Chapter 23 - The Evolution of Populations

• When it comes to evolutionary change in populations, we may define evolution on the smallest scale, known as microevolution, as a change in allele frequencies in a population across generations.

• Microevolution is caused by factors other than natural selection. Natural selection, genetic drift (chance occurrences that modify allele frequencies), and gene flow (the transfer of alleles across populations) are the three primary processes that can induce allele frequency change.

• Each of these processes has a different impact on the population’s genetic makeup. Only natural selection, on the other hand, continuously enhances the degree to which organisms are well fitted for life in their environment (adaptation).

• Evidence of food source selection is shown in the attached image.

• The data are adult beak depth measurements of medium ground finches hatched before and during the 1977 drought. Natural selection resulted in a higher average beak size in the population in one generation.

• Darwin offered copious evidence in The Origin of Species that Earth's life had developed through time, and he postulated.

• Natural selection has been identified as the major mechanism for this transformation. He discovered that people differ in their innate characteristics and that such distinctions are subjected to selection, resulting in evolutionary change. Despite the fact that Darwin recognized that variation is heritable, he was unsure of the specifics of how creatures pass on heritable characteristics to their offspring.

• Only a few years after Darwin's publication of The Origin of Species, Gregor Mendel published a seminal work on inheritance, in the pea plants Mendel presented a model of heredity in that publication.

• A population, or a confined collection of organisms belonging to the same species, is bound together by its gene pool, which is the sum of all the alleles in the population.

• If the population is big, mating is random, the mutation is minimal, there is no gene flow, and there is no natural selection, the allele and genotype frequencies will remain constant in Hardy-Weinberg equilibrium.

• If p and q indicate the frequencies of the only two potential alleles at a specific locus in such a population, then p 2 is the frequency of one kind of homozygote, q 2 is the frequency of the other type of homozygote, and 2pq is the frequency of the heterozygous genotype.

• Allele frequencies in a population can be altered through natural selection, genetic drift, and gene flow.

• Individuals with particular hereditary qualities are likely to live and reproduce at a faster rate than other individuals due to those features under natural selection.

• Chance variations in allele frequencies across generations tend to diminish genetic diversity in genetic drift. The movement of alleles across populations, known as gene flow, tends to diminish genetic differences between groups over time.

  

• One organism has greater relative fitness than another organism if it leaves more fertile descendants. The modes of natural selection differ in their effect on phenotype as shown in the attached image above.

• Natural selection, unlike genetic drift and gene flow, continuously raises the frequencies of alleles that improve survival and reproduction, therefore enhancing the degree to which organisms are well-suited for living in their environment.

• Secondary sex traits can develop through sexual selection, giving individuals an advantage in mating.

  • The term Balancing selection refers to a phenomenon that occurs when natural selection maintains two or more forms in a population.

• Historical limitations limit evolution. Each species has a lineage with modifications from ancestral forms. Evolution does not start from the beginning with the ancestral anatomy; rather, evolution co-opts existing structures and adapts them to new conditions. We may assume that if a terrestrial species were to adapt to an environment where flying would be advantageous, it would be preferable to simply develop an extra set of limbs to act as wings.

• However, evolution does not function in this manner; rather, it operates on the qualities that an organism already possesses. As a result, in birds and bats, an existing set of limbs took on new tasks for flying as these organisms evolved.

• Adaptations are frequently tradeoffs. Each creature must perform a variety of tasks. A seal spends some of its time on rocks; it could presumably walk better if it had legs instead of flippers, but it wouldn't be able to swim as well.

• Our prehensile hands and flexible limbs give us a lot of adaptability and athleticism, but they also leave us prone to sprains, torn ligaments, and dislocations: For agility, structural reinforcing has been sacrificed.