Intelligence (biology)

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In biology, 'intelligence', in the broadest sense of the term, refers to the ability of an organism to adapt to its environment through learning and through shaping the environment, the organism employing its cognitive abilities to do so. 'Intelligence', in that sense, translates as the ability of an organism to exhibit such adaptive plastic behavior (Stanovich 2009).

Diverse notions of intelligence generally converge on the fundamental purposes of intelligence--adaptation to the environment and learnng from experience (Cianciolo and Sternberg 2004).

There is no universally accepted definition of animal intelligence, or procedure to measure it. Intelligence may be defined and measured by the speed and success of how animals, including humans, solve problems to survive in their natural and social environments (see also [Pearce 1997]). These include, for example, problems related to feeding, spatial orientation, social relationships and intraspecific communication. However, what animals must learn in their environments and how they accomplish this can differ considerably. Accordingly, behavioral ecologists have proposed that intelligence is nothing but an aggregate of special abilities that evolved in response to specific environments [Lockard 1971]. (Roth and Dicke 2005)

In humans, ourselves, we recognize that such intelligent behavior, such adaptative ability, includes rational decision-making and creative thinking, and wisdom—suggesting that otherwise the risk of non-adaptive, or mal-adaptive, behavior might increase significantly. Intelligent behavior also includes the skill of shaping the environment when it otherwise requires one to adapt to it or suffer suboptimal consequences, and knowing when and how to escape from the environment requiring adaptation (Matthews et al. 2004).

…most people would say that the ability to think rationally is a clear sign of a superior intellect…To think rationally means adopting appropriate goals, taking the appropriate action given one’s goals and beliefs, and holding beliefs that are commensurate with available evidence (Stanovich 2009, pp 2-3).

Adaptation in respect of human intelligence targets the realization of one's personal goals, not only the realization of the inherited biological goal of survival and reproductive success.

Thus, we may conceptualize human intelligence broadly in terms of one's aptitude for success in adapting to circumstances that threaten achievement of one's biological and personal goals. It may seem a contradiction to credit intelligence to the success in achieving personal goals that may lead to mental or physical dysfunction, but when cognitive science reveals personal goals arise largely from non-conscious mentation, the contradiction resolves by crediting such deficient intelligence to the non-conscious mind (Kahneman 2011)

In a narrower sense, intelligence in humans refers to the combination of cognitive abilities that determine one's score in standard tests that measure Intelligence Quotient (IQ). Traditional intelligence tests do not assess intelligence in the broad sense of the term (Stanovich 2009).

The universality of intelligence among living systems

Evolution: the unifying principle of intelligent systems

All living systems exhibit some form of intelligent behavior, in that evolutionary forces generate organisms adapted to their environment, adapted for success in meeting their universal biological imperatives for survival and reproduction, requiring varieties of skills/functionalities differing among species and environments and capacities for learning and memory. A terrestrial green plant, for example, exhibits intelligent behavior when it bends its stalk in keeping with the movement of the sun—heliotropism—maximizing exposure of its leaves for capture of solar photon energy (Hèader and Lebert 2001). A motile, free-swimming bacterium exhibits intelligent behavior when it actuates a unique swimming strategy that greatly facilitates its search for food—chemotaxis (Eisenbach and Lengeler 2004). A vervet monkey exhibits intelligent behavior when it generates for itself and its conspecifics a unique vocal warning signal for each type of predator it sees in the vicinity, allowing itself and its family to adopt the best defensive strategy for each type of predator.

Those kinds of intelligent behavior reflect the forces of organic evolution in service of the biological imperatives of survival and reproductive success. Within species such intelligence exhibits variations in degree among individuals in a given generation, variations upon which natural selection operates in mediating evolution.

In humans in particular, evolutionary forces operate in the service of sociocultural as well as biological imperatives, expressed by some biologists as imperatives for replication respectively of memes and genes.

Measuring intelligence

Measuring the intelligence of an individual organism requires performing some kind of intelligence testing, in which case what the intelligence test measures defines 'intelligence' in that circumstance. In that regard, intelligence is what intelligence tests measure.

To say that intelligence is what intelligence tests measure is an incomplete statement but it is not vacuous. The content of a battery of test items is defined by what is common to the set of items which were used to construct it. These items are not chosen haphazardly but selected to convey, as far as our crude notion will allow, what we mean by the word 'intelligence'. In a real sense, this set of items is a way of saying what we mean by 'intelligence'.

The crucial question is: what does this test battery measure? The answer to this question is our provisional definition of intelligence. Intelligence, we repeat, is a collective property of the set of items. If the individual items have meaning, so does the aggregate (Bartholomew 2004).

Commonly administered intelligence tests such as those that measure so-called Intelligence Quotient (IQ) or Scholastic Aptitude (SAT) fail to measure an important component of cognitive function, namely that relating to the ability for rational thought and decision making, thinking and decision making that work to serve the achievement of one's goals and to formulate goals in one's best interest biologically and socioculturally (Stanovich 2009).

IQ test scores depend also in part upon motivation to do well on the test (Duckworth et al. 2011).

What do intelligence tests test? Both intelligence and test motivation. Why is this a problem? Because test motivation on low-stakes intelligence tests can partially confound IQ outcome associations…Our conclusions may come as no surprise to psychologists who administer intelligence tests themselves (Haywood 1992). Where the problem lies, in our view, is in the interpretation of IQ scores by economists, sociologists, and research psychologists who have not witnessed variation in test motivation firsthand. These social scientists might erringly assume that a low IQ score invariably indicates low intelligence (Duckworth et al. 2011).

