Pumping Up Intelligence
Abrupt Climate Jumps and the Evolution of
Higher Intellectual Functions during the Ice Ages
William H. Calvin
University of Washington
Seattle WA 98195-1800 USA
The title is not a metaphor, though past tense
might be better as this chapter is about how each of the many hundred
abrupt coolings of the last several million years could have served as a
pump stroke, each elevating intelligence a small increment - even though
what natural selection was operating on was not intelligence per se.
While we often use the term 'intelligence' to encompass both a broad
range of abilities and the efficiency with which they're enacted, it
also implies flexibility and creativity, an "ability to slip the
bonds of instinct and generate novel solutions to problems" (Gould
and Gould 1994, p. 70). Those three pillars of animal intelligence -
association, imitation, and insight - are also impressive (Byrne 1994),
as are the occasional symbolic (Deacon 1997) and reasoning (Gould &
Gould, 1998) abilities. But Piaget (1929; 1952) said that intelligence
is what you use when you don't know what to do, when neither innateness
nor learning has prepared you for the particular situation.
Intelligence is improvisational. Still, most of the time, not much
improvisation is necessary; the individual has encountered somewhat
similar situations before, has a repertoire of actions, and simply
starts one - and gropes, using feedback's progress reports to guide to
the goal. No major planning is needed in most cases, and thus not much
in the way of intellectual wherewithal. This suggests a focus on those
few behaviors that require an elaborate multistage plan prepared during
"get set." An example would be the ballistic movements
(hammering, clubbing, throwing, kicking, spitting) where the speed of
feedback is so inadequate (they're often over-and-done by the time that
progress reports can start modifying the movement), where only
near-perfect plans will succeed.
What the mind is often seeking during "get set", I suspect,
is coherence - finding a conceptual combination of sensory
input, memories, and movement plans that fit together particularly well
- though, because of novelty, most will rate less than the "perfect
ten" of exact, unambiguous fits. Similar to this is Barlow's (1987)
suggestion that intelligence is all about making a guess that discovers
some new underlying order. "Guessing well" neatly covers a lot
of ground relevant to higher intellectual functions: finding the
solution of a problem or the logic of an argument, happening upon an
appropriate analogy, creating a pleasing harmony or witty reply, or
guessing what's likely to happen next.
Higher Intellectual Functions
Because they all involve pattern-finding and all emphasize human
abilities not widely shared with the other apes, I want to restrict
myself here to the higher intellectual functions. I will use
"intelligence" as a term denoting the speed-and-scale of
individual performance of them, not unlike the manner in which much of
the variance of the general factor g can be accounted for
(Jensen 1992) by the subtests that emphasize speed of performance and
the number of items that must be borne in mind simultaneously - as in
those multiple choice analogies: A is to B as C
is to [D, E, or F] which require six concepts to be
simultaneously managed. Closely related is our ability to remember phone
numbers long enough to dial them. Many people can retain a seven-digit
number for 5-10 seconds, but will resort to writing it down if faced
with an out-of-area number or an international one of even greater
length. When getting close to your limit, you try to collapse several
items into one chunk, so as to make more room (Simon, 1983).
Definitions of "higher intellectual function" vary; I tend
to use the phrase to refer to the structured mental abilities
syntax, the structuring schemes of phrases and clauses
used to disambiguate sentences longer than a few words, e.g., "I
think I saw him leave to go home" has nested embedding involving
four verbs. (Syntax is an evolutionary puzzle because there aren't
obvious intermediate forms in development or aphasia between short
structureless protolanguage sentences and recursive embedding.)
planning, those speculative structured arrangements,
e.g., "Maybe we can go to the country this weekend if I get my
work finished, but if I have to work Saturday, then maybe we can go to
a movie on Sunday instead." (Squirrels hoarding nuts isn't
planning but an innate behavior triggered by longer nights releasing
more melatonin from the pineal. Holding an intention for a few hours
isn't planning either, and I'd also exclude foraging behaviors that
could be explained more simply by choosing between familiar migration
routes. Perhaps we should reserve the term for something that requires
multiple stages of the move to be assembled in advance of action,
rather than organizing the later stages after getting the initial
moves in motion, which goal-plus-feedback can accomplish.)
chains of logic, our prized rationality. But the
emphasis here is on novel chains, not routine ones. The most mindless
of behaviors may be segued, the completion of one calling forth the
next: courtship behavior may be followed by intricate nest building,
then a segue into egg laying, then incubation, then the stereotyped
parental behaviors. (Kφhler's chimps, that piled up boxes to reach
the hanging banana, might qualify under the novel chaining
requirement, if simpler explanations can be eliminated.)
games with arbitrary rules, such as hopscotch. (Both Pan
species, chimpanzees and bonobos, have a version of "blind man's
bluff" - but it isn't structured.)
music of a structured sort, such as harmony and
counterpunctual themes. (Perhaps not rhythm per se but certainly
rhythms within rhythms.)
