The Origin of Sex

The Origin of Sex

It is generally understood that the prototype of our life was born approximately 3.5 billion years ago near deep-sea hydrothermal vents where magma erupts in the ocean.

Because those prokaryotes and the more evolved protists are the origin of life, they are undoubtedly our ancestors.

So, when and how is it thought that "sex" was created? We opened up "The Origin of Sex" (by Lynn Margulis and Dorion Sagan).

In this book, the definition of "sex" presents a concept far removed from the image of "sex" that we think of, involving male and female animals and plants or sexual acts. According to it, "Sex first appeared in bacteria."

It appeared in microorganisms of 0.5 to about 5 microns, and furthermore, large and complex microorganisms called protists (single-celled eukaryotes) emerged. Meiosis (reducing chromosomes by cell division) and fertilization (restoring the chromosome count by cell reintegration) were already being performed in these single-celled protists, and in bacteria, biological mixing and integration at the molecular level, such as DNA molecule splicing (cutting and connecting) and repair, are considered the origin of sex.

In other words, the existence of opposite sexes accompanied by reproduction is not a condition; rather, the origin of "sex" is captured by what happens at the cellular level.

From this, both the sex of primitive microorganisms and human sex are identical in the act itself at the molecular level. This is because descendants can be increased whether or not sexual reproduction is undergone.

"In the presence of low-molecular-weight compounds within the cell and special enzymes called polymerases (nucleic acid synthases), DNA synthesizes the next DNA molecule." (From "The Origin of Sex")

"Within the cells of a growing organism, DNA replication is created, RNA containing the information stored in the DNA is synthesized, and new proteins are synthesized from that RNA. The cell takes in food, processes it according to the instructions of DNA and RNA, and when the volume doubles, it finally divides. One DNA molecule becomes two through replication, and one cell becomes two cells through reproduction." (Ibid.)

Here, self-maintenance activity through reproduction at the molecular level indicates cell succession with new continuity through DNA complexing. Since the birth of self-maintenance ability on Earth, cell division has been repeated without disappearing, and the sustainability of life created by nature is a priori systematized. It can be said that this is because a mechanism for stopping is not built into DNA.

In somatic cell division, after sister chromatids are formed, they are separated at metaphase, the sister cells that reach each spindle pole decondense, the microtubules disappear, the nuclear membrane and nucleolus are formed again, the Golgi apparatus is reformed, and it is cut from the equatorial plane. What is surprising is that tiny cells such as eukaryotic cells can complete this action on their own.

Although human science can analyze it, it cannot create life at this stage, which can be called a primitive cell, and can only utilize the mechanism of its generation.

In the process of evolution, reproduction was carried out, and even the separation of males and females into different individuals occurred. Even this was not something humans arranged, and we have no choice but to stand at the limit of life where we enjoy the results.

Cells include prokaryotic cells without a nucleus and eukaryotic cells with a nucleus. In these prokaryotic cells, there are organisms called prokaryotes.

For example, those that reproduce asexually, such as E. coli, lactic acid bacteria, and gonococci. On the other hand, in eukaryotic cells, there are eukaryotes.

Eukaryotic microorganisms have a wide range, from single-celled organisms such as green algae and ciliates to multicellular organisms such as cats, penguins, roses, mushrooms, and seaweed.

These are diverse, including those that reproduce sexually, those that undergo mitosis, and those that fertilize after meiosis. Humanity is also included here.

Cells can be said to be the primordial life since life was born on Earth. At that time, the Earth did not yet have an ozone layer, and destructive rays harmful to life, such as ultraviolet rays and radiation, were pouring down.

Then, why was the prototype of life able to continue to exist in such a critical environment? There is a theory that life was born near magma in the ocean, and those harmful rays luckily had difficulty reaching it.

However, prokaryotic cells began to divide and proliferate on their own, and even acquired the resistance to repair DNA damaged by harmful rays such as ultraviolet rays.

There are two types of this repair, and it is known that the two helices of DNA fuse.

If one helix is damaged, because of complementary molecules, a completely different new DNA molecule is fused as a source of information for damage repair.

This is called the damaged DNA repair mechanism. If both DNAs are damaged, they replicate themselves within the damaged DNA. This is called the SOS repair mechanism. (Refer to B. Alberts' "Molecular Biology of the Cell", etc.)