The Evolution of Life: A Genomic Perspective
“There is grandeur in this view of life, that whilst this planet has gone cycling on according to the fixed laws of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
~Charles Darwin, ‘On the Origin of Species’
Look at the world around you. There is so much beauty, so much elegance in its immense diversity that you end up wondering- ‘how the hell?’ That one ball of rock in a remote corner of the Milky Way, a segment of the infinite expanse of the universe could host such vibrance in the variety of its life forms seems utterly fascinating. Creationists very conveniently decided to put it all down to God who created all life in a matter of weeks. Well, it was surely worth being sceptical about. Anyways, we still don’t seem to have a definitive answer after all this time, do we? But that’s the beauty of Science- it always leaves a scope for speculation. Darwin speculated, so did his successors. Nonetheless, the idea of evolution has left us in awe of the mystery of life and that of its perpetual progress. Did we evolve from slime? It’s definitely not a very optimistic hypothesis but is certainly more plausible. There is a sense of divinity in it after all, that we are all related in our most basic level of existence, even beyond the boundaries of our humanity.
Now let’s talk about genes. Darwin’s theory of natural selection assumed that life adapts itself with time and place and thus gives rise to its new avatars. But how did it all take place at the very fundamental stage? There comes the pivotal, in fact indispensable role of genes. Mutations in the DNA lead to certain structural or chemical changes in the organism that either make it vulnerable to extinction or give it an advantage over the rest of population. Thus, favourable changes accumulate and disadvantageous ones disappear leading to completely new species in the long run of time. But most likely enough, DNA has a much more ancient history. Infact, DNA’s transcriptional counterpart RNA has been widely accepted as the most primitive constituent of an independent life form. RNA, like DNA, can make copies of itself and carry forward genetic information. Moreover, it can also act as an enzyme, as Ribozyme, involved in synthesis of proteins. So, evidence suggests that the first independent definable form of life was perhaps nothing more than self-replicating RNA molecules. DNA also evolved in the meantime and gradually we had single celled structures- the ‘grandfather’ prokaryote. With an increasing diversity of genes, more varied structures must have developed. Some of these prokaryotes engulfed each other (Endosymbionts) and formed some permanent obligate associations. Those were the first Eukaryotic cells with semi-independent organelles like Mitochondria and Chloroplasts. Again, DNA played a role. These organelles, or symbionts, which were genomically independent, created more complex functional units within a cellular system. So, more genetic diversity led to more cellular complexity. Some novel properties developed in those cells apart from reproduction, which was very likely the only distinguishable mechanism of life until then. For example, the Great Oxidation event began when autotrophic photosynthetic cells of Cyanobacteria devised a new pathway for cellular respiration, one in which oxygen happened to be a by-product. Eventually, the amount of oxygen rose in the atmosphere triggering a new wave of natural selection. Organisms that had more tolerance towards oxygen, which was most likely poisonous at that time, increased in numbers. This led to a multiplication of oxygen dependant way of life.
Coming to a more recent history, the first population of animals was most likely water-borne. The first fishes and chordates appeared in the Cambrian explosion, about 541 mya. In the Devonian period, probably because of widespread drought, some of these fishes had to come to land in search of other inland water bodies. Those that survived the migration most obviously had genetic mutations that gave them the ability to breathe in oxygen without water. These evolved into amphibians, thanks to Darwin’s laws. Also, some traitors left their aquatic abode entirely and became reptiles; however there still are exemptions (e.g, the crocodile). Following the great extinction event of the Permian period, birds and mammals evolved in more or less the same manner, triggered by ‘anarchy’ of the genes. That same anarchy eventually led to the greatest anarchists of all-humans. Evolution of humans again has its own long history marked by a crucial role of genes. In a nutshell, these nucleotide sequences are apparently the architects of life.
Isn’t it wonderful- that the grand spectrum of this biological variety can be traced back to those seemingly remote chemicals hidden deep in the recesses of each individual cell; that there is a whole microcosm that exists within an organism, us included, that reflects itself back into the universe around us? I feel a sense of mystery and gripping adventure in the realms of the genome. After all, that curiosity and excitement of the unknown is what has driven us to this peak of evolution so far and I hope that the science of DNA will foster us into newer heights, not just intellectually but also in terms of entanglement of life as a whole.http://www.geneticengg.com/2017/01/31/the-evolution-of-life-a-genomic-perspective/http://www.geneticengg.com/wp-content/uploads/2017/01/neanderthal-girl-131202-640x437.jpeghttp://www.geneticengg.com/wp-content/uploads/2017/01/neanderthal-girl-131202-640x437-150x150.jpegEvolutionary BiologyGenome engineering“There is grandeur in this view of life, that whilst this planet has gone cycling on according to the fixed laws of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” ~Charles Darwin, ‘On the Origin of Species’ Look at the...Rajit RoyRajit Royrajit.firstname.lastname@example.orgEditorGeneticEngg.com