Is Your Brain Perfectly Designed?
Your brain is perfectly
A product of evolution, the
brain is shaped by natural
selection and includes
many inefficient hacks.
THE COMPLEXITY OF THE BRAIN
The most basic myth about the brain is the deep-seated intuition
that the brain is a masterpiece of neural design. The brain is
highly complex, but it is simply the end result of millions of
years of evolution. Every complexity in our brains arose from a
very long history of tiny tweaks—which are still in progress. And
some of these tweaks are more akin to inefficient hacks than to
When it comes to the adaptive but imperfect design of our brains,
the material nature had to work with were cells. In the brain, these
cells are called neurons. Our neurons point to the less-than-
perfect process out of which the human brain emerged.
here are a few different types of neurons that seem to play roles
in functions such as fine motor coordination, social interactions,
and self-awareness, but they are also present in other animals,
and they might have arisen through successive tweaking of the
basic neuron. Natural selection ended up with a hacked set of
new cells, not a carefully designed foundation on which to build a
To understand how this might happen on a slightly larger scale,
consider how self-awareness and identity develop in children.
They’re not born with the same self-consciousness that ultimately
plagues their teenage years. And the process takes time and
experience with the environment, not just some biological process
in a vacuum.
In addition to being shaped by evolutionary tweaks and personal
life experiences, another factor that makes our brains far from
perfect is noise, or randomness—for example, the random firing
of action potentials.
The Blind Watchmaker
Faisal, Selen, and Wolpert, “Noise in the Nervous System.”
QUESTIONS TO CONSIDER
What makes us so prone to latch on to brain myths?
What dangers are there in harboring such misinformation?
What are the unique challenges of thinking about thinking, as opposed
to thinking about anything else?
Are Bigger Brains Smarter?
The bigger the brain, the better.
Intelligence and brain size,
even in humans, are only
moderately correlated. When
you look across species, the
correlation is even smaller.
BRAIN SIZE AND INTELLIGENCE
Compared with many other species, humans are born with fairly
small brains, leaving infants pretty much defenseless and unable
to survive without a lot of care and attention at least for the first
year. Wouldn’t it make more sense, from the perspective of our
chances of surviving long enough to reproduce, if we were born
with more developed brains, making us at least capable of feeding
ourselves, if not avoiding being eaten?
Consider the notion that there exists some kind of measurable
general intelligence. Figuring out what it is and whether and how
it can be developed or enhanced is a billion-dollar question that
psychologists have been trying to answer for decades.
Brain Myths Exploded:
Lessons from Neuroscience
school and how far they will get in their careers. And it correlates
with total brain volume, though only moderately so.
That means that a significant portion of the variability in this
general intelligence factor has nothing to do with the size of your
brain. Height is also associated with
, so taller people might be
smarter, on average, given their bigger brains.
factor was suggested and fairly widely accepted, it
was further divided into 2 types: fluid intelligence and crystallized
intelligence. You can think of them as the difference between quick
thinking and wisdom. Fluid intelligence peaks in your 20s, while
crystallized intelligence remains steady, or steadily increases,
throughout adulthood, depending on how you use your brain.
But despite the evidence for the existence of a
fluid or crystallized, not all psychologists are happy with the notion
that there is one major underlying ability. Perhaps the most famous
is Howard Gardner’s multiple intelligences theory,
which considers the soft skills, such as social graces, that might
not be captured on traditional IQ tests.
In his theory, Gardner suggests that there is no single factor,
but that intelligence comes in many kinds, including musical
intelligence, visuospatial, verbal-linguistic, logical-mathematical,
bodily-kinesthetic, and so on.
Gardner’s theory caught on quickly, but despite the intuitive
attractiveness of the idea, the evidence supporting his theory is
slim to nonexistent.
Luckily for science, Albert Einstein’s brain was saved for
postmortem analysis. At least in 4 different sections of his brain,
and at least compared with a certain cohort of war veterans, the
ratio of neurons (generally thought to be the content of the brain)
Lecture 2 • ARE BIGGER BRAINS SMARTER?
to glial cells (which provide the neurons with the basic necessities
of life and ensure that they can concentrate on firing off, or not,
a signal) was found to be lower in Einstein’s brain than in his
COMPOSITION OF BRAIN REGIONS
If overall size is not the answer, perhaps it’s the composition of
specific brain regions—those that are important for the types of
thinking that IQ tests measure. And there are plenty of studies
that have found correlations between different aspects of
neuroanatomy and IQ test performance.
OUR SPECIAL BRAINS
Brazilian neuroscientist Suzana Herculano-Houzel devised a way
of counting the cells in the brain that has called into question the
very idea that our brains are special. In fact, she argues that the
endurance of the encephalization quotient might have more to do
with confirmation bias than with any real evidence because it’s the
one measure of intelligence that makes our species an outlier.
Chudler, “Brain Facts and Figures.”
