This blog has been in a coma for sometime, and I dont have any hope of writing anything new, in the near future. As I was listening to this podcast episode where Noam Chomsky was being interviewed about his work in linguistics, I was reminded about an article I had written a couple of years back for Science Reporter, a government run science magazine. It does not have a website where you can read the article online, but I have a scanned copy with me.
It is my longest article ever (and therefore the one with the maximum goof ups too, I guess), but given the drought on this blog, I thought I could inflict this upon you, just so you dont start raising your hopes of seeing the death of this blog. Not so soon, people, not so soon!
Having not much to do at work yesterday, and not having an internet connection, I started reading this paper on evolutionary psychology, that I had stored sometime back on my phone. It is an interesting and informative paper, which I intend to read again (I normally need 2-3 readings of a paper to really understand it), but there was one point in the paper where it stuck me that the authors were probably attacking a straw man. But first, we will see what is evolutionary psychology.
We are all products of evolution and have no problem in believing that our hands, eyes, ears were all sculpted by Natural Selection. So, when someone asks why we evolved eyes, we dont hesitate to say that we have eyes because it helps us find predators, so we can run away from them, find food to eat, find mates to mate and so on. But we hesitate to think that our behaviour too could be a result of evolution. Or at least, we dont attribute evolutionary purposes to our behaviour as readily as we assign such purpose to parts of our physical body. Evolutionary psychology addresses this gap. It studies our behaviour, psychology, by looking at what pressures in our ancient past would have driven us to the way we behave today. The problem today with evolutionary psychology, it appears, is that many scientists are putting forward theories that are not really testable, or at least not have been tested. Read this post from Jerry Coyne to get an idea of the issue.
Now coming back to that paper I referred to in the first sentence. It is a good paper that covers the issues in evolutionary psychology and explains them clearly, but the following question posed stood out for me.
Don’t people just solve problems using rationality? Wouldn’t one domain-general rationality mechanism be more parsimonious than postulating many domain-specific mechanisms?
In human readable English, the question means this. Dont people always use their brains and rationally think about the consequences when faced with a particular question in hand and then behave in a manner best for them? Or are there circuits in our brain that are specific to the situations we are in, which means we react immediately without any logical thought process? The authors point this out and give the following example to explain why domain general rationality does not seem to be how our brains behave.
Domain-general theories of rationality imply a deliberate calculation of ends and a sample space of means to achieve those ends. Performing the computations needed to sift through that sample space requires more time than is available for solving many adaptive problems, which must be solved in real time. Consider a man coming home from work early and discovering his wife in bed with another man. This circumstance typically leads to immediate jealousy, rage, violence, and sometimes murder (Buss, 2000; Daly & Wilson, 1988). Are men pausing to rationally deliberate over whether this act jeopardizes their paternity in future offspring and ultimate reproductive fitness, and then becoming enraged as a consequenceof this rational deliberation? The predictability and rapidity of men’s jealousy in response to cues of threats to paternity points to a specialized psychological circuit rather than a response caused by deliberative domain-general rational thought. Dedicated psychological adaptations, because they are activated in response to cues to their corresponding adaptive problems, operate more efficiently and effectively for many adaptive problems. A domain-general mechanism “must evaluate all alternatives it can define. Permutations being what they are, alternatives increase exponentially as the problem complexity increases” (Cosmides & Tooby, 1994, p. 94). Consequently, combinatorial explosion paralyzes a truly domain-general mechanism (Frankenhuis & Ploeger, 2007).
I have written an article earlier on the gene’s eye view for the New Indian Express on how it is because there is a genetic advantage in loving children that we ended up being so nice to our progeny and ended it with the following paragraph.
This does not mean that every time parents tend for children, they do calculations in their heads, or that they do it for selfish reasons without genuine love. It only means that evolution has come up with emotions like love and empathy as a mechanism for the genes to achieve their goals.
