6: The Evolution of Populations and Species
- Page ID
- 69829
- Introduce the concept of evolution at the population level
- Explore mechanisms of evolution with an emphasis on natural selection
- Determine how to quantify evolution using the Hardy-Weinberg equation
- Apply the mechanisms of evolution to the production of new species
- 6.1: Introduction
- All life on Earth is related. Evolutionary theory states that humans, beetles, plants, and bacteria all share a common ancestor, but that millions of years of evolution have shaped each of these organisms into the forms seen today. Scientists consider evolution a key concept to understanding life. Natural selection is one of the most dominant evolutionary forces.
- 6.2: Population Evolution
- Initially, the newly discovered particulate nature of genes made it difficult for biologists to understand how gradual evolution could occur. But over the next few decades genetics and evolution were integrated in what became known as the modern synthesis—the coherent understanding of the relationship between natural selection and genetics that took shape by the 1940s and is generally accepted today.
- 6.3: The Hardy-Weinberg Equilibrium
- The Hardy-Weinberg law argues that the gene frequencies and genotype ratios in a randomly-breeding population remain constant from generation to generation. Evolution involves changes in the gene pool, while a population in Hardy-Weinberg equilibrium shows no change. Hence, populations are able to maintain a reservoir of variability so that if future conditions require it, the gene pool can change.
- 6.4: Population Genetics
- Individuals of a population often display different phenotypes, or express different alleles of a particular gene, referred to as polymorphisms. Populations with two or more variations of particular characteristics are called polymorphic. The distribution of phenotypes among individuals, known as the population variation, is influenced by a number of factors, including the population’s genetic structure and the environment.
- 6.5: Formation of New Species
- Although all life on earth shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and have offspring that can then successfully reproduce. Scientists call such organisms members of the same biological species.
- 6.6: Reconnection and Rates of Speciation
- Speciation occurs over a span of evolutionary time, so when a new species arises, there is a transition period during which the closely related species continue to interact.
Natural selection is one of the most dominant evolutionary forces. Natural selection acts to promote traits and behaviors that increase an organism’s chances of survival and reproduction, while eliminating those traits and behaviors that are to the organism’s detriment. But natural selection can only, as its name implies, select—it cannot create. The introduction of novel traits and behaviors falls on the shoulders of another evolutionary force—mutation. Mutation and other sources of variation among individuals, as well as the evolutionary forces that act upon them, alter populations and species. This combination of processes has led to the world of life we see today.
Contributors and Attributions
Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at http://cnx.org/contents/185cbf87-c72...f21b5eabd@9.87).