Obviously, if one relaxes the nested-or-chained structural
requirement, there are various primate behaviors that are possible
I am focusing here on structuring because humans exhibit such a large
increment in ability over our Pan cousins across these five
areas - and because I am interested in whether there is a "common
core" of neural machinery that is shared by all such structured
behaviors, one where improvements in any one of the five might improve
the other four "for free."
Evolutionary arguments often commit the reification fallacy (a
"gene for intelligence"). Indeed, we often assume that an
abstraction like language implies a real concrete entity such as a
"language module." (Separate, of course, from any planning
module! And so on, to the balkanization of the mind.) Yes, there is
localization of function - and we certainly tend to name a cortical area
according to the first of its functions we discover - but multiple
functions are commonplace (see chapter six of my Cerebral Code
for a discussion of how a neocortical area could alternate between being
a narrow specialist and performing as a general-purpose scratch board).
Language in the Multiple Use Context
Multiple uses of a structural entity are common, and a familiar
example is the "curb cut" where the steplike curb is locally
smoothed into a gentle ramp. What paid for curb cuts was, of course,
wheelchair requirements. But as soon as a curb cut is in place, 99
percent of the traffic is for secondary uses such as bicycles,
suitcases, baby carriages, grocery carts - none of which would have
"paid for it."
A secondary "free" use may, of course, later pay for
further improvements (just imagine the skateboarders holding a bake sale
to pay for widening!), suggesting that the evolutionary history of
higher intellectual function might first emphasize one structured use
and later others. If the notion of a "free lunch" offends,
note that it is commonly assumed that music is a spare-time use of the
language-related parts of the brain, that there was likely little
natural selection for four-part harmony via barbershop quartets.
Language is the most defining feature of human intelligence: without
the orderly arrangement of verbal ideas permitted by syntax, we might be
little more clever than Pan. For a glimpse of life without
syntax, consider the Sacks (1989) description of Joseph, an 11-year-old
deaf boy. Because he could not hear spoken language and had never been
exposed to fluent sign language, Joseph did not have the opportunity to
learn syntax during the critical years of early childhood:
"Joseph saw, distinguished, categorized, used; he
had no problems with perceptual categorization or generalization, but
he could not, it seemed, go much beyond this, hold abstract ideas in
mind, reflect, play, plan. He seemed completely literal -- unable to
juggle images or hypotheses or possibilities, unable to enter an
imaginative or figurative realm....He seemed, like an animal, or an
infant, to be stuck in the present, to be confined to literal and
immediate perception, though made aware of this by a consciousness
that no infant could have."
"Language cortex" isn't just the traditional Broca and
Wernicke areas but much of the lateral aspects of the temporal and
frontal lobes, plus the parietal lobe areas near the left sylvian
fissure (see, for example, Ojemann 1991). Language localizations have a
strong overlap with nonlanguage sequential functions such as sound
strings and hand-arm sequencing (most aphasics have some form of
hand-arm apraxia; see Kimura 1993).
And this overlap brings me to an important point: the use that
initially "paid" for the structuring abilities seen in the
higher intellectual functions need not be any one of them. The original
"wheelchair" analog could, for example, be the structured
planning needed for some nonintellectual function, such as the
ballistic hand-arm movements used for hammering, clubbing, and throwing.
Throwing is a particularly interesting possibility because targets
are located at many different distances and elevations, making each
hunting throw a novel situation, quite unlike the more stereotyped dart
throws and basketball free throws where long practice can "find the
right groove." There is also a premium on being right the first
time, as dinner is likely to flee if you miss.
Apes have elementary forms of the rapid arm movements that we're
experts with - hammering, clubbing, and throwing - and one can imagine
hunting and toolmaking scenarios that, in some settings (more in a
moment), were important additions to the basic hominid gathering and
scavenging strategies. The evolutionary rewards for individuals having
better-than-average projectile hunting skills could thus set the stage
for free secondary uses, such as planning on longer time scales, such as
logical trains of thought, and perhaps even music and syntax. Some of
these, once they had a chance to show their stuff, are exposed enough to
natural selection to "pay" for further improvements - and thus
improve throwing accuracy, pari passu (Calvin, 1983, 1993,
Finding the Right Level
Although it seems to have played little role so far in our modern
concepts of intelligence, the concept of levels of organization
is a common one in the sciences. Much of guessing well involves finding
the right level at which to address a problem, neither too literal nor
too abstract - or, sometimes, inventing a new level on the fly.
