Diurnal Cycles

We sleep everyday. Its is our body’s way to rejuvenating itself so we can face the next day. The fascinating fact about this is that almost all living things on the earth exhibits this phenomenon. It is this mere fact that has prompted me to write this blog.

So why do living things sleep?

The simple answer: rejuvenation. But if you think of rejuvenation in terms of biology it is enormously complex. You should rather focus on why is sleep such a common phenomenon.

If you think evolutionary science then you’d use natural selection as your first method of arguing and then come to a road block. Because sleep is a maladjusted trait. There is no immediate survival significance to it. It is not like the fight/flight response which most living things have which tries to keep them alive in situations of stress. Sleep, with this analogy, accomplishes the exact opposite. Imagine being hunted while your body aches to find some rest.

So the nearest answer that comes to me now is photosynthesis.

Sounds Weird?!

We get most of our energy from consumption of food. But the cells in our body derive the energy from carbohydrates and proteins, which comes as a result of the intake of food. Food is broken down into such simpler substances that our body cells can consume.

So why photosynthesis?

It is not photosynthesis per se, but the phenomenon is an integral part of understanding the riddle. Plants derive their energy by a process called photosynthesis. But plants only happened later on. You’ve all studied photosynthesis while studying about plants probably; and you probably associate it that way too. But photosynthesis was one of the ways those primitive life forms actually lived. It is simply the conversion of the energy of sunlight to simple sugars like carbohydrates.

In plants, such cells consume these carbohydrates for energy at a later time. It is just that during sunlight specific cells on the plants are involved in the creation of carbohydrates. The cells consume these carbohydrates to do various functions (repair, reproduce, etc). Well when the sun’s not out there and these cells go out on doing what they do, there would be no carbohydrates to provide energy for other cells to carry out cellular functions. This could result in an whole imbalance to the living system – death.
So ultimately what do the cells do? They simply lower their activity. In terms of natural selection, one can argue it is this trait of cellular behavior which enabled the plants to survive.

But why do those cells lower in activity during night time?

Simple. Perhaps there is another more precise theoretical explanation, but, in simple words, it is simply how their ancestors would have survived!

But I am not meaning to say that we evolved from cells that make the tree/flower in your garden. Sunlight was an ever prevailing source of energy; it is also one of the most ancient. For any organism – be it cellular or more complex – finding food/hunting during the hours of the sunlight, was much easier. Energy wise, it was more efficient to look for food during sunlight, rather than during the night.

But you must understand these were how some of the prehistoric and ancient of living organisms on earth survived. The rest of the story is all about how evolution and natural selection made it all the way.

Update (14th Sep 2013): Photosynthesis could be a wrong idea all together to explain why we all sleep. Because I recently read about the Ediacaran and Cambrian biota. Most of the insects have their genealogical trails way back to the Cambrian era. Most animals which lived during that time were sea creatures; they lived close to the sea bed. This rules out sunlight being a prevalent source of energy for them. At least I think that is so...so there must be another explanation...

Variation in the species

Frankly there isn’t nothing much to type here. Pretty much everything was mentioned in the last post which highlights the fact that sexual reproduction is a very inefficient form of reproduction.

But then this begs the question: why does it exist even now?

I had linked to the article which was my original inspiration. There are actually four theories which explain the phenomenon. What most caught me was the Lottery Principle. In essence it says variation in a specie of cells is good. Usually the cells have to protect themselves from invading colonies of viruses or bacteria. If all the cells had the same makeup their defense strategies would most probably be the same. And if this is something that the invading colony can conquer then what mostly happens here is the extinction of the whole species. But with variation some individuals are equipped more “gifts” to better obviate the attack.

There are two things that can happen here. Either the fit individual is able to ward off the attack and destroy the individuals of the invading colony; thereby allowing the weaker individuals to survive. Or the fit individuals flee the scene leaving the weaker ones as bait. Whatever be the case, from the invading colony perspective, it simply means that one tactic alone is not enough to attack and obliterate the other species. This results in the other species having a chance to survive.

So that is the gist of a cell’s reproductive life.

But what has happened over the years because of this variation?

You ended up being different from your siblings, parents, friends at school, work, or, play, etc. So obviously no one is born equal. Everyone has their own gifts and curses within them. But lets not interpret this universal fact politically and fight with everyone.

The history of life on earth is replete with irony

How many wars have we fought just because one race of people are different from the other? How many of these wars were fought completely ignorant of this universal fact of life: we are all simply different. There has undoubtedly been instances where individuals of the same specie (not just in the human species) fought with each other because they were “different”. There has been instances where a group of individuals fought with another group of individuals because they were “different”.

The amazing fact in all of this “difference” is that, at a time when the whole specie was in threat (due to attack, or natural calamity, etc) all differences simply vanish. Sometimes even the warring individuals have to unite, setting aside their differences, to save their own species from being extinct.

I do realize that this “uniting” or “coming together” is a prehistoric phenomenon; a very very old one. But it is also something that symbolises life of earth.