Natrual variations i think
The post-eradication era is a period of history for which there has been no precedent whatsoever in terms of a zero base of immunity. Cessation of immunization will eventually create a population susceptible to widespread infection in the event of accidental or intentional reintroduction or re-emergence of the eradicated virus. Thus, even after immunization ceases, vaccine production must continue.
However, many currently available vaccines may not be appropriate for continued post-eradication vaccine production or reinstatement. Vaccines must be continually improved and ongoing vaccination research maintained. Other potentially useful antiviral strategies—antivirals, prophylaxis, and probiotics—must also be considered as means to strengthen the immune system and serve as adjuvant or prophylactic therapies.
In the case of polio, for example, it remains to be determined which vaccine (oral polio vaccine [OPV] or inactivated polio vaccine [IPV]), or variant thereof, should be produced in the post-eradication, post-vaccination era. A detailed plan for vaccine production will require more information on OPV-derived viral persistence and transmission, as well as continuing dialogue between public health and research communities in order to ensure that appropriate vaccination research continues.
Answer:
The answer to the given question is C.
Explanation:
Natural selection:
The population contains both superior as well as inferior organisms where natural resources are limiting so it will cause competition between organisms. As a result of competition, it will select superiors, and inferiors are deleted and they are given reproductive advantages. Due to this reproductive advantage new population emerges. It is more suitable for the environment.
Natural selection divides into three parts that are directional, disruptive, and stabilizing selection.
This is an example of natural selection. Environmental conditions create pressure on the individuals and if they can survive and become fittest, their number increases in the population. This is according to Darwin's theory in the struggle for existence. These organisms survived as the fittest organisms to match climatic conditions.
Stabilizing selection: This operates when features coincide with the optimal environmental conditions and the organisms survive in a population. Stabilizing selection pressures do not promote evolutionary change but tend to maintain stability within the population from generation to generation.
In the beginning, directional selection - the organism develops characters to survive in response to gradual changes in the environmental conditions. It works on a range of phenotypes existing within a population and exerts selection pressure which moves the mean phenotype to one phenotypic extreme. When the mean phenotype overlaps with the new optimum environmental conditions, stabilizing selection will take over.
