Download Can Individuals Evolve?

Mechanisms of Evolution
Headings
Vocabulary
Important Info
What is Going On?
The tree is getting larger. Did
the tree evolve?
Can Individuals Evolve?
• Individuals CANNOT change their
genes and evolve!
• Populations, not individuals, evolve
• Unfit individuals may not survive and
reproduce (pass on their genes)
• Natural selection acts on the “gene
pool”: all the genes in the population
Changes in Genes Lead to
Evolution
1. Mutations: caused by environmental
factors or by chance
• If the change is beneficial, becomes part
of the gene pool
2. Genetic Drift: random events affect
numbers of genes in pool
• Weather; natural disaster
3. Gene Flow: individuals leave a
population
Small vs. Large Gene Pools
• All these
changes affect
small
populations
much more than
larger ones
Natural Selection Acts on
Differences in
Populations
There are 3 types of natural
selection patterns:
1. Stabilizing Selection
• Average individuals in the population
have the advantage
• Reduces differences within the
population (become more alike)
2. Directional Selection
• Favors one of the two “extremes” of a trait
• Ex: Long beaks are advantage for
woodpeckers. Eventually, beaks will
become longer in the population.
3. Disruptive Selection
• Favors those with either extreme of a trait
• The “middle of the road” individuals will
eventually be eliminated from the
population
Evolution of a New Species
• This is called “speciation”
• Populations can no longer
interbreed and produce
fertile offspring
Cladograms: How to Read and Interpret
This cladogram shows a relationship
between 4 species. They share a common ancestor
at the root of the tree.
• Note that this cladogram is also a
timeline. The oldest organism is at
the bottom of the tree.
• The four species at the top of
the tree are DIFFERENT species.
Making new species is called SPECIATION.
Branches on the tree
represent
SPECIATION: the
formation of a new
species.
• The event that causes
the speciation is
shown as the fork of
the “V”.
Species B and C each have unique characteristics.
They also share a common ancestor with Species A.
A clade is a group of organisms that come from a
common ancestor.
If you cut a “branch” off the tree, you have all the
organisms that make up a clade.
Consider this cladogram:
Q: Which species is
the oldest?
A: Sharks
Q: Which 2 species
most recently
shared a common
ancestor?
A: Crocodiles and
dinosaurs/birds
Q: Primates and
rodents share
what unique