The Evolutionary Advantage of Dominant Hands: Why Ambidexterity Isn't Always an Evolutionary Edge
Placental mammals, including humans, tend to develop a dominant hand, which gives a clear preference to one side over the other. This preference is evident in various aspects of daily life, such as driving, using tools, and even sports. However, the question arises: why do we develop this preference if ambidexterity might seem to offer an evolutionary advantage?
Why the Dominance of One Side?
While marsupial mammals like kangaroos and tushkans exhibit a more symmetrical walking pattern, placental mammals tend to have an inherent preference for one side, often referred to as the dominant hand. This is a trait seen in various species, where one limb is used more frequently and efficiently, leading to a preference for one side over the other.
Modern Ambidexterity
Today, we often display ambidexterity in ways that are not necessarily symmetrical. For instance, while driving in the UK predominantly requires the right hand for steering and the left for gear selection, the effort required is shared between both hands and legs. Forklift operators use the left hand for steering and the right hand for operating hydraulic controls, indicating that we can adapt to use both sides effectively.
Similarly, when using cutlery, even if the right hand is more dominant, some individuals prefer to use a knife in the left hand and a fork in the right. This flexibility can be observed in various daily activities, such as firing a rifle with the left hand or riding a bicycle with the left hand for more stability.
Evolutionary Perspective
The human brain is incredibly complex and energy-intensive. A larger brain size is a significant evolutionary adaptation, but it comes with a cost. By having a dominant hand and focusing brain resources on one side, we make a strategic trade-off that can support other important functions.
One of the main reasons for developing a dominant hand is the conservation of brain real estate. The motor cortex, responsible for controlling fine motor functions, is more developed on the side of the brain that controls the dominant hand. This means that individuals with a dominant hand have a more specialized and larger motor cortex area dedicated to the dominant side, which can improve the precision and control of specific tasks.
In contrast, ambidexterity does not necessarily provide a survival advantage because it would require more brain resources to be equally proficient with both sides. This trade-off is a common pattern in evolutionary biology, where species develop specialized traits to optimize certain functions, even if it means not being as proficient in other areas.
Conclusion
In conclusion, the dominance of one side is a result of evolutionary strategies aimed at optimizing brain and muscle resources. While ambidexterity might seem beneficial in certain scenarios, the evolutionary trade-off of having a dominant hand provides more specialized and complex motor functions that are crucial for survival and daily life.