Evolution of Species

Introduction

  • Charles Darwin is the father of evolutionary theory. He defined Evolution as the “descent with modifications”, which indicates that the plants and animals existing at present are modified descendants of somewhat different plants and animals, which lived in the past.
  • Thus, evolution is the process of gradual developmental modification so as to establish diversity and Complexity in the living world.
  • Evolution is change in the heritable characteristics of biological populations over successive generations.
  • These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction.
  • Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation.
  • Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population.

Natural Selection

  • Natural selection is the process through which species adapt to their environments. It is the mechanism that drives evolution.
  • It is an important mechanism of evolution, the change in the heritable traits characteristic of a population over generations.
  • Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which in his view is intentional, whereas natural selection is not.
  • Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations.
  • Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits.
  • The environment of a genome includes the molecular biology in the cell, other cells, other individuals, populations, species, as well as the abiotic environment. Because individuals with certain variants of the trait tend to survive and reproduce more than individuals with other less successful variants, the population evolves.
  • Other factors affecting reproductive success include sexual selection (now often included in natural selection) and fecundity selection.
  • The genetic basis of a phenotype which gives it a reproductive advantage may become more common in a population. Over time, this process can result in populations that specialise for particular ecological niches (microevolution) and may eventually result in speciation (the emergence of new species, macroevolution). In other words, natural selection is a key process in the evolution of a population.

Evolutionary trend

  • The trend in evolution means that there is ‘steady change is taking place in the adaptation of a particular group of species’.
  • It can either goes with evolutionary lineage or any other attribute in life of organisms.
  • In the geological time scale, there are several species where their evolutionary trend has estimated and give evidence that the nature is selecting the best traits and the evolution is taking place in the species.
  • The evolution helps in understanding how the organism has adapted to the particular environment.
  • Homonidea: family of homo sapiens.
  • Equidea: It the family of
  • Proboscidae: It is the family of elephants.