j.ADHD: An evolutionary brain condition

It is an error to imagine that evolution signifies a constant tendency to increased perfection. That process undoubtedly involves a constant remodeling of the organism in adaptation to new conditions; but it depends on the nature of those conditions whether the directions of the modifications effected shall be upward or downward. Thomas Huxley

About 2.5 million years ago, hominids started out with a brain weighing approximately 400-450 grams, but around 200,000 to 400,000 years ago, our brains became much bigger than those of other primates. Now, we humans walk around with brains tipping the scales at 1350 to 1450 grams.  As humans, we enjoy a much larger neocortex that separates us from other species, through our deep thinking, high cognition and intelligence. Marsel Mesulam in the millennium issue of “Brain and Cognition” argued about the still continuation of evolutionary process of brain plasticity and connectivity that have made human cognition flexible, and prone to learning, development and advancement of language and change. He views novelty seeking and diversity in inventing “thousands of languages to express the same thoughts, thousands of cuisines to satisfy the same hunger, and thousands of diversions to dissipate the same boredom” as evidence to such evolution and adaptation of our brain. He poses questions such as ” Will cognitive evolution force new speciation, perhaps into Homo ultrasapiens

If that is true that ADHD is associated with high intelligence, then this brain condition that is developmental and shares similar neuroanatomical pathway with intelligence, could be an adaptive and evolutionary process like intelligence. An evidence of such contention is the rise in the prevalence of ADHD, from as low as 1% in the past to as high as %16 according to some statistics.  ADHD has already been proposed by some scientists (e.g. Cardo and colleagues, Williams and Taylor) to be an evolutionary step in the  natural selection for its traits of risk taking behaviours, competition, unpredictable behaviours. 

Jensen and colleagues have considered “ADHD as a Disorder of Adaptation” and reason that plasticity of our brain has been an adaptive and an evolutionary process with ADHD as a fit example.  These authors argue that increased motor activity or hyperactivity is adaptive for a successful constant exploration of the environment for threats and opportunities. Attentional Processes (Scanning and Rapidly Shifting Attention) and vigilance is necessary to monitor dangers and threats, according to this model, while overfocused attention could be quite maladaptive in high- threat or highly novel environments. In regard with “impulsivity”, this group defines impulsivity as “an organism’s quick response to environmental cues while not considering alternative responses to the cues.” These authors consider timing of response, or immediate, vs. delayed, or non-response is quite adaptive. 

Jensen and colleagues argue that the modern societies specially in the current school environments, ADHD children with “response-readiness”, attentional shifting and high motor activity and response are not favored, but children with more passive and attentional focus, motor passivity, less distractions, processing funnel information through single modality, e.g. passive listening or reading. Such environments limit opportunities for shifting attention, fast motor response and demand delay of recognition for efforts. “Most school environments favor the “problem-solving” individual, able to maintain intellectual activity with motor quietness, screen out distractions, sustain attention, and delay response until all aspects of a situation have been analyzed.” These authors consider the modern early environments in the children’s lives, e.g. fast pacing watching television and playing video games, in contrast to the slow paced school-related tasks that emphasize logic, sequence, discipline, and detachment, as more triggering for such “response readiness”, hyperactivity and attentional shifting of ADHD children. “We hypothesize that scanning or shifting attentional systems can be “up-regulated” as a function of externally driven stimuli during early development (i.e., set on “high scan”), possibly at the expense of attentional systems for focusing and selecting.” 

 Read more in the book “ADHD:Revisited” available a Amazon, Kindle books.