Archive for September, 2011

This week was a presentation by Dieter and Netzin Steklis:

For the purposes of the presentation, intelligence was characterized by cognition, cognition being flexible, creative behavior solutions. We would like two questions to be answered– the objective question of what does the data (on intelligence) say? (sans interpretation), and more subjectively, what would we like that data to inform? For example, Dr. Masel uses it as a check against a bias towards human exceptionalism.

In terms of quantifying intelligence, humans are compared to primates because we share the same taxonomic order, and thus (whether by correlation or causation) similar, visual based learning styles. Any comparison to animals that are much more reliant on other senses would leave them at a disadvantage. For example, recognizing oneself in the mirror is typically classified as a sign of elevated intelligence…but a dog does not rely on visualization nearly as much as smell. Would a dog that recognized its own scent be of equivalent intelligence to any animal that could identify its reflection?

So what makes humans special? An initial response could be brain size. But alas, Neanderthal skulls show significantly larger endocranial volumes than that of Homo sapiens…suggesting larger brain size (although this could be accounted for by larger sinuses as an adaptation to severe cold).

Next idea, brain size proportional to total body mass. Having a larger brain is very metabolically expensive. Humans show a disproportionately larger brain and smaller gut. The thought is that maybe switching to a diet higher in meat (or cooked vegetables) allowed for a smaller gut size, and thus a larger brain (given that raw foliage digestion takes a lot of energy).

There is a correlation between brain size and longevity. “Bigger brains take longer to cook.” Humans also show a stretching of all the stages of life compared to other primates. We are the only mammals (besides killer whales and short finned pilot whales) with a menopausal life period. This could be explained by kin selection (non-reproducing adults stick around to help raise offspring) and/or the childcare trade-off hypothesis (continuing to have children jeopardizes the fitness of older offspring). However, this does not provide and definitive answers to the human intelligence question.

So nothing particularly brilliant comes from looking at absolute brain size or brain size corrected for body size. Some have considered testing the size of the neocortex to that of the paleocortex. The neocortex is largely responsible for social intelligence, and with no surprise, strongly correlated to the mean group size (number of intraspecies members an individual commonly interacts with). But! Skipping over much of the remaining presentation given time restrictions (as per usual), the punchline of the lecture was that in measures of cognition, gross absolute brain weight was the best predictor of of a “good score” at non-social cognition tests in primates.

Post Contributed by L.B.

ADDENDUM (Contributed by N.S.)
Brain measures of intelligence have focused on the relative amount of neocortex (either relative to the rest of the brain or to the brain stem) based on the idea that the neocortex is primarily responsible for intelligence (i.e., flexible learning strategies, creativity). Non-neocortical brain components, therefore, are viewed as the “house-keeping” (or “somatic”) components, while the neocortex governs cognitive functions. This is a very crude approximation of the brain’s division of labor, however, as we are mapping our (dichotomous) taxonomy of function onto the brain (reminiscent of the old phrenology school of Psychology), which more and more studies of brain function tell us does not “carve nature at the joints”. For example, our functional categories of emotion and cognition are far more interwoven in the brain and behavior than our taxonomy implies. (See much of the work by Damasio and colleagues; also see Byrne’s idea of fluidity, not strict modularity, between physical and social cognition—e.g., corvid intelligence can’t be explained as social intelligence, but in response to physical challenges.) Also, many “non-cognitive” brain components (e.g., the cerebellum) play a role in cognition. As a result, brain and cognitive evolution have involved a reorganization of many neocortical and non-neocortical brain parts (e.g., limbic system components, such as the amygdala), which therefore yields only partial correlations between relative neocortex size and intelligence.

So then what characteristics of the brain correlate (and hopefully functionally relate) with intelligence? In a one-two punch, Deaner, van Schaik and colleagues were able to show (a)first, that some primate taxa are ‘smarter’ than others in domain general intelligence cognitive abilities (e.g., detour problems, object discrimination learning, reversal learning, oddity learning, delayed response)*, then (b) that absolute brain size best predicts cognitive performance**.

*Deaner, R. O., van Schaik, C. P., & Johnson, V. (2006). Do some taxa have better domain-general cognition than others? A meta-analysis of nonhuman primate studies. Evolutionary Psychology, 4149-196.

**Deaner, R. O., lsler, K., Burkart, J., & van Schaik, C. (2007). Overall brain size, and not encephalization quotient, best predicts cognitive ability across non-human primates. Brain, Behavior and Evolution, 70(2), 115-124.

This finding that whole brain size best explains the variance between primates in measures of general intelligence also connects up well with the points made by Roth (this week’s readings) about the importance of raw computing power (partly a function of number of computing units—i.e., mostly neurons) that also depends on such factors as neuronal density, and axonal fiber dimension (i.e., the efficiency of the “wiring”).

None of this is meant to degrade or even dethrone the role of neocortex in cognitive performance. After all, cortical degeneration in humans (as in Alzheimer’s or Picks disease—various dementias) is clearly linked to loss of cognitive functions. Much of the human neocortex is dominated by the analysis of visual input, fine hand-eye motor coordination, and circuits for impulse control and representation of other’s mental states (or mindreading, ToM). That’s why much of our thinking is in the visual realm, for example, and we readily attribute agency to things and events. However, the mental operations we define as intelligent, are clearly widely distributed throughout the brain, with the neocortex playing a vital but not a sole role.

