin tablet. As alcoholics intake a high amount of kjs via
their alcohol Im wondering if the aggression they can show is tied to high
kilojoule intake as well not just the mood effects alcohol causes. Anyone
know of any information on this?

cheers,

Amanda said at August 4, 2005 11:13 AM:

HELP!!! My two year old is about to turn 3 next month and i have a 17 month old, (both boys) ever since my oldest was about 14 months he has been very mean to other babies cousin mainly. But now that my youngest son was born my oldest will be very mean mostlywhen we arent looking. He'll push on his head if hes laying down, push him down, throw things at him and laugh about it. I dont want something serious to happen to either one of them. I snk him but hes in the stage where he thinks hes the boss. Any advice????

Amanda said at August 4, 2005 11:13 AM:

Jamie said at January 9, 2006 10:59 AM:

help! my 4 year old strangles my cats along with trying to strangle me and his mother. what do i do and how should i act?

Jamie said at January 9, 2006 11:00 AM:

help! my 4 year old strangles my cats along with trying to strangle me and his mother. what do i do and how should i act?

Lena said at January 13, 2006 05:41 AM:

Could it be that brain grey matter decreases as violence increases? Maybe its not that less brain matter contributes to the tendency to be violent, but that acts of violence or even violent thoughts cause the reduction in brain grey matter. Are people born destined to be violent as determined by their genes? Or do we have choices? I say every act we do is by choice, some may have a harder time because of exposure to violence within their families and communities and so become somewhat desensitized, but that does not make one unaccountable for their actions. People know the difference between right and wrong. We have to be very cautious about determining cause and effect, as it may have an impact on judicial and social practices/policies.

Tina Grizzle said at January 20, 2006 02:31 PM:

I have a 3 year old, he wakes up all hours of the night digs in the trash and also stand in my roonm and just stares at me and my husband in bed and when i say something he runs. He is very violent to youunger sister and to older brother as well as me. What do I do?

Alicia said at January 24, 2006 07:45 PM:

I have a 2 1/2 year old son and a 3 month old son. I am very concerned about the way that my 2 year is with the baby, he is very aggressive, and always acts like he's going to punch or kick or squeeze the baby. And he is very sly when he thinks no one is paying attention. I am a stay at home mom, and my husband is only home on the weekends.It just doesn't seem to be doing any good trying to punish him by whipping him,doing things back to him that he's done to the baby, or taking his things away. I punish him and 5 minutes later he's trying to do the same thing again. I am also concerned with the developmental effects that it's having on the baby. He is 3 monthes old and has not even begun to turn over, because I'm affraid to lay him in the floor. I'm affraid that my 2 year old is going to hurt him really bad. Help me please I need some advice.

thanks, alicia mckesson

Alicia said at January 24, 2006 07:46 PM:

thanks, alicia mckesson

ALICIA said at January 24, 2006 08:04 PM:

MY 2 YEAR OLD IS VERY VIOLENT WITH MY 3 MONTH OLD. PUNISHING HIM IS NOT WORKING, AND I'M A STAY AT HOME MOM. MY HUSBAND IS ONLY HOME ON THE WEEKENDS, SO I NEED TO FIND A WAY TO GET MY 2 YEAR OLD TO LISTEN TO ME, BEFORE HE REALLY HURTS MY 3 MONTH OLD. I COULD REALLY USE SOME HELP.

THANKS, ALICIA

Dubya said at August 23, 2006 01:28 PM:

May I suggest an exorcist?

shannon said at September 19, 2006 03:51 AM:

Hi.. i can relate to all of you... my daughter who just turned 2 years old (she is also the size of a 4 year old) was caught trying to strangle a 1 year old little girl at the store. This little girl was half the size of her. I know she ment no harm because she was trying to hug her but she was sqeezing her neck so hard the girl was turning blue. I then yelled at her to let her go and she gave me an evil look and scratched the crap out of the little girl's face! I need help! nothing is working, my mom says it is because she is spoiled and use to it being all about her! What do you think? Im scared crapless cause i have another one on the way in 3 months! HELP PLEASE any suggestions please email me. maybe we can help each other! pookey069@yahoo.com Thanks

JPJeffries said at August 29, 2007 09:27 PM:

To the moms who are going crazy with violent 2 year olds, here is a useful link and summary of one of the action points.
Good luck (and remember that most of us live past 2 yrs old and most of us live despite having older siblings)... it will most likely get better no matter what you do...

http://moxie.blogs.com/askmoxie/2006/03/qa_aggressive_2.html
"One highly effective way to deal with this kind of violent outburst is to recognize that it's from the frustration and allow the kid to have those feelings. Instead of trying to get the kid not to hit, give the kid a a designated object to hit/bite/scratch/push/throw. That way the kid is still allowed to release the frustration, just not at people or animals. If you're consistent about using a designated object, eventually the kid will ask for that object when the frustration strikes."

dd said at January 17, 2008 09:13 AM:

hi, i have a 2 year old daughter she is very violent towards my older daughter and younger son,i cannot leave them in the same room together, i have tried everthing with her,but nothing works,she punches,kicks, throws things at them stranggles them , help!

Tina said at March 17, 2008 10:21 AM:

My son is mean to cats as well. But on top of that he is Borderline ADHD and he is developmentaly behind and we think it has something to do also with that Sensory (what everver it is called)he wakes up 2-5 times a night sometimes wanting MOMMY to lay with him until he goes back to sleep. When my husband is alone with him he sleeps through the night most of the time when I am gone on weekends working with my sister whom is an Accountant as an Assistant Bookkeeper. I have 5 children and NONE were like my 4 year old.

My son is almost 4, but not until October. He throws things at them, tries to hold them upside down and anything else to bother them, we have 3 cats. I heard it takes longer for cats to get use to children, but this is a long time and none like him. 2 of our cats which will NOT come out of the room all day. Only when he is not around. The cats chase him while hissing and growl at him. What can I do to prevent this behavior? ANY SUGGESTIONS? Or is there something else wrong that Doctors are not finding?

Any help would be appreciated. What can we do? We are almost on the verge of putting him up for adoption. THAT IS HOW BAD IT IS.