Herculano-Houzel, “The Human Brain in Numbers.”
Hines, “Neuromythology of Einstein’s Brain.”
Plomin and Spinath, “Intelligence.”
Toga, Wright, and Thompson, “Genetics of White Matter Development.”
QUESTIONS TO CONSIDER
What advantages might a bigger brain afford?
If it’s not size that differentiates us in terms of intelligence or other
factors, what might the physical signature of genius be? Or is there one?
Is Mental Illness Just a Chemical Imbalance?
When the chemicals
in your brain are out of
balance, your brain can’t
chemicals in the brain, are
only one part of healthy
brain function, and their
levels are in constant flux.
CHEMICALS IN THE BRAIN
There is one major difference between the way that chemicals enter
the brain and how they roam around the rest of the body. Your body
has a built-in protection system: When foreigners invade, your body
unleashes an immune response to fight them off.
The term “schizophrenia” is often misinterpreted to mean split
personality. When someone does something out of character, his
or her behavior is sometimes described as schizophrenic. Not only
is this use of the word offensive to individuals who suffer from the
disease, but it’s also simply incorrect.
The chemical imbalance myth is also tossed around liberally with
depression. The chemical imbalance theory of depression has its
roots in the serendipitous discovery of tricyclic antidepressants
such as imipramine.
Ban, “The Role of Serendipity in Drug Discovery.”
Barton, Esler, Dawood, and Lambert, et al, “Elevated Brain Serotonin
Turnover in Patients with Depression.”
DeWall, Gillath, Pressman, and Black, “When the Love Hormone Leads
Lacasse and Leo, “Serotonin and Depression.”
QUESTIONS TO CONSIDER
How do brain chemicals, neurotransmitters, and hormones enhance
the ways that neurons can communicate with one another?
How can one neurotransmitter, such as dopamine, have such different
functions, from enabling working memory to giving us the experience
Are Creative People Right-Brained?
Logical people are
left-brained and creatives
The hemispheres are highly
interconnected and work
together in sync much of
the time. Although there
is some lateralization of
function, many functions are
bilateral, and the left brain is
necessary for creativity
RIGHT VERSUS LEFT
An idea that has been overused and misinterpreted by many
people is the notion that the left side of your brain is logical and
analytical while your right side is creative—and instead of working
together, these 2 hemispheres are in competition with one
another. And if you can tap into your right brain, releasing it from
dominance by the left, you can be more creative, or that you need
to shut down your overbearing left hemisphere to do something
original and artistic.
STUDYING PATIENTS WITH SEIZURES
To understand what underlies the left/right brain myth, why it’s
wrong, and how much more interesting the truth is, we need to
Brain Myths Exploded:
Lessons from Neuroscience
go back to a time before neuroimaging—with the psychologists
who were among the first to suggest that the 2 hemispheres of the
brain might play different roles.
Around the same time, a neuropsychologist named Roger Sperry,
together with his student Michael Gazzaniga, began testing
these so-called split-brain patients to find out what aspects of the
human mind are processed in each hemisphere of the brain. This
pioneering work seeded the left/logical, right/creative brain myth.
Patients who have had half
of their brains surgically
removed demonstrate just
how malleable lateralization
can be. Removing half a brain
is called a hemispherectomy,
and it’s a last-resort treatment for patients with a damaged hemisphere that is threatening or
harming the rest of the brain.
Turk, Heatherton, Macrae, Kelley, and Gazzaniga, “Out of Contact, out of Mind.”
Wolman, “The Split Brain.”
QUESTIONS TO CONSIDER
Why would it be helpful to have some functions localized in one
hemisphere or the other?
In a healthy person, whose corpus callosum (the fiber tract that joins
the 2 hemispheres) is intact, is there more communication between the
hemispheres than within them? What does that mean in terms of how
we understand lateralization?
How is it possible that a person can be born with only one hemisphere
and not know it?
How Different Are Male and Female Brains?
Men’s and women’s brains
are structurally different.
The similarities between the
brains of men and women
far outweigh the differences,
and the differences are
difficult to tease apart from
MEN VERSUS WOMEN
It is a popular myth that men are smarter than women simply
because, on average, men have bigger brains. The relationship
between brain size and intelligence is complicated, and bigger
doesn’t mean much when you compare individuals, because
brains can be more or less densely packed, with faster or slower
connections. In addition, many women have brains that are larger
than those of most men.
In biology, morphological differences between males and females
of the same species are known as sexual dimorphisms. The
difference between the peacock’s and the peahen’s tail is an
There are several key differences in the brains of heterosexual
men and women that are worth highlighting.
Three regions in the brain that, on average, have been shown to
be different in men and women, after correcting for body size, are
the amygdala, an almond-shaped structure that plays a key role in
the emotional modulation of memory; the hippocampus, whose job
is to lay down new long-term memories and to navigate through
space; and the corpus callosum, the fiber tract that joins the left
and right hemispheres. But the story isn’t quite as simple as we’d
like it to be.
