While my ideas about the nature of matter are a little bit out there, my ideas about the early stages of life vary little from the established view and as a result my speculation isn’t particularly groundbreaking or controversial. It is still fun to engage in, however.
As I look at what I know about cells in general and the differences between eukaryotic cells and bacteria, I see something interesting: the double membrane. Bacteria have a double membrane. Our cells do not. The nuclei of our cells do have one, however. Bacteria are much smaller than our cells. So are the nuclei of our cells. In fact, the nucleus of one of our cells looks an awful lot like a bacteria surrounded by a large cell wall. The biggest difference between them is that our cells’ nuclei contain only DNA and RNA. The double walls of bacteria also contain proteins and the biological machinery needed to manufacture them.
The starting point for my ideas about the early stages of life on earth was this similarity. I imagined a world where the earliest cells were like the nuclei of eukaryotic cells, without a cell wall around them. I imagined the large cell wall to be a defensive measure, and went from there.
I’ve thought some more about it and now start my speculation at the point where DNA, RNA and proteins existed. I am not speculating on how they came about. That is far beyond me. From what I have read recently, however, it is possible that natural chemical gradients played a role in their development.
As I read articles about new scientific research, it is clear that some biologists are focusing on natural versions of the chemical gradient in cells as the places where RNA and proteins might have formed first (it seems like there used to be a consensus that RNA existed first, but that seems to be weakening). Chemical gradients exist at cell walls, where there is a concentration of negative ions on one side and positive ions on the other. This makes the ions want to cross the cell wall, and that movement makes energy available to the cell.
I have read that clays could have created natural pockets where chemical gradients occurred naturally. I have also read about life in the ocean crust. Either one seems like a natural place for life to have spent its earliest stages.
In any case, before cells or anything like them existed, isolated self-replicating genes existed first. Then those genes grouped together in communities to form chromosomes. One of the mistakes I see in biology is to see life as a competition between species. This is missing the point. Life is a competition between genes, which tend to cooperate in groups in order to get ahead. I will talk more about that later.
I speculate that life was initially immobile. This means that each “cell” was closely related to all the cells around it. We wouldn’t call it a cell, though, since it would have no need of a cell wall. We could call it a pre-cell.
The DNA of pre-cells would have varied little from the DNA of its neighbors, but it might have been very different from the DNA of distant pre-cells, as differences gradually accumulated over distances. This is something we observe in human languages.
National languages, where everyone in a country speaks almost the same way, are a new phenomenon and owe their existence to mass communication. Before that, languages existed in dialect continuums, and many or most languages still exist this way. In the Middle Ages of Europe and into the modern era, a person could usually understand the residents of Happy Town where they lived and the inhabitants of all the towns within a certain distance, including the people who lived in OK Town at the edge of that area. They could not understand the people who lived far away in Sad Town.
As you traveled, it would be harder and harder for people to understand you, until you finally had to resort to hand gestures, another language or an interpreter. Of course, there were still abrupt language borders like the ones between French and German or German and Polish. People speaking those languages couldn’t understand each other, no matter how closely they lived to each other.
The differences in language were small from town to town, but they added up over long distances until communication was impossible. Before mass communication, the language of Italy, Spain, Portugal and France was like this. Germany still is like this in some ways. The names of languages like French, Spanish, Portuguese and Italian were political names, not linguistic ones because there weren’t any boundaries in this area where people’s language suddenly changed (except of Basque country, where people still speak a language that is completely different from any other language in Europe).
If pre-cells were immobile, then they would have been surrounded by closely related cells. They could have shared their DNA with each other. They could also have shared RNA and proteins and even their replication machinery. The idea of separate species would have been nonsensical. Pre-cells essentially would have been a single species, with a great deal of gradual variation.
At some point, viruses evolved. They are essentially parasitic robbers. They hijack the DNA replication machinery that allows cells to create copies of themselves. They cheat the system and kill the cells whose machinery they use.
Viruses could have traveled through pre-cell communities, draining them of energy and resources. Pre-cells that could throw up a wall around their replication machinery would have had an advantage against the viruses. (I have read that viruses have played a big role in evolution–I’m just extending it back a bit farther.)
