Origin of Life
* The origin of life is interlinked with the evolution of the earth, which is linked with the evolution of the universe.
* The universe is vast and comprises many galaxies and is almost 20 billion years old.
* The Big Bang Theory refers to a singular huge explosion which caused the infinitesimally small, hot and dense universe to expand and then cool.
* Panspermia is the oldest theory expounded by the Greeks which assumes that units of life called spores were transferred to different planets.
* The theory of Spontaneous Generation believed that life came out of decaying and rotting matter such as straw and mud.
* Louis Pasteur founded the theory of Biogenesis, which explains that life comes only out of pre-existing life.
* The theory of Chemical Evolution, which states that the first life forms arose from non-living molecules through evolutionary forces, is now widely accepted.
Evolution of Life Forms
* Most religious literature believes in the divine creation of the world.
* Religious thoughts about creation faced opposition in the 19th century from naturalists such as Charles Darwin and Alfred Wallace.
* Charles Robert Darwin suggested that complex organisms have evolved from simple ancestors.
* Darwin published the Theory of Evolution in 1859 in his book ‘On The Origin Of Species’.
* Darwin and Alfred Wallace pointed out that natural selection was the mechanism of evolution.
* Wallace did extensive field work in the Amazon River Basin and the Malay archipelago.
* Darwin and Wallace suggested that existing life forms share similarities and common ancestors which were present during different geological periods.
Evidence for Evolution
* The evolution theory becomes more evident with the study of fossils.
* Fossils are the preserved remains of animals, plants and other organisms found in the sedimentary layers of rocks.
* Fossils suggest that some life forms varied during various periods of the earth’s history.
* Radioactive dating is one of the techniques used to determine the actual or relative age of the earth’s crust, fossils and old artefacts.
* Fossils help compare the internal anatomy or organisms of the past with that of today. This is also known as comparative anatomy.
* Fossils are also of great help in morphological and anatomical studies.
* When the same structures develop along different directions because of specific needs of different animals, they are known as homologous structures.
* When anatomically different structures evolve to perform similar functions in different organisms, they are known as analogous structures.
* In a mixed population, organisms which can adapt have better chances of survival and increasing their population size.
Adaptive Radiation
* Charles Darwin observed the concept of adaptive radiation in the finches of the Galapagos Islands.
* Adaptive radiation is a type of evolution in which species in the same geographic area, derived from a common ancestor, successfully adapt themselves to their natural environment due to natural selection.
* In adaptive divergence, animals of the same or closely related group exhibit great divergence in their morphology when found in a different habitat. For example, the finches of the Galapagos Islands.
* In adaptive convergence, animals of unrelated groups occupying the same habitat exhibit common features. For example, Australian marsupials.
Biological Evolution
* Darwin pointed to natural selection as the most vital concept in evolution.
* Natural selection allows organisms to inherit traits from previous generations.
* Darwin thought that the rate of appearance of new life forms was linked with their life span.
* Darin believed that inherited variations in organisms helped them utlilise natural resources to the maximum and survive.
* The theory of natural selection stresses of the fittest.
* Darwin refuted the old theory of evolution of the sue and disuse of organs propounded by French naturalist Jean-Baptiste Lamarck.
* Gregor Johann Mendel, the founder of genetics, pointed out that inheritable factors influences genotypes.
* Hugo de Vries argued that suede mutations in populations brought about evolution.
The Hardy-Weinberg Principle
* English mathematician Godfrey Hardy and German physician Wilhelm Weinberg founded the Hardy-Weinberg Principle.
* As per the Hardy-Weinberg Principle, allele and genotype frequencies in a population remain in genetic equilibrium unless specific disturbing influences are introduced.
* The totality of alleles of all genes in a population is the gene pool, which remains constatnt for a given population. no mutations, random mating and non-occurrence of migration.
* Genetic equilibrium is affected by factors such as gene migration, gene flow, genetic drift, mutation, genetic recombination and natural selection.
* Natural selection can give rise to situations such as stabilization directional change and disruption.
A Brief Account of Evolution
* Cyanobacteria or ‘blue-green algae’, was the first form of life on earth formed around 2,000 MYA.
* The geologic time scale is divided into eons- Precambrian and Phanerozoic.
* Different life forms evolved in the three eras of the Phanerozoic eon.
* In the Cambrian period, plant life consisted of primitive algae and sea weeds while animal life consisted of invertebrates such as sponges, starfish and sea urchins.
* The Ordovician period marked the evolution of the first vertebrate, the jawless fish around 350 MYA.
* The Pteridophytes of the Carboniferous era formed coal deposits.
* Amphibians are said to have evolved from lobe-fin such as the Coelacanth during the Carboniferous period.
* In the Permian period of the Paleozoic era, amphibians evolved into reptiles.
* Dinosaurs were a diverse group of reptiles which survived successfully for 160 million years during the Jurassic period of the Mesozoic era.
* The evolution of mammals was a slow process that began in the Cenozoic era and spanned 70 million years.
Origin and Evolution of Humans
* Man, chimpanzees, gorillas, orangutans and human beings are four memberspecies of the hominidae family.
* Dryopithecus was a genus of ape that lived in East Africa, Europe and Asia around 25 TO 9MYA.
* Ramapithecus was a primate that lived between 2 million and 14 million years ago.
* Australopithecines lived in the grasslands of East Africa around 2 MYA.
* The first human-like being was Homo Habilis who lived in sub- saharan Africa between 2 million and one point 5 MYA.
* Homo erectus were human beings of medium stature who walked upright and flourished till about 2, 000, 000 years ago.
* Neanderthal Man, with brain size of 1,400 cubic centimeters lived in Europe, Northern Africa and Eastern and Central Asia between 1,00,000 and 40,000 years ago.
* The Neanderthal man wiped out by the Cro-magnon man or Homo sapien fossilis about 25,000 years ago.
* Homo sapiens sapiens evolved between 75,000 and 10,000 years ago during the Ice Age.