The centuries-old history of mankind knows many hypotheses about the origin of life on Earth. From the most ancient centuries, there are two completely opposite points of view on this issue. One of them claims that living is born from inanimate - this is abiogenesis. The second is of the opinion that living things can arise only from living things - this is biogenesis. What is the difference between theories of biogenesis and abiogenesis, we will try to understand this article.
History of views
The idea of the origin of life clearly correlates with the level of knowledge of a particular era. In ancient times, when the level of knowledge was still small, the theories of the origin of life are striking in their fantasticness. Here are some views of philosophers and naturalists of the past. For example, Empedocles (V century BC) believed that trees carry eggs. Aristotle (IV century BC) claimed that lice come from meat, and bedbugs come from animal body juice. These views of the spontaneous generation of life as such existed until the middle of the 17th century, when the English philosopher F. Bacon (1561-1626) theoretically, and the Italian physician F. Redi (1626-1698) and Louis Pasteur (1822-1895) practically proved the impossibility of spontaneous generation . It was then that these two opposite camps began to form, two mutually exclusive theories of the origin of life - biogenesis and abiogenesis.
Bit of theory
By abiogenesis (from the Greek prefix of negation - a, bio - life and genesis - origin), we understand the theory of the emergence of organic structures from inorganic and outside a living organism. In a broad sense, abiogenesis is a theory of the origin of living from nonliving. And here you need to clarify what to consider life and when the inanimate becomes alive. And since today the definition of life is interpreted differently and from different points of view, there are many supporters of both abiogenesis and biogenesis.
Life in the theory of abiogenesis
In this concept, the most important are the genetic and evolutionary criteria that determine life. All other criteria - thermodynamic and environmental - are recognized as secondary. The provisions of the concept of the hypothesis of abiogenesis are as follows:
- Living and nonliving differ in chemical composition and its features (metabolism). All theories in this area are called biochemical abiogenesis.
- The origin of life occurred precisely on Earth, in a natural way and with the expenditure of free energy. This is the result of the appearance of complex organic substances from simple inorganic substances with the advent of new chemical reactions between them. All theories of the origin of life in this direction are called geocentric.
- The main properties and signs of living things are metabolism, self-reproduction of their own kind, heredity and variability.
Thus, abiogenesis is geocentric and chemical theories that explain the origin of living things.
Life as a result of biogenesis
Biogenesis focuses on thermodynamic and environmental properties that distinguish living from nonliving. At the same time, genetic, evolutionary and biochemical approaches are considered additional. The concepts of biogenesis are as follows:
- Living, as well as non-living, are two interconnected and inseparable states of matter. These theories are called physical.
- The thermodynamic (opposition to entropy) and systemic (subordination and stable dynamic connections) component are the main properties and signs of life.
- Life arose in the Universe, and the Earth’s biosphere is a manifestation of the living part of the Cosmos. These theories are called cosmic.
Biogenesis, therefore, is a cosmocentric physical theory of the origin of life.
Modern views
Modern science adheres to a point of view that integrates all concepts into a single system of knowledge about how inanimate matter turned into living matter. As the most likely pathway to the origin of living, modern science recognizes that the initial stage is abiogenesis. And it consists of 3 initial stages:
- The appearance of biological monomers.
- The formation of biological polymers.
- The appearance of membrane structures and primary protozoa - protobionts.
Further, the development of life on earth went easier - according to the evolutionary mechanisms of C. Darwin (heredity, variability and selection).
Non-biological formation of organics
Chemical evolution or prebiological abiogenesis is the occurrence of organic substances from inorganic ones. In 1924, the Russian academician A.I. Oparin (1894-1980) suggested that zones of increased concentrations (coacervates or coacervate drops) spontaneously form in the solutions saturated with high molecular weight compounds, which are isolated from the environment but maintain exchange with it. The theory of Oparin in 1929 was supported by the English scientist John Haldane (1892-1964), and the theory of coacervates firmly entered into science, which suggests the spontaneous generation of organic substances in the early stages of the development of our planet with unique physical conditions.
Evidence of the Abiogenesis Hypothesis
At first, it was not possible to prove the possibility of spontaneous synthesis of organic substances from inorganic ones. However, today certain steps have already been taken and the results have been obtained.
It all began in 1953, when chemists Stanley Miller and Harold K. Urey conducted an experiment with primary broth (a medium similar to the prebiotic on Earth). The influx of energy (up to 60 thousand V) under pressure and at a temperature of 80 degrees Celsius led to the formation of fatty acids, urea and several amino acids (protein monomers). And already in 2008, American biologists created a “protocell” with a membrane; in 2011, Japanese biologists published works on the creation of a vesicle with a membrane and the ability to divide.
Shakiness of positions
Despite the successes of biologists in experimental attempts to confirm the Oparin-Haldane theory of the origin of life on the planet in coacervates, all the structures obtained are still far from the structure of a living cell. The world community does not recognize these experiments as undeniable evidence of just such an origin of life. Both biogenesis and abiogenesis are theories that have not yet been experimentally confirmed. Given that the path from inorganic molecules to a living cell was a long one, with many forks and stops, scientists can only hypothesize how this path could have been traveled. But all these hypotheses do not prove that this is exactly what happened on Earth many billions of years ago.
The probability is completely unbelievable
The random occurrence of a living cell in the primary broth is calculated mathematically. British mathematician Fred Hall using modern computers has calculated the probability of an amoeba protein being accidentally formed. And this probability turned out to be negligible - 1/10 * 40,000. Recall that this is under some ideal conditions. And this leads to certain thoughts and gives arguments to supporters of other theories and concepts of the origin of life on our planet.
Incredible likely
But, as you know, everything is relative. On our planet and in our world - this is an indisputable fact. Here are a few examples that will make you wonder - is it really impossible to have such an accident as the appearance of life in the primary broth.
- If a person had a life expectancy of 100,000 years, then we would be guaranteed (that is, 100%) would die in a plane crash.
- The probability of winning the Cool Million lottery is 1 in 5,200,000. Nevertheless, the American Valerie Wilson won the main prize twice: in 2002 and 2006.
- In 2009, the Bulgarian lottery "6 of 41" in two runs with a difference of 4 days dropped the same numbers (4 15 23 24 35 42). The probability of such an event is 3.61 • 10 −14 .