Have you ever wondered, why are there so little insects in the colder regions? Or why you have a 8.5 meter long intestine? Or why hasn't a giant cockroach invade your city already just so that you do not have to take that school exam of yours?
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| "I'm in yo city, eating yo lunchboxes." |
Turns out they all have one unifying factor, that is, SIZES! Forget what the experts said, size
does matters.
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| Except for your favorite Happy Feet. |
Cold regions that have eternal winter such as the arctics and antarctica are devoid of animals that are smaller than a fox. In fact, if I may generalize (of course, there are always rare exceptions in biology), reptiles and amphibians are no where to be found in areas of freezing temperature, so are birds and insects (Birds and insects usually migrate to warmer places during winter). This is because bigger animals are better at keeping warmth within their body than smaller animals. How exactly?
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| Uh... Don't try this at home? |
You have an intestine that is about 5 times longer than your height. But why do you need an intestine that long. Well, the high school biology answer to that is just to increase, surface area for food absorption. You already know that. But then again, why do you need increased area for food absorption? Worms have a straight gut that is as long as its body, it didn't need an intestine that is as long as a spaghetti.
And why don't we have giant cockroaches, if not at least as big as our arm or something? Or let us expand the question and ask, why don't we have giant insects the size of a cat or a dog? Why not giant human beings 50-foot tall? Is Godzilla possible?
Alright, I hope I raised enough questions to keep your attention. I will explain away the answers to these questions, with biological principles and some maths (not much, you do not have to be an Asian to understand them :D ).
The animal kingdom, I must say, has to be one of the weirdest thing to happen to the universe. To have matters (atoms and molecules) coming together to form reproducing lifeforms is one thing, to evolve into a being that are mobile is another miracle altogether! Okay, that has nothing to do with the topic today, but putting that aside, I want to point out another thing to you. If you noticed, of ALL the animals that exists today, none of them come in the wrong sizes, they are all just the right size, right shape, right proportion, just like the story of Goldilocks. Now what do I meant by that?
Suppose you have a gazelle (a deer-like animal native to Savannah), you increase the size of the gazelle by ten times but keeping the proportion of the body the same, what would happen? Immediately, the gazelle's bone will crack under the enormous weight of its body, but it doesn't happen when it is just as it is, that is - just the right size. On the contrary, if you shrink the gazelle down by the factor of ten, it won't be crushed by its weight (in fact the gazelle will feel itself so much more lighter), but again it will not survive for long, because its body is inefficient at functioning on an animal that can fit on your palm, it will need so much more food (I'm talking about in relation to the body, not the absolute amount. Of course, a mouse-sized gazelle eat less than a real gazelle), and its body will be incapable of producing enough energy.
This biological principle pertaining body sizes is really based on simply mathematics. Now let me show you, with a more relatable example. Humans are on average about 5-foot tall (we shall take the average at 5-foot for the sake of simplifying calculations). Let's say we try to increase our size by ten times in all dimensions, that is - height, width, and breadth; we will have a human being that is 50-foot tall, has the same body shape and proportion as a human who is at normal height. According to mathematics, although the human had only increased his height by ten times, he have about a thousand times increase in volume!
10 fold increase in height, width, and breadth = 10 * 10 * 10 = 1000 fold increase in volume!
Now let's make the assumption that the density of the human does not change when he "grows", we can deduce that a thousand times increase in the volume means a thousand times increase on his weight! The person now has to bear a weight 100 times more than he have to compared to when he is normal.
1000x increase in weight / 10x increase in size = 100x more weight to carry!
Let's not forget about our bones. Our bones of course, will have a thousand times increase in volume too, but only a hundred times increase in the cross-section area. Put that into equation and we have:
1000x increase in weight / 100x increase in bone cross-section area = 10x more pressure on bones!
Incidentally, our strongest bones (femur) breaks at this amount of pressure. So, can you imagine how much exoskeleton strength does a cockroach has to have if it were the size of a building? It is simply not economical.
