mod 7 Evolution, Speciation, and Phylogenetics Study Notes

Definition: A change in genetic and phenotypic variation in a population over time.
Example species: Chimpanzee, scientific name Pan troglodytes.
Evolutionary timeline of cranial capacity in the human lineage includes:
- Australopithecus africanus
- Time: 2.5 million years ago
- Cranial capacity: 487 mL
- Homo habilis
- Time: 1.89 million years ago
- Cranial capacity: 506 mL
- Homo rudolfensis
- Time: 1.8 million years ago
- Cranial capacity: 586 mL
- Homo ergaster
- Time: 1.78 million years ago
- Cranial capacity: 825 mL
- Homo heidelbergensis
- Time: 0.35 million years ago
- Cranial capacity: 1310 mL
- Homo sapiens neanderthalensis
- Most recently studied, with varying volumes up to 1650 mL
- Homo sapiens sapiens (Modern Humans)
- Time: 0.03 million years ago
- Cranial capacity: 1616 mL

Allele Frequencies:
- Example of an allele frequency shift from an original to new generation (Original Generation: WW, Ww, ww; New Generation: Frequency of W = 13/18 = 0.72, frequency of w = 5/18 = 0.28)

Stabilizing Selection: Intermediate phenotypes favored (example: robins laying typically four eggs).
Directional Selection: One extreme phenotype is favored over others.
Disruptive Selection: Multiple extreme phenotypes favored; can lead to speciation.

Process by which populations evolve to become distinct species.
Species concepts include:
- Morphospecies Concept: Species defined by morphological differences.
- Ecological Species Concept: Species as groups adapted to specific niches.
- Biological Species Concept: Groups of interbreeding populations reproductively isolated from others (Ernst Mayr, 1942).
Reproductive Isolation:
- Pre-zygotic isolation: Prevents fertilization through factors like temporal, mechanical, and behavioral barriers.
- Post-zygotic isolation: Occurs after fertilization, leading to issues such as infertility or failed development.

Phylogenetic Tree: Illustrates evolutionary history of species or groups.
- Node: Represents a common ancestor from which species diverged.
Synapomorphies: Shared derived traits that suggest recent divergence (e.g., vertebrate phylogeny with traits like jaws, hair, etc.).
Homologous vs. Analogous Structures:
- Homologous Structures: Traits shared due to common ancestry (e.g., bat wing and human arm).
- Analogous Structures: Traits that arise independently due to similar environmental pressures, not shared ancestry (e.g., wings of bats and birds).

Fossils provide evidence of evolutionary changes over geologic time.
Significant mass extinction events:
- Permian-Triassic Extinction: Most catastrophic event approximately 252 million years ago.
- End-Cretaceous Extinction: Resulted in the disappearance of dinosaurs and the rise of mammals.

Divergence from common ancestors began approximately 8-6 million years ago.
Notable species in Homo lineage include:
- Homo heidelbergensis: Estimated brain volume around 1300 mL.
- Homo neanderthalensis: Closest extinct relative, extinct approximately 24,000 years ago.
- Homo sapiens: Behavioral modernity evidenced through cultural evolution and innovations appearing around 50,000 years ago.
Out-of-Africa Hypothesis:
- Suggests that modern humans originated in Africa and migrated to populate the rest of the world, arriving in North America around 15,000 years ago.

Natural selection leads to differences among populations through processes such as mutation, migration, genetic drift, and selective advantages within environmental contexts.
Understanding speciation and phylogeny provides insights into the evolutionary history and relationships among species as well as their adaptations over time.