Introduction:

Evolution is stated as 'common descent'. Due to descent with modification, all living things share the similar basic features: they are made up of cells, take chemicals and energy from the environment, respond to the external stimuli and reproduce. Living things are diverse as individual organisms exist in most of the environments all through the Earth, and the traits or feature which let them to survive in such environments are quite diverse. Most of the fields of biology give proof which evolution via descent with modification occurred in the past and is still occurring.

Evolution affects each and every feature of the form and behavior of organisms. Most of the prominent are the specific behavioral and physical adaptation which is the outcome of natural selection. Such adaptations raise fitness by aiding actions like finding food, avoiding predators or fascinating mates.

Evidences of Evolution:

The proofs or evidences supporting organic evolution are derived from the number of fields of biology which are as follows: Fossil evidence, Anatomy evidence, Biochemical evidence and Biogeographical evidence.

1) Fossil Evidence:

Fossils are basically the remains and traces of past life or any other direct proof or evidence of the past life. Most of the fossils comprise only of hard parts of organisms, like bones, shells and teeth, as these are generally preserved after death. The soft portions of a dead organism are frequently consumed through scavengers or decomposed by bacteria. Occasionally, though, an organism is buried rapidly and in such a manner that decomposition is never finished or is completed so gradually that the soft portions leave an imprint of their structure. Traces comprise trails, burrows, footprints, worm casts or even preserved droppings.

The huge majority of fossils are found embedded in the sedimentary rock. Sedimentation, a process which has been going on since Earth formed, can occur on land or in bodies of water. The weathering and erosion of rocks generates particles which differ in size and are termed as sediment. As such particles build up, sediment becomes a stratum (pl., strata), a recognizable layer of rock. Any given stratum is older than the one above it and younger than the one instantly below it, so that the relative age of fossils can be found out based on their depth.

Paleontologists are biologists who study the fossils record and from it draw conclusions regarding the history of life. Specifically interesting are the fossils which serve up as transitional links among groups. For illustration, the famous fossils of Archaeopteryx are intermediate among birds and reptiles. The dinosaur-like skeleton of this fossil consists of reptilian features, comprising jaws having teeth and a long, jointed tail, however Archaeopteryx as well had wings and feathers, all recommending that reptiles evolved from birds.

The absolute dating process relies on radioactive dating methods to assign an actual date to a fossil. All radioactive isotopes encompass a specific half-life, the length of time it takes for half of the radioactive isotope to change to the other stable element. Carbon 14 (¹⁴C) is the merely radioactive isotope in the organic matter. By employing both relative and absolute dating process, we can learn from fossils about the different organisms and environments which existed across the planet all through any period of time.

2) Biogeographical evidence:

The other kind of proof or evidence which supports evolution via descent with modification is found in the field of biogeography, the study of distribution of species all through the world. Various mammals and flowering plants evolved separately in each and every Biogeographical area and barriers such as mountain ranges and oceans prevented them from migrating to the other areas.

Most of such barriers occur via a process termed as continental drift. That is, the continents have never been fixed; instead, their positions and the positions of the oceans have modified over time. The distribution of numerous organisms on earth is explicable by knowing when they evolved, either prior to or after the continents moved apart.

3) Anatomical evidence:

The fact that anatomical similarities be present among organisms gives additional support for evolution through descent with modification. Vertebrate forelimbs are employed for flight (like birds and bat), orientation throughout swimming (like whales and seals). Running (like horses), climbing (like arboreal lizard), or swinging from tree branches (like monkey). Yet all the vertebrate forelimbs have the similar set of bones organized in the similar manner, in spite of the dissimilar functions. The most reasonable description for this unity is that the basic forelimb plan belongs to a common ancestor and then the plan was altered in the succeeding groups as each continued all along its own evolutionary pathway. Structures which are anatomically identical as they are inherited from a common ancestor termed as homologous structure structures. In contrary, analogous structures serve the similar function, however are not constructed likewise nor do they share a common ancestry. The wings of birds and insect and the eyes of octopi and humans are analogous structure and are identical due to a common ancestry. The presence of homology, analogy, is proof that organisms are associated.

