Natural selection is the process by which individuals with characteristics that are advantageous for reproduction in a specific environment leave more offspring in the next generation, thereby increasing the proportion of their genes in the population gene pool over time. Natural selection is the principal mechanism of evolutionary change, and is the most important idea in all biology. Natural selection, the unifying concept of life, was first proposed by Charles Darwin, and represents his single greatest contribution to science.
Natural selection occurs in any reproducing population faced with a changing or variable environment. The environment includes not only physical factors such as climate or terrain, but also living factors such as predators, prey, and other members of a population.
Mechanism of Natural Selection
The mechanism of natural selection depends on several phenomena:
• Heredity: Offspring inherit their traits from their parents, in the form of genes.
• Heritable individual variation: Members of a population have slight differences among them, whether in height, eyesight acuity, beak shape, rate of egg production, or other traits that may affect survival and reproduction. If a trait has a genetic basis, it can be passed on to offspring.
• Overproduction of offspring: In any given generation, populations tend to create more progeny than can survive to reproductive age.
• Competition for resources: Because of excess population, individuals must compete for food, nesting sites, mates, or other resources that affect their ability to successfully reproduce.
Given all these factors, natural selection unavoidably occurs. Those members of a population that reproduce the most will, by definition, leave more offspring for the next generation. These offspring inherit their parents' traits, and are therefore also likely to succeed in competition for resources (assuming the environment continues to pose the same challenges as those faced by parents). Over several generations, the proportion of offspring in a population that are descended from the successful ancestor

Uloborid spider eggs and spiderlings. In any given generation, populations tend to create more offspring than can survive to reproductive age.
increases, and traits that made the ancestor successful therefore also increase in frequency. Natural selection leads to adaptation, in which an organism's traits conform to the environment's conditions for existence.
An operational definition is used for a behavior so that the
behavior can be properly described and understood. Without an operational
definition, it would be difficult to describe behavior without being subjective.
Therefore, behavior cannot be understood and cannot be correctly addressed. It
is also important to understand how behavior functions so that the antecedents
and consequences of behavior can be observed. Thus, what reinforces or affects the
behavior can be better understood. Lastly, an operational definition is
objective and specific, therefore, behavior can be described across different
settings and times.
Changes in the transcription of mRNA or the translation of a polypeptide are not considered to be mutations because they are not permanent changes to the cell.
Explanation:
The half-life of mRNA and proteins is short. mRNA has an average of 10 hours of life span while proteins have an average of several days. Therefore mutation in these biomolecules will only persist as long as this mutated mRNA of protein exists. After its life-span, the molecule is degraded and replaced by a non-mutated mRNA or proteins. This is because the piece of DNA that codes for the mRNA and subsequent protein is not mutated. A mutation on DNA is the permanent kind of mutations because DNA is a highly stable molecule that stores information about the cell.
