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CONSCIOUSNESS REDUX

NEUROANATOMY Does Size Matter?

A recent discovery proves embarrassing to any notion of humanity’s innate superiority

While “size does not matter” is a uni- versally preached dictum among the politically correct, everyday experience tells us that this can’t be the whole sto- ry—under many conditions, it clearly does. Consider the size of Woody Allen’s second favorite organ, the brain. Adjectives such as “highbrow” and “lowbrow” have their origin in the belief, much expounded by 19th-century phre- nologists, of a close correspondence be- tween a high forehead—that is, a big brain—and . Is this true? Does a bigger brain make you necessari- ly smarter or wiser? And is there any sim- to fourth decade of life. An MRI study whereas writer Anatole France’s brain ple connection between the size of a ner- of 46 adults of mainly European descent could barely bring half of that weight on vous system, however measured, and the found that the average male had a brain the scale at 1,017 grams. (Note that post- mental powers of the owner of this ner- volume of 1,274 cubic centimeters (cm3) mortem measures are not directly com- vous system? While the answer to the for- and that the average female brain mea- parable to data obtained from living mer question is a conditional “yes, some- sured 1,131 cm3. Given that a quart of .) In other words, gross what,” the lack of any accepted answer milk equals 946 cm3, you could pour a varies considerably across healthy adults. to the second one reveals our ignorance bit more than that into a without What about smarts? We all know of how intelligent behavior comes about. any of it spilling out. Of course, there from our day-to-day interactions that is considerable variability in brain vol- some people just don’t get it and take a Bigger Is Slightly Better ume, ranging from 1,053 to 1,499 cm3 in long time to understand a new concept;

The brain continues to grow men and between 975 and 1,398 cm3 in others have great mental powers, al- )

until it reaches its peak size in the third women. As the density of brain matter is though it is impolite to dwell on such dif- Koch just a little bit above that of water plus ferences too much. Think of Bertie CABE (

some salts, the average male brain Wooster, an idle but clueless rich man, c BY CHRISTOF KOCH weighs about 1,325 grams, close to the and Jeeves, his genius valet, in a series of proverbial three pounds often cited in novels by P. G. Wodehouse and their ); SEAN); M Christof Koch is president U.S. texts. successful British adaptation to the and chief scientific officer of Removing brains after their owners small screen. the Allen Institute for Brain died revealed that Russian novelist Ivan Individuals differ in their ability to illustration Science in Seattle. He serves on Scientific American Turgenev’s brain broke the two-kilo- understand new ideas, to adapt to new

Mind’s board of advisers. gram barrier, coming in at 2,021 grams, environments, to learn from experience, ALAMY (

