Glossary
Adaptation
A heritable trait that has evolved through natural selection and increases an organism's fitness in its specific environment.
Example:
The thick blubber of a polar bear is an adaptation that helps it survive and thrive in extremely cold Arctic environments.
Artificial Selection
The intentional breeding of plants or animals by humans for specific desirable traits, leading to significant changes in populations over generations.
Example:
Farmers selectively breeding corn plants for larger, sweeter kernels over many generations is an example of artificial selection.
Bottleneck Effect
A sharp reduction in the size of a population due to environmental events or human activities, resulting in a significant loss of genetic diversity.
Example:
When a natural disaster like a flood drastically reduces a deer population, the surviving individuals may have a much smaller and less diverse gene pool, illustrating the bottleneck effect.
Cladograms
Diagrams used in cladistics to show hypothetical evolutionary relationships between groups of organisms based on shared derived characteristics (synapomorphies).
Example:
A cladogram might group birds and reptiles together based on shared characteristics like amniotic eggs, even though they appear very different, indicating a common evolutionary lineage.
Endosymbiosis
The theory that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by ancestral eukaryotic cells and established a symbiotic relationship.
Example:
The fact that mitochondria have their own circular DNA, similar to bacteria, supports the theory of endosymbiosis.
Fossil Record
The totality of preserved remains or traces of organisms from the past, providing direct evidence of evolutionary change over geological time.
Example:
The discovery of dinosaur bones and ancient plant imprints in sedimentary rock layers contributes to the fossil record, showing how life has changed over millions of years.
Founder Effect
A type of genetic drift that occurs when a new population is established by a small number of individuals, whose gene pool may not reflect the genetic diversity of the original larger population.
Example:
A small group of migrating birds establishes a new colony on a remote island; the genetic makeup of this new colony might differ significantly from the original mainland population due to the founder effect.
Gene Flow
The transfer of genetic material (alleles) from one population to another, typically through the migration of individuals or gametes.
Example:
When pollen from a distant population of wildflowers is carried by wind to a new meadow and fertilizes plants there, it introduces new alleles through gene flow.
Genetic Drift
Random fluctuations in allele frequencies within a population from one generation to the next, especially pronounced in small populations.
Example:
If a small group of butterflies is isolated on an island, a random event like a strong wind could disproportionately kill off individuals with a certain wing color, causing a shift in allele frequencies due to genetic drift.
Geographical Distribution
The study of where species live and how their distribution patterns provide evidence for evolution and common ancestry.
Example:
The fact that marsupials are predominantly found in Australia, despite similar habitats elsewhere, is explained by their unique evolutionary history and geographical distribution.
Hardy-Weinberg Equilibrium
A theoretical model describing a population that is not evolving, where allele and genotype frequencies remain constant from generation to generation under specific conditions.
Example:
If a population of fish experiences no mutations, random mating, no gene flow, no genetic drift, and no natural selection, it would be considered to be in Hardy-Weinberg Equilibrium.
Molecular and Cellular Similarities
The presence of shared fundamental biological molecules (like DNA, RNA, proteins) and cellular structures across diverse organisms, indicating common ancestry.
Example:
All living organisms use the same genetic code to translate DNA into proteins, demonstrating profound molecular and cellular similarities that point to a common ancestor.
Mutation
A random, permanent change in the DNA sequence of an organism, which can introduce new alleles and genetic variation into a population.
Example:
A spontaneous mutation in a fruit fly's gene might cause it to develop white eyes instead of red, introducing a new trait into the population.
Natural Selection
The process by which individuals with advantageous heritable traits in a specific environment are more likely to survive and reproduce, passing those traits to their offspring.
Example:
In a forest, green beetles are camouflaged better than brown beetles on leaves, so more green beetles survive to reproduce, leading to an increase in the frequency of the green allele in the population through natural selection.
Origin of Life
The scientific study and hypotheses concerning the natural processes by which life on Earth arose from non-living matter.
Example:
Scientists conduct experiments to understand how simple organic molecules could have formed on early Earth, contributing to our understanding of the origin of life.
Phenotype
The observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment.
Example:
A person's curly hair, blue eyes, and ability to digest lactose are all aspects of their phenotype.
Phylogenetic Trees
Branching diagrams that illustrate the evolutionary relationships and common ancestry among different species or groups of organisms over time.
Example:
A phylogenetic tree can show that humans and chimpanzees share a more recent common ancestor than either does with gorillas, illustrating their evolutionary divergence.
Speciation
The evolutionary process by which new and distinct species arise from a common ancestral population, often due to reproductive isolation.
Example:
If a river changes course and divides a population of squirrels, over many generations, the two isolated groups might evolve so differently that they can no longer interbreed, leading to speciation.
Variation
The presence of diverse traits or characteristics among individuals within a population, some of which are heritable.
Example:
Within a population of sunflowers, some plants might grow taller, some might have larger flower heads, and others might bloom earlier, showcasing the variation present.