One's IQ score can sometimes mean the difference between life and death. If one commits a crime ordinarily punishable by execution (death penalty) one cannot receive the death penalty if one's IQ on a reliable IQ test falls below a threshold value considered to indicate mental retardation, no matter how heinous the crime, according to a U.S. Supreme Court ruling (Atkins v. Virginia 2002).

Hampshire and colleagues (2012) report that muliple independent brain networks operate during IQ test tasks, rendering IQ scores artifactual to "tasks recruiting multiple networks", which dissociate on correlation with demographic variables.


An organism exhibits intelligent behavior when it successfully adapts to the stimuli impacting upon it, however limited the informational content of the stimuli. The stimuli might result from events occurring internally, such as dehydration leading to a search for water, or recall of stored memories leading to self-interested social interactions. Or the stimuli might result from events occurring externally, such as odors leading to a search for food, or changes in market conditions leading reevaluation of investment strategies. Successful adaption implies behavioral responses that serve the short and long term biological and/or sociocultural interests of the organism, and the balance of short and long term interests.

 · The role of sensory receptive ability

The ability of an organism to exhibit intelligent behavior depends in part on the width of its sensory input spectrum — the number of sensory input types — and in part on the character and breadth of the sensory input channels. The greater the number and types of sensory input channels, and the greater their informational density, the better chance the organism has to adapt to real-time changes in its surroundings, in particular when receiving limited information about the changes, and in particular when adaptation requires novel response patterns (Agutter and Wheatley 2007).

 · The role of behavioral response ability

The more different and effective ways an organism can respond behaviorally, the more flexibility it will have to adapt to changes in its surroundings (Agutter and Wheatley 2007).

 · The role of brain size

Larger brain size can permit greater capacity for processing the information needed to adjust behavioral output to input (Agutter and Wheatley 2007). A greater capacity for processing information necessarily adds complexity to neuronal networks, achievable in part through more sensory input and processing networks, more networks interacting, larger memory capacity, more synthetic (creative) networking. More networks, more interconnections, more neurons—more mass.

Physical laws may limit the relationship between brain size and intelligence in living systems (Fox 2011)...

 · The role of interconnectivity

The more dense and varied the neuronal connections between sensory input and behavioral output, including connections to memory, the more flexibility an organism will have to adapt to changes in its surroundings.

Brain size alone is not sufficient. The more routes there are between stimulus and output, and the more indirect and cross-connected these routes become, the greater the flexibility and novelty of behaviour. Therefore, the brain of an animal that can behave intelligently has enormous numbers of indirect, cross-connected routes between inputs and outputs (Agutter and Wheatley 2007).

Recent studies have shown that the functional connections of the brain network are organized in a highly efficient small-world manner, indicating a high level of local neighborhood clustering, together with the existence of more long-distance connections that ensure a high level of global communication efficiency within the overall network. Such an efficient network architecture of our functional brain raises the question of a possible association between how efficiently the regions of our brain are functionally connected and our level of intelligence. Examining the overall organization of the brain network using graph analysis, we show a strong negative association between the normalized characteristic path length of the resting-state brain network and intelligence quotient (IQ). This suggests that human intellectual performance is likely to be related to how efficiently our brain integrates information between multiple brain regions. Most pronounced effects between normalized path length and IQ were found in frontal and parietal regions. Our findings indicate a strong positive association between the global efficiency of functional brain networks and intellectual performance (van den Heuvel et al. 2009).

 · The role of memory

 · The role of learning



  • Duckworth AL, Quinn PD, Lynam DR, Loeber R, Stouthamer-Loeber M. (2011) Role of test motivation in intelligence testing. PNAS 108 (19):7716-7720.
    • Intelligence tests are widely assumed to measure maximal intellectual performance, and predictive associations between intelligence quotient (IQ) scores and later-life outcomes are typically interpreted as unbiased estimates of the effect of intellectual ability on academic, professional, and social life outcomes. The current investigation critically examines these assumptions and finds evidence against both.
    • After adjusting for the influence of test motivation, however, the predictive validity of intelligence for life outcomes was significantly diminished, particularly for nonacademic outcomes. Collectively, our findings suggest that, under low-stakes research conditions, some individuals try harder than others, and, in this context, test motivation can act as a third-variable confound that inflates estimates of the predictive validity of intelligence for life outcomes.
  • Fox D. (2011) The Limits of Intelligence. Scientific American. July.pp. 36-43.
    • "The laws of physics may well prevent thehuman brain from evolving into an ever more powerful thinking machine."
  • Adam Hampshire, Roger R. Highfield, Beth L. Parkin, Adrian M. Owen. (2012) Fractionating Human Intelligence. Neuron 76 (6): 1225.
    • "Highlights from authors and the journal: (a) We propose that human intelligence is composed of multiple independent components; (b)Each behavioral component is associated with a distinct functional brain network; (c) The higher-order “g” factor is an artifact of tasks recruiting multiple networks; (d) The components of intelligence dissociate when correlated with demographic variables. | Despite more than a century of research, the biological basis of intelligence remains unclear. Hampshire et al. demonstrate that intelligence is a multifaceted construct, supported by multiple specialized brain systems, each with its own independent capacity.
  • Haywood HC (1992) The strange and wonderful symbiosis of motivation and cognition. Int J Cogn Ed Mediated Learn 2:186–197.