So I never thought that we were always doing a rational analysis of the situation before we react to something. Our brains definitely seem to be wired for some quick reactions (imagine your son who is about to fall down and hurt himself seriously. Would you calculate how much of your genes he has got before trying to save him?) We obviously have some context specific wirings in our head. So it is hard to see why anyone would believe in such patently wrong ideas. I, obviously, do not know the history of this field and there might have been people who have argued that way, but today it seems to be impossible that there could be people who support this theory.
Assuming some one does believe in domain general rationality (assuming the straw man is not just a straw man but a real person), the author’s point of there existing too many permutations for us (men) to evaluate and to react, when we see our spouse in bed with another man, though correct, is a round about way of countering the argument. An easier way to argue against domain general rationality is that if that were true, then this man who sees his bed in wife with another man though initially gets jealous and angry (because, if his wife becomes pregnant now, he cannot be sure if he is the father) must immediately calm down if he sees that this other man was wearing a condom (which means he couldnt have impregnated his wife). I am sure those supporters of the rationality theory will also agree that this scenario will never happen? So, what are they supporting then?
It has been more than 3 months since I wrote my last post. While I have never been a daily poster, this is way too much delay between posts even for me. The blame (you readers, might like to use the word “credit”) goes to my two children and insane work schedules at my workplace. Though I have not been writing much, I have not stopped thinking about it. And every time I see my children I am reminded of the wonders of the universe.
The last time it happened was when Aman was jumping standing on my tummy with me holding his hands for balance. It is almost impossible to believe that a year and a half ago, he did not even exist. A year ago, he was not more than the size of a peanut, he was not even a “he” then. But today, there they are, with all their body parts in perfect shape (more or less), the entire body working together well, growing up at an astounding pace, and slowly gaining intelligence. And that is what fills me with wonder. Let me explain.
I have talked multiple times about evolution, and how we all ended up here. Evolution by Natural Selection is fundamentally simple. Genes change randomly. And bodies change accordingly. The better suited bodies survive better, and naturally, the genes that made the better suited bodies survive too. That is the crux of evolution by natural selection. But that hides an awesomely complex phenomenon. When genes change, how do bodies change accordingly? Or, how do genes make bodies?
Darwin’s theory considers this to be a black box. It assumes that when genes change, bodies change too, which is true. But it does not talk about how that happens. It does not need to. But this area is called developmental biology. I have not read much on this, except for a single book “Endless Forms Most Beautiful” by Sean Carroll. But the feat achieved by the genes is impressive. From a single cell containing the DNA, it goes on to this 2 feet form jumping on my tummy.
Take for example the five fingers of one’s hand. Each of our fingers are different and cannot be substituted with one another. So, the body must know, that at one extreme there must be the thumb and at the other extreme there must be the little finger. And the rest of the fingers needs to be in order too. The extremes should not be mixed up either. Similarly, your hand must sprout from your shoulder and not from your hips. Every positioning has to be accurate with extremely narrow margins of error. Timing too has to be perfect. The cleft lip problem we see in children, is because of a timing issue in development. There must be a 4 dimensional map somehow, so that the body can be accurately built. How does it happen?
The entire development happens with the help of what are called switches, or from my programmer’s perspective, if-then clauses. Coming back to the example of the five fingers, there is a chemical, whose concentration varies along the entire breadth of the base of the hand (when the fingers are yet to be built). Where there is high concentration of that chemical, the genes start building a thumb, at slightly lower concentration, it builds a pointing finger, even less concentration, the middle finger, and so on till the little finger. This means, the genes that build the thumb, do their job, only if a certain amount of concentration of that chemical is achieved. If very high concentration, then thumb. If very low concentration, then little finger. It is this kind of logic that builds the entire body.
Let not this simple example of the hand, make you think, body building is a simple thing. For example, though concentration of a chemical explains the orientation of the fingers, what guarantees that this chemical does not appear near the knee or the elbow, or on the face? We will need to go one step back and then we will see, that this chemical is built by other genes, which are activated only at the base of the hands. That too is another switch.
If at the base of the hand, then release the chemical. ==> If chemical found, then build finger.