Levels are best defined by certain functional properties (Calvin
& Bickerton, 1999), not anatomy. As an example of four levels, fleece
is organized into yarn, which is woven into cloth,
which can be arranged into clothing. Each of these levels of
organization is transiently stable, with ratchet-like mechanisms that
prevent backsliding: fabrics are woven, to prevent their disorganization
into so much yarn; yarn is spun, to keep it from backsliding into
A proper level is also characterized by "causal decoupling"
from adjacent levels (Pagels, 1988); it's a "study unto
itself." For example, you can weave without understanding how to
spin yarn (or make clothing). Chemical bonds illustrate a proper level:
Mendeleyev discovered the patterns of the table of elements, and thereby
predicted the weights and binding properties of undiscovered elements,
without knowing anything about the underlying patterns of electron
shells (or the overlying patterns of stereochemistry).
Mental life can pyramid a number of levels, thereby creating
structure. Some of the major tasks of early childhood involve
discovering four levels of organization in the apparent chaos of the
Infants discover phonemes and create standard categories for
them; six-month-old Japanese infants can still tell the difference
between the English /L/ and /R/ sounds but after another six months of
regular exposure to the Japanese phoneme that lies in between them in
sound space, the baby will treat the occasional English sounds as mere
imperfect versions of the Japanese phoneme (Kuhl et al 1992) and so be
set up for later confusing the English words 'rice' and 'lice'.
With a set of basic speech sounds, babies start discovering
longer-duration patterns amid strings of phonemes, averaging nine new
words every day during the preschool years.
Between 18-36 months of age, they start to discover
still-longer patterns of words called phrases and clauses, rules such
as add -s for plural, add -ed for past tense.
After syntax, they go on to discover Aristotle's rule about
narratives having a beginning, middle, and end (and they then demand
bedtime stories with a proper ending).
Indeed, we find it very rewarding to discover half-hidden patterns
all through life: that's the basis for the popularity of crossword and
jigsaw puzzles. It's why science is so much fun.
Pyramiding four levels in a mere four years is impressive. But levels
can also be created on the fly, as we seek an analogy or make a novel
abstraction. To spend more time at the more abstract levels in this
house of cards, the prior ones have to be sufficiently shored up to
prevent backsliding over your concentration span.
From Stratified Stability to Darwinism
But there's no child inside the head to stack up those higher stories
of the house of cards, so what self-organizes a higher level? In the
simpler physical systems, noise (as in diffusion) can provide the raw
material for self-organizing structures (such as crystals). As Bronowski
(1973) observed: "The stable units that compose one level or
stratum are the raw material for random encounters which produce higher
configurations, some of which will chance to be stable..
there is an organizational principle in the universe that is even more
elementary than Darwin's, it is Bronowski's.
But, as Darwin first realized, competitions between stable
alternatives can improve the results, providing a quality bootstrap
under certain conditions. Not all of what is loosely called
"Darwinian" qualifies, however, as many pruning processes do
not have a result that copies and competes. As I have discussed
elsewhere (Calvin 1996, 1997), there appear to be six essential features
of a recursive Darwinian process:
It involves a pattern. Classically, this is a string
of DNA bases called a gene. But the pattern could be a melody or the
brain activity associated with a thought.
Copies are somehow made of this pattern, as when cells
divide or you whistle an overheard tune. Indeed, the unit pattern is
defined by what's semi-reliably copied, e.g., the gene's DNA sequence
is semi-reliably copied while whole chromosomes or organisms usually
Patterns occasionally change. Point mutations from
cosmic rays may be the best known alterations, but far more common are
copying errors and (as in meiosis) shuffling the deck.
Copying competitions occur for occupation of a limited
environmental space. For example, several variant patterns called
bluegrass and crabgrass compete for my back yard.
The relative success of the variants is influenced by a multifaceted
environment. For grass, it's the nutrients, water, sunshine, how
often it's cut, etc. We sometimes say that the environment
"selects" or that there is selective reproduction or
selective survival. Darwin called this biasing by the term 'natural
The next generation is based on which variants survive to
reproductive age and successfully find mates. The high mortality among
juveniles makes their environment much more important than that of
adults. This means that the surviving variants place their own
reproductive bets from a shifted base, rather than the original center
of variants at conception (this is what Darwin called an inheritance
principle). In this next generation, a spread around the
currently successful is again created. Many new variants will be worse
than the parental average but some may be even better
"fitted" to the environment's collection of features.
From all this, one gets that surprising darwinian drift toward
patterns that almost seem designed for their environment. In the
cardboard version of darwinian, particular parts such as "natural
selection" are often confused with the entire darwinian process,
but no one "essential" by itself will suffice. Without all six
essentials, the process will shortly grind to a halt.
For example, neural patterning in development (all of that culling of
cells and synapses) is an example of a sparse case: just a pattern
carved by a multifaceted environment. There is no replication
of the pattern, no variation, no population of the pattern to compete
with a variant's population, and there's nothing recursive about
achieving quality because there's no inheritance principle. It's very
useful but it's not a quality bootstrap.