22 SCIENTIFIC AMERICAN MIND JANUARY/FEBRUARY 2016 Exploring the riddle of our existence

to think abstractly, to plan and to rea- In healthy volunteers, total brain volume is there a difference in the basic number son. Psychologists have sought to cap- weakly correlates with intelligence, with of switching elements? ture these differences in mental capaci- a correlation value between 0.3 and 0.4 It is also well established that the cra- ties via a number of closely related con- out of a possible 1.0. In other words, nial capacity of  neanderthalen- cepts such as general intelligence (g, or brain size accounts for between 9 and sis, the proverbial caveman, was 150 to general cognitive ability) and fluid and 16 percent of the overall variability in 200 cm3 bigger than that of modern crystalline intelligence. These differenc- general intelligence. Functional scans, . Yet despite their larger brain, es in people’s ability to figure things out used to look for brain areas linked to par- Neandertals became extinct between on the spot and to retain and apply in- ticular mental activities, reveal that the 35,000 and 40,000 years ago, when sights that they learned in the past to parietal, temporal and frontal regions of Homo sapiens shared their European current circumstances are assessed by the cortex, along with the thickness of environment. What’s the point of having psychometric intelligence tests. These these regions, correlate with intelligence big brains if your small-brained cousins observations are reliable, in that differ- but, again, only modestly so. Thus, on outcompete you? ent tests strongly correlate with one an- average, a bigger brain is associated with other. They are also stable across de- somewhat higher intelligence. Whether a Brain Size across Species cades. That is, measures such as the in- big brain causes high intelligence or, Our lack of understanding of the mul- telligence quotient (IQ) can be repeatedly more likely, whether both are caused by tiplicity of causes that contribute to intel- and reliably obtained from the same other factors remains unknown. ligence becomes even more apparent when subjects nearly 70 years later. Recent experiments take into account looking outside the genus Homo. Many Differences in general intelligence, the particular connections among neu- animals are capable of sophisticated be- assessed in this way, correlate with suc- rons in certain regions of an individual’s haviors, including sensory discrimina- cess in life, with social mobility and job brain, much like a neural fingerprint. tion, learning, decision making, planning performance, with health and with life They do better at predicting fluid intelli- and highly adaptive social behaviors. span. In a study of one million Swedish gence (the capacity to solve problems in Consider honeybees. They can recog- men, an increase in IQ by one standard novel situations, to find and match pat- nize faces, communicate the location and quality of food sources to their sisters via the waggle dance, and navigate complex RUSSIAN NOVELIST IVAN TURGENEV’S BRAIN mazes with the help of cues they store in short-term memory. And a scent blown BROKE THE TWO-KILOGRAM BARRIER. into a hive can trigger a return to the site WRITER ANATOLE FRANCE’S where the bees previously encountered this odor, a type of associative memory BRAIN WAS BARELY HALF THAT. that guides them back and that was made famous by Marcel Proust in his Remem- brance of Things Past (À la Recherche du deviation, a measure of variability, was terns, to reason independently of specif- Temps Perdu). The insect does all of this associated with an amazing 32 percent ic domains of knowledge), explaining with fewer than one million neurons that reduction in mortality. Smarter people about 25 percent of the variance in this weigh around one thousandth of a gram, do better in life. Whereas a high IQ may measure from one person to the next. less than one millionth the size of the hu- not predispose people to be happy or to Our ignorance when it comes to how man brain. Yet are we really a million understand the finer points of dating, the intelligence arises from the brain is ac- times smarter? Certainly not if I look at highly intelligent are more likely to be centuated by several further observa- how well we govern ourselves. found among hedge-fund managers than tions. As alluded to earlier, the adult The prevailing rule of thumb holds among supermarket checkout clerks. male’s brain is 150 grams heavier than that the bigger the animal, the bigger its What about any numerical relation the female’s organ. In the neocortex, the brain. After all, a bigger creature has between brain size and intelligence? Such part of the forebrain responsible for per- more skin that has to be innervated and correlations were difficult to establish in ception, memory, language and reason- more muscles to control and requires a the past when only pathologists had ac- ing, this disparity translates to 23 billion larger brain to service its body. Thus, it cess to and their content. With neurons for men versus 19 billion for makes sense to control for overall size structural MRI imaging of brain anato- women. As no difference exists in the av- when studying brain magnitude. By this my, such measurements are now routine. erage IQ between the two genders, why measure, humans have a relative brain-

MIND.SCIENTIFICAMERICAN.COM SCIENTIFIC AMERICAN MIND 23 CONSCIOUSNESS REDUX

Human Bottlenose Manatee

Chimpanzee Polar bear African lion Cat Mouse

From man to mouse: Frontal slices of eight mammalian brains reveal the immense variety in the size of the organ and the patterning of surface convolutions that have evolved over the course of tens of millions of years. The smoothness of the manatee’s brain surface contrasts with the cauliflowerlike branching in the . Structural differences extend down to the microscopic scale. Scientists are still laboring to understand what the varying means for animal intelligence.

to-body mass of about 2 percent. What group. Thus, if we consider all Yet it is not quite clear what all this about the big mammals—, dol- and compare them against the cat as a means in terms of the cellular constitu- phins and ? Their brains far out- reference animal (which therefore has an ents of brains. Neuroscientists always weigh those of puny humans, up to 10 ki- EQ of 1), people come out on top with an assumed that humans have more nerve

lograms for some whales. Given their EQ of 7.5. Stated differently, the human cells where it counts, in the neocortex, VOL. 5, ARTICLE NO. 29. body mass, ranging from 7,000 kg (for male African elephants) up to 180,000 kg (for the blue ), their brain-to- body ratio is under a tenth of a percent. A STUDY OF PILOT WHALES PLAYS HAVOC Our brains are far bigger relative to our WITH THE NOTION THAT HUMANS HAVE MORE size than those of these creatures. Smug- NERVE CELLS WHERE IT COUNTS THAN ness is not in store, though. We are out- classed by shrews, molelike mammals, ANY OTHER SPECIES ON THE PLANET.  NEUROANATOMY, IN FRONTIERS whose brain takes up about 10 percent of their entire body mass. Even some birds FELIPE,  IN beat us on this measure. Hmm. brain is 7.5 times bigger than the brain than any other species on the planet, no e One small consolation is an invention of a typical weighing as much matter the size of their brain. of neuroanatomists called the encepha- as we do. Apes and monkeys come in at A 2014 study of 10 long-finned pilot lization quotient (EQ). It is the ratio of or below five, as do and other whales from the Faeroe Islands plays the mass of the brain of the species un- cetaceans. We finally made it to the top, havoc with this hypothesis. Caught as der investigation relative to a standard validating our ineradicable belief in hu- part of a local hunt in the cold waters of