You can go one step back and ask how the body decides when a hand is built. And this questioning can continue backwards still you reach the egg. To be sure, these switches are almost never based on a single chemical. Typically they will depend on multiple circumstances. If-this-and-that-but-not-that-and-that,-then-do-this is the kind of logic we will get to see usually. These are influenced by external factors too, since what the mother eats and what she does, could lead to a change in chemical composition of the womb that could in turn affect development. That is why mothers are asked to have nutritious food and to avoid things like cigarettes, when pregnant.
The science of developmental biology is not as well known among the general public as other areas in biology, but it is interesting because it tells us how our astonishingly complex bodies that don’t miss a beat for 70-80 years, are built. I don’t have any illusions that I have explained much in that area in this post, but I hope to have evoked in you a sense of curiosity as to how indeed are bodies built from a single cell. In my next post, I will look at a different reason, this time at a cosmic level, why our very existence should be a source of wonder.
I occasionally buy the magazine Science Reporter, run by CSIR, a government funded research body. The quality of the articles is not usually great, but in the March 2012 issue, there is an article on evolution of sex which exposes a fundamental problem in thinking about Natural Selection. So let us have a look at what that is so that we understand Natural Selection better.
I have earlier mentioned that evolution by natural selection is best understood when looked at from the perspective of the gene. Talking about the genes as if they are conscious entities striving to maximise the number of copies of itself in the population is a good way to understand Natural Selection. Of course, genes are no more goal seeking entities than a table or a chair, but a gene that happens to contribute towards the individual’s well being, will leave more copies of itself (by leaving more children), and so by default such genes tend to survive well.
If the purpose of a gene is to make maximum copies of itself, then sex seems to be a disadvantage because from the gene’s perspective sexual reproduction means that it has only a 50% chance of having a copy of itself in the children. For example, a gene in your mother will only have a 50% chance of being in you. So is the case with every gene in your father. But in case of asexual reproduction, every gene in the parent will definitely be in the child (except for the occasional random mutation), since the child is just a clone of the parent. So genes in asexually reproducing organisms will leave twice the number of copies when compared to sexually reproducing organisms. This is referred to as the dual cost of sex. To compensate for this, sex must some how bestow benefits to a sexually reproducing gene that is at least twice that of an asexually reproducing organisms.
And it is this advantage that scientists are facing a tough time to understand. It is not for lack of attempts though. I don’t intend to lay out what scientists think on this. If you want to understand that you can refer to this absolutely fantastic book, by Matt Ridley, called The Red Queen. I cannot recommend it enough. It cost me somewhere between Rs. 250 and Rs.300. For such a price, the book is a treasure.
Now coming to the common understanding of natural selection. At one time, there was this idea of “Group Selection” that was popular among evolutionary biologists. The idea is that a gene that gives an advantage to the group of individuals to which it belongs, will tend to survive more. For example, consider a gene that makes the individual ready to sacrifice one’s life to save the clan he/she belongs to. It is definitely an advantage to the clan, because such dedicated soldiers will do much better in protecting the clan than those who are worried about their own lives. Thus, it was supposed, a gene that works for the betterment of the group will leave more copies (after all the clan is protected).
This argument, that something that is good for the group will spread, in spite of the disadvantage to the individuals, was widely touted and believed. The problem with such an argument is simple. Imagine a group that has individuals ready to put down their lives for the group’s sake. And suppose, that in this group a child is born who is more bothered about his own life than about the clan’s. Such individuals will stay away from any clan fights and thus have very little chances of dying without reproducing. So the genes of such individuals begin to spread. Thus the group will slowly start to have more and more individuals, who are selfish. Thus the gene for sacrifice will stop spreading.
One might say that, this is the case even within a single individual. After all, an individual too is a collection of genes, and since the gene’s eye view is the best perspective on natural selection, the genes too can be selfish and need not be bothered about the individual. But the difference between the group and the individual is the idea of a reproductive bottleneck. For a gene in an individual, the only way for it to make copies is to make more copies of the individual, since that is the only way they can leave offspring. Thus, all the genes within an individual will cooperate for the benefit of the individual. But in case of a group, all the individuals within the group do not reproduce in one go, or through one such common pathway. Each one can reproduce on its own. This lack of a reproductive bottleneck leaves Group Selection without a mechanism to work. That is the reason why it is not considered to be true.
