Does Size Matter? No. It’s Only Important To Be The Right Size

The discussion today is about whether size of organisms (individual forms of life) matter at all. Size does not seem to matter among the animal kingdom and plant kingdom. A very tall person has his advantages and disadvantages as the smaller person has

American GI soldiers in their 20s did much better than the six footer Pashtuns in Afghanistan because of their superior weapons. Shorter Japanese soldiers were more than a match for taller GIs during the Second World War 2. Thin and skinny Vietnamese routed the well-fed and robust French and American armies. The size has to be right for a particular purpose. Size does not matter to the Gurkhas in any battle.

Bigger mammals (breast-feeding animals including humans) have longer life span than small ones, but taller individuals within the same species will on average have shorter life span.

As animals get bigger in size eg  a tiny mouse to a huge elephant, nature has it that the pulse rates slow down and life spans stretch out longer so that the number of heart beats during an average stay on Earth, tends to be the same, which is around a billion and half. It is just that a mouse uses its energy quickly than an elephant.

A mouse and an elephant make a lot of difference in their size. But being the right size of a particular

animal is equally important. It is not always bigger animals can do bigger things. A flea can jump up about 2 feet while a large man can jump about 5 feet. As a matter of fact, the height to which an animal can jump is more nearly independent of its size than proportional to it.

It is thought that as organisms grow in size they become more efficient. That’s why nature has evolved large animals like elephants. It’s a much better way of utilising energy.

Among our hunter-gatherer ancestors in the Palaeolithic era, size didn’t matter. They lived in bands that hunted together. Only a few became influential because of their greater wisdom and led the band, not because of their size. In fact, there was not much difference between humans and chimpanzees or bonbons. Dominant males, such as gorillas, orang-utans fight each other for possession of females. Males are bigger than females with superior weapons like sharp canine teeth.

This essay is inspired by JBS Haldane (1892-1964), a British geneticist who made science popular. He died in Bhubaneswar in India, living there and doing research. He died of cancer often humouring about it.

This incredible fellow wrote an essay in 1926, “On Being the Right Size. Size matters, but not in the way a city-stomping Godzilla or King Kong might hope. “He wrote: “Size inevitably comes at a cost of ever-greater complexity. Comparative anatomy is largely the story of the struggle to increase surface in proportion to the volume, which is why intestines are coiled and human lungs pack in a hundred square yards of surface area. And “Complexity is a Goldilocks tool [a tool used for identifying genomic regions that are ‘just right’] for the large, widening the zone of ‘just right’.”

Haldane explains why for every type of animal there is a most convenient size. And a large change in size carries with it a change in form.  A hare cannot be as large as a hippopotamus, or a whale cannot be as small as a catfish. As an example, a deer with thin legs is to become as large as a cow, it will break its leg bones to carry its body weight as the human thigh bones will break under about 10 times the average human weight.

A tall giraffe has disadvantage of pumping the blood to its brain from its heart that is way down in its body

Tall animals such as giraffe has difficulties as it has to pump its blood to its brain to greater height than a man and therefore, require a larger blood pressure and tougher blood vessels. As we know many people die from a burst artery in the brain (stroke). This danger is greater for a giraffe. Because it is very tall it has also to stretch out its legs obliquely outward to get stability. On the flip side, as it is very tall it can reach leaves to eat that other animals can’t reach.

There is advantage in being small too. A typical small microscopic worm like rotifer (found in millions everywhere there is water or moist area, has a smooth skin through which all the oxygen it requires

can soak in. It has a straight gut with sufficient surface to absorb its food, and a simple kidney to get rid of water products.  If the rotifer were to increase, Haldane argues, its dimensions 10 fold in every direction and its weight increased a thousand times so that if it is to use its muscles as efficiently as its counterpart, it will need a thousand times as much food and oxygen per day and will excrete a thousand time as much of waste products. But it is not structured in that way.

There are thus advantages and disadvantages about being big in animals. There is also the important factor of metabolism and physiology, which has to be adjusted according to size. A cat for example, is 100 times more massive than a mouse but lives only 3 times longer. Because the cat’s heart beats are a third as fast as that of mouse. But they tend to be roughly the same around a billion and a half in a life time. The mouse dies earlier as it uses its energy more quickly than a cat. The same is true for plants. The simplest plant, such as the green algae (kung in Manipuri) which is neither plant nor animal nor fungus, growing in stagnant water or on the bark of trees, are mere round cells. They need only a small amount of oxygen and sunlight to make their food (sugar).

The higher plants that need to make more food, increases their surface by putting out leaves and roots to manufacture the food.

Other disadvantage of bigger animals is with gravity. I f you drop a mouse down a thousand metre mine shaft and on arriving at the bottom, nothing will happen to it apart from a slight shock. A rat will be killed and a horse slashed, says Haldane. It’s because the résistance presented by air to the movement of the mouse is relatively 10 times greater than the driving force ie gravity. Elderly human beings mostly women, when falling from such a low height (standing height) will often break the neck of their thigh bone.

Insects do not have any problem with gravity. A very good advantage. It can fall without any danger. If you shock a fly and throw it to the ground, nothing will happen to it. Or they can cling to the ceiling upside down. Daddy long legs do not collapse on their long flimsy eight legs. But they are vulnerable to the surface tension of water that can trap its legs.

A man coming out of a bath, carries with him a film of water about one fifth of an inch in thickness. This weighs about a pound (nearly a half of kilogram). A wet mouse has to carry its own weight of water, whereas a wet fly has to lift many times its own weight of water. That’s why once wetted with water or any liquid, a fly is in serious danger of drowning as it cannot fly off carrying such a heavy load, like an overloaded helicopter.

One distinct advantage of bigger size is that it enables itself to keep warm. All warm-blooded animals at rest, lose the same amount of heat from a unit area of the skin. To replace the heat they need food proportional to the surface not to their weight. A mouse eats about one quarter of its own weight of food every day, which is mainly used to keeping it warm. For this reason small animals cannot live in cold countries.

In the arctic region, except the foxes there are no reptiles like snakes or amphibians like frogs, which are called cold-blooded animals with no self-heating mechanisms. In humans, little organelles inside the cells called mitochondria produce most of the body heat by using oxygen and nutrients we eat. Our body also can also generate heat by using a tissue called brown fat to keep warm when we shiver.

I will end this piece with a very good news for short people. Latest research in 2014, from the department of Geriatric medicine at the University of Hawaii by Bradley Wilcox and his team, found that shorter men will have the last laugh all the way to their grave, as they are more likely to have a protective form of a longevity gene, leading to smaller body size and a longer lifespan.

Dr IM Singh

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