brain belonging to the same taxonomic manity’s exceptionalism. the North Atlantic, between Scotland SOURCE: “THE OF THE BRAIN, THE HUMAN NATURE OF CORTICAL CIRCUITS,CREATIVITY,” AND BY JAVIER INTELLECTUAL D PUBLISHED ONLINE MAY 16, 2011

24 SCIENTIFIC AMERICAN MIND JANUARY/FEBRUARY 2016 CONSCIOUSNESS REDUX

Who Has the Most Brain Cells? 40

Pilot whale 30

umber (billions) 5 centimeters

20 Human

Harbor porpoise Minke whale 10 Harp seal Rhesus monkey Neocortical Neuron N Neuron Neocortical

0 Domestic pig Bat 0 1,000 2,000 3,000 4,000

Brain Weight (grams)

Bested by a dolphin: The long-finned pilot whale appears to have more neurons in the neocortex—an area devoted to higher mental processes—than any other mammal, about twice the number found in the human cortex. This type of dolphin and its mas- sive brain are shown in the two images at the right. )

and Iceland, these graceful mammals— what gives? Is the complexity of the brain size or absolute number of neurons pilot whale pilot also known as blackfish—are actually nerve cells themselves substantially less that distinguishes us. Perhaps our wir- dolphins. The number of nerve cells than cells found in people, or is the way ing has become more streamlined, our making up their highly convolved neo- these neurons communicate or learn less metabolism more efficient, our synapses cortex was estimated in a few sample sophisticated? We don’t know. more sophisticated. slices and then extrapolated to the entire People forever ask for the single thing As Charles Darwin surmised, it is very structure. The total came to an astonish- that distinguishes humans from all oth- likely a combination of a great many dif-

); ÓLAVUR); FREDERIKSEN ( ing 37.2 billion neurons. Astonishing er animals, on the supposition that this ferent factors that jointly, over the gradual­

brain because this implies that the long-finned one magical property would explain our course of evolution, made us distinct from pilot whale has about twice as many evolutionary success—the reason we can other species. We are unique, but so is ev- neocortical neurons as humans do! build vast cities, put people on the moon, ery other species, each in its own way. M

VOL. 8, ARTICLE NO. 132. PUBLISHED ONLINE If what matters for cognitive perfor- write Anna Karenina and compose Ero- mance is the number of neocortical neu- ica. For a while it was assumed that the rons, these dolphins should be smarter secret ingredient in the MORE TO EXPLORE than all other extant creatures, includ- could be a particular type of neuron, ); HEIDI); S. MORTENSEN ( ■■The , the Human ing us. Whereas the highly playful and so-called spindle or von Economo neu- Nature of Cortical Circuits, and Intellectual chart social dolphins exhibit a variety of skills, rons, after Baron Constantin von Econo- Creativity. Javier DeFelipe in Frontiers in including the ability to recognize them- mo (1876–1931). Neuroanatomy, Vol. 5, Article No. 29. selves in a mirror, they do not possess But we now know that not only great Published online May 16, 2011. ■■ language or any readily discernible pow- apes but also whales, dolphins and ele- Quantitative Relationships in Delphinid Neo- cortex. Heidi S. Mortensen et al. in Frontiers ers of abstraction that stand out from phants have these neurons in their fron- in Neuroanatomy, Vol. 8, Article No. 132. NOVEMBER 26, 2014 ( SOURCE: “QUANTITATIVE RELATIONSHIPS IN DELPHINID NEOCORTEX,” BY HEIDI S. MORTENSENET AL., NEUROANATOMY, IN IN FRONTIERS those of other nonhuman animals. So tal cortex. So it’s not brain size, relative Published online November 26, 2014.

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