You might have pondered over the thought that when did humans come to earth or what was the first creature like on earth? What was earth like before all this concrete jungle? What came first- plant or animals or both originated simultaneously? These are only a few questions that we have asked ourselves from our childhood. With so many theories from around the world given by many people in different timelines, evolution is truly a subject of keen interest. Evolution is a wide subject and includes various topics under it, here’s a short glimpse of it.
WHAT IS EVOLUTION?
Stanford Encyclopedia of Philosophy states that – Evolution in biology typically refers to the changes in the proportions of biological types in a population over time. Evolution basically means an orderly change from one condition to another condition.The Father of evolution is Charles Darwin. The term ‘Evolution’ was coined by Herbert Spencer. Many theories, books and works were published stating different theories.
BIG BANG THEORY
Big bang theory is the leading theory which thoroughly explains the origin of the universe. This theory was put forward by Georges Lemaitre in 1927. According to it, the universe originated about 20 billion years ago due to thermonuclear explosion of a dense entity. This single huge explosion which is quite unimaginable in physical terms, is known as the big bang theory. The universe expanded and hence, the temperature came down. The gaseous clouds which were formed by the big bang started condensing under the gravitation and converted into many flat discs like a structure called nebula, made up of atoms and small particles. Solar nebula was one of them and it formed our solar system. The very hot central part of the solar nebula became still hotter and converted into what we know today as the sun. Later on, thanks to condensation of atoms and dust particles moving around the sun other planets were formed. In the solar system of the Milky Way galaxy, earth was supposed to have been formed about 4.5 billion years back. There was no atmosphere on early earth and it formed later on. Just two years later in 1929, an astronomer named Edwin Hubble noticed that other galaxies were moving away from us. And that’s not all. The farthest galaxies were moving faster than the ones close to us.
THEORIES OF ORGANIC EVOLUTION
1. LAMARCKISM (Theory of inheritance of acquired characters)-
The first ever logical theory of evolution was proposed by a French naturalist Jean Baptiste de Lamarck (1744- 1829) and the book which he wrote was Philosophie Zoologique (1809).
BASIC CONCEPTS OF LAMARCKISM-
INTERNAL VITAL FORCES:
Due to the presence of some internal vital forces all organisms have the tendency to increase in size of their organs or entire body.
EFFECT OF ENVIRONMENT AND NEW NEEDS:
Environment influences all types of organisms in the surrounding. Changing environments give rise to new necessities and demands. New needs or desires produce new structures (doctrine of desire/ appentency) and change habits of the organism.
USE AND DISUSE OF ORGANS:
If any organ is continuously used over generations, it would become better developed due to constant use whereas less used organs result in its regression and ultimately it becomes vestigial organs.
INHERITANCE OF ACQUIRED CHARACTERS-
During the lifespan of an organism, new characters develop due to the effect of environment, internal vital forces, new needs or use and disuse of various organs. According to Lamarck, all these acquired characters are inherited from generation to generation (but that is not the case). Due to continuous inheritance through several generations, the variations are accumulated to such an extent that these can even play a major role in generating a whole new species.
EXAMPLES OF LAMARCKISM-
- Lamarck gave the example of giraffes who in an attempt of foraging leaves on tall trees had to adapt by making their neck elongated. As they passed on this acquired character of elongation of neck to subsequent generations. Giraffes gradually over the years came to acquire long necks.
- Aquatic birds expanded their toes and developed webbed feet. Snakes lost their leg and started to slither or creep.
⇒Lamarck had said that the evolution of various life forms had occurred but is driven by the usage or disuse of organs. Nobody believes this speculation any more.
2. DARWINISM (Theory of Natural Selection)
This theory was put forward, as the name suggests, by Charles Darwin. He was very much influenced by two books- first, ‘Principle of population’ by Malthus, second, ‘Principle of geology’ by Charles Lyell. Darwin took a voyage around many places on H.M.S. Beagle ship. Alfred Wallace, a naturalist who worked in Malay Archipelago had also come to similar conclusions around the same time and he sent his conclusions to Darwin in the form of a chart. This theory was mentioned in Darwin’s book On the Origin of Species
BASIC CONCEPTS OF DARWINISM-
Branching descent and Natural selection are the two key concepts of Darwinian Theory of evolution.
NATURAL SELECTION/ SURVIVAL OF THE FITTEST–
Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable that is, they all are different in some ways. Hence, those who are better fit in an environment would be selected by nature and love more progeny than others and this is what Darwin called natural selection and implied it as a mechanism of evolution.
STRUGGLE FOR EXISTENCE–
Natural resources are limited and populations are stable in size, so there is constant competition for resources. It is of three types:
- INTRASPECIFIC STRUGGLE: Competition among individuals within the same species, most acute type of struggle.
- INTERSPECIFIC STRUGGLE: Competition among the individuals of different species and this type of competition is the most potent force for organic evolution.
- ENVIRONMENTAL STRUGGLE: Struggle between organisms and surrounding.
All the organisms are capable of producing enormous number of offsprings but actually population size is limited.
VARIATIONS AND HEREDITY:
The characteristics which enable some to survive better in natural conditions like climate, physical factors, etc are called adaptive or useful variations while others are called non – adaptive or harmful variations.
ORIGIN OF NEW SPECIES-
Due to heritable variations and natural selection, there would be change in characteristics of population and hence new species arise.
Darwin’s theory couldn’t explain few concepts like there was no mention of genetics, existence of vestigial organs, differentiation between somatic and germinal variations.Though this theory explained survival of fittest but was unable to tell about arrival of fittest.
One question which is often asked is that what exactly is evolution- a process or the result of a process? What world we see today, whether organic or inorganic, these all are glorious stories of evolution. When we describe the story, we describe evolution as a procedure. Then again, when we explain the tale of life on earth, we treat evolution as an outcome of a process called natural selection. It’s still not quite very distinct whether to regard evolution and natural selection as process or consequence of unknown processes.
What are your views on this?
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