The existence of a cell wall would have freed the pre-cells from their fixed locations. Life could now move. This would have put cells in competition with unrelated cells–no more sharing–and life could now develop on different paths. Species could now exist and the great domains of life like bacteria, archaea and eukaryotes could have their beginnings.
The viruses then developed ways to penetrate the cell wall, prompting the cells to throw up a second wall. The differences in this outer wall are one of the primary ways bacteria differ from archaea and these differences were the very things that allowed biologists to isolate archaea as a separate domain of life from bacteria.
At this point, I imagine that most protein production occurred outside the cell walls. Viruses are interested in the DNA replication machinery, not the proteins. Then something happened that put cells’ proteins in danger. For one reason or another, proteins became lunch for other species.
This development was countered in basically two different ways. Eukaryotic cells, which include plants and animals, threw up walls around their protein-production machinery. This is the cell wall of the eukaryotic cell.
In this imagined view of cellular development, bacteria and archaea simply brought in much of their protein production to the inside of their walls, in contrast to eukaryotic cells that threw up a large wall around it. To me, this is like people living in wealthy medieval houses where production all occurred in the yard. Marauding robbers threatened them. Some people took the production indoors where it was safe, and others built a wall around the yard to protect it.
The mitochondria could have been surrounded by the cell wall at the same time. Mitochondria are essentially the power plants of eukaryotic cells, producing energy for the cell. Our cells can actually create energy without them, but the process is much slower and eukaryotic cells (including our own cells) could never do the things they do without the extra energy provided by mitochondria. Mitochondria are similar to bacteria and they are believed to have evolved from a species of bacteria that was captured by the first eukaryotic cells. A similar situation exists with the chloroplasts of plants, in which light is turned into energy (although plants also have mitochondria).
Biologists debate occasionally whether the mitochondria invaded the first eukaryotic cells or if they were captured. If my version of events actually happened, then there was no need for either of those scenarios. Mitochondria could have simply been hanging around when the outer cell wall went up. They could have already had a symbiotic relationship with the cells they surrounded.
Interestingly, if mitochondria already had a symbiotic relationship with the forebears of eukaryotic cells, that could have made all the difference. The predecessors of eukaryotic cells would have needed to protect the mitochondria as well, and those same mitochondria would have provided them with the energy they needed to build a large wall.
At this point, cells would look very similar to the single-celled life that still exists today. The basic domains of life would have been created. The next development would have been sex. Sexual reproduction basically involves mixing two different sets of genes to create a new, unique mixture. Biologists debate why species do this. The basic question they pose is: “If it ain’t broke, why fix it?” Why do species take a successful combination of genes and totally mess it up?
Here is where I bring back the idea that genes are the competitors in evolution, not species. I think that the biological purpose of all living things is to act like a vector for genes, allowing them to reproduce and continue making copies of themselves. I don’t think it matters to a gene what species it is in.
I think of species as being similar to fantasy football teams in a league where your team has to have a winning season to play next year. In the real world, there is one and only one Tom Brady, and he plays on one and only one football team, the New England Patriots. His unique abilities benefit one and only one team. In a “lose and you’re out” system, he could be out of football in one season, no matter how great a quarterback he might be. But in the fantasy football world, his abilities can benefit an infinite number of fantasy teams, many of which would lose and many of which would win. In fantasy football, he essentially exists as a theoretically infinite series of clones with a huge variety in their chance of success. This is the case with genes in the real world.
When a person creates a fantasy football team, they gather together the best players they can get. Those players exist on many other teams, in combination with many different sets of teammates. This is also the case with genes in the real world. Some of our genes exist in many, many species and work alongside other genes that are very, very different from ours. Fruit flies and nematode worms have some of the same genes as we do.
Shuffling genes the way sex does gives genes a chance to play with different teammates, much like getting on a different football team. It allows genes to play on a wider variety of genetic teams, increasing their chances of being on a winning team somewhere and surviving into the next season, or generation.
And that is my speculative view of the development of life from DNA, RNA and proteins to cells and the development of sexual reproduction.