A recent 快猫短视频 article, 鈥淭he most ancient piece of you鈥� (4 November 2017), discussed the common ancestors of living beings today. But are plants included in this universal common ancestor? If so, are we linked to plants in very early stages of evolution?
鈥� The short answer is yes, very much so. Leaving aside what may have happened in the primordial ooze, early life consisted of simple prokaryotic cells. These used DNA as their genetic mechanism, but it was not segregated from the rest of the cell as it is in the more advanced eukaryotic cells that make up plants, animals and fungi.
There were two different groups of prokaryotic cells 鈥� archaea and bacteria 鈥� with a huge variety of metabolic systems. Both bacteria and archaea are still widespread today. How the eukaryotic nucleus evolved is still unclear, but key biochemical pathways suggest that the eukaryotic cell evolved from the archaea.
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The eukaryotic cell gained its supremacy from its engulfment of, and symbiosis with, a bacterium that became the mitochondrion. This oxidises food molecules to provide energy for all the other chemical processes of the cell. Separating these chemical pathways from the rest of the cell gave the eukaryote a huge metabolic advantage. So, we are all descended from both archaea and eubacteria (which have a rigid cell wall), and our mitochondria have their own DNA and bacteria-like ribosomes.
鈥淓arly life gave us two different groups of prokaryotic cells, archaea and bacteria鈥�
The next key symbiosis was when a mitochondria-containing eukaryote cell engulfed a photosynthetic bacterium, which became the chloroplast (a process that happened more than once). These cells could now use light to create their food, making them the first plants. The different requirements for finding food as opposed to capturing light soon led to the differences between plants and animals we see today.
But we are all related.
Guy Cox, Australian Centre for Microscopy and Microanalysis, University of Sydney, Australia
鈥� Inference from genetic data suggests humans and plants last shared a common ancestor around 1.6 billion years ago. This is substantially later than the last common ancestor of all life (assuming life evolved just once), which may have existed up to 3.8 billion years ago.
This is because plants, animals, fungi and protists (such as slime moulds) all form a major grouping derived from eukaryotic cells, which evolved relatively recently in life鈥檚 history. For several billion years after life鈥檚 origin, it would have existed in a form more similar to the relatively simple prokaryotic cells that characterise bacteria and archaea today.
Eukaryotic cells have membrane-bound compartments inside them, such as the enclosed nucleus containing the cell鈥檚 DNA. Believe it or not, animals and fungi are more closely related to each other than either of them is to plants, based on genetic dating of the lineage divergences within the eukaryotes.
Sam Buckton, Churchill College, Cambridge, UK
鈥� For an account of the search for the last universal common ancestor, or LUCA, may I recommend Richard Dawkins鈥檚 book The Ancestor鈥檚 Tale. It takes the form of a Chauceresque pilgrimage back through our evolutionary tree, meeting common ancestors each time a fork joins our path.
Edna Richards, Welwyn Garden City, Hertfordshire, UK
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