There are exceptions to this which beautifully illustrate the point being made. Imagine a group of bees. As is common knowledge, bees usually have one queen that does all the reproducing. The rest of the worker bees are sterile in that they cannot reproduce. Thus if the genes in the sterile workers have to leave copies, the only way to do that would be to help the queen to reproduce (since the workers share genes with the queen, who is after all their mother). In this case, the queen acts as the reproductive bottleneck and thus in bees, you find individuals who are ready to put down their lives for the group.
Thus the existence of a trait cannot be explained by listing out the advantages it gives to the population. The only way to explain a trait is to explain the benefit to the individual and thereby to the gene. Now I come to the article that I referred to in the beginning. The author talks about how the sex is an advantage because it protects us from parasites and thus prevents the species from going extinct. If I have done my job well, so far, you will spot the problem right away. The genes are not worried about the species going extinct. It is only bothered about itself, and about the individual (to the extent that the individual benefits the gene, which in most cases is quite a bit). And that is what is wrong with the article.
So I wrote a letter to the editor pointing this out. I am reproducing it here.
This is regarding the article titled “Evolution of Sex” in the March 2012 issue of Science Reporter. In this the article talks about how sex evolved and why it is advantageous, but there is a fundamental problem in the author’s approach to this question of sex.
It has long been recognised by most evolutionary biologists, except for a few on the fringe, that group selection does not work and there is no evidence for it happening. But the idea was popular at one time. And that has left a hangover. This hangover is visible in this article too. The last paragraph of the article says:
“Why did sex evolve? From the evolutionary point of view sex is definitely an inefficient way to reproduce, but it acts as a safeguard against extinction”
That traits are selected to prevent species from going extinct is a group selectionist argument. This assumes that natural selection works to help species or groups survive. This is not true. Natural selection works only for the benefit of the gene. All the genes in an individual have to reproduce via the individual, who acts as a genetic bottleneck, and thus in most cases what is good for the individual is also good for the gene. There are exceptions for that too. But no gene is selected for the survival of the groups (except in cases like eusocial insects, where there is a genetic bottleneck like the queen). Thus the idea that something is good because it prevents extinction of the species, is flawed.
Earlier in the article too, one can see this sentence.
“If all organisms continue to reproduce asexually, the genetic variations of its species as a whole will slowly grind to a halt and it becomes likely that a parasite that can kill one member of the species can wreak havoc on the entire population, which will not be able to get rid of the harmful effects of mutation”.
Here too, the author talks about parasites being the bane of the species. That parasites are considered an important cause for the evolution of sex is true, but that is not because it will “wreak havoc on the entire population” but because without sex, it puts the individual at a disadvantage when facing parasites. The difference, though seemingly subtle, is key to a correct understanding of evolution by natural selection.
The author of the science reporter article is a “Retired reader and Head, Department of Zoology, Madurai College, Madurai. He has a teaching experience of 35 years”. What surprises me is how somebody who has so much experience misses this very important point.
PS: For a recent kerfuffle on this topic, you can refer to this post by Jerry Coyne. The name of this post is inspired from the name of his website (he does not like people calling it a blog).