4) Biochemical evidence:

Nearly all the living organism makes use of the similar basic biochemical molecules, comprising DNA, ATP (adenosine triphosphate) and numerous identical or almost similar enzymes. Moreover, organisms make use of the similar DNA triplet code for the 20 amino acid in their proteins. As the sequences of DNA bases in the genomes of many organisms are now known, it has become obvious that humans share a huge number of genes having much simpler organisms. It seems that life's vast diversity has come about by just a slight difference in many of similar genes. The result has been broadly divergent kind of bodies. When the degree of similarity in DNA nucleotide sequences or the degree of similarity in amino acid sequences of proteins is examined, the more identical the DNA sequences are, usually the more closely associated the organisms are. For illustration: humans and chimpanzees are around 99% identical!

Adaptation:

Adaptation is the procedure which makes organisms better suitable to their habitat. As well, the word adaptation might refer to a trait that is significant for an organism's survival. For illustration: the adaptation of teeth of horses for grinding of grass. By utilizing the word adaptation for the evolutionary method and adaptive characteristic for the product (that is, the bodily part or function), the two senses of the word might be differentiated. Adaptations are generated through natural selection. The given definitions are proposed by Theodosius Dobzhansky.

- Adaptation is the evolutionary method whereby an organism becomes better capable to live in its habitat or habitats.

- Adaptedness is basically the state of being adapted: the degree to which an organism is capable to live and reproduce in a given set of habitats. 

- An adaptive feature or trait is a feature of the developmental pattern of the organism that lets or improves the probability of that organism surviving and reproducing. 

Adaptation might cause either the benefit of a new feature, or the loss of the ancestral feature. An instance which exhibits both kinds of change is bacterial adaptation to the antibiotic selection, having genetic changes causing antibiotic resistance by both modifying the target of the drug, and raising the activity of transporters which pump the drug out of the cell.

Adaptation takes place via the gradual modification of existing structures. As a result, structures having similar internal organization might have various functions in the related organisms. This is the outcome of a single ancestral structure being adapted to function in many ways. The bones in bat wings, for illustration, are much identical to those in mice feet and primate hands, due to the descent of all such structures from a common mammalian ancestor. Though, since all living organisms are associated to certain extent, even organs that appear to encompass little or no structural similarity, like arthropod, squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can based on a common  set of homologous genes which control their assembly and function; this is termed as deep homology.

Speciation:

Speciation is basically the origin or evolution of new species. Speciation has occurred if one species gives mount to two species, each of which continues on its own evolutionary pathway. Species is a Latin word meaning 'type' or 'appearance' Species is stated as a group of subpopulations which are able of inter breeding and are isolated reproductively form other species. The subpopulations of the similar species can exchange genes; however various species don't exchange genes. Species have traditionally been illustrated on the basis of their physical form or morphology.

Sympatric speciation:

At times a genetic barrier (that is, reproductive barrier) prevents reproduction among a part of a population of a species by other members. Such a part of population generally occurs in plants because of polyploidy. Polyploidy is a mutation in which the normal diploid number of chromosomes becomes twice or trebled (2n becomes 3n, 4n, 5n and so on) in a part of the population of a species due to certain irregularities throughout the cell division. The polyploid part of the population is then not able to interbreed (mate and reproduce) by other and becomes a new species.

Models of speciation:

There are basically two accepted models of speciation which have given rise to the biodiversity:

1) Phyletic Gradualism model:

The two species from common ancestor steadily become more and more structurally different acquiring adaptations exclusive to each. Darwin as well assumed that evolution is a slow and gradual procedure.

2) Punctuated equilibrium:

A new species occurs via main changes in the starting and then remain constant for longer periods before changing again. This model was recommended through paleontologists (that is, scientists who study fossils), Niles Eldredge and Stephen Jay Gould.

Mechanisms of speciation:

The main four mechanisms of speciation are as follows:

1) Allopatric speciation: It is the classic island speciation introduced by Darwin and later extended, most particularly through Ernst Mayr. Individuals of a species migrate to the island and become isolated from their parent population; natural selection then acts to transform the founder population.

2) Peripatric speciation: It is much similar to the Allopatric speciation however in this case the 'island' does not have to be the oceanic island; it could be an isolated mountain top or forest for instance.

3) Parapatric speciation: It is much similar to the sort of thing Darwin assumed happened when a species expands its range and enters a latest habitat or niche. Natural selection will favor local adaptation to meet up the demands of this latest environment.

4) Sympatric speciation: It is possibly what Darwin meant when explaining local adaptation to various environments in a species range. When new variants occur which are better appropriate to a specific niche they will be favored through natural selection.

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