According to Darwin\'s Principles, what pre-conditions are required if a populat

Question

According to Darwin's Principles, what pre-conditions are required if a population is to evolve by natural selection?

What was Darwin's model for heredity, and how did it weaken his argument that natural selection was the only adequate explanation for adaptation?

What are the possible explanations for the existence of several different alleles in a population? (e.g., why hasn't one been fixed and the other gone extinct?).

How can migration influence the frequency of alleles in a population? (Think of the model of migration to an island from the mainland. What happens to the island's allele frequencies over time due to migration from the mainland population?)

If you detect a deviation in genotype frequencies from that expected by the Hardy-Weinberg relation, what possible explanations should you consider for the differences?

Under what conditions will natural selection cause evolutionary change in one situation and no evolutionary change in another?

What are some of the genetic mechanisms leading to new genetic variation?

How did the popular notion of evolution in the late 19th and early 20th centuries differ from Darwin's original notions and from the Modern Synthesis of Evolutionary Theory?

Compare homologies and analogies before and after Darwin. (i.e., how did Darwin change our interpretations of homologies and analogies from those of Aristotle?)

Distinguish between our modern notions of Evolution and Natural Selection.

Explanation / Answer

According to Darwin's Principles, what pre-conditions are required if a population is to evolve by natural selection?

1: process by which forms of organisms in a population that are best adapted to the environment increase in frequency relative to less well-adapted forms over a number of generations.
2: the non-random and differential reproduction of different genotypes acting to preserve favorable variants and to eliminate less favorable variants; viewed as the creative force that directs the course of evolution by preserving those variants or traits best adapted in the face of natural competition

Pre-conditions for natural selection.  The preconditions to natural selection are excess fecundity and the consequent competition for limited resources. Weeds produce many more seed than will survive. Many more seed germinate and form seedlings than will mature to produce their own seed. Only the successful competitors will reproduce, mortality is very high.

Four (4) conditions for natural selection. Four conditions are needed for natural selection to occur: reproduction, heredity, variation in fitness or organisms, variation in individual characters among members of the population. If they are met, natural selection automatically results.

1: Reproduction:  the act or process of producing offspring
    A condition necessary for evolution to occur is that a parent plant produces more offspring than can normally survive. The net (average) result of reproduction is that a parent plant leaves one descendant that reproduces, yet many more are produced that die. See Life History for full treatments of reproduction in weedy populations.

2: Heredity:  the mechanism of transmission of specific characters or traits from parent to offspring.
inheritance: the transmission of genetic information from ancestors or parents to descendants or offspring.
    A condition necessary for evolution to occur is that the traits of the "fittest" phenotypes that survive are inherited by the successful progeny. The offspring must tend to resemble their parents. Molecular genetics and biochemistry provide significant information about how this process occurs.

3: Variation in fitness of organisms. Definitions of fitness:
1: the average number of offspring produced by individuals with a certain genotype, relative to the numbers produced by individuals with other genotypes.
2: the relative competitive ability of a given genotype conferred by adaptive morphological, physiological or behavioral characters, expressed and usually quantified as the average number of surviving progeny of one genotype compared with the average number of surviving progeny of competing genotypes; a measure of the contribution of a given genotype to the subsequent generation relative to that of other genotypes
    A condition necessary for evolution to occur is variation in fitness of organisms according to the state they have for a heritable character. Individuals in the population with some characters must be more likely to reproduce, more fit. Organisms in a population vary in reproductive success. We will discuss fitness in Life History when we discuss competition, interference and the effects of neighbor plants. See also pages on Fitness & Fecundity in the reproductive life history section.

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