On Being the Right Size
In his article, “On Being the Right Size”, J.B.S. Heldane explains his theory on everything having a perfect size. He states that animals will not be able to follow their normal living habits if they were enlarged or reduced more than three times, in the case of large animals, or 100 times, in the case of small animals.
The reason for this is concerned with proportion. If a small animal such as a mouse were to become 5ft long, its heart would not be strong enough to pump blood throughout its body. If a large mammal like a giraffe were to become smaller, it would not be able to maintain its footing because of winds and ground vibrations.
Being small or being large is neither good nor bad in itself. Heldane explains that there are both advantages and disadvantages in being either very small or very large. An insect can fall off a 12-story building and hit the ground a few seconds later without noticing. It is also able to crawl on a ceiling without having to worry about gravity. However, a small insect cannot keep itself warm in the winter and will eventually die. On the other hand, large animals would certainly not survive a high fall and can surely not walk on ceilings, but they can keep themselves warm in winter.
Furthermore, Heldane explains how each animal or insect has a certain size for a reason. This size always maintains the best balance of advantages and disadvantages in a certain situation. For each animal or insect, this is the ‘perfect size’.