There is a need for more research on sex differences in the
brain, because these differences, when they are real, have direct
implications for our health. There is a difference in prevalence,
for example, for many psychiatric and neurological disorders
between the sexes. And to properly treat men and women with
these disorders, we need to understand the differences in
Coffey, “Sex Differences in Human Brain Aging.”
Joel, Berman, Tavor, Wexler, and Gaber, et al, “Sex beyond the Genitalia.”
McCarthy, Arnold, Ball, Blaustein, and De Vries, “Sex Differences in the Brain.”
Murphy, et al, “Sex Differences in Human Brain Morphometry and Metabolism.”
Ruigrok, Salimi-Khorshidi, Lai, and Baron-Cohen, et al, “A Meta-Analysis of
Sex Differences in Human Brain Structure.”
Lecture 5 • hOw DIFFERENT
AND FEMALE BRAINS?
QUESTIONS TO CONSIDER
Is there such a thing as a male and a female brain?
Could you tell just by looking at it?
How much of the brain differences we see in men and women are a
result of culture, rather than biology? Can we ever tease those 2 apart?
How Accurate Is Your Memory?
Your memory is an accurate
reflection of what happened
in the past.
Memory is reconstructive.
Each time we remember an
event, we have to build up
the memory from scratch,
and every instance of
remembering changes the
way that the memory will be
retrieved in the future.
HOW MEMORY WORKS
You experience the world through your senses—your eyes, ears,
nose, and so on. So, you’re already limited in terms of what you
can remember by what you actually perceive and, importantly,
what you paid attention to in the moment.
Moreover, of all your senses, only your sense of smell has a direct
route to your medial temporal lobe, the part of your brain that lays
down new long-term memories. That’s why smells are particularly
effective in helping you remember the past.
All the other senses make their way there but pass through at
least one other region along the way, where the information is
sorted, integrated with other senses, or manipulated in some
THE 7 SINS OF MEMORY
Amnesia isn’t the only way that memory fails us. Psychologist
Daniel Schacter has devised a great rubric for how our memory
flaws can be classified: the 7 sins of memory. There are 3 sins
of forgetting or omission (transience, absentmindedness, and
blocking); 3 sins of distortion or commission (misattribution,
suggestibility, and bias); and the sin of persistence.
. Some memories simply become inaccessible with
the passage of time. They are transient. And for most people,
this is a good thing. There’s no need to clutter your mind
with details of everything you’ve ever done or experienced.
We’ve adapted the ability to pull out the important things—
to remember the gist of what happened rather than every
minute detail. From the gist, we can then reconstruct the
full narrative if we so desire, but this reconstructive process
doesn’t necessarily lead to a fully accurate recollection of
what actually happened.
. This sin underscores the role of
attention in memory. If you fail to properly encode information
when it’s presented to you, it doesn’t stand a chance.
Absentmindedness is likely the culprit behind much of
everyday forgetfulness. It is evidence of the fact that we’re
limited in terms of how many things we can pay attention to
at once. And if you’re not paying attention, it’s harder for the
hippocampus to take note of the details.
. Sometimes the information you’re trying to retrieve
is temporarily inaccessible. One example of blocking is the tip-
of-the-tongue phenomenon, which feels as though you know
the answer, but it’s just out of reach of your consciousness.
Removing the stress of trying to remember often gets rid
of the block. Word-finding difficulties can be symptoms of
neurodegenerative diseases, such as Alzheimer’s disease.
. This sin happens when we attribute a memory
to the wrong time, place, or person. Source confusions, when
we misattribute the source of a piece of information, are
particularly problematic in eyewitness testimony. Older adults
are more prone to source confusions, and it looks like the
frontal lobes are responsible for these errors.
. Source confusions are common, but the
effects of suggestibility on memory are particularly dramatic
in the work of psychologist Elizabeth Loftus. Suggestibility is
the tendency to take information provided in the context of
remembering and to add that information to your memory of an
event. Indeed, Loftus has shown that people can be induced
to falsely recall detailed memories of events that never
simply by a specific type of leading questioning and
some help from a confederate.
. This sin refers to the fact that our memory of the past is
skewed by our current thoughts, feelings, and beliefs. People
tend to exaggerate the overlap between their past and current
. Unlike the previous sins, which represent
failures in the ability to remember, this sin describes what
happens when we fail to forget. Memory can be intrusive—and
pathologically so for victims of trauma and abuse. Generally,
persistent remembering is related to emotional memories, in
which the amygdala plays an important role.
Schacter, “The Seven Sins of Memory.”
QUESTIONS TO CONSIDER
If memory is reconstructive and prone to inaccuracies, what is the
purpose of it?
How should we interview potential eyewitnesses to get the most
accurate picture of what actually happened?