A caveat is in order: We have to bear in mind that the work by Deaner et al., only speaks to differences AMONG PRIMATES in absolute brain size and intelligence. We cannot automatically assume that the same therefore holds for comparisons within other orders of mammals or between orders or larger taxonomic entities. (We would not to assume that a whale, because it has a larger brain, is smarter than a human, or a horse is smarter than a monkey, or a reptile with an absolutely larger brain more intelligent than a bird with a smaller brain.) For example, primates as a group may be generally smarter than other mammals because they evolved a more densely packed cerebral cortex, and/or because they evolved neural specializations that support representational capacities (e.g., TOM-like skills). Thus primates as an order may be generally smarter than birds not just because they have absolutely larger brains, but also because of derived brain features (specializations). At the same time, some birds (e.g., corvids) have evolved specializations for apparently sophisticated mental abilities (mirror self-recognition, understanding other’s knowledge or perspective) that seem even to exceed those of some primates (monkeys), and while these cognitive specializations appear to be achieved without a neocortex and by smaller brains, they may or may not be linked to generally higher intelligence (as defined earlier).

Punch line: In accounting for differences in general intelligence among PRIMATES, absolute brain size matters: The whole brain (as an undivided functional system where number of computing units, density, etc matter) best explains differences in general intelligence among primates. And, though neocortical function plays a key role in human intelligence, it is not the sole source of general intelligence across species. Thus within primates, humans are uniquely big-brained and this accounts for much of our greater general intelligence. Were Neanderthal’s therefore smarter than fully modern humans? Possible, but unlikely. Remember that absolute brain size accounts for most but not all the variation in species differences in intelligence. It is therefore likely that cognitive (and concomitant brain) specializations evolved (such as for symbolic language) after Neanderthals that launched modern human cognition into a qualitatively distinct “cognitive niche” (after Pinker) that made possible subsequent cultural and technological achievements the Neandertal brain could not even imagine. Our apologies to the Neandertals…


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The focus of this semester’s forum will be the evolution of human intelligence. For the first meeting of the semester, we read Chapter 2 from Jared Diamond’s book, “The Third Chimpanzee,” titled, “The Great Leap Forward.” In it, Diamond discusses human evolution since our split from chimpanzees and attempts to identify some of the components that make humans unique.

Our discussion began with an update on the current state of knowledge of recent human evolution. When the book was written, in 1991, it was generally thought that culture alone, not biology, has driven human evolution since the Neolithic Revolution, as 40,000 years could not be enough time for biological evolution to produce noticeable change. (Note that this was the opinion of anthropologists, but the broader evolutionary biology community did not agree, as such an idea was inconsistent with standard evolutionary thought.) Since then the biological evolutionary arguments have become stronger and now it is believed that human change is driven by a co-evolutionary feedback cycle between culture and biology. Some evidence of genetic and neurological change over the last 40,000 years has been proposed, but relating it directly to genetic change via evolutionary processes is difficult. A simple question was raised, “While a Cro-Magnon man may look physically like a modern human, could he learn to use a computer?” The answer to that question is not clear, but what is clear is that a time span as short as 40,000 years is definitely enough time for biological evolution to produce change and so the question of biological versus cultural evolution remains an open question.

Another correction to the 1991 literature is that we now have solid evidence for interbreeding between early Homo sapiens as they migrated out of Africa and Neanderthals present in Europe at the time. The bottom line is this: if you are of African descent, you share none of your genome with Neanderthals, however, if you are of non-African descent, approximately 2.5% of your DNA comes from Neanderthals.

The main undisputed message from the reading was that the Great Leap Forward really did appear abruptly, in terms of an explosion of complex art and tool use, however, the cause(s) of this abruptness are largely unknown.

As the discussion developed, we talked about the changes in brain size since humans split from chimpanzees. We were reminded to be careful about assuming progress as there is no true directionality in evolution. In fact, there have been periods of decreasing brain size and it would be misleading to assume that intelligence is purely a product of bigger and “better” brains.

The rest of our discussion was devoted to defining “intelligence” and deciding what aspects of the definitions we will talk about this semester.

Definition 1
“Sine Qua Non” Humanity. This latin phrase means “without which there is nothing.” And in our context, without intelligence, there is no humanity. This definition is a major motivator of this semesters topic, but doesn’t really get us anywhere in terms of defining “intelligence.”

Definition 2
Intelligence is a faculty of _________.
-Brain *
-Neocortex !*
-Whole body *
-Mind !*
-Group !*
-Self/Ego/Identity !
-Will !
-Executive function !*

Definition 3
Intelligence is a faculty for _________.
-Consciousness !*
-Agency (requires counterfactual) !
-Problem solving *
-Processing information *
-Reasoning (induction, deduction, intuition, dialectic) !*
-Logic *
-Memory *
-Learning *
-Skill Acquisition *
-Valuation *
-Abstraction *
-Empathy !*
-Theory of Mind !*
-Reflection *
-Prediction *
-Language !*
-Perception *
-Communication *
-Social Relation management !*
-Tool use *
-Sentience ! (*)
-Executive functioning !*
-Physical spatial awareness *

As we developed our lists, we gave special designation to those that are interesting (!) and those that are tractable (*). The items that are both interesting and tractable will form the bulk of our discussions this semester (highlighted in bold).

Post contributed by J.L.

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