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.
In fact, the average male will produce roughly 525 billion sperm cells over a lifetime and shed at least one billion of them per month. A healthy adult male can release between 40 million and 1.2 billion sperm cells in a single ejaculation.
Answer: Letter E - exons are cut from the strand and removed
Explanation:
Letter A and B are incorrect because the poly-A tail and guanine cap are added to the 3’ and 5’ end respectively. They aid in translation of the mRNA, while serving as protection. The poly-A tail is repeated adenine nucleotides, while the guanine cap is a modified guanine nucleotide.
Letter C is incorrect because alternative splicing is one mechanism for generating variation, and is thought to be one of the reasons for why humans have smaller genomes than other organisms and still maintain high complexity. Alternative splicing is incredibly important because it produces more than one transcript from a pre-mRNA.
Letter D is incorrect because introns are the non coding portions of the mRNA. They are excised to make a smaller mRNA transcript, and one that contains all the protein genes.
This letter E is the correct answer, because exons are the coding portions of the mRNA, and are not excised during RNA processing.
Hope that helped! If I made a mistake, please let me know.