I remember Richard Dawkins saying “Your own existence is the most astonishing fact you will ever have to face. Don’t ever get used to it”. By asking us not to get used to it, he is exhorting us understand how great the fortune of existence that has been bestowed upon us is and to make the fullest of it. I was reminded of this quote, a few days back, while commuting to office on train reading “Just Six Numbers”, by Martin Rees. The book talks about how there are 6 basic numerical values that determine the fate of the universe. In one of the chapters he explains how early stars cook basic atoms like Hydrogen and Helium into atoms higher up the periodic table. As I was reading this I saw three people seated next to me discussing ideas to win a photography contest in their company. The discussion itself was not very interesting, but since I was reading about how the atoms that make us were themselves made, I suddenly realised how astounding it is that 7,000,000,000,000,000,000,000,000,000 atoms came together temporarily* to form a group, called Martin Rees, learnt enough to write a book, which is read by another group of about the same humongous number of atoms (7 followed by 27 zeroes), which, called Madhav by other similar groups in the universe, understands it, and not only sees 3 more similar groups of atoms discussing something as abstract as ideas for a photography contest, but also understands to a reasonable extent how those and other similar groups of atoms came about starting right from their origin dating back to about 13,750,000,000 years ago till date. I want to say I was moved, but am holding back because it would have been a ridiculous understatement.
Even though evolution by natural selection is a simple idea, there are some beautiful things it explains which otherwise would have left us baffled. In today’s post I would like to discuss one such fac(e)t of evolution. That is, the short-sightedness of evolution and the consequent imperfect designs of the bodies of individuals. We will also see how this feature of evolution explains a fascinating and famous fact.
The fact first. There is a nerve called the recurrent laryngeal nerve which runs from our brain to our voice box and is present in all mammals. The word recurrent means it branches off from another main nerve. This nerve connects our brain and our voice box (larynx). The curious thing about this nerve is that, in order to go from the brain to our larynx (in out throat), it goes down to our heart (past our voice box) takes a u-turn and then comes back up to enter our voice box in our throat. It is as though it was following a long detour to avoid a one-way road in Chennai. Why should it go down and then come up? Why cant it go directly from the brain to the voice box?
To understand why those questions are important and to realise how bad the design is, we must look at Giraffes. In the giraffe, with its very long neck, the voice box is in the top of the neck, and its heart in its body below the neck. Imagine the nerve that needs to go from brain to its voice box, at the top if its neck, going all the way down the neck to the heart and then coming back up. In Giraffes, the detour by this nerve is as much as 15 feet. That is more than two and half times the height of an average adult human. What a waste of raw material that went into making the nerve, and the energy needed to keep it running? If you don’t trust me, you can see the real nerve, in this dissection of a Giraffe’s neck, done in a classroom. (The video is not for those who are averse to dissections, and hence avoided Biology in their 12th standard)
I intend to explain this fact using an analogy. All of you would have played the game of Tetris. In it, blocks, each consisting of 4 squares, but arranged in 7 different ways (called tetrominoes), keep falling from top, with which we have to keep completing lines at the bottom. The goal of the game is to arrange the blocks in such a way that no gaps exist. The key constraints of the game are that, you cannot undo what you have done, and you do not know what will come next. You have to play the game with what is on hand.
Naturally, you would do a much better job were you given all the blocks upfront, instead of one by one, and are also allowed to go back and change any of your moves, or even start from scratch if you feel you have gone wrong. With the usual Tetris, you would see that many decisions look stupid in hindsight, but since you cant predict what is coming (the blocks are falling randomly), and neither can you undo what you have done already, that is the best you could have done in that situation.
Something similar happened with the recurrent laryngeal nerve. All we mammals evolved from fishes. In fishes this nerve branch went from the brain to one part of their gills directly. There was one artery, a tube that carries blood from one’s heart to other parts of the body, which was then out of the pathway of this nerve. Thus the nerve went directly from the brain to the gills. But with evolution, this artery, that was initially out of the way, slowly started coming in between the brain and the connecting part of the gill. And it was this part of the gill that later becomes the larynx. So this artery started pushing the nerve slowly, away from the shortest path from the brain to the gill (later larynx). Like a marathon winner running through the winning ribbon, the artery started going through the path between the brain and the voice box, thus stretching the connecting nerve into a sort of a horizontal “U”. That explains, to a certain extent, why the nerve takes that detour.
But what do I mean, when I say that the artery pushes the nerve away from its shortest path. Does it push some extent daily, or say, hourly? No. In evolution, when we say something happened, it means it happened across many generations. That is, if the present generation has the nerve extended a bit, its children, or grand children, or somewhere down the line, it gets pushed further. And some more, even more further down the line. That is how the “pushing” happens.
