Chapter 13: Processes of Evolution

Merged flashcards from Chapter 13 of Principles of Life, 3rd Edition.

Evolution

Change in the genetic composition of populations over time

• These changes can be observed and measured, allowing for the study of biological diversity

Evolutionary theory

The understanding of evolutionary change processes, achieved through a large body of evidence

• Enables greater biological development, understanding, and prediction

• Term refers to the scientific understanding of change rather than simple observations

Jean-Baptiste Lamarck

A scientist that, in 1809, presented strong evidence for the fact of evolution but lacked a viable explanation of how it occurred

Charles Darwin

A scientist who developed the foundations of evolutionary biology through his observations of finches on the Galapagos Islands, presenting his book On the Origin of Species in 1859

1. Species change over time

2. Divergent species share a common ancestor, and have diverged over time

3. Changes in species can be explained by natural selection

What were Darwin’s three propositions for explaining evolutionary change?

Descent with modification

The divergence of two different species from their original common ancestor

Natural selection

The increased survival and reproduction of some individuals compared to others, based on differences in their traits

1. More individuals of most species are born than survive to reproduce

2. Offspring are not identical to their parents

3. Humans had selected plants and animals based on desirable traits, resulting in changes

What were Darwin’s prior observations supporting his theory of natural selection?

Artificial selection

The selective breeding process, as performed by humans, in order to cultivate desirable traits that were not necessarily advantageous in nature

Alfred Russel Wallace

An English naturalist that presented his ideas of evolutionary theory alongside Charles Darwin in 1858, following his studies of plants and animals in the Malay Archipelago

Population

A group of individuals of a single species that live and interbreed in a particular geographic area at the same time

• Evolution acts on these, not individuals

Mutation

Any change in the nucleotide sequences of an organism’s DNA, performed at random

• Natural selection acts on this depending on whether this is beneficial or harmful

• Enables genetic variation even without other evolutionary processes, accumulating over time

Alleles

Different forms of a gene that exist as a result of mutation

• Individuals have no more than two of these

Gene pool

The sum of all copies of all alleles at all loci found in a population, representing the total variation

Allele frequency

The proportion of each allele in the gene pool

Genotype frequency

The proportion of each genotype among individuals in the population

Adaptation

A favored trait that spreads in a population by natural selection, created through genetic variation

• Can be identified through measuring reproduction rates among organisms

• Seen with wing tails on moths distracting predation by bats

Gene flow

The migration of individuals and movements of gametes between populations

• This can change allele frequencies, adding new alleles or changing proportions

Genetic drift

Random changes in allele frequencies from one generation to the next, potentially with non-biological causes like natural disasters

• Can accumulate to produce large changes in frequencies over time

• Creates even larger effects with dramatic size reductions in a population bottleneck

Population bottleneck

Environmental events where only a few individuals survive out of a typically large population, potentially creating vastly different allele frequencies and reduced genetic variation

Founder effect

A shift in genetic drift that occurs after a few individuals move to a new region, having effects similar to a population bottleneck

Nonrandom mating

This occurs when individuals in a population do not choose mates at random, such as plants preferentially performing self-fertilization

• Increases the frequency of homozygous genotypes (when mating with similar genotypes) or heterozygous genotypes (when mating with different genotypes)

• Only results in allele frequency changes if reproductive success increases, such as with sexual selection

Sexual selection

A type of nonrandom mating that occurs when individuals of one sex mate preferentially with particular individuals of the opposite sex rather than at random

• Seen with bright colors and courtship displays in males of many species, improving either competitiveness or attractiveness

• Primarily focuses on reproductive success, not survival (such as bright colors attracting a predator later on)

Fitness

The reproductive success of a particular phenotype, relative to other phenotypes

Qualitative traits

Traits that are distinguished by discrete qualities, such as smooth or wrinkled pea texture

Quantitative traits

Traits that are likely to show continuous qualitative variation, such as body size

Stabilizing selection (purifying selection)

Natural selection on quantitative traits favoring average individuals

• Reduces variation while maintaining the mean

  • Often selects against deleterious mutations to the usual gene sequence

• Most common action of natural selection

Directional selection

Natural selection on quantitative traits favoring one direction away from the mean of the population

• For a specific variant, this is referred to as positive selection due to the increase in frequency

• Seen with Texas Longhorns evolving longer horn length due to predation in the wild

Disruptive selection

Natural selection on quantitative traits favoring both directions away from the mean of the population

• This increases variation in the population

Polymorphism

The presence of two or more variants of a character in the same population

• Natural selection often preserves variation in this way

Frequency-dependent selection

Selection that changes in intensity with the proportion of individuals in a population having the trait

• Seen with P. microlepis, which prey on fish from one side in equal numbers in order to preserve their distorted mouth characteristic in nature

Heterozygote advantage

The advantage of having two different alleles in an organism compared to having two of the same alleles due to greater adaptability to environments

• Seen with the Colias butterflies of the Rocky Mountains, due to their need to survive in cold and hot temperatures seasonally

Clinal variation

A pattern of gradual change in phenotype across a geographic gradient due to environmental changes

• Seen with T. repens clovers producing varying levels of cyanide due to European temperature differences making production hazardous in colder areas