Review
- Basic idea: “Descent with modification, change in genetic composition over time from generation to generation”
- Specific: the process by which frequency of heritable traits in population changes from one generation to the next
- A population is evolving if their allele frequencies are changing
- Model for evolution: survival and reproduction
Evolution: Earlier Theories
- Use and disuse: describe how body parts of organisms can develop with increased usage while unused parts weaken → idea was correct like among athletes
Inheritance of acquired characteristics: described how body features acquired during an organism’s lifetime (ex: muscle bulk) could be passed onto offspring → idea was incorrect bcuz only genetic material of cells can be passed on
- Catastrophism: The reason for different fossils in different strata of rocks was because of mass extinction events (true)
- Strata: layers of rock
Evidence for Evolution
- Paleontology: provides fossils of extinct species → changes in species and formation of new species can be studied
- Fossils removed from successive layers of sediment (deeper = older) show gradual changes alternating with rapid changes
- Large, rapid changes produce new species
- Age of fossils determined using C-14 dating; older = less C-14
- Biogeography: the study of the distribution of species → reveal that unrelated species in different regions in the world look like when found in similar environments
- Ex: rabbits did not exist in Australia until introduce by humans → native Australian wallaby resembles rabbit both in structure and habit
- Embryology: reveals similar stages in development among related species → similarities establish evolutionary relationships
- Gill sites, arches, and tails are found in mammal embryos
- Comparative Anatomy: describes two kinds of structure used to establish evolutionary relationships among species + there are heritable variations among individuals
- Homologous Structures (homologies): body parts that resemble one another in different species because have evolved from a common ancestor
- Anatomy may by modified for survival in specific environments→ homologous structures may look different, but will resemble one another in pattern (Similar structure, diff function)
- Forelimbs of cats, bats, whales, and humans are homologous bcuz evolved from common mammal
- Vestigial Structures: body parts that used to serve function in common ancestor but not anymore
- Ex: remnants of limbs in snakes, hindlimbs in whales, and wings of flightless birds
- More recent homologous characteristics shared by smaller group
- Analogous structure (analogies): body parts that resemble one another in different species, not because evolved from common ancestor, but because evolved independently as adaptations to similar environment (similar structure and function)
- Ex: fins and body shapes of sharks, penguins, whales, and poiposies bcuz are adapted to swimming
- Results from Convergent Evolution: when similar environmental pressures and natural selection produce similar traits in unrelated organisms
- Homoplasy: trait species share due to convergent evolution
- Molecular Biology: examines nucleotide and amino acid sequences of DNA and proteins from diff species
- Closely related species share higher % of sequences than distantly related species
- More than 98% of sequences in humans and chimpanzees are identical
- Shows how morphology is not only way
- More than 98% of sequences in humans and chimpanzees are identical
Distantly related species have different DNA bases and lengths bcuz of deletions & insertions
- Molecular data more accurate/reliable bcuz directly shows genetic makeup
- Bcuz of redundancy of the genetic code, gene bases in different species can differ slightly and produce same protein
- Use base sequences NOT base-pair percentages to infer relatedness