Making Darwinism Fast Enough
Speed is of the essence in behavior, however, and one might
reasonably worry about whether a neocortical version of the darwinian
process can operate quickly enough to provide an answer within the
windows of opportunity afforded by either hunting or social repartee.
There are at least four "catalysts" which can greatly speed up
Systematic recombination (crossing over, sex)
generates many more variants than do copying errors and the far-rarer
point mutations. There's also nonsystematic recombination, such as
bacterial conjugation or the conflation of ideas.
Fluctuating environments (seasons, climate changes,
diseases) change the name of the game, shaping up more complex
patterns capable of doing well in several environments. For such
jack-of-all-trades selection to occur, the climate must change much
faster than efficiency adaptations can track it (more in a minute).
Parcellation (as when rising sea level converts the
hilltops of one large island into an archipelago of small islands)
typically speeds evolution. It raises the surface-to-volume ratio (or
perimeter-to-area ratio) and exposes a higher percentage of the
population to the marginal conditions on the margins.
Local extinctions (as when an island population becomes too
small to sustain itself) speed evolution because they create empty
niches. The pioneers that rediscover the niche get a series of
generations with no competition, enough resources even for the odder
variants that would never grow up to reproduce under any competition.
For a novel pattern, that could represent the chance to
"establish itself" before the next climate change, for which
it might prove better suited than the others.
There are also catalysts acting at several removes, as in Darwin's
example of how the introduction of cats to an English village could
improve the clover in the surrounding countryside: The (i) cats would
(ii) eat the mice that (iii) attack the bumble bee nests and, thereby,
(iv) allow more flowers to be cross pollinated. Although a Darwinian
process will run without these catalysts, using Darwinian creativity
often requires some optimization for speed.
Explaining how neocortical circuitry can implement the six essentials
and the four catalysts on a milliseconds-to-minutes time scale, thereby
facilitating intelligent "get set" groping, lies beyond the
scope of this article (see Calvin 1996, 1998b). However, these ten
facets of a rapid evolutionary process will be useful in considering how
we got our big brains so quickly (2.5 million years is quick). What sped
up the slow biological evolution of the rapid neural evolutionary
machinery underlying the higher intellectual functions?
Hominid Evolution and the Ice Ages
The earliest known changes in hominids, seen soon after the
australopithecines diverged from the other Pan cousins about
five million years ago, were rearrangements of hips and knees for
upright posture. Brain size (an admittedly inadequate indicator of
functional capacities) didn't change very much, remaining in the great
ape ballpark. But a number of interesting things all started to happen
between three and two million years ago.
The archaeologists have traced stone tools back that far: the
simplest types (the split pebbles which make such good cutting edges
for getting through animal hides) go back to about 2.5 million years,
with much more elaborate ones developing by 1.5 million years ago.
While various mammals use found objects to open shells and
the like, simple toolmaking (shatter a rock and select the sharp
edges) seems to have been on the rise by 2.5 million years ago.
The onset of the ice ages has been moved back to about the same
time by the paleoclimatologists. Since then, ice sheets have slowly
built up. They melt off somewhat more quickly (the rise in sea level
takes about 8,000 years) and remain at a minimum for another similar
period. The major meltoffs occurred about every 40,000 years - until
about 0.7 million years ago, when a 100,000-year cycle became more
prominent. It isn't clear what this has to do with African-based
hominid evolution, as the average temperatures there only drop about 5°C
during the colder periods, enough to create some glaciers on the
equatorial volcanos but hardly enough to create a wintertime for
animals living in the Rift Valley. All of the ice sheets that formed
at higher latitudes were surely unseen by our African ancestors.
And brain size finally starts to change back about 2.4 million
years ago as the australopithecine lineage split off a distinctive Homo
lineage with increased cranial capacity (and it kept increasing in
size; nothing of the kind is known for other animals). Many animal
lineages also split between 3 and 2 million years ago: chimp-bonobo,
gibbon-siamang, mastodon-elephant (accelerated speciation is best
studied, however, in the antelope and pig lineages).
What do these three things have to do with one another, or with
intelligence? Cause and effect? Or merely three independent trains set
in motion by the major rearrangement of ocean currents and climate that
followed the damming up of the "Old Panama Canal" about 3
million years ago, when North and South American finally joined up and
forced the equatorial currents that equilibrated the Atlantic and
Pacific Oceans into a long detour around the southern continents?
The Mark Twain Transition Time Principle
The writer Mark Twain once observed that "A round man cannot be
expected to fit into a square hole right away. He must have time to
modify his shape." Evolution can often track climate changes,
selecting for variants with more or less body insulation. Indeed, up
until a decade ago, we thought that the ice ages were "glacially
slow," that slow changes in the earth's orbit caused gradual
cooling, which caused more ice to gradually form, and sea level to
gradually lower. No animal lived long enough to realize that climate
changes were happening because the change during the lifetime of any one
generation was so minuscule.
