Evolution

Origins of life Origin of species (diversification of life)

Origins of adaptation

The reproductive process in biology inevitably produces evolutionary change

• Mutations will occur: p(mutation)>0. • To the extent that populations are separated

from one another, divergence will occur. • i.e., some amount of evolution is an

inevitable result of thermodynamics associated with reproduction.

Evidence of Evolution Ch 24

• Change through time: –  Fossils: extinction, transitions, environmental change

–  Comparative studies: vestigial traits –  Current studies: drug resistance, etc

•  Species are related to one another. –  Biogeography

–  Homology: structural, developmental, molecular (genetic)

Fossils

Georges Cuvier (1773–1838)

• First detailed study of fossils.

• Comparative anatomy. • Correlation of parts. • Extinction.

Fossil dating

Generic dating. Ppres = Porig (2 (-age/halflife)) – Isochronic dating is better in

that it avoids assumption that there was no daughter isotope at t=0, and will signal if new material was added to the site at a later date.

Fossil Dating

• Radioactive decay and absolute age:

• earth 4.6 by old. Life arose ~3.8 by ago. First Eukaryote fossils ~1.5 by ago.

• Humans diverged from other Apes ~5 my ago. Homo sapiens ~0.5 my ago.

Extinction

• The Irish elk: actually an extinct deer. Widely distributed in Pleistocene.

• Cuvier 1812 described fossil remains. Evidence of extinction.

• Many examples are now known of extinct creatures preserved as fossils from all eras.

Transitional forms • Birds and other dinosaurs • Whales and Ungulates

Darwin noted that fossils in an area often resembled organisms living in the area

Vestigial traits

• Reduced or modified function.

• Even molecular examples: L-gulano-γ-lactone oxidase: gene required to synthesize vitamin C.

•  non functional in humans, guinea pigs.

Environmental Change

Species are related to other species

•  Species fall into groups within groups. Indicates branching evolutionary processes; descent with modification. Doesn’t occur with man-made objects or rocks and minerals.

Galapagos Islands

Homology

• Genetic: even the codons (3 base code for each amino acid) are preserved across wide arrays of organisms.

Homology–Developmental

• Human coccyx • Gill pouches in Tetrapods

(p. 512) • Goethe and the sutures in

the skulls of apes and humans.

Structural/developmental homology

Structural homology–cont’d

• Bone for bone homology (some fusion/loss) across array of Tetrapods

Origin of Adaptation

• Originally thought of as design: God conferred appropriate structures on organisms. Chain of Being.

• Lamarck proposed Evolution to explain the nested pattern of similarity. Mechanism: use and disuse (organismal drive or will) and inheritance of acquired characteristics.

Darwin 1809–1882

• Malthus’ essay on population growth invoked the idea of competition in a high mortality environment.

• Developed an explicit model model of natural selection.

Natural selection

• Organisms in a population vary with respect to various traits.

• Some of this variation is heritable.

• In each generation more individuals are produced than can survive (struggle for existence)

• The subset that survive each generation will be enriched for heritable variation that allow them to outcompete other variants.

Natural selection and antibiotic resistance.

•  Mycobacterium tuberculosus

TB an important disease

• ~25% of deaths in NY City in 1804.

• Treatment in early 20th century: pneumothorax and rest.

• With advent of antibiotics, TB declined in 1950s.

• Began to increase again in 1980s and 90s.

Oft repeated scenario…

• Individual enters hospital with symtoms of TB.

• Treated and observed for a number of weeks until judged cured.

• Returns some months later with renewed case of TB–unresponsive to antibiotics.

What happened?

• Did variation exist in the original infecting population?

• Was the variation heritable? • Did the new variant affect reproductive

success? • Did selection occur?