Endosymbiont Hypothesis and Membrane Invagination Hypothesis

Concept of Evolution

In a bid to discuss the cause of the diversity of life and correlation amongst living organisms, two schools of thought emerged in the earlier 19th century. Creationists believed in the Theory of SpecialCreation, whereas evolutionists believed in the Theory of Natural Selection. According to the theory of special creation, all living things originated in their present forms especially and specifically created by Nature. Amongst the scientists who believed in divine creation was Carolus Linnaeus (1707-1778).

The concept that organisms might develop through time, with one kind of organism causing another kind of organism, is an ancient one, existing from the days of Aristotle. Aristotle recognized that organisms varied from relatively basic to really complicated structures. However, the present-day principle of evolution is based on known history.

Let us now talk about some details of the work done by these scientists. As you know, Carolus Linnaeus in the eighteenth-century classified organisms. He grouped similar species in the same genus and similar genera in one family. But as a natural theologian, he thought that species were permanent creations. A century later, the taxonomic system of Linnaeus ended up being a centerpiece in Darwin’s arguments for evolution.

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Evolution from Prokaryotes to Eukaryotes

Among the speculations attempting to explain the origin of life is that it might have begun deep in the oceans, in undersea warm springs called hydrothermal vents. These vents could have provided the energy and basic materials (for the origin and survival of early life kinds. A group of bacteria, called archaebacteria-that tolerate temperatures as much as 120 ° C and appear to have actually undergone less evolutionary change than any other living species supports this vent hypothesis.

The nutrients produced in the primitive environment would have limited early life. If life were to continue, another source of nutrients as needed. Photosynthesis, probably released living organisms from a diminishing supply of nutrients.

The first photosynthetic organisms most likely used hydrogen sulfide as a source of hydrogen for reducing CO2 to sugars. Later, water served this same function, and oxygen freed by photosynthetic responses started to accumulate in the environment. Earth and its atmosphere slowly started to alter.

Ozone in the upper atmosphere started to filter ultraviolet radiation from the sun, the reducing atmosphere slowly ended up being an oxidizing atmosphere, and a minimum of some living organisms started to utilize oxygen. About 420 million years ago, enough protective ozone had actually developed to make life on land possible. Ironically, the modification from a reducing environment to an oxidizing environment also implied that life could no longer occur abiotically.

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The first cells were more than likely really simple prokaryotic forms. The prokaryotes might have developed more than 3.5 billion years back. Eukaryotes are believed to have first appeared about 1.5 billion years ago.

Endosymbiont Hypothesis

The eukaryotic cell may have developed when a large anaerobic (living without oxygen) amoeboid prokaryote ingested small aerobic (living with oxygen) bacteria and stabilized them instead of absorbing or digesting them. This concept is referred to as the endosymbiont hypothesis and was first proposed by Lynn Margulis.

According to this hypothesis, the aerobic bacteria turned into mitochondria, which are the sites of aerobic respiration and many energy conversions in eukaryotic cells. The belongings of these mitochondria like endosymbionts brought the advantage of aerobic respiration to the host.


Flagella (whiplike structures) might have arisen through the consumption of prokaryotes similar to spiral-shaped bacteria called spirochetes. Intake of prokaryotes that looked like present-day cyanobacteria might have caused the endosymbiotic development of chloroplasts in plants.

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Membrane Invagination Hypothesis

Another hypothesis for the evolution of eukaryotic cells proposes that the prokaryotic cell membrane invaginated (folded inward) to confine copies of its hereditary product. This invagination led to the formation of a number of double membranes bound entities (organelles) in a single cell. These entities might then have actually evolved into the eukaryotic mitochondrion, nucleus, chloroplast, and so on.


Whatever the exact mechanism for the advancement of the eukaryotic cell might be, the formation of the eukaryotic cell led to a significant boost in the intricacy and diversity of life-forms on the earth. At first, these newly formed eukaryotic cells existed only on their own.

Later, nevertheless, some most likely developed into multicellular organisms in which different cells became specialized into tissues, which, in turn, formed organs for many different functions. These multicellular kinds then adjusted themselves to live in a huge range of environments.