Though it is somewhat easy to see, how the stretching happens, what is the analogy with the Tetris game? More specifically, seeing what are the constraints on evolution that are similar to the two constraints in the game explains why the stretching happened.
The first constraint is obvious. One would never know what the next mutation is going to be. Nor can one know how the environment is going to change tomorrow. This is the counterpart of the constraint in Tetris, where you cannot predict what block is going to come down next. This feature of not being able to see into the future, is one constraint faced by evolution.**
The other constraint in Tetris is that you cannot undo what has been done. Understanding this in evolution needs a bit of explanation. In every generation from fishes to mammals, the neck might have stretched only very very gradually, and in most cases not at all. But the way evolution proceeds is by natural selection. A change will survive if it is not detrimental to the body. The very small stretching of this nerve, would not have given any great disadvantage to the individual when compared to its peers. When comparing fishes and mammals you see that the detour of the nerve is a waste of resources. But when seen from parent to child, it would not have caused a huge disadvantage (it wouldn’t have been even noticeable). So it was not “selected out” of the species. You could argue, that a mutation could have come up where the nerve did not pass around the artery, but went straight from brain to heart, which could have been selected “for”. But the point is that, that would have been too huge a change to have come about with one mutation. And any mutation that attempted it would have been detrimental to the individual involved. Thus individuals whose nerve stretched a little bit was preferred over individuals whose nerve “attempted” to take a short cut.
The problem is that to move from the point where the nerve is stretched with a detour, to the point where the short cut is used, a lot of intermediate generations were needed. But, for these intermediate generations, the change would have been dangerous. To see that, let us assume, that this change to use the short cut needs two steps. One is a nerve cut off, and the other is a reconnection using the short cut. But the first generation that has its nerve cut off, will have lesser probability to survive (or at least not be able to survive long enough to reproduce), because its voice box will not function. Thus the second change cannot arise. Of course, my two-step assumption is very simplistic, as the actual change will need lot more steps, but it serves the purpose of realising why achieving this short cut, is tough. Thus evolution continued to work by just stretching the nerve on its detour and that is how the “no undo” constraint plays out**. The key is that evolution always has to work starting from where the earlier generation left off. It cant create something radically new overnight. It has to work on what was given to it by the earlier generation.
Here is a video that explains this. I don’t know who it is in the video, though.
And thus it is, that we have ended up with less than perfect design. There are many more examples of this in our body. Another of those “flaws” is the blind spot in each of our eyes. We will discuss that some other time.
* – This fascinating fact becomes even more fascinating, when we learn that the atoms that we are made of as a baby are not the same atoms that stay with us throughout our life. Our body is made of different sets of atoms at different points of time. Atoms keep entering our body, replacing other atoms that move out. It is somewhat surprising to think, that even though the same material is not used to make our body throughout our life, we still retain all the memories, functions, diseases etc. The analogy can be made to a Company that when started off would have had different employees, but employees keep moving out and coming in, keeping the Company as a unit. Something similar happens in our body.
** – Undoing is very tough, though not always impossible. Life originated in the seas, and then some species moved to land. But later, some of them went back to the sea, and again came back to the land. So undoing happens, but it is tough.
There is one idea in science, that is unquestionably the simplest but at the same time, explains so many things that we see around daily, that it forms the backbone of an entire field of science: Biology. That idea is evolution.
Everybody has heard of evolution, and would readily say that it means we came from monkeys. But I have a suspicion, that not everybody understands it well. That suspicion, comes from the fact that, I did not understand it, till a few years back. You might say, “neither do I understand E=mc2, even though I have heard about it. So why does it matter knowing evolution?”. But what is different about evolution by natural selection is that, this is an idea, which, once you learn it, will make you feel, “Oh! I could have thought of that myself”. The basic premise is so extraordinarily simple and straightforward. I bet you cant say that about E=mc2.
Evolution by Natural Selection can be explained in 3 points.
