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.
EtBr inserts between the stacked bases in the DNA double helix.
Explanation:
EtBr is used for visualizing DNA bands as it fluoresces under the UV illumination.
EtBr is an aromatic compound that is capable of inserting itself between the stacked bases of the DNA double helix.
The hydrophobic environment around the base pairs where the EtBr intercalates is responsible for the fluorescence. As the EtBr molecule intercalates between these base pairs the cation of EtBr sheds the water molecules associated with it and this causes it to fluoresce under UV light as water is a quencher of fluorescence.
False. The driving for is the partial pressure gradient of O2 (PO2 difference), not the PCO2 gradient.
However, keep in mind that an increase in PCO2 can facilitate the unbinding of oxygen from hemoglobin. This is due to a decrease in pH associated with PCO2 increase. The H+ ions bind to hemoglobin and decrease it's affinity for oxygen, this is called the bohr effect. But the PCO2 is not the main driving force of oxygen unbinding.
C. The small rocks are mechanically weathering the larger rocks and erosion is morning the pieces downstream
There is no chemical change in this so it has to be mechanically. Than erosion is causing the rocks to be moving the pieces downstream. Deposition means another thing...
