Endosymbiotic theory, which is often referred to as “symbiogenesis,” is an evolutionary theory that attempts to explain the origin of eukaryotic cells. It is a hypothesis which essentially postulates that prokaryotes were what gave rise to the first eukaryotic cells and, if true, would rank amongst the most important evolutionary events in our history.
Eukaryotic cell organelles include mitochondria that is found in animals or fungi and the chloroplasts that are found in plants. Mitochondria are one of several different organelles that are found in the cells of every single eukaryotic cell.
Thanks to sequencing technologies, symbiogenesis has grown in prominence as a theory over the last several decades. There are several competing theories, including non-evolutionary theories, to explain the origin of eukaryotic cells, and the science behind the theory is still in its beginning stages, but it does help to explain the symbiotic relationships that two different species are dependent upon for their mutual survival.
The Details Behind the Origins of Eukaryotic Cells
In the Endosymbiotic theory, the idea is that a eukaryotic mitochondrion evolved from an autotrophic bacterium that had been engulfed by the eukaryotic cell. This cell was able to arise when an anaerobic prokaryote lost its cell wall because it was unable to use oxygen for energy. The flexible membrane underneath began to grow and then fold in on itself, which led to the creation of a nucleus and additional internal membranes.
In other words, the eukaryote cell would eat the prokaryote, but would not actually digest it. It would instead keep the bacterium in a symbiotic relationship so that the two co-exist together. The symbiont would then begin to lose some of its genetic material as it forms into a mitochondrion.
This process would then continue because the eukaryote and mitochondria are still existing in a symbiotic relationship. The theory holds that the eukaryote and mitochondria symbiont would eat an autotrophic eukaryote cell, but again not actually digest it. As before, the new cell would also be kept as a symbiont. The secondary symbiont would also lose some of its genetic material during this process and this would be the foundation of the creation of a chloroplast.
It is believed that this process would have occurred in the earlier days of our planet’s history. It could be as much as 2.5 billion years ago. By having the prokaryote utilizing cellular respiration to convert organic molecules into energy, the cells would be too small to be digested by a eukaryotic cell, but would instead live inside the hose cell, contributing to the host’s eventual evolution.
When Was Endosymbiotic Theory First Proposed?
Endosymbiotic theory was first proposed by Konstantin Mereschkowski in 1910. He worked as a botanist and through his work, found the ideas described above to be plausible. It would be more than 50 years before the microbiological evidence discovered by Lynn Margulis in 1967 would help to substantiate the theory.
Mereschkowski primarily researched lichens and had previously published some of the initial fundamentals of symbiogenesis in a 1905 paper that explored the origins and nature of chromatophores in the plant kingdom.
Lichens were his primary point of fascination in the development of this theory because he found that there was a symbiotic relationship between algae and fungi. With over 2,000 specimens collected, it is still in the possession of Kazan University where much of his work takes place.
Evidence from biochemical and molecular sources suggests that mitochondria were developed from proteobacteria and chloroplasts came from cyanobacteria, which would eventually help to form the backbone of life on our planet as we know it.
How Endosymbiotic Theory Influences Evolution
When many discuss the theory of evolution, it is usually the theory that was proposed by Charles Darwin that is looked at. Endosymbiotic theory is more of a rebuttal of Darwinian evolution because it does not rely on the idea that natural selection can explain the full branches of biological novelty. Symbiogenesis offers an alternative where acquisition and inheritance of microbes is the primary life development factor.
The evidence to support Endosymbiotic theory is a list that is quite lengthy.
- Mitochondria and plastids are formed through a process that is similar to binary fission, which is the form of cell division that bacteria use.
- When mitochondria or chloroplasts are removed from a cell, then the cell loses the ability to create new ones.
- Porins are found in the outer membranes of mitochondria, chloroplasts, and bacterial cells.
- Certain mitochondria and plastids contain a single, circular DNA molecule that is similar to bacterial DNA is size and structure.
- Mitochondria and plastids have small genomes when compared to bacteria. Neither organelle is capable of surviving outside the cell, which supports the idea of increased dependence as offered through Endosymbiotic theory.
- Ribosomes found in mitochondria and plastids are more like those found in bacteria than in eukaryotes.
- Some species of lice have multiple chromosomes in the mitochondrion. This, along with other genetic evidence, suggests that mitochondria have multiple ancestors that were acquired by symbiogenesis on several different occasions instead of just one single incident.
When looking at Endosymbiotic theory through modern science, it appears that there were extensive mergers and rearrangements of genetic material in several of the original mitochondrial chromosomes. In looking at lice at this level, it shows that the symbiotic relationships in the ancient world could have formed to work together in a way that could create the building blocks of life as we know it on our planet today.
How Endosymbiotic Theory Affects Creationism
In many circles, the idea that evolution and creationism could work together is seen as absurd. They are often treated as two conflicting theories. Yet the processes described in Endosymbiotic theory correspond with the creation processes that are described within the first chapter of the book of Genesis.
This means there must be a separation between “Old World” creationists and “New World” creationists when it comes to looking at actual creation theory. New World creationists view the book of Genesis literally, with creation taking 6 literal days. From an Old World perspective, the “days” mentioned in Genesis could be an indeterminate amount of time.
This means the process of Endosymbiotic theory for the origin of eukaryotic cells could help to explain how God created the world just as they would help to explain how the world naturally evolved on its how without supernatural influence.
Why You Need to Get to Know Angomonas Deanei
Angomonas denai is a protozoan. This parasite is found in the GI tract of insects. In a closer inspection of this parasite, it has been found that it is a hose to symbiotic bacteria. The symbiont relationship is so extensive, in fact, that the two have formed a permanent relationship. Neither can survive on its own without the other.
This relationship serves as a model for evidence of endosymbiotic theory in practice today in nature. It was first discovered in 1973 and its cell membranes exhibit unusual features that include membrane lipids that are mostly present in the symbiotic prokaryotes of eukaryotic cells.
The One Issue with the Endosymbiotic Theory
When we discuss evolutionary theories or creationism, the goal is often an attempt to explain the origin of the universe. The fact is that no one understands what the universe was like right before or right after matter was created. At some point, primordial energy, space, and time had to arise somehow. The Endosymbiotic theory does not make an attempt to explain the start of the universe.
It instead attempts to explain the start of how life as we know it was able to form.
Theories are mathematical models that allow us to be able to make a prediction about the world and how it behaves. At the quantum level, which is sub-atomic, we can make predictions about behavior in terms of distance, but not about how the universe itself formed.
This is why it is important to understand what the purpose of a theory happens to be. For some, the creation of the universe is tied to the creation of the planet. For others, these are two separate events that require two separate theories to create a plausible explanation.
It could be that life on our planet is unique because of the factors explained through Endosymbiotic theory. It could also mean that the origin of eukaryotic cells is very common throughout the universe and that life is evolving in unique ways on many different planets that have yet to be discovered.
Our universe may be entirely unique. It may just be one of many universes that exist on a scale that goes beyond anything that exists in our imagination. Some may feel that the universe was made for us, while others believe that we were made through a natural process. The bottom line is this: we exist. How we exist may be explained by the endosymbiotic theory of the origin of eukaryotic cells or some other theory.
We must keep asking questions. Only when we continue to seek with an open mind will we be able to find our answers.