Evolution &
Systematics
How organisms change over time and how scientists study their evolutionary relationships.
Evolution is the process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. It involves cumulative changes in the heritable characteristics of a population over time.
Mechanisms of Evolution
Biological evolution occurs through several key mechanisms that change the genetic composition of populations over generations.
Natural Selection
Survival and reproduction of individuals with favorable traits. Example: Peppered moths evolving darker wings during the Industrial Revolution for better camouflage.
Genetic Drift
Random changes in allele frequencies, especially in small populations. Example: A natural disaster reducing a population size significantly, leaving a small, random group of survivors.
Gene Flow
Movement of individuals (and their genetic material) between populations. Example: A bird flying to a new island and mating with the local population, introducing new alleles.
Mutation
Spontaneous changes in the DNA sequence. Example: A DNA copying error during cell division leads to a new feather color in a bird species.
Sexual Selection
Selection through mate choice or competition for mates. Example: Peacock feathers being large and colorful to attract peahens, even if they aren't ideal for avoiding predators.
Evidence of Evolution
Scientists draw from multiple fields of study to reconstruct the history of life on Earth. These different lines of evidence all point to a common conclusion: organisms have changed over vast periods of time through the process of evolution.
Systematics
Taxonomy is the science of classifying and naming living organisms based on their characteristics and evolutionary relationships.
- Domain — broadest classification group
- Kingdom — groups organisms based on major characteristics
- Phylum — groups organisms with similar major body structures
- Class — groups related organisms within a phylum
- Order — groups related organisms within a class
- Family — groups closely related organisms within an order
- Genus — groups very closely related species
Connect the Concepts
In summary, evolution is the driving force of biological diversity, powered by specific mechanisms and supported by vast evidence. By studying systematics and reconstructing phylogenetic trees, we can map out these complex relationships and trace the lineage of all life back to common ancestors.
Key Terms
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Evolution
A process of gradual change that takes place over many generations, during which species change some of their physical characteristics.
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Natural Selection
The process whereby organisms better adapted to their environment tend to survive and produce more offspring.
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Phylogeny
The evolutionary history of a species or group of related species.
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Taxonomy
The branch of science concerned with classification, especially of organisms; systematics.
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Speciation
The formation of new and distinct species in the course of evolution.
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Cladistics
A method of classification of organisms according to the proportion of measurable characteristics that they have in common.
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Homology
Characters in different organisms that are similar because they were inherited from a common ancestor that also had that character.
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Genetic Drift
Variation in the relative frequency of different genotypes in a small population, owing to chance disappearance of genes.
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Gene Flow
The transfer of genetic material from one population to another.
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Systematics
The study of the diversification of living forms and their evolutionary relationships.