BIO II: CHP 22

Common Ancestry

Scientific principle that all life on Earth descends from a shared ancestral origin or organism

What's a Theory?

A unifying idea that connects many tested hypothesis supported by evidence

What's a Hypothesis?

Tentative explanation for an observation

Is Evolution a Theory?

Yes.

Evolution

Change in a population of organisms & allele frequencies over time. Common descent with modifications. Mechanisms that shift allele frequencies (ex. genetic drift, gene flow, mutation & Natural selection)

Theory of Common Descent

All modern organisms descended from a single common ancestor

Artificial Selection

Process where humans choose specific plants or animals to breed based on desirable traits

Natural Selection

The process in which organisms with traits best suited to their environment are more likely to survive, reproduce, and pass those traits (alleles) to their offspring. These passed on traits can give rise to new species.

Who Proposed the Theory of Evolution by Natural Selection?

Charles Darwin & Alfred Russel Wallace

Adaptation

Heritable trait that increases an organisms ability to survive and produce an offspring in a particular environment. (increases individual's fitness in a particular environment relative to individuals lacking that trait). NOT ALL traits are adaptive

Microevolution

Genetic adaptation within a species

Macroevolution

Emergence of new species from existing ones. Evidence is found in fossils.

Geologic Time Scale

A chronological timeline that divides Earth's 4.5-billion-year history into standardized intervals based on rock layers and fossil records

How Old Is Life & How is it Shown?

Scientists use radioactive isotopes to determine the absolute ages of rocks and fossils. Geologic data shows that Earth is about 4.6 billion years old, while fossil evidence shows that the earliest signs of life appeared about 3.85 billion years ago.

Species Change Over Time

Fossils provide evidence for extinct species, Darwin interprets that extinct species are evidence that species are dynamic and can change over time

Transitional Forms

The law of succession: Similarity between fossils and living species in the same geographic area (biogeography)

Environmental Change

Earth’s topography and environment have changed over time. Fossil evidence and geologic evidence, including plate tectonics, support this

Vestigial Traits

Reduced or incompletely functioning structures that are similar to functioning structures in related species

Vestigial structures

Remnants of features that served a function in the organisms ancestors

Divergent Evolution

When species share a common ancestor but become increasingly different as they adapt to different environments or ecological niches.

Example: Darwin’s study of mockingbirds where they were superficially similar, but the different islands had distinct species (Genus Mimus). However, they share a common ancestor. They’re different because of adaptation to different ecological niches.

Structural Homologies

Structures in different species that are similar because of common ancestry, (ex. morphological traits: same general limb structure in vertebrates)

Developmental Homologies

Similarity in embryo morphology and/or pattern of tissue differentiation that point to a shared common ancestry

Genetic Homologies

Similarity in the DNA sequences of genes from different species

Homology

Genetic similarities due to common ancestry

Analogous/Convergent Traits

Similar traits that are NOT inherited from a common ancestor

Darwinian Fitness

The ability of an individual to produce offspring relative to other individuals in the population, passing its genes to the next generation (more surviving offspring = higher fitness)

Analogous Structures vs Homologous Structures

Analogous structures arise by convergent evolution while homologous structures exist because of common descent

Genetic Constraints

When one selection on alleles for one trait causes a correlated but suboptimal change in another trait, the possible evolutionary outcomes are limited (Genetic correlation)

Lack of Genetic Varaiton

Constrains evolution, natural selection can work only on existing variation in a population

Historical Constraints

All traits evolve from previously existing traits, adaptations are constrained by history