Life is abound, myriad, sorted and all around us. Our home in universe on a geoid ball aka Earth is nothing short of a wonder. A blue marble with moving milky air, here and there, along with wheatish-green cut-outs as its continents with oceans around and abound. Earth’s long walk from a lifeless rocky ball to a majestic living form took breathtaking billions of years. An incomprehensible yet fascinating thing that we can simply be in awe of it. One might say, that’s how other planets and stars carve out. To an utter bewilderment and amazement, not everyone out there gets to be an earth- the only known planet adorned with colourful, complex and breathtaking life forms.
These life forms, however myriad they might seem, have been broadly categorised into Prokarya and Eukarya. The Archaea and Bacteria are prokaryotes: no-nuclei-single-celled organisms. While Eukarya, includes us, other animals, and plants are multi-cellular-nuclei based life forms. Researchers have been on a look-out for more evidence in search of LUCA-Last Universal Common Ancestor- but Archaea is how far we know yet.
Most life as we know now is sustained mainly by the oxygen. One would be amazed to know that this life support of ours was once a catastrophe which virtually wiped almost all life, in its adolescent stage, on earth. Imagine! The protector and nurturer of today was once going full THANOS here on earth. How? Well, let's peek farther into the baby days of earth.
Our earth was formed around 4.6 billion years ago (BYA) and the Archean aeon began around 4 BYA- the habitability boundary started from there. Earth had its first nascent life forms called Archaea, early microbes, about 3.7 BYA most plausibly under the sea. The atmosphere on earth was enriched with nitrogen, methane and carbon dioxide. Archaea were anaerobic so they didn’t need oxygen to survive; probably sustained by the hydrothermal vents on sea floor. Oxygen wasn’t even in the picture as most of it was locked in water molecules under sea.
So it wasn’t the mighty sun but the earth’s primordial soup that sustained first life on earth. But it was soon to be changed. Somewhere between 3.5 and 2.5 BYA, one of these microbial species harnessed the capacity for photosynthesis- the advent of energy automation! The life on earth was poised to change itself and the earth with it, too.
The photosynthesis produced oxygen and sugar. These first free oxygen molecules went up to meet the other gaseous dudes and sugar catered to the energy needs of Archaea. These oxygen spewing chimneys gave us the first Cyanobacteria. This ancient bacteria, holding advantage over others, could produce its own energy. The consequence: more Cyanobacteria, more oxygen, some more Cyanobacteria, and very higher oxygen levels in the atmosphere. The other life forms which survived on oxygen-less environment found higher oxygen abundance to be toxic.
Ergo, the wiping out of species was inevitable causing the first mass extinction of virtually all life form, barely sparing Cyanobacteria. The other factor was earth’s temperature. Until oxygen happened, the methane rich atmosphere kept the earth atmosphere very hot by trapping more heat. Its natural chemistry with oxygen released water and carbon dioxide- not so good at trapping heat- making earth less and less warmer. Eventually, the first and possibly the longest ice age-The Huronian Galciation (2.4 to 2.1 BYA)- dawned on earth.
a.k.a. The Great Oxygenation Event or The Oxygen Catastrophe.
Evidently, the aerobic life on earth adapted to this new change over a million years. Cyanobacteria got wholly consumed by a prehistoric microbe and gave this microbe its own photosynthesis factory and Cyanobacteria became chloroplasts. Eukarya arrived! Thus, earth entered into the grand beautification sprouting new life forms from plants (autotrophs) to animals (heterotrophs) and we end up having a long history of evolution of multiple species through epochs, including us- the Homosapiens.
The long process of nature and nurture has endowed different species with unique traits through evolution. In case of humans it is our paramount faculties of language and imagination. Our intelligence coupled with these unique faculties have enabled us to be a dominant specie on earth- for better and for worse.
Ever wondered how varied, uniquely beautiful, awe-inspiring, and sometimes frightening life-forms look the way they do. What causes those particular designs, appearances and traits. How does this mind-boggling task of creating life is achieved without any visible facility located somewhere in all its grandiosity. It’s bewildering to accept that nature delivers biological life through and inside a biological life itself. We are the tools, raw materials, design, and blueprint nature puts in the crucible. It's an even more arduous task to comprehend nature's work and try to put into perspective with our limited cognition.
It’s then a matter of gratitude only that nature has endowed us with the ability to marvel at its mysterious workings and solve those mysteries. It’s this constant pursuit of unriddling which provides meaning, exhilaration and adventure to our existence. No matter how distinctive we look or operate, fundamentally and physically, we are nothing more than a set of encoded instructions passing across space-time and through each other.
The most fundamental to nature's life-creation is a Gene- a helical two strand structure- inside the DNA within the cells. The inconceivability of its complexity lies in the fact that these tiny and seemingly invisible genes creates the majestic life-form exhibition on earth and perhaps beyond.
The inquiry into organisms forming other organisms dates back to the times of Greeks. It wasn't only about organisms birthing organisms but also why only similar kinds of those or the 'likeness'. Why doesn't one organism turn into another. Well, the answer to all this has to do with genetics and evolution. It’s this journey of inquiry, by great minds of the yore and lore, into the fundamentals of life formation that we are going to try to delve in this mini-series.
Genes are housed in chromosomes, thread like structure in cells. A person has 46 chromosomes with 23 each from both the parents. Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA becomes more tightly packed during cell division and becomes available for researchers to study under microscope. The full repository of an organism’s genetic instructions is called its ‘Genome’. The human genome contains around 21 to 23 thousand genes which write, compile and run us.
The intial inquiry into ‘likeness’ piqued the curiosity of Pythagoras (around 530 B.C.), a half scientist-half mystic, who proposed one of the earliest theories to explain the similarity between parents and their children. The core of his idea was that hereditary information (or ‘likeness’) was principally carried in male semen. He argued that in heredity too a triangular harmony was at work, drawing analogy from his famous theorem. The mother and father were two independent sides and the child was the third-the biological hypotenuse.
A century after Pythagoras’s death, Plato, writing in 380 BC, was intrigued by this metaphor. He went even further with the idea of children being derivatives of their parents and talked about the possibility of hacking the same to birth children who are the perfect combinations of their parents breeding in perfectly calibrated times. Though disapproved later by Aristotle, this stream of thinking would still find its takers at the turn of the 20th century to defame humanity. (More on this in next part.)
It was Aristotle who systematically dis-mantled Pythgoras’s theory of heredity in his treatise-Generation of Animals- which would serve as a foundational text for human genetics akin to Plato’s Republic: a founding text for political philosophy. Aristotle posited that children can inherit features from both parents, and sometimes skip generations, as compared to prevailing notion of male semen exclusively carrying traits. Aristotle also thought that the transmission of heredity may be likened to transmission of information which can help create an organism from scratch.
This inquiry didn’t see a substantial advancement in the coming two thousands years, until it was poised for transformation in the 19th century with the ingenuity of a 22 years old young clergyman, Charles Darwin, who boarded the fateful HMS Beagle in 1831. A 5-year long journey covering Galapagos islands, off the Pacific coast of South America, that ushered the field of evolution into a wonderful sprouting that so many evolutionary mysteries have been solved within two centuries only after that.
More on this story in the upcoming parts.