Human Evolution
The evolutionary process leading to the appearance of modern humans is known as Human Evolution. If we talk in simple terms then Human Evolution means the development of human beings on earth. It is all about changes, improvement and modification from simple life forms. Human Evolution study is very complicated so this study falls under a lot of scientific fields including physical anthropology, paleontology, embryology and genetics etc
Origin of life
Scientists hypothesise that the universe came into existence about 14 billion years ago with a colossal explosion.
This theory attempts to explain the origin of universe, approximately 20 billion years ago, when the universe was very hot and dense and expanding rapidly. After initial expansion, energy conversion had occurred to form various subatomic particles including protons, neutrons and electrons. With the cooling of universe, after thousands of years, some other reactions lead to the formation of first electrically neutral atoms.
The atoms formed by big ban were hydrogen, helium and some traces of lithium.
Mainly, it was known that the life originated approximately 3,600 million years ago. This was evident by the discovery of fossil of cyanobacteria. The early thought was that living things arose from non-living things i.e. spontaneous generation, which was disproved by Louis Pasteur.
Still scientists are unable to identify ”Origin of life”
Mostly accepted theory of “Origin of life” states that life originated or earth through physicochemical processes of atoms that combined to form molecules to produce inorganic and organic compounds.
Some theories that explain the scientific basis or organic evolution are
Lamarckism
Lamarck had mainly thrown more light on the concept of evolution and provided two main ideas .
- “Theory of use and disuse:” i.e., the body parts used more often become stronger and larger, while the parts that are not used gets degenerated and disappear. i.g Human Tail
- “Inheritance of acquired characters:” i.e., the physical change acquired by an organism over the period of time according to environment hence also called the theory of adaptation.
Darwinism
He made the most impressive study on evolution. He got an opportunity to travel on HMS Beagle ( a ship) on which he sailed around the world.
Darwin found a living laboratory of evolution in Galapagos Islands and found closely related species of Finches.
The common bird of Galapagos Islands, the finches were markedly different from the finches of the main land. From this island only, he took an idea for his theory of natural selection.
Key information
- The rate of appearance of new forms is linked to the life cycle or life span.
- Nature selects for fitness, based on characteristic which are inherited.
- Organism adapt to survive otherwise hostile environment.
- Adaptive ability is inherited, i.e., on the basis of genetics.
- Fitness is the end result of the ability to adapt and get selected by nature.
Mutation Theory
Mutation is defined as the phenomena in which DNA sequences are altered and consequently result in changes in the genotype and the phenotype of an organism. The factors that cause mutation are known as mutagens. The mutagens can both be physical or chemical.
Mutation can occur in two forms
i) Gene Mutation
ii) Chromosomal Mutation
Hugo found mutation in evening primrose and proposed that the new species arise by sudden variations.
Salient features of mutation theory
- Evolution is a jerky process where new varieties and species are formed by mutations.
- Mutation or discontinuous variations are the raw material for evolution.
- Mutation may be sudden or operational.
- All mutations are inheritable.
- One type of mutation can appear in different individuals.
Evidences of Organic Evolution
Various evidence in support of organic evolution comes from different sources.
- Evidence from Morphology and Comparative Anatomy
- Evidence from connecting links
- Evidence from Genetics
- Evidences from Embryology
- Evidences from Fossils
Evidence from Morphology and Comparative Anatomy
i) “Homologous Oragans:” These are the organs having same embryonic origin and basic structure but have different functions. e.g., forelimbs of grog, bird and human.
ii) “Analogous Organs:” These are the organs having similar functions but different in embryonic and basic structure e.g., wings of insets and birds.
iii) “Vestigial Organics:” These are non-functional organs which were functional in the ancestral forms e.g., underdeveloped libs of snakes, feather or kiwi, human skin hair, vermiform appendix, etc. Sudden reappearance or re-functioning of some ancestral organs is called atavism or reversion.
Evidence from connecting links
A number of organisms have characteristics of two different group, thus are called connecting links.
Some examples of connecting links are
| Organism | Connecting link ( in between) |
|---|---|
| Euglena (Protozoa) | Animal and Plant |
| Proterospongia (Protozoa) | Protozoa and Porifera |
| Neopilina (Mollusca) | Annelida and Mollusca |
| Dipnoi (Lung fish) | Pisces and Amphibia |
| Archaeopteryx (Aves) | Reptiles and Aves |
| Prototheria (Mammalia) | Reptiles and Mammalia |
Evidence from Genetics
Different hybrid varieties of any particular species show close resemblances to their close relation. e.g., mule originated from hybridisation of horse and donkey.
Evidences from Embryology
The theory of recapitulation of biogenetic Law was proposed by Haeckel. It states that an individual in its development (ontogeny) tends to repeat the stages passed through by its ancestors (Phylogeny) e.g., ‘Ontogeny recapitulates Phylogeny’. Organism of different groups resemble with their embryos.
Evidences from Fossils
Remains of ancient lives, as bone, teeth, shale, etc are called fossils. These are generally found in sedimentary rocks. Age of fossil is determined by lead-uranium method, carbon dating method. Fission track and electron spin resonance methods. Coprolites are fossils, with faeces containing salt of phosphates.
This evolutionary process shows changes and development series in humans with time.
Ancestor Series
Dryopithecus
They lived 20 to 25 million years ago. They were ape-like in appearance and were hairy having arm and legs of same length, large brain and walked like gorillas and chimpanzees.
Ramapithecus
They lived 15 million years ago. They were more man like and are also hairy, walked like gorillas and chimpanzees.
Tanzania
They lived 4 million years ago. They were smaller than 4 feet and walked upright and appear man like primater.
Homohabilis
They lived 2 million years ago. They are fruits eaters. They have brain capacities of between 650cc-800cc. They use stone weapon for hunting. They appear like humans.
Homan Erectus (Java Man)
They lived 1.5 million years ago. They were probably meat eaters and have brain capacity of around 900cc. Their height was about 5 ft 8 in tall.
Neanderthal man (Primitive man)
They lived 1 million - 40000 years ago. They have brain capacity of around 1400cc. They used hides to protect themselves and buried their dead.
Homo Sapiens (Modern Man)
After last glacial period or ice age modern man have evolved. They have brain capacity of 1450cc.
Important information
First mammals were like shrews.
Dinosaurs were considered as land reptiles and biggest of them was Tyrannosaurus about 20 feet in height..
Lobefins evolved into first amphibians that lived on both land and water. These were considered as the ancestors of modern frogs and salamanders.
It is believed that in future, humans could change due to various factors like gene mutation, gene recombination, natural selection, etc. HL sapiro named the future man Homo Sapiens Futuris.
References
Human Evolution
Age of the earth
Human Evolution
Mutation
Evolution
Some Important Connecting Links
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