A small study in France found a link between eye dominance and dyslexia. Lack of a dominant eye was associated with dyslexia. The researches speculate that dominance is important in discerning similar letters like "b" and "d".
Lack of eye dominance is similar to being ambidextrous, where there is no clear "handedness". That is, the person who is ambidextrous can dribble, shoot, pass or "juke" with equal facility with either hand. A player who can only dribble or shoot with one hand is much, much easier to defend than a player who can do so with either hand.
Malcolm Gladwell, in studying hockey, determined that competitive, team sports stratify athletes at a very young age. The most promising 8 and 10 year olds go to "camps" and find mentors not available to less gifted 8 and 10 year olds. While the originally less gifted 8 year old can learn to dribble with equal facility with either hand, the ambidextrous athlete can do so from day one. The less gifted never have the opportunity to catch up.
It is unclear why "handedness" evolved. It is clear that it would have become extinct if it did not offer a huge competitive advantage. Some possibilities include:
- Hygiene: Separating the eating hand from the wiping hand.
- Vestigial origin: Incrementally increasing brain size could only support the increased dexterity on one side of the body
- Tool use: Tool like spears and bows put enormous demands on one side of the body. Funneling activities to one side resulted in hypertrophy of one side allowing larger spears, longer range and deeper penetration.