It is quite pertinent that I am writing this in the backdrop of the novel-Coronavirus 2019 outbreak in China and now across the world. Viruses, despite being one of the simplest life forms – so simple that they cannot even replicate by themselves, have survived the evolution race by being super nimble. They are currently giving a head-on challenge to the most dominant species on the planet.
With this chapter we are going to revisit the story of evolution of life on earth with the second chapter from Carl Sagan’s Cosmos. If you are new to this blog, this is the second part of my illustrated chapter-wise summary for the book Cosmos written by Carl Sagan.
Here’s a quick TL;DR version..
If you are interested to know the details and hear some interesting stories on the way.. read on!
Probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed. There is grandeur in this view of life. That, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
-Charles Darwin, The Origin of Species, 1859.
Carl Sagan explores the topic of origin of life by starting with a broad question – “Considering that the building blocks of life, the organic molecules, are found in abundance in the clouds of gas and dust spread throughout the cosmos, is the evolution of life, given enough time, a cosmic inevitability?”.
Sagan challenges the commonly stated remark about the Earth being a “lucky coincidence”, perfectly suitable for life with its moderate temperature, liquid water, oxygen atmosphere, and so on. Are we confusing the cause and the effect here? The earthlings find the planet cosy, because they have evolved to survive in its atmosphere. The earlier forms of life that were not well adapted died. We are descended from the organisms that survived.
The following fascinating story from the samurai clan from Japan called Heike illustrates this phenomenon well.
Crabs with the samurai’s face
In the year 1185, there was a bloody war between the samurai clans of the Heike and the Genji. The Heike were outnumbered and outmaneuvered. The seven year old Heike emperor was taken into the sea by his guardian grandmother and sunk to avoid being captured by the enemy. The entire Heike clan was destroyed except for forty-three ladies that went on to have offsprings with the fisherfolk and established an annual festival to commemorate the battle.
The fishermen say that the Heike samurai wander the bottoms of the sea still – in the form of crabs. There are crabs that are found here with markings on their carapace that look like the face of a samurai. Interesting! Isn’t it?
So how did the Heike crab come about to have samurai-like markings? The explanation is pretty simple. When caught, the crab with the samurai-like markings are not eaten by the fisherfolks, but returned to the sea. If you are a crab, then having the markings on your carapace increases your chance of survival. Eventually, there came to be a great many samurai crabs.
This process is called artificial selection. In the case of the Heike crab, this was driven unconsciously by the fishermen. But humans have deliberately selected plants and animals that suit their needs and cultivated them into their present forms – the domesticated animals like rabbits and sheep and cows, and species of plants and vegetables with increased yield. The selection is forced on the species by the external factors dictated by human beings.
If humans can make new varieties of plants and animals, must not nature do so also?
That the mechanism of evolution is natural selection was initially proposed by Charles Darwin and Alfred Russel Wallace in a joint paper in 1858. They stressed that nature is prolific, that many more creatures are born than can possibly survive and that therefore the environment selects those varieties which are, by accident, better suited for survival. Mutations provide the raw material of evolution. Nature selects those few mutations that enhances survival, resulting in a series of slow transformations of one life form into another, the origin of new species.
Many people were scandalized by the ideas of evolution. Most cultures credit the lifeforms on earth to some variation of a Great Designer. But, isn’t the idea of this Great Designer being this slow and continuous cycle of transformations even more grand and beautiful?
Evolution of life on earth
Then, Sagan takes us through the 4 billion years of journey of life on earth in great detail. I will attempt to keep it succinct.
Earth condensed out of interstellar gas and dust some 4.6 billion years ago.
The first strands of life emerged around 4 billion years ago in the oceans in the form of very crude molecules that could create copies of itself. This was the earliest ancestor of DNA, the master molecule of life on Earth that carries the genetic instructions. A mutation is a change in the nucleotide copied in the next generation. Most mutations are harmful and die out. A rare happy accident creates a slight advantage for the organism’s survival. As time went on, the primitive molecules turned into a single cell organism. Eventually, single celled organisms joined together to form the first multicellular plants.
Photosynthesis happened by about 3.4 billion years ago. Till about one billion years ago, blue-green algae (also called cyanobacteria) dominated the planet and had started to create a lot of molecular oxygen. So much that the earth’s hydrogen-rich nature altered into an oxygen-rich atmosphere.
But oxygen is also highly caustic for organic molecules and caused near-extinction of anaerobic organism. This event is called the Great Oxygenation Event.
Life had arisen almost immediately after the origin of the Earth, which suggests that life may be an inevitable chemical process on an earth-like planet. But life did not evolve much beyond blue-green algae for 3 billion years, which suggests that complex life forms may be harder to evolve.
Till this point, evolution must have been painstakingly slow.
But, by about 1.2 billion years ago, sex happened. Two primitive organisms could now exchange their genetic material and form a third variation. Things sped up, thereafter.
By around 600 million years ago, a proliferation of new life forms emerged, in an event called the Cambrian explosion. Most major animal phyla appeared during this period.
The first fish and the first vertebrates appeared. Plants moved to land. First insects evolved. Amphibians, able to survive on both land and water; the first trees and first reptiles appeared; the dinosaurs evolved. Ancestors to the dolphin and whales arose alongside the first primates.
P.S: A biologist will probably shoot me on seeing the above illustration. Scientifically accurate classification is way too complicated for a blog post like this and also way beyond my own knowledge on this topic.
Less than 10 million years ago
The first creatures who closely resembled human beings evolved, accompanied by a spectacular increase in brain size. Only a few million years ago, true humans evolved. Now, this most evolved species on the planet has become an imminent danger to every other branch of this evolutionary tree. A quarter of mammals are at risk of extinction according to the IUCN Red List.
Life in another world
But, this is the story of evolution of life on earth. Can life emerge on another planet with very different circumstances? How different will it be from life on Earth?
Our understanding of biology is limited to one kind of organic chemistry and one chain of evolutionary events only. Even our science fiction remains limited to a variant of E.T that looks somewhat like the familiar creatures on earth. Our understanding is on this topic is very limited.
Sagan concludes the chapter with the following words
“The search for life elsewhere is not going to be easy. However, it is very much worth seeking because we may not be the only voice in this cosmic fugue.”Carl Sagan
Did you know? Sagan assembled the first physical messages sent into space: the Pioneer plaque and the Voyager Golden Record, universal messages that could potentially be understood by any ET that finds them..
Well, I sure hope they do that before we annihilate ourselves!
P.S: If you have want to read more on on this topic, Indica by Pranay Lal is another very interesting book exploring this theme with great detail.
I hope you have enjoyed reading this chapter summary. You can subscribe to this blog by clicking on the “Subscribe” button seen somewhere below to receive an update when a new blog is posted. You can also read the rest of this series here. Also, please check out my other comics here and my first children’s picture book here.
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