An Evolution Analysis of IQ:
Connection Between Brain Size and Intelligence
Student Name: Huasheng Wang
Student Number: 1131928
Tutorial Number: T28
Group Member 1: Isabel Ormond
Group Member 2: Jing Guo
Group Member 3: Janine Moloney
Group Member 4: Shelly Luong
Trigger Number: 1
Level of Analysis: Evolution
Date: February 23, 2012
Words and phrases such as "brainy" and "got a big brain" are often used as a compliment for highly intellectual individuals. Yet, cases of evolution being a constant unidirectional process are seldom, and the correlation between a bigger brain, higher intelligence and higher fitness remains largely untested. On the one hand, higher intelligence aids in food foraging, mate seeking and predator avoidance (Chittka & Niven, 2009). On the other hand, the energy and alimentary cost of producing and maintaining a brain are high; consequently an unnecessarily huge brain will create deficits in body nutrition supply. Larger brains result, at least partly, from the need of larger neurons necessary for larger animals to perform basic biophysical activities. Hence, from an evolutionary perspective, a bigger brain size does not necessarily have connection with intelligence.
There is no universal definition of animal intelligence. Intelligence may be defined and measured by how animals can solve problems swiftly to survive in their natural and social environments (Roth & Dicke, 2005). Problems arise when trying to implement this definition in experiments because of reporting biases as the way animals adapt to their environments can differ considerably (Roth & Dicke, 2005). Thus, intelligence needs to be operationally defined before being studied. The purpose for brain development and intelligence improvement is to provide higher fitness. Therefore, experimental approaches often focus on a specific range of behaviours, such as food storing or bower-building complexity in birds (Madden, 2001). Behavioural flexibility is a generally used indicator of intelligence, proposed by several comparative and evolutionary psychologists and cognitive ecologists (Gibson, 2002), resulting in the discovery of novel solutions that are not regularly performed by the animal (Gould, 2003). Behavioural flexibility is one of the many attributes of intelligence that can be objectively and quantitatively studied. New Caledonian crows have little access to metal wire in their wild habitat, yet observations have shown a captive female spontaneously bent a piece of straight wire into a hook and used it to lift a bucket containing food from a vertical pipe (Weir, Chappell & Kacelnik, 2002). There can be little argument whether such an action is out of the ordinary.
Monkeys possess brains that are much smaller than those of ungulates, but their higher cognitive and behavioural flexibility is undisputed. Also, the 1.35 kg brain of Homo sapiens is significantly exceeded by the brains of elephants and some cetaceans, in spite of being arguably the most intelligent species on earth (Roth & Dicke, 2005). Thus, a larger brain by absolute size alone does not necessarily assure greater intelligence. The next general factor is relative brain size. Mammals with larger brains with respect to their body size are often assumed to be more intelligent. However, researches have shown that, as body size increases, brain size increases with a decreasing ratio to the size of the body, following a power function with an exponent of 0.6–0.8 (Hofman, 2003). This means that with increasing body size, brains become larger in absolute size, but smaller in relation to body. Among large mammals, humans have the relatively largest brain (2% of body mass), whereas shrews, the smallest mammals, who exhibit supposedly much less cognitive and behavioural flexibility, have brains of up to 10% of their body mass (Roth & Dicke, 2005). Therefore, the relationship between relative brain size and intelligence is inconclusive, either.
In conclusion, although brain size is often assumed to have a direct relationship to the individual's intelligence level, this evidence found is not consistent. Despite ample evidence of the links between neural measures and various lifestyles in mammals, brain size and intelligence are not directly correlated. Moreover, a balance exists between energetic demands, ecological conditions and neuronal mass. Intelligence is influenced by many factors and brain size alone can merely reflect a few aspects of intelligence.
References
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