1. Features are inherited from parents to offspring while reproduction.
2. Some of these features might vary a little, due to random changes, called mutations, while copying DNA from parent to child. The DNA is the information passed on from parent to child which contains the genetic instructions for building an individual from a single cell.
3. The changes in features (as a result of change in DNA due to mutations) might be beneficial or detrimental to the ability of the individual to survive and reproduce. Individuals whose DNA has changed “positively”, will lead to that individual surviving better in its environment than the others whose DNA has not changed or whose DNA has changed for the worse. Since it is these changed individuals who will survive better, and will have more children, their DNA (inherited from the parents along with the beneficial change) will start spreading through the population.
A hypothetical example: If the previous points sounded a bit vague, imagine a species of deer in a forest. One of the most important things it has to do is to run away from predators, like Cheetah, as quickly as possible, lest it becomes their food. Now the speed and the stamina that the deer possesses while running, is crucial to ensure that it outruns that its predator and survive. Imagine 10 sibling deers out of which there are 2 deers A and B who have undergone changes in DNA while it was being copied from its parents. The rest have exactly the same running genes as its parents, and they run more or less at the same speed of their parents. But A’s DNA underwent a random change (or mutation) (possibly due to errors while copying the DNA from parent to child similar to the way we make mistakes while copying a page of text to another page). Also assume that this change in DNA plays a crucial role in running and helps A to run faster than its parents. Similarly, assume B’s DNA too underwent a random change, but its change was for the worse. That is, its change has led to its running slower than its parents.
In such a scenario it is obvious that when a Cheetah notices these siblings playing together and starts chasing them, there is a very high chance that it is B, that will die first. A and the rest being faster than B (since A has had a positive change, and the rest did NOT have the negative change that B had in its DNA) will survive. In a similar way, after B’s death, A will have a higher chance of survival among the remaining 9. Hence, A has the maximum chance to live to become an adult and reproduce. And while A reproduces, it will pass on its modified faster running gene to all its children. If this change in DNA is crucial and significant enough, then after many generations, all the members of this species in this forest will have the faster running gene, simply because of the fact that anybody who does not have it, will be the first one to fall prey to the Cheetah.
This example captures the essence of Evolution by Natural Selection. Evolution tells us that all the species that exist today have branched off from one single instance of life that was created about 3,500,000,000 (3.5 billion) years ago (as per today’s evidence). Natural selection is the process where nature selects which genes survive. In our example the individual with the faster running gene will survive, since nature, in the form of a Cheetah, decides which of the different varieties of genes live. It is the survival of the genes that is crucial since even though the individual will eventually die, its genes will continue to exist since its children will now have the same genes.
In the above example, the Cheetahs too will possibly undergo evolution since they too need to run faster to capture food. Otherwise they will die of starvation. But let the example not make you think that the expression “Survival of the fittest” is only about running, fighting and other such macho features. Fitness includes everything that enables the individual to survive and pass on its genes. Let us look at a real life example where evolution by natural selection has been observed directly.
A real life example of selection: The peppered moth, is a very common example given to demonstrate how selection works. It is a light coloured moth with black spots. In England, there used to be many such white moths which survived well, since they lived on trees covered with Lichens (a composite of fungus and algae), and hence were very well camouflaged. This prevented the predators from finding the moths. Look at the pictures of a white peppered moth and the Lichens below, to see how easy it would have been for the moths to hide from the predators on Lichen covered trees. But when Industrial revolution happened, the Lichens were killed due to the soot that came from the industries and the trees too were covered by the black soot. This meant that the white moths could not camouflage themselves and were easily found and eaten by their predators. Now because of the soot, black moths began to survive well, since they were camouflaged well against the black trees, and soon the area was full of black moths. The black moths were previously at a disadvantage since predators can find them easily. At that time nature (the predators) chose black peppered moths for consumption, but now it was the turn of the white peppered moths. This is a clear example of how selection works. A curious thing about this episode is that the story did not end there. After environmental regulations came in, white moths have again flourished.
