“Species change”
These two words have influenced human culture, knowledge and understanding more than all the religious scriptures combined. These two words have often been described as “the best idea anyone ever had”. So what does this really mean? A dog gives birth to a pup, a cat gives birth to a kitten. We don’t see a lion giving birth to a wolf. If every animal gives birth to its own species, then what does it mean to say that Species Change?
A hundred and fifty years ago, a young English Naturalist was aboard the ship HMS Beagle, surveying the coast of South America, collecting and studying the plants and animals that he found along the way. He also discovered a lot of fossils on the journey, and he collected them, not knowing which animal they belonged to. He noticed that the fossils resembled some of the animals that lived in South America, but they were also very different. For example, he knew there were sloths living in South America, but he found fossils of a giant sloth many times bigger than those that were alive. Many such fossils led him to conclude that these animals were clearly extinct, but they were somehow connected to the ones that were still alive today. He wondered if the fossils belonged to the ancestors of the animals that live today.
On this journey, he encountered a cluster of 13 islands called the Galapagos islands, just off the South American coast. He noticed many animals on those islands, but mainly, giant tortoises and a type of small birds called finches. At first, it seemed completely normal, until our Naturalist found something very odd. He saw that the natives living in those islands can look at a bird or a tortoise, and figure out which island it came from, out of the 13. He saw that even though they were all finches and tortoises, they were all slightly different depending upon which island they came from. The tortoises from each island differed in their shell shape or color or size and so on. For example, on one island, all the tortoises had dome shaped shells. On another island, the tortoises had shells that curved upwards above their neck.
And on one island, the finches had short wide beaks, while on another island, the finches had long slender beaks.
He wondered why these changes were so, but he could not figure it out then. He knew one thing for certain: this was not random. Something was very clearly making it such that each island had a particular variety of the animal.
Upon arriving back to England, the naturalist set to organise his collected animals, and figure out a pattern. That is when he notices a very important clue from a very unexpected place: his home. He notices the obvious fact that none of his children look similar to any other, even though they share the same parents. This makes him wonder: the different types of animals in the islands, are they also different looking children of common ancestors? If so, what has made one type prominent on one island?
He looks back at his notes from the island and there it was, the answer. He sees that the clue has been in plain sight. He notices that on the island where the finches had short, hard beaks, the primary food source were seeds and nuts. And in the island where the birds had long slender beaks, the primary food source was nectar from flowers. And he formulates a theory. He has the best idea ever.
This naturalist was Charles Darwin. This discovery led him on a path that would solve so many mysteries and revolutionize human understanding of what life is.
This was what Darwin figured out:
Variations occur naturally in individuals.
Every animal is capable of producing more offspring than the environment can sustain. Therefore there is always a struggle for survival
Only the individuals with the variation that is best fit for survival in a particular environment, survive in that environment, out of the large number of individuals.
The unfit variations die.
Therefore after one generation, the surviving individuals all have, to some degree, the variation fit for survival.
When these individuals reproduce, these characteristics are passed down to the offspring.
Again, in the next generation, there are more individuals than the environment can sustain. So again there is a struggle for survival. Where in the last generation only the best survived, now only the best of the best survive, because almost all of the population has the characteristics of the best individuals from the last generation.
So now, a population that is even more well suited for that environment survives at the end of the second generation.
This cycle, when repeated for thousands of generations, results in an almost new species that is best suited for survival in that environment.
In short, variations accumulated for long enough, cause species to change.
Let’s explore this with the example of the finches.
Let us take a sample set of 100 finches. Just like each child is different, even though they come from the same parents, each individual finch will be different. So some finches will have short beaks, some will have longer beaks, some will have sizes in between. Let’s release these finches into an island where the only food source is nectar from flowers.
The birds that have long slender beaks will find it very easy to acquire nectar from flowers. They will grow in size, and they will feed more and frequently. Since they have enough and abundant nutrition, they will reproduce often and healthily.
On the other hand, the birds with short beaks will find it difficult to eat nectar from flowers. They don’t feed often, and so lack nutrition. They are weak, and reproduce rarely or not at all. In the extreme case, they die.
After one generation, The long beaked finches have reproduced often with healthy offspring, where the short beaked birds have not reproduced much, and even if they did, the offspring are undernourished and weak. Even though all children are different, the offspring of long beaked birds have a higher probability of being born with long beaks themselves, also an obvious observation we can make from human children. Children are different, but they have characteristics of their parents. This results in a considerably higher number of long beaked birds in the second generation.
This cycle, repeated over hundreds of generations and thousands of years, results in a population of birds where almost all of them have the long and slender beaks fit to survive in that environment.
Similarly, in the island that only has seeds and nuts, the same thing would happen the other way around. Birds with short hard beaks will live and birds with long slender beaks will eliminate themselves.
So from a sample set of finches that had random types of beak, naturally, through death and survival, two sets of finches with two particular beak shapes are “selected”.
This is what Darwin termed as “Natural Selection”. Darwin himself states that the name “Natural selection” makes us think that there is a “selector”, a conscious being selecting which animal survives, but that is not so. Darwin makes it clear that there is no selector, but the unfit animal simply dies before reproducing, thus enabling the fit animal to procreate and dominate the population. As such, there is a tremendous amount of death involved in Natural Selection. And it is a slow process. Asking “Why can’t I see evolution?” is a flawed question. It is incredibly slow, it takes millions and millions of years. What we can find is traces and evidence of evolution left behind from the past, like fossils. A major piece of evidence that confirms Darwin's theory of evolution through natural selection is the fossil record. Darwin even predicted some of the intermediate fossils that were later discovered.
There are two main drives that propel natural selection:
What you eat
What eats you
The above example of finches is a case of “What you eat” since the selection happens because of the adaptability to food source. On the other hand, a rat that has evolved a special skill to burrow in a way that snakes do not find its nest, is driven by “What eats you”.
When Darwin put forward this idea, everything changed. It is not an exaggeration. Before Darwin, it was commonly believed that God created all the animals, and God’s creation is perfect, and perfect things do not change. But Darwin threw God out the window with two words. His book, “On the Origin of Species” explained things that a hundred religious texts couldn’t explain in the past.
Okay, so a few birds die, few birds live, cool. How does this explain single cellular organisms evolving into multicellular beings? How does this explain wings? How does it explain eyes? Don’t worry, these issues will be discussed in a future article from Aviyal. It is just extrapolation on an incredibly large scale.
Darwin’s theory teaches us great knowledge, but also greater humility. We are not special, created in God’s own image and placed on earth to do whatever we want. We are no more special than dogs or cats or insects. We came from apes. We came from fish. We came from bacteria. As Carl Sagan puts it, "We evolved from microbes in muck". Our origins are humble. It was a turn of random evolutionary events that led us to evolve intelligence instead of strength or teeth or claws. We would do well to use that intelligence to do good and treat everyone kindly.
Do you have any questions? Do you disagree with anything in the article? Wanna read about the evolution of a particular animal or an organ? Or any other feedback? Let us know in the comments.
Mozhi, (August 02, 2021)
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