Now, I will not present an argument for reduced efficiency when our size is reduced proportionally. Simply because 1) There are no maths for it as a far as I know, and 2) It is not known whether we can survive is we downsize all our dimensions by 10 times. However that does not mean biologists do not have a case for it. We can see all around us, most tiny animals have very simple systems that keep them alive, which leads to a hypothesis that simple systems are more efficient and easier to manage at small scale. The realm of mammals and complex organ systems ends as soon as it reaches the size of your thumb, anything smaller beyond that are simpler lifeforms. Therefore, I suspect that complex systems are being selective against in favor of simpler systems that function more efficiently in small-scale organisms.
Speaking of small animals, let's take a look at another organism. This time, the humble earthworm. Simple, straight-forward, the earthworm is basically just a mobile tube (or hollow cylinder, whichever you prefer). It has no brain, just some basic neuron that acts according to stimuli received; a straight gut, surrounded by a layer of muscle, no bones, no flashy displays, just essentials that keep it alive and moving.
The beauty about earthworms and other similar-sized organisms is - they do not require a specialized respiration and digestive system. Small creatures have large surface area compared to their volume, we say in biology they have large surface-area-to-volume ratio, therefore they can have enough oxygen just by simple diffusion through their skin, the oxygen intake will be sufficient and can be delivered to all body cells. Ditto to the digestive system, they have a low body volume, which means less cells to feed, that is why they only have a straight gut, not the winded and elaborated ones we and other larger animals have.
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| Nom nom nom |
But if you increase the size of the earthworm to, let's say, the size of an anaconda. Not only it will require to eat faster than this guy eats his hot dogs just to get enough fuel, it will suffocate because the oxygen just can't diffuse fast enough to reach all body cells to keep it alive. (Not to mention it will poo as much as it eats)
That is when your 8.5 meters intestine comes in. With more surface area to absorb nutrient, you do not have to eat that much just to extract enough energy to power your body. By the time the food reaches the exit of your gut system, it probably have very little nutrients left to be absorbed. (I have heard somewhere that your feces still have enough nutrients to nourish you for a few days, but let's just leave that thought right there.)
That being said though, it doesn't mean that being small is good because we need only to maintain systems with low upkeep, or being big is worse because of the complications that are more likely to occur on our body systems. But there is one thing that definitely gives an advantage to bigger animals and that is body temperature control.
Let us go back to the question on why aren't there any small animals in cold climates. The explanation given above is that bigger animals are better at keeping warmth in their body than smaller animals. True. But let's put it in mathematical terms and see why.
Returning to the principle of surface-area-to-volume ratio, I had mentioned that smaller animals have larger surface-area-to-volume ratio (let's call it SA/V ratio here onwards). It means, smaller animals have more surface area per volume of body, or to every unit of volume of the body, there are more surface area. That is not the case for bigger animals, though, they have a smaller SA/V ratio. In other words, the surface area of the
bigger animals are
smaller in relative to
smaller animals.
This brings a great advantage to the bigger animals in colder conditions. Because let me tell you this, almost all of the energy extracted from our food goes into producing body heat to keep our essential organs working, which means almost all the energy lost from our body is in the form of heat through the skin. Therefore, when each unit volume of the body is producing equal amount of heat, the animals with smaller SA/V ratio (big animals) are going to lose heat through the skin
slower compared to animals with larger SA/V ratio (which in this case is the small animals).
That is why, small animals tend to die rather easily in freezing weather, because their body loses heat faster than they can generate heat. To compensate for this disadvantage, smaller animals have to eat a lot. How much? Imagine this, a mouse has to eat about a quarter of its own weight daily. Convert this into the human scale, it's like us eating about 15-17kg of food per day! And all of that food goes into producing enough body heat to survive. So, economically speaking, it is better for smaller animals to migrate to warmer areas than to live searching for extra food each day in cold areas, a herculean task given the scarcity of food in colder regions. (Some smaller animals hibernate in winter, which uses less energy and therefore conserving the energy.)
So, is it better to be a smaller or a larger animal? There is no correct answer to that. We should all appreciate the fact that evolution is a very beautiful thing itself. And that all animal lineages that survived long enough passing the test of time, to this date, should be considered a success story in their own right.
With that I shall end my sloppily organized and rather incoherent attempt at writing a science article. I shall hope that you will leave this post with a little more understanding about the biological principles behind the body sizes. And your homework for today is, answer one of the unanswered questions above. Is Godzilla possible? If so, what kind of body systems must it develop to survive as an organism?
Till next time, cheers.