BIOL 112 Lecture 1

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Chapter 22: Descent with Modification

A Darwinian View of life

Theory of Evolution

Original thesis by Charles Darwin: The Origin of Species

Based on 3 observations: (theory is meant to explain...)

1. Adptation: Animals are well-adapted to their environment
2. Shared Characteristics: Different animals have a lot of things in common
3. Rich Diversity: The number of species on the planet is huge

Common Ancestry: time ------------>

Ancestor |-- gen 1 | |-- gen 2 | | |-- gen 3 | | `-- gen 3 | `-- gen 2 | |-- gen 3 | `-- gen 3 `-- gen 1

   |-- gen 2
   |   |-- gen 3
   |   `-- gen 3
   `-- gen 2
       |-- gen 3
       `-- gen 3

Natural selection = evolution; gen $n$

Phylogenetic trees (cladograms):

e.g. root is ancestor of all animals and leaves are species

tree representation of time/diversity branching.

closer forks are more recent

above animals, all life can be traced to common ancestor.

Before Darwin

1. Aristotle's Scala Naturae put forth that organisms were unchanging—no evolution
   • Arranged organisms by increasing complexity (with something visible to naked eye—fungi perhaps—, and humans on top, of course)
2. Genesis: creation, unchanging

(continued in BIOL 112 Lecture 2)