What happens if the climate changes abruptly, so that adaptations
over the generations cannot track it? So that the habitat is largely
disrupted (no more customary plants or prey, a different setting for
reproduction, etc.), all within one generation's time on earth?
There is a general answer to this (Calvin, 1996b) and a much more
specific one. The general answer is that the circumstance provides a
selective pressure for versatility, one that counters the usual
lean-mean-machine tendencies that reduce unneeded anatomy and behavior
in the name of efficiency. Evolutionary theory suggests a tendency
towards the latter if the environment remains the same for long
enough. But when the habitat changes so drastically in so short a
time, only reserve capacity in behavior can solve the problems. Lean
mean machines don't survive the downsizings very well. The more
versatile may have what it takes.
The more specific answer, however, is grass.
Abrupt Climate Change
Inferring ancient climates can be done from layers of sediments that
accumulate in lake and ocean floors. From cores, one can study such
proxy climate indicators as pollen types and oxygen isotope ratios, and
how they change over time. But there's a problem: worms and
bottom-scavenging fish stir the bottom, mixing together hundreds (if not
thousands) of years of sediments. Like a moving average of a
stock-market index, a smoothed record of paleoclimate can miss some
dramatic fluctuations that made and lost fortunes.
When year-by-year high-resolution records became available from
Greenland ice cores, where tree-ring-like records can be seen, we became
aware that climate could - and frequently did - change quite rapidly. We
now know that this is not merely a peculiarity of Greenland, that these
were worldwide events in many cases. Unlike the high latitude ice
sheets, these abrupt climate shifts affect the tropics as well.
Atop those glacially slow rhythms, abrupt coolings and warmings have
often occurred. By 'abrupt' is meant decade transition times; 'often'
means every few thousand years; these flips may last for centuries (or
even 1500 years) before flipping back, just as abruptly. Obviously, this
is not the abrupt climate change which volcanos and Antarctic ice sheet
collapse can cause; it's bistable. Ocean circulation seems to have
several modes, and when it switches between modes, the abruptness of the
transition profoundly affects ecosystems. In the tropics, average annual
temperatures fall by 3-5°C. In Europe, it's more like 5-9°C and some
high latitude locations cool more than twice as much.
The magnitude of the temperature change isn't the big
problem. It's how fast it occurs, Mark Twain's problem. If
these coolings were to occur slowly, with temperature ramping down over
500 years, one might expect high altitude plants and animals to slowly
move down the hillsides into the valleys below. Each generation of
hominids could have continued to make a living in much the way their
parents taught them, though their diet mix would shift over the
centuries. But with major changes within a decade, other events
First comes drought (there is much less evaporation from tropical
oceans, which also reduces a major greenhouse gas, water vapor). Then,
similar to what we saw in the 1997-98 El Niρo, vast fires occur even in
tropical forests. After that comes a succession of plants leading, over
a few centuries, from grass to forests (of species better suited to the
new annual temperature).
For many terrestrial species, this is a trial - and, eventually, an
opportunity. Because of vanishing resources, the habitat becomes patchy.
There are refugia, where a more-or-less traditional way of life can be
maintained, but they don't support very many. These subpopulations
inbreed because the resources are too scarce to support a journey to
find another subpopulation. But they tend to mix during the downsizing
itself, as stray individuals locate remaining subpopulations. Some
subpopulations may form up entirely from strays.
Thus an abrupt cooling is likely to provide three (recombination,
climate stress, parcellation) of the catalysts that speed up
evolutionary processes. The fourth, re-expanding into empty niches, may
occur during an abrupt warming (which is accompanied by increased
rainfall), where pioneers discover new territories of untapped
resources, and have many offspring survive, even the odder ones.
The foregoing is likely true for many mammalian species, not just our
ancestors. The remaining great apes likely went through this cycle many
times. What was special about hominids?
Eating grass indirectly. In the first few years after the great
forest fires, it is a boom time for the remaining grazing animals, with
all that grass and all of those succulent shoots. But the waterholes
would be scarce, and so whole herds would bunch together to visit the
remaining waterholes. They would lose a few peripheral individuals to
the predators that lay in wait there.
What was so special about hominid predators lingering around the
waterholes? For one thing, upright posture. The grazing animals have
innate "search images" for four-legged predators; they keep
their distance. But bipeds can get much closer (as my colleague Arnold
Towe notes, if you drop down on all fours, grazing animals move away
promptly). Upright posture may, if efficient enough, allow hominids to
run animals to exhaustion. But clearly, at some stage, projectile
predation became a part of the picture (Calvin 1993). Even something so
simple as flinging a tree branch can be effective in the context of a
tightly-packed herd at a waterhole: the herd immediately starts to wheel
around and flee, but the branch lands somewhere in their midst and trips
an animal or two. Attempts to get back up are delayed by other animals
stampeding past, and injuries will often occur. In any event, the
hunters will often have time to run up to a downed animal before it can
escape. Chimpanzees love to fling branches and they also covet fresh
meat -- but don't seem to have made the connection, perhaps because of
lacking savannah waterholes frequented by herds. Following a
cool-crash-and-burn downsizing, there are lots of temporary savannahs.
