Evolution

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

1. 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

1. 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

1. 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

1. 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

1. Embryology: reveals similar stages in development among related species → similarities establish evolutionary relationships

• Gill sites, arches, and tails are found in mammal embryos

1. Comparative Anatomy: describes two kinds of structure used to establish evolutionary relationships among species + there are heritable variations among individuals

1. 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

1. 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

1. 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

                             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