Speciation: You might still say, “This might explain how white moths evolve into black moths, but they are all still moths, right? How can this explain the enormous variety of life that we see around. It is easy to see how features within a species might change like a cheetah or a deer running faster than its peers. But How do a cheetah and deer come about? How do different species come about?”. Speciation (how species come about) is an important field of Biology. But we can easily see how the previous examples can be extended to see how species evolve. And for that let us consider a few members of a species, say rats, that has been introduced into a new island where no rats existed before. Being a new island, the conditions might be drastically different from where they lived previously. Let us say that one of the changes in conditions is that it is very cold. Thus if one of the children of the pioneering rats, has slightly more fur than the rest, then it might survive better, and have more children thus producing more rats with fur. The ones without fur will have lesser chance of surviving. Thus, over many generations rats might evolve fur. Another change in condition could be that there could be lesser predators here, which could mean that they would rather spend their energy on other things like finding food and reproducing, rather than running around avoiding being food themselves. Thus rats that will have lesser speed will survive better, since for them the effort spent of running could be spent on something else more useful for their new environment. Another change in condition could be that the island could be full of water-bodies, and hence some rats which can survive a bit longer in water, might have a better chance of catching a fish for food. Thus slowly, over generations, the rats that survive longer in water might have better chances of surviving. To move around in water, they might start evolving fin like things. And so on. Thus a rat with fur, of a bigger size, with fins and that can survive in water will become completely different from the rats that were introduced first into the island. Thus a new species is created. This is just an example, that I came up with, for understanding how species could evolve.
Gradual change: Note that in the example above, one single rat does not grow fur or start swimming in its own lifetime. The change happens over generations. Change is for the species not for the individual. Moreover, an ordinary rat does not give birth to a new species of rat. At every stage of reproduction, the children vary only very slightly from the parent. It is only if you look at the starting and ending products, that you will see the drastic change. Evolution of every species is also the same. A monkey like ancestor does not give birth to a human being overnight. No individual of a species gives birth to an individual of another species. Features change very slowly, gradually. So gradually, that at no stage can you say that the offspring is different from the parent.
If this sounds weird, imagine that since your birth, your doting parents had taken photographs of you every day and arranged them chronologically in a flip book (like the flip books I used to see when in school, where you can see a batsman playing cover drive. Here is an example.) you can see yourself growing up in front of your eyes.
If you compare each page of the your life’s flip book with the previous one, you will never be able to say that on this particular day you have changed a lot from the previous day. Every day’s photo seems to the same as the previous day’s. But over a 60-70 year period, the amount of change that can accrue is unbelievable. There is no clear delineation from a child to an adult to an old person. What we know is that at 5 years one is a child, at 30, definitely an adult, and at 70, an old person. But when exactly does one become an adult from a child, is tough to say.
In the same way, it is tough to say when the monkey like ancestor become a human being, or to answer who was the first human being (can you tell me the first day when you were an adult?) or the first chimpanzee, the first dinosaur or any species for that matter. But there is one example which clearly explains the impossibility of drawing boundaries between species.
Thus we are, through a continuous unbroken series of lineage, connected to the first life form that existed about 3.5 billion years ago. And each individual living today (including the whales, the lizards, the plants, the bacteria, the fungi, the peppered moth, the lichens) you can trace your relationship, in exactly the same way as you can trace it for your close human cousins. We are all cousins, (with varying degrees of removal) literally. Take any two individuals, and they would have had a common ancestor some time back (you and your brother’s common ancestors are your parents, you and your first cousin’s are your grand parents and so on).
Given two species, this website, TimeTree, can tell you when the common ancestor between the two species lived (Mya stands for Million years ago, which is the unit used in the website). You can spend quite a bit of your time, finding common ancestors.
This idea was that of Charles Robert Darwin and Alfred Russell Wallace, who came to these conclusions independently. Isn’t it wonderful to know that the mosquito you just killed is your cousin, and so is the okra that you just cut for your lunch (as I once told my mom)? And all this knowledge from
the simple idea that those that are better at surviving, survive. Neat, isn’t it??