An Increased Oxygen Concentration Level Causes Insects To Grow In Size

I was watching the 9th episode for the new Cosmos: A Space Odyssey series when the Astronomer/Physicist Neil Degrasse Tyson explained a principle on why insects that was alive on Earth 300 Million years ago (called the Carboniferous Period) could be able to grow to incredible sizes.

The way I understood his idea was that insects are basically animals, in the animal kingdom. That means that they will need like all animals Oxygen to be able to get to all of their tissue. Flora Organisms, aka within the Plant Kingdom, need the other type Carbon Dioxide.

It turns out that insects don’t have lungs. The insects that were living back then was able to bring the O2 into their bodies through outside their bodies by some type of opening (I suspect that he means like any orifice, like a mouth) by transporting the oxygen through a network of tubes.

If the insect was too large, the outer reaches of the tubes, closest to the orifice’s opening adjacent to the opening to the outside of the body, would be absorb all that oxygen before the oxygen reaches the internal organs. Imagine your skin getting all the O2 but the O2 never reaches your heart. However, the carboniferous period’s atmosphere supposedly had twice the level of oxygen as current day.

This means that insects could grow much bigger and still get enough oxygen in their bodies. The result is that the dragonflies would grow to the size of eagles and the millipedes can grow to the size of alligators.

So I started to think about the consequences of what would happen to the evolution of humans if the atmosphere of Earth increased in O2 levels.

Would an increased oxygen concentration level in the earth’s atmosphere cause mammals, specifically humans to get larger in size over time too?

I have before asked the theoretical question and did some calculations to guess whether there is a limit to how large humans can get. What we could come up with were three main constraints which would limit the size of humans.

• The natural material strength of articular cartilage, the collagen in joints, and fluids like those found in the synovial joint of the knees and the nucleus pulposus. – Too much mass on top of the body would crush the tissue below it, like the IVDs would be crushed. (Remember that humans is one of the few animals which walk completely upright. Most mammals have 4 legs, not two arms and two legs. That means their entire body weight is equally distributed into quarters. We put so much emphasize on our heights because we walk on two legs and are upright aka erect! If we had 4 legs on the ground, we would not care about height, but length instead, like how one measures a fish.)
• The surface area over volume/mass ratio of a the person would decrease to a point where the mass could burst out of the person. (Remember that as a person increases vertically, their weight/mass increases at a cubic rate (^3) while the surface area increases at a squared rate (^2). This is why a person 5 feet tall can weight 100 lbs, 6 feet at 200 lbs, and at 7 feet tall at 400 lbs. With every feet we go up, our weight goes up at a faster rate than our skin (and maybe also skeletal structure) can handle)
• The corollary to the 2nd point is that the heat transfer limitations of a thick enough skin to hold all that volume/mass in the body means that the body would hold all the heat inside. The result is the internal organs turned into liquid from being heated to an insane level.

This new point that DeGrasse Tyson makes shows that we forgot at least one more critical point, which is that as a person’s body increases, the amount of length of blood vessels the blood would have to be pumped through increases dramatically. It may not seem like a lot of distance to cover but it was said that all the blood vessels in one person lined together on a straight line is supposed to reach from one coast of North America to the other coast.

I remember watching a documentary where it was revealed that current Indiana Pacer’s Center Roy Hibbert, standing at 7′ 2″ has a heart size that is twice as big as the average human. Obviously his heart has to do a much higher level of output of blood pumping to get the nutrients in the blood to all the places in his body. There is only so far a biological instrument like the heart can grow up to before the 4 chamber system can not contract and relax fast enough to pump the necessary flow of blood around the entire body.

(On a side note, primatologist have confirmed the existence of a distance relative the gigantopithecus, which is believed to be up to 10 feet tall. Assuming that the legends of the Bigfoot and Yeti is not true, but fabrications of the human mind, we still have one scientific claim that shows that theoretically, humans can reach the 10 feet mark in height.)

However, it may not just be the heart/blood/nutrient transport problem, which the increase in O2 would fix. It might also be a neuro-chemical problem, where the nerve fiber bundles are so long that the electrical signals from the dentrite-axon-threshhold electrical mechanism to just not work well enough and never reach the brain.

Remember again how Robert Wadlow died. His lower legs supposedly did not have the nerve endings working properly. I am guessing that the incredible length of his legs mean that the distance for the electrical signals from pain or stimuli to reach his brain became a constraint. When his lower leg got a small scratch, he did not feel the scratch. The result is that an infection started without him feeling anything, until he noticed it and by then it was too late.

Of course, Wadlow’s case suggest that there could be a 5th limitation placed on the human body, which is that once you get too tall/large, the nerve responses decrease since there is a much longer distance for the electrical signals to travel to reach the brain.

However, I am going to make a guess that it might be reasonable to suspect that if we increased the level of O2 in the atmosphere, the overall human race over time would increase in height at a higher rate than what is expected of it with average levels of O2. It is already guessed by some futuristic thinkers that the human race would increase in height over time anyway on average as the ability to have access to good nutrients would improve over the coming centuries. I am just saying that a O2 increase might make our whole race just slightly bigger.

At least with the increased O2 levels, the 4th major limitation would be remove which would prevent the human mammal from getting bigger.

(Something I didn’t even consider is that like insects with their exoskeletons, humans have more than just two orifices to take in oxygen. We know about our mouth and nose, which sucks in the air, which is around 20-21% O2. However, most people don’t realize that we also breathe through our skin, at around 1% of our total intake. If O2 is increased, there should be a slight increase in the rate of cellular chemical activity at least in the epidermal cells close to the outside of the body. This could stimulate an increase in proliferation of cell mitosis, specifcally chondrocytes when the organism is still growing.)

Of course, as mammals, we are warm blooded animals. Maybe O2 increased would cause biochemical reactions in our bodies which make the internal temperature increased. We would obviously need more food caloric intake to sustain a homeostatic state of temperature balance. It could have the opposite effect, and decrease the rate of human evolutionary growth if the body just became too hot internally.