Chattering between two climate states thus has the potential to speed
up evolution, and cool, crash, and burn cycles provide some
opportunities that our upright australopithecine ancestors might have
exploited. What, however, makes this an important driver for hominid
evolution and intelligence, as compared to a bookshelf full of varied
suggestions on what might have been behind it all?
Compared, say, to the invention of the carrying bag? The basic idea
of a carrying bag must have been very important for both gathering and
for small-game hunting. But one cannot reinvent the carrying bag for
extra credit. Some inventions can be repeated; for example, the aquatic
mammals have all discovered that a small reduction in body hair buys
them greater swimming efficiency. Another reduction buys them even more.
No matter where along the "growth curve" they are, another
increment has additional rewards. (There is, however, a limit: you can
only become so naked.) Some growth curves are also steeper than others,
faster at driving evolution than slower candidates (which might, like
many on that bookshelf of plausible candidates, have done the job in the
long run). So the steepness and extent of growth curves are important
considerations in sorting out where our intelligence came from.
There are two aspects of the "eat grass indirectly"
scenario which have long growth curves, and they involve things where we
humans have considerably enhanced abilities over the great apes. They
can also be "pumped" in one percent increments to produce
many-fold improvements. Neither is that abstraction called
'intelligence' but either could be the wheelchair-like curb cut that
gave higher intellectual functions their entry-level jobs.
Cooperation and Group Selection
The "good of the group gene" possibility was dismissed a
few decades ago (see Sober and Wilson 1998) on the theoretical grounds
that it would, like a leaking tire, backslide. Even if somehow
concentrated into a subpopulation yielding a majority of cooperators,
you'd still expect that tendencies to share could be swamped by all the
non-reciprocating freeloaders, who would out-reproduce the sharers.
If this were the prime consideration, of course, we would also have
to conclude that car tires would never work because they all, sooner or
later, go flat. We just pump them back up occasionally, and the
cool-crash-and-burn cycle suggests both a concentration mechanism and a
pump that might allow widespread cooperation to become established for
long enough to invent other solutions to the freeloader problem.
There is a certain amount of random recombination of populations
during the downsizing, as noted earlier. It is not unlike randomly
selecting a jury of 12 from a jury pool of many hundreds. Even if the
jury pool is representative (half male, 90 percent right-handed,
appropriate racial mixtures), some individual juries are dramatically
different (all of one sex or race, all left-handed, and so forth).
That's just one of the well-known phenomena of probability theory
("drawing small samples without replacement"). So even if
innate tendencies toward cooperation were only prominent in 10 percent
of the population, after parcellation many subpopulations would have
none and some might have a majority.
These "island" subpopulations are not competing with one
another like football teams, thanks to those resource-free gaps; they
are fighting the environment in the cool-crash-and-burn case, and most
subpopulations disappear with time. When conditions allow populations to
re-expand, there will be, after expansion into interbreeding
"continental" populations, a higher proportion of those
"genes" that helped some subpopulations survive the
This, too, is susceptible to the "Why us?" objection as it
would seem to apply to many mammalian species, and the answer may lie in
what is shared. Groups with a majority of cooperation genes
might spend less time arguing (and thereby wasting time which could be
spent in locating more food) and fighting (thereby both losing time and
risking injury) during the downsizing. This is particularly attractive
because of the long growth curve for cooperation, as noted earlier. Or
what's shared is language, where in order to realize its benefits, you
might need a sizeable proportion of those with beginner's traits.
Or, as Derek Bickerton has proposed (see Calvin & Bickerton
1999), cognitive capacities (mental categories for giver, recipient,
beneficiaries, type of action, and so on) to keep rough track of
freeloading tendencies might allow "Who owes what to whom" to
find another use, namely saying "Who did what to whom."
Solving the cheater problem in reciprocal altruism could thus be the
"wheelchair" that paid for the argument-structure scheme of
handing syntax, until structured language started earning its own way.
This by itself would constitute a large step up in intelligence.
