Info

Interbreeding population (parent species)

Daughter species B

Time

Interbreeding population (parent species)

Daughter species B

Time

24.3 Speciation May Be a Gradual Process In this hypothetical example, genetic divergence between two separated populations begins before reproductive incompatibility evolves.

Agelaius phoeniceus (female)

altered by natural selection over time. But not all evolutionary changes result in new species: A single lineage may change over time without giving rise to a new species.

The critical event in speciation is the separation of the gene pool of the ancestral species into two or more separate and isolated gene pools. Subsequently, within each isolated gene pool, allele and genotype frequencies may change as a result of the action of evolutionary agents. If two populations are isolated from each other, and sufficient differences in their genetic structure accumulate during the period of isolation, then the two populations may not be able to exchange genes when they come together again. As we will see, the amount of genetic difference that is needed to prevent gene exchange is highly variable. Gene flow among populations may be interrupted in two major ways, each of which characterizes a mode of speciation.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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