Darwin defined the term Evolution as “descent with modification.” In common terms, biological evolution is the process of change by which new species develop from preexisting species over time and in genetic terms, evolution can be defined as any change in the frequency of alleles in populations of organisms from generation to generation.
“Nothing in biology makes sense except in the light of evolution”. Theodosius Dobzhansky
Usually evolution and natural selection are regarded as synonyms ( because of popularity of Darwin and his concept), but Natural selection is one of mechanisms by which evolution works.
Darwin concepts of evolution :
Darwin’s observations during his travels resulted in some outstanding books including his famous 1859 book origin of species , which established evolution by common descent as the dominant scientific explanation of diversification in nature. He put forward four fundamental concepts in his most famous work :
-More young are produced each generation than can survive to reproduce.
-Individuals in a population vary in their characteristics. Some differences among individuals are based on genetic differences.
– Adaptation: all organisms adapt to their environments.
– Individuals with favourable characteristics have higher rates of survival and reproduction.
“In the survival of favoured individuals and races, during the constantly-recurring struggle for existence, we see a powerful and ever-acting form of selection.” Charles Darwin
One of Drawin’s most revolutionary idea was that all organisms on earth are related and connected to each other like branches of a giant TREE OF LIFE
“From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so they can be classed in groups under groups.” Charles Darwin
Modern theory of evolution:
Today’s evolution theory is primarily based on two important facts :
All living things are related to one another (to different extents) through common decent (share common ancestors), have developed from other species, and all life forms have a single common ancestor. Each organism presently living on earth has arisen from 3.8 billion years ago common ancestor. Thus making us all belong to one huge family. Understanding the evolutionary relationships between members of family will give us an idea how we, and all diverse life forms around us come into existence.
A new species results from random heritable genetic mutations (changes). Mutations that result in an advantage to survive and reproduce are more likely to be retained and propagated than mutations that do not result in a survival to reproduce advantage.
Evidence for evolution in action :
The wide of evidence is available for common descent, indicating occurrence of evolution, leading to variety of life forms on earth.
But for this post we just briefly discuss about evidence provided by Fossils and Molecular data.
Fossils are the remains of creatures which existed long ago.(Oldest Known fossil is 600 MYA, as we known life existed from 3.8 billion years ago and to simplify this confusing number game Dinosaurs became extinct 65 million years ago)
-Older geological strata contain extinct organisms
– Fossils in adjacent strata are typically more similar than fossils in non-adjacent strata
-Fossils become progressively more different from contemporary species in progressively older (lower) strata.
-Fossils appear in the order which we would predict from the universal tree
Closely related contemporary species are typically also close geographically, regardless of their habitat or specific adaptations
Fundamental aspect of life :
– All known extant organisms are based on the same fundamental biochemical organisation: genetic information encoded as nucleic acid (DNA, or RNA for viruses), transcribed into RNA, then translated into proteins (that is, polymers of amino acids) by highly conserved ribosomes.
– Perhaps most tellingly, the Genetic Code (the “translation table” between DNA and amino acids) is the same for almost every organism, meaning that a piece of DNA in a bacterium codes for the same amino acid as in a human cell.
-All species use catalysts (enzymes) based on protein molecules built from the same set of 20 amino acids (from more than 390 naturally occurring)
– ATP is used as energy currency by all extant life.
– All species use extremely similar metabolic pathways and enzymes for their basic metabolism (e.g., glycolysis, the citric acid cycle, and oxidative phosphorylation).
Related stuff on web for in depth reading :