18: Evolution, Darwin, and Evidence

• fixed ideal species: based on the belief that organisms are genetically suited for the world. The belief is that the species are "fixed" in traits and characteristics because no more changes need to occur.

• scala naturae
– (ladder of nature)

Orderly, nested classification system
• Binomial naming (species, genus, etc.)

• fossils are a record of change over time caused by catastrophic events
• Connected fossil structures with likely habitats

• rock strata mark relative ages
• species changed because of local extinctions
– area recolonized by different species

1. is a goal oriented process
2. it moves toward a more perfect/complex species/organism
3. an organims can evolve in its lifetime
4. an organism can influence its own evolution in response to its environment
5. it is a completely random process

it is the change in organisms throughout Earth's history (descent with modification)

• Father of Modern Geology
• uniformitarianism expanded Hutton’s ideas:
– same geologic processes in past as today
– same rate as today
• thus earth is extremely old!

him and Darwin were colleagues

1. Organisms adapt ot their food source and environment
2. antibiotic resistance in bacteria
3. the fossil record (many extinct species)
4. transition of adaptive form over time (homologous strucutures)
5. similarity of cell structures, proteins, & DNA corresponds to relatedness, The genetic code is universal!
6. unique (endemic) species on islands are similar to nearest mainland species

distribution of species that corresponds to geographic history
Ex: australian marsupials are isolated

unrelated species have similar adaptations (analogous structures) under similar environmental conditions
• Why? -- convergent evolution (natural selection acted in same way under same conditions)
• Ex: torpedo shape for swimming (dolphins, seals, and sharks are diff species but all have the torpedo shape to swim better in their environment)
-thick thorns and stems in deserts

remnants of ancestral (homologous) structures with no present adaptive function
• Ex: blind cave salamanders have eyes--- Why?
–infer: descended from a species that could see

Homology = forms related by common ancestry

–Homologous structures are derived from a common
ancestor (but may be modified for
different functions)

EX: forearm limbs of different mammals have the same boine structure but have diff, functions

All present life is related thru “descent with modification” from a common ancestor in past.

– Part 2: Natural selection is the mechanism for evolution.
• Obs. #1: Heritable variation exists in most species

Obs. #2: All species produce more offspring
than the environment can support. Many,
many offspring die before maturity!

Ex: –farmers can enhance small heritable variations by
artificial selection (breeding)

Inference #1: There is unequal reproductive success among individuals (this is the “selection” part)
– those with the “best” traits (help them survive & reproduce in their environment) leave more offspring than others.

Inference #2: Those heritable, favorable traits (adaptations) accumulate over vast time, matching the species to its environment ... AND eventually lead to new species

• linked evolution to adaptation
–extinct species have been replaced by descendants w/
new features
»these adaptations helped them survive in
environment

• first to propose a mechanism for evolution:
–“use & disuse” “use it or lose it”
–“inheritance of acquired characteristics”
–but, it’s wrong!

Planting seeds of this bonsai bush and expecting the resulting shrub to look just like this one ( a carefully trimmed bonsai with a specififc design)