Precision Throwing as Curb Cut
Another ape-to-human improvement with a long growth curve is the
precision throwing which is so handy for expanding hunting abilities
beyond that seen in the other predators. Hunting herd animals also has a
link to cooperation, as any one prey animal is usually too much for one
hunter to eat; one simply has to give away most of it as the chimpanzees
do ("tolerated scrounging") and hope for reciprocation when
someone else gets lucky. As Frans de Waal (1996) observed:
If carnivory was indeed the catalyst for the
evolution of sharing, it is hard to escape the conclusion that human
morality is steeped in animal blood. When we give money to begging
strangers, ship food to starving people, or vote for measures that
benefit the poor, we follow impulses shaped since the time our
ancestors began to cluster around meat possessors. At the center of
the original circle, we find a prize hard to get but desired by
many... this small, sympathetic circle grew steadily to encompass all
of humanity -- if not in practice then at least in principle.... Given
the circle's proposed origin, it is profoundly ironic that its
expansion should culminate in a plea for vegetarianism.
And, of course, hunting was one of the only solutions to an
environment where, for a few centuries, you either had to eat grass or
eat an animal that ate grass.
The side-of-the-barn accuracy needed for flinging branches into
waterhole herds may not have much of a growth curve by itself (it
doesn't matter which one you trip), but it could have gotten hunters
onto the bottom on the precision-throwing growth curve. Being able to
hit smaller herds has an even higher payoff. So does throwing from
farther away (herds eventually become wary), which also reduces risk to
the hunter. One can use other projectiles, such as rocks. One can become
accurate enough to hit lone animals. Then there are spears, and their
augmentation by launching sticks, and so forth. Each improvement has an
additional payoff: more days that you and your dependents can eat nice
sterile, high-calorie, low-toxicity fresh meat. (Cooking has made the
world much safer for vegetarians and scavengers.)
It's easy to see how natural selection could have repeatedly improved
throwing, but what does it have to do with higher intellectual function?
As noted, all of the ballistic movements require much detailed planning
during "get set" as feedback is too slow. While many ballistic
movements have some payoffs even when stereotyped, the hominid hunter
cannot function like the frog throwing its tongue when a fly is heading
into its "gunsight." There is no standard throw because of the
"approach distance" problem; each throw is a somewhat novel
problem in both elevation and range, even if using a standard projectile
size and weight.
And, beyond planning and versatility demands, there is the problem of
timing jitter (Calvin 1983). If you throw at a rabbit-sized target a
car-length away, and release 5 milliseconds too soon, you'll overshoot
the target. At two car lengths away, the launch window shrinks
eight-fold. Redundant motor programs, each with independent noise, can
solve this double-the-distance problem by using 64 times as many motor
programs in parallel.
Even the four-fold increase in the number of neocortical neurons
during hominid evolution cannot solve this jitter problem (by itself, it
would only buy a 25 percent increase in approach distance). Many-fold
increases in parallelism can only be done by temporarily borrowing
helpers from association cortex during "get set."
I have developed this jitter-reduction idea elsewhere (Calvin 1983,
1993, 1996b). What's important for intelligence is to recall Kimura's
(1993) result from aphasics, that most also suffered from hand-arm
sequencing problems when confronted with novel sequencing tasks (apraxia)
- and to recall Ojemann and Mateer's (1979) result from the perisylvian
core of language cortex, about the overlap of nonlanguage sensory and
motor sequencing tasks. If there is a common neural sequencing machinery
for mouth-and-face, hand-and-arm, sensory-and-motor, language cortex is
an obvious candidate (Calvin & Ojemann 1994).
And this can explain how a curb cut paid for by natural selection for
precision throwing might greatly augment planning on other time scales.
The structured aspect of the higher intellectual functions could easily
arise from the nested embedding aspect of throwing: the shoulder motion
is atop the forwards motion of the trunk; planning the elbow rotation
needs to similarly work from the velocity of the upper arm; the wrist
flip needs to be planned in light of the prediction of all those
compounded motions controlling the lower arm's velocity, and so forth.
All of the coordination must be done in advance, tweaking the parameters
to find one of the dozens of possible combinations that will hit the
target amidst a sea of solutions that will miss. This is nested
embedding of much the same sort as shown in those binary diagrams of
phrase structure, the other major way of doing syntax (see Calvin &
Bickerton 1999). As you assemble words to find a coherent sentence to
speak, you grapple with a problem analogous to novel hand-arm
Whatever paid for it in natural selection terms (and I assume it was
different things at different times), such a multiple-use neural
sequencer would have major implications for the structured higher
intellection functions, and thus for intelligence.
The Pump Run by Bistable Climate
Pumping up intelligence is thus a real possibility - even though the
natural selection that paid for it may be as remote as wheelchairs are
from skateboards. Higher intellectual functions may have some silent,
nonintellectual partners, those novel ballistic movements.
Ignoring compound interest considerations for a moment, how many
strokes on the pump, and of what size, would be sufficient to produce
the many-fold increases in the mental functions that separate the Pan
and Homo species? There were several dozen biphasic
cooling-warming events (each lasting between 70-1500 years) in the last
ice age alone, between 117,000 years and 11,000 years ago. There were
dozens of ice ages and, although the high-time-resolution records do not
extend to cover them yet, cores with thousand-year resolution can pick
up the longer-lasting ones. These longer-lasting biphasic events have
now been tracked back to 1.1 million years ago. From what we know of the
oceanographic mechanisms (see Broecker 1997, 1999; Calvin 1998a), I
would guess that some will be found between 2 and 3 million years ago --
but not in the period before the Isthmus of Panama forced the major
detours in ocean currents.
