Darwin
In 1859, Darwin published The Origin of Species, in which Darwin elucidated the evolution of life in nature from low to high.
Darwin was also the first to imagine a genealogical map that reflects the evolution of species as a "tree of life" and simply drew what the tree looked like in On the Origin of Species.
Like real trees, the "Tree of Life" has tree-like branches, with the end of the branch node representing the living species.
According to Darwin's understanding, the process of going back from these terminal nodes to the trunk is like going back in time, while the small branches and thicker "branches" represent the most recent common ancestors of the different branches.
For example, if humans and chimpanzees originate from a common ancestor, the two branches representing humans and chimpanzees converge at the same node; if you continue to follow the branch that humans and orangutans make up, you can find nodes representing mammals, vertebrate subphyla, and animal kingdoms. Eventually, as the branches gradually diminish, the roots of the tree represent only one organism, the common ancestor of all life on Earth.
The most primitive life
Since then, scientists have been searching for what Darwin called "the most primitive life form."
fossil
The most direct evidence for exploring the origin of life, then, is fossils. Fossils are the remains of ancient (generally 10,000 years ago) life preserved in rocks, and they depict the evolutionary history of life like photos.
ANONYMOUS
But searching for fossils of life billions of years ago on a vast earth is like finding a needle in a haystack. As a result, scientists can only assume the common ancestor of all life on Earth, LUCA. But no one knows its chemical composition, and no one knows what it was like billions of years ago.
As a result, more scientists are beginning to realize that fossils are not the only way to study the evolution of life on Earth.
When human technology stagnates, there will always be a person who will rise to the challenge at the right time.
At this time, a scientist began to realize that the imprint of early life on Earth actually existed in the genome of today's organisms.
Carl Us
This scientist is the American biophysicist Carl Us, who studies evolutionary biology.
Urs was not only one of the most creative and revolutionary biophysicists of the 20th century, but also one of the most talented thinkers in biology.
He almost overturned biologists' understanding of LUCA and laid a completely new theoretical foundation for the evolutionary mechanism of life on Earth.
On December 30, 2012, at the age of 84, Carl Us died at home, and many have compared his achievements to those of Einstein and Darwin.
Because the most important discovery of Us is to find a completely new category of life on Earth, archaea.
The most notable feature of archaea is that they are able to survive in environments that most living organisms cannot survive, which also indicates that they are likely to be the oldest life on Earth.
Although Uce is considered one of the most important scientists in biology in the world, he did not pay much attention to the life sciences when he was young.
Born in Syracuse, New York, USA, as a student, he liked to delve into mathematics, because mathematics is both objective and logical, which allows Uth to relax in a noisy environment, which shows that he is very shy and shy.
It is precisely because of this character that he does not dare to communicate with people that Makesus away from most of the open academic conferences. It is precisely this that has led the public to underestimate the impact of his work and to believe that most of his revolutionary theories will one day have a huge impact on the life sciences.
After pursuing an undergraduate degree in mathematics and physics at Amherst College, the second-ranked liberal arts college in the United States, Urs continued to stay here to do research.
Like many prospective physicists of his time, Usa was influenced by Schrödinger's legendary book What Is Life, in which the great theoretical physicist boldly predicted:
Genetic material is an information molecule that may resemble the two symbols "•" and "—" in a civilian Morse code, and stores genetic information in a permutation and combination. ”
This earth-shattering prophecy shocked many people, and Us was no exception. When he went on to pursue his Ph.D. at Yale University, his research direction shifted to biophysics.
After graduating with his Ph.D., Us prepared to spend another two years earning a medical degree, but ultimately did not succeed. It can be seen from here that Us is not a genius type like Einstein, but belongs to the acquired diligence type.
Later, he secured a position in biophysics at the General Electric Laboratory in Schenectady, New York.
Watson and Crick
At the time, geneticist Watson and biophysicist Crick had already identified the structure of DNA, the double helix, a major discovery that had led academics to re-explore the hidden mysteries of genetics.
Us spent all 5 years of his arrival in Schenectady on the working principles of the genetic code.
We know that nucleic acids - DNA + RNA each have 4 bases, and the genetic code is a group of 3 bases, and it needs to correspond exactly to 20 amino acids to ensure that amino acids synthesize protein precursors in a precise way.
Us understands the conversion of genetic information between DNA and proteins as a translation process, but he was initially unclear about how genetic information is "translated" into proteins.
So, Us turned his attention to the translator of the genetic code, the ribosome. Ribosomes are biological macromolecules with RNA as the main component that translate the genetic code on DNA into amino acid sequences.
Newcastle disease virus
In fact, as early as his doctoral studies, when Us studied the Newcastle disease virus, he developed a strong interest in the little-known ribosome. It wasn't until Schenectady that he had time to devote himself to the study of this biological macromolecule.
Crick
Although the genetic code has been cracked by Crick and his colleagues:
Codons with DNA or RNA sequences in groups of three nucleotides are translated into amino acid sequences of proteins for protein synthesis.
But Uth wants to interpret the process of the genetic code encoding amino acid sequences from a new perspective.
Crick and others see Us's work as a mathematical solution to physical problems, but ironically, Uth, who was once obsessed with mathematics, sees the genetic code as a unique biological phenomenon.
