2. Formation of Species
• Speciation: process of
forming new species
• Results in many related
populations
• May remain similar or
become quite different
3. Concepts of “Species”
• 1) Morphological: species defined by appearance
• Does not account for individual variations
• 2) Biological: species defined by reproduction
patterns
• Does not explain interbreeding species
• 3) Modern: species are similar in appearance and
can interbreed to produce fertile offspring
• Concept currently used in Biology
Manchester
Terrier
Dandie
Terrier
4. Isolating Mechanisms
• Speciation occurs when members of a species stop
interbreeding and split
• Become isolated from each other
• 2 Types Isolating Mechanisms:
• 1) Geographic
• 2) Reproductive
5. Isolating Mechanisms
• Geographic Isolation: the
physical separation of
members of a population
• i.e.: by canyons, mountains,
rivers, etc.
• Once physically separated,
will continue to diverge until
they can no longer mate
• ALLOPATRIC SPECIATION
6. Isolating Mechanisms
• Reproductive Isolation:
members of a population no
longer able to mate successfully
• i.e. due to disruptive selection,
changes in mating habits, etc.
• Once separated, will continue to
diverge
• Prezygotic vs postzygotic isolation
• SYMPATRIC SPECIATION
7. Rates of Speciation
• Gradualism: some species evolve gradually & at
stable rate
• Although speciation may take millions of years, it is not
always gradual
8. Rates of Speciation
• Punctuated
Equilibrium: when
species evolve in rapid
spurts of great change
• Involves long periods of
no change between
“growth spurts”
• Usually due to natural
disasters
9. Phylogeny
• Phylogeny: the evolutionary history
of an organism (how that organism
evolved)
• Can be used to create a:
• A) Cladogram
• Shows how species diverged from
one another as they evolved from a
common ancestor
• Closer together on cladogram =
more recent common ancestor
• B) Phylogenetic Tree
• Shows hypothetical relationships
among organisms
• Tree of Life