So there are hundreds of events of pretty much the same type each
time: abrupt cooling, crashing populations, and burning ecosystems. This
suggests that a one percent increment each time might be sufficient.
However, there were likely many more events (and so even smaller
increments might suffice) because the typical abrupt cooling or warming
chattered between modes like an old fluorescent light tube before
finally settling down in the new mode. Typically, there would be a
century where the temperature and rainfall whipped back and forth
between modern and ice-age values a few times, where vast storms churned
a lot of dust into the atmosphere (the isotopic signature of the dust in
the Greenland cores suggests that much came from the Great Gobi Desert).
Such flickering climate would have run the population
contraction-expansion cycle a few times within a single "madhouse
This type of pumping and multiple use shows how big steps up in
functionality (say, from unstructured protolanguage to structured
syntax) can arise from a series of small changes in nonintellectual
functions. It may be that something else from that bookshelf of
plausible suggestions will prove to run the evolutionary ratchet more
quickly than my combination of grass, throwing, and cooperation. But if
we are to ever give an explanation for how an ape can turn into a human,
we will likely have to address the profound challenges and unusual
opportunities given our ancestors by the fickle climate.
During the two decades that this theory has been
under construction, I have profited from numerous suggestions. The most
recent extensions of the theory have benefitted much from a stay at the
Rockefeller Foundation's Bellagio Center and from workshops organized by
the LaJolla Origins of Humans group (sponsored by the Preuss Foundation
and the Mathers Foundation) and by the Center for Human Evolution at the
Foundation for the Future.
Afterword: The Future's Intelligence Test
It has been 8,200 years since an abrupt cooling of even half the
magnitude discussed here (the Little Ice Age starting about 700 years
ago was an order of magnitude smaller). Everything we know about the
geophysical mechanisms (see Broecker 1999, Calvin 1998a) suggests that
another one could easily happen - indeed, that our greenhouse-effect
warming could trigger an abrupt cooling in several different ways.
Because such a cooling would occur too quickly for us to make
readjustments in agricultural productivity and associated supply lines,
it would be a potentially civilization-shattering affair, likely to
cause a population crash far worse than those seen in the wars and
plagues of history.
The best understood part of the flip-flop tendencies involves what
happens to the warm Gulf Stream waters, with the flow of about a hundred
Amazon Rivers, once they split off Ireland into the two major branches
of the North Atlantic Current. They sink to the depths of the
Greenland-Norwegian Sea and the Labrador Sea because so much evaporation
takes place (warming up the cold dry winds from Canada, and eventually
Europe, so that it is unlike Canada and Siberia) that the surface waters
become cold and hypersaline - and therefore more dense than the
underlying waters. At some sinking sites, giant whirlpools 15 km in
diameter can be found, carrying surface waters down into the depths.
Routinely flushing the cold waters in this manner makes room for more
warm waters to flow far north.
But this sinking mechanism can fail if fresh water accumulates on the
surface, diluting the dense waters. The increased rainfall that occurs
with global warming causes more rain to wall into the oceans at the high
latitudes. Ordinarily, rain falling into the ocean is not a problem --
but at these sites in the Labrador and Greenland-Norwegian Seas, it can
be catastrophic. So can meltwater from nearby Greenland ice cap,
especially when it comes out in surges. By shutting down the
high-latitude parts of this "Nordic Heat Pump," these
consequences of global warming can abrupt change Europe's climate. If
Europe's agriculture reverted to the productivity of Canada's (at the
same latitudes but lacking a preheating for winds off the Pacific
Ocean), 22 out of 23 Europeans would starve.
The surprise was that it isn't just Europe that gets hit hard. Most
of the habitable parts of the world have similarly cooled during past
episodes. Another failure would cause a population crash that would take
much of civilization with it, all within a decade.
Ways to postpone such a climatic shift are conceivable, however --
cloud-seeding to create rain shadows in critical locations are just one
possibility. Although we can't do much about everyday weather or
greenhouse warming, we may nonetheless be able to stabilize the climate
enough to prevent an abrupt cooling.
Devising a long-term scheme for stabilizing the flushing mechanism
has now become one of the major tasks of our civilization, essential to
prevent a drastic downsizing whose wars over food would leave a world
where everyone hated their neighbors for good reasons. Human levels of
intelligence allow us both foresight and rational planning. Civilization
has enormously expanded our horizons, allowing us to look far into the
past and learn from it. But it remains to be seen whether humans are
capable of passing this intelligence test that the climate sets for us.