We all know what life is, yet if you were asked to provide a comprehensive definition of life, you may find yourself struggling. Maybe the most simplistic definition you can blurb out is: something that can grow and reproduce. However, this definition would fall short from encompassing many organisms we know are alive. What about individuals that are sterile? What about mules or worker bees? They may not be able to reproduce but we know for sure they are alive. Truth is, sometimes there is no way to summarize complex things with simple definitions. If we were to dissect life in its key elements we would find that we need something to store genetic information, we need an apparatus that can generate energy, a chemical machinery that will generate the “bricks” of life and of course an apparatus to reproduce.
If it wasn’t easy to lay down a good definition for life, imagine what would happen if we mention evolution. Most people are happy to stick to what Darwin said, yet when Darwin formulated his theory, he did not have many of the tools we have today. He did not have a microscope and he did not know what DNA is, let alone imagining the concept of gene. In this post, it is not my intention to bash down Darwin theories, I just want to provide some complementary information.
So, what did Darwin say? He formulated the theory of natural selection, he believed that only individuals with traits that favor survival would live to pass along their traits. His theory was the seed for many “trees of life”. In these trees when branches diverge from the primary trunk there is no way to go back. Each branch is a different species that, by evolving, becomes more distant from its ancestors.
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What happened after Darwin was that we started using microscopes
to observe cells and new behaviors emerged. Constantin Merezhkowsky in the late
nineteenth century, noted that cells could absorb something like a bacteria to
their own advantage. He was fond of Diatoms, these are a type of micro-algae that
live in the oceans. These organisms obtain their energy through photosynthesis.
The machinery they use for this purpose are the chloroplasts. To Merezhkowsky,
chloroplasts really looked a lot like bacteria. So he postulated that plants
and animal cells were very much alike, but along the way, one cell type acquired
photosynthetic bacteria, becoming like our plant cells today. Merezhkowsky
introduced the concept of symbiogenesis, which is basically the merging of two different
life forms to originate a brand-new new form of life.<o:p></o:p>
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<o:p>Image of a Diatom - CC by 2.0</o:p>
Merezhkowsky was not alone, soon he was joined by an
American biologist, Ivan Wallin. He speculated that our cells too absorbed some
bacteria, originating what today we call mitochondria. I wonder what Darwin
would have thought about that. Anyway, in the late 50s things would change even
further when Watson and Crick discovered the true nature of DNA. Until this
moment, the only way to pass along traits we thought possible, was through
reproduction. The branches in the tree of life did not suppose to merge ever
again. Yet, what Darwin could not have known, was that there is a chance to
transfer genetic information through something called horizontal gene transfer.
This means that some organisms can assimilate genetic material from other
organisms without reproduction. In other words, it turns out life is more like
a mosaic. <o:p></o:p>
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Fast forward to the mid-90s, we developed really efficient
and fast ways to sequence DNA. We even managed to sequence the human genome and
we did not stop there! What we found was that as we sequenced different genomes
and developed tools to search through this huge amount of data, there were entire
chunks of bacterial of archeal genes within other organisms. The tree of life
did not look like a tree anymore, it started looking more like a web. The proof
of horizontal gene transfer is also proof of symbiosis between different
species.
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<o:p>Image CCO Creative Commons</o:p>
There are examples of this all over the place. For example,
in 1928, Fred Griffith noticed that when he mixed one strain of dead bacteria
with a different strain of live bacteria, the dead strain would magically come
back to life. In truth, these were not zombie bacteria, but the live strain of
bacteria managed to absorb some genes of the dead strain. This is exactly how
bacteria acquire resistance to antibiotics with dramatic consequences for us. <o:p></o:p>
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Probably the best example of this was in Japan after WWII.
The bacteria responsible for dissenteria, the Shigella dysenteriae, was
spreading quickly, acquiring antibiotic resistance at an alarming rate. Nothing
seemed to stop them anymore and by the late 50s, the Shigella acquired
resistance to at least 4 different antibiotics, becoming a superbug. This was
not the result of Darwinian evolution, it occurred in a too short time for that,
this change was made possible by horizontal gene transfer between different
strains of these bacteria. So, in a kind of twisted way, what was responsible
for survival were not the organisms that were most fit, but were the genes being
hosted in them. If we look at this from a different view, we can say that genes move “horizontally”
to fulfil their own selfish interests. I wonder what Darwin would have thought
about that.
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<o:p>How Charles Darwin would have looked today by @elvisxx71</o:p>
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<o:p>References: </o:p>
https://en.wikipedia.org/wiki/Konstantin_Mereschkowski<o:p></o:p>
https://en.wikipedia.org/wiki/Ivan_Wallin<o:p></o:p>
https://en.wikipedia.org/wiki/Frederick_Griffith
The Mitochondria Problem by Ivan E. Wallin
https://www.elsevier.com/books/molecular-biology/clark/978-0-12-813288-3
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Earlier today I read an article by @kralizec, https://steemit.com/science/@kralizec/light-powered-hybrid-nano-organisms-making-plastic-and-fuels. In a way, this kind of interaction between living and non living elements creates another kind of evolution that would probably have astonished Darwin, wouldn't it? Perhaps even alarm him. I think you're right. As soon as we think we've settled upon a definition of life, the goal post moves.
5 years studying medicine and not once had I thought about how difficult it is to properly define the concept of "life", and I admit I didn't remember very well how bacteria adquired resistances to antibiotics. Thank you very much for this article, sir!
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I enjoyed reading your post. We live in a world in which oversimplification of things is the norm and your post just achieved the contrary: the fact that things are really more complex than they seem. Life and evolution can be defined in different ways and there always be disagreement.
Thank you, I am glad you appreciated it
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Very nice way of putting things together. This post really makes me thinking. At the end, life can be seen as a capacity of transferring genes in one way or the other. Is this the message you tried to convey?
I have troubles with that sentence… It is a bit too philosophical for me as it yields to the notion of consciousness, but at the level of the genes. This is something, without working in this area, I can’t buy :)
Thank you for your comment. Actually when I wrote that sentence I was thinking about a book entitled: "The selfish gene" by Richard Dawkins. The author mentions that that sentence should not be taken literally, genes do not have a consciousness but they propagate in interesting ways.
I am very happy to trust this. However, consciousness often leads to crazy discussions among certain people... Also in the quantum mechanics domain with the nature of the observer (huuu I should write about that one day).
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