Evolution and Origin of Life: Key Concepts and Theories in Biology

Early Earth Atmosphere

Primarily $CO_{2}$, CO, $H_{2}O$, $N_{2}$, methane ($CH_{4}$), and ammonia ($NH_{3}$); notably lacked oxygen ($O_{2}$).

Miller-Urey Experiment

1950s experiment that produced organic molecules (amino acids) from inorganic gases and electrical sparks.

Endosymbiotic Theory

Theory that mitochondria and chloroplasts originated as independent prokaryotes engulfed by early eukaryotic cells.

Evidence for Endosymbiosis

Mitochondria and chloroplasts have their own DNA, bacterial-like ribosomes, and reproduce via binary fission.

Biological Fitness

The combination of physical traits and behaviors that help an organism survive and reproduce in its environment.

Homologous Structures

Structures with similar internal bone patterns but different functions; evidence of a common ancestor.

Analogous Structures

Structures with similar functions but different internal builds; result of convergent evolution, not common ancestry.

Vestigial Structures

Organs or structures that no longer serve a function but are remnants from an ancestor (e.g., whale hind leg bones).

Directional Selection

Natural selection that favors individuals at one end of the phenotypic curve (e.g., long-necked giraffes).

Stabilizing Selection

Natural selection that favors average individuals and acts against extremes (e.g., human baby birth weight).

Disruptive Selection

Natural selection that favors both extremes of a trait over the average (e.g., birds with only small or large beaks).

Genetic Drift

Random changes in a gene pool, typically occurring in small populations.

Bottleneck Effect

A sharp reduction in population size due to a random event, drastically reducing genetic variation.

Founder Effect

Occurs when a few individuals start a new population, carrying only a fraction of the original gene pool's alleles.

Reproductive Isolation

Barriers (habitat, temporal, behavioral, or mechanical) that prevent two populations from interbreeding.

Convergent Evolution

Unrelated organisms evolve similar traits because they occupy similar environments (e.g., dolphins and salmon).

Divergent Evolution (Adaptive Radiation)

The process where one species evolves into many different forms to fit different niches.

Coevolution

Two species evolving in close relationship with one another (e.g., an orchid and its specific moth pollinator).

Antibiotic Resistance

Natural selection where bacteria with spontaneous mutations survive antibiotics and pass resistance to offspring.

Speciation

The formation of a new species resulting from reproductive isolation and genetic changes over time.