In Uth's eyes, the genetic code is a time machine for the evolution of life, allowing him to go through successive generations all the way back to the most distant and ambiguous beginning of the evolution of life.
Moreover, Urs did not measure the difference between species by differences in characteristics, as the famous French vertebrate Joofér Saint-Hilaire looked for similarities between human arms and whale fins.
Because Uth believes that by studying the evolutionary process of protein translation mechanisms, the evolutionary relationships between species can be more clearly understood.
Us decided to continue the search for a solution to the problem.
In 1969, Us wrote an unusual letter to Crick.
In his letter, he wrote: "By extrapolating the genetic sequences of very old ancestors, one can finally understand the evolution of cells. ”
Uth is very clear and bold in stating that he intends to use DNA to reveal the "internal fossil record" hidden deep in all cells to establish a true evolutionary relationship between organisms.
This bears a striking resemblance to the whole genome sequencing as we know it today, which shows that Us has a superior and far-reaching foresight.
It was precisely because Uth recognized the great potential of molecular biology that he was convinced that the genetic code would eventually be able to fill the evolutionary gap that fossils could not record.
To realize this idea, he decided to sequence the genomes of all living things and trace the evolution of life on this basis.
It should be noted that not all species have the same protein composition, and Uth needs to find those proteins that all living creatures use as research objects.
Because the synthesis of these proteins is so precise and mutations are so rare, it's easy to trace the evolutionary relationships of species back billions of years.
Moreover, differences in amino acid sequences can reflect differences in DNA sequences, the carriers of genetic material. Therefore, by comparing DNA and RNA sequences, the time for species differentiation can be calculated.
16srRNA
Us set out to study a ribosome sequence called 16SrRNA, a name derived from the sedimentation coefficient of this ribosome when centrifuged. 16SrRNAs are studied because they contain enough information to reflect differences between species, and their structure is relatively simple, making it easy to obtain a complete nucleotide sequence.
At the time, all sequencing was done by hand, and automated sequencing technology came out decades later.
Fred Sanger
The Uss team used a technique invented in 1965 by the British biochemist Fred Sanger (One of the few scientists who have won two Nobel Prizes in his lifetime):
Enzymes are used to snip the RNA into small pieces that can be sequenced, then sequence these small pieces, and finally re-stitch the complete nucleotide sequence.
In its inception, the study proceeded rather slowly, taking months to determine the sequence of just one 16SrRNA. And because the technology was so costly, Us had to seek funding from NASA's Space Biology Program.
For most scientists, this kind of research can be extremely tedious, but Urs enjoyed the process. For him, it's like completing a huge puzzle piece step by step, with unique fun that no one else can comprehend.
Methane bacteria
In the spring of 1976, the Uss research team accumulated a large number of 16SrRNA sequences of bacteria. They have since turned their attention to another unique microbe, the methane bacterium.
Methane bacteria are extremophiles that get their name from their unique ability to produce methane during energy metabolism.
Because the methane bacterium can be observed with the naked eye, scientists have long considered it a type of bacteria.
But Uth's results of sequencing methane bacteria with the 16SrDNA gene showed that methane bacteria did not belong to the category of bacteria at all.
Uce immediately realized that the discovery by himself and his colleagues had upended the existing taxonomic system.
In fact, there is a third branch in addition to the original eukaryotes and prokaryotes, and this branch is separated from the "trunk" shortly after the birth of life.
Archaea
Uce named the creatures of this branch "archaea", which were later called "archaea", meaning "ancient bacteria". What's more interesting is that archaea are closer to humans than bacteria.
The "Tree of Life" by Us
After that, Us began to redraw the "Tree of Life". In the "Tree of Life" drawn by Us, all the branches that make up Darwin's "Tree of Life" can be merged into a large trunk. When this "Tree of Life" is finally drawn, it looks more like a complex and asymmetrical snowflake consisting of 3 trunks. Each of these 3 trunks extends in different directions, and Ush calls these 3 trunks "domains".
This discovery is the famous "Ush Revolution" in the field of microbiology.
In 1977, this paper on archaea was published in the Proceedings of the National Academy of Sciences. However, it has attracted a lot of doubt, ridicule and even anger from everyone.
Some scientists believe that Us is nothing more than a strange hermit who solves an unsolvable problem, and this discovery is of little significance.
Other scientists argue that his data is too fragmented to redraw the "tree of life."
Other scientists find his behavior odd and unbelieving to believe his findings.
Ernst Meier
German-American Ernst Meier was also one of the most influential evolutionary biologists of the 20th century. However, his criticism of Us was the fiercest. Meier even told The New York Times that Us's research was pure nonsense.
Uce's way of fighting back was to write letters to the editors of the New York Times, but this did not help his situation. When the academic conference on the theme of archaea was first held, Us was not even invited to attend. It wasn't until the mid-1980s that Us's views received some acceptance.
In 1992, he was awarded the Levenhoek Medal by the Royal Netherlands Academy of Sciences, the highest honor in microbiology, which is awarded every 10 years.
Later, The journal Science called Us's dramatic struggle a "scarred revolution in microbiology."
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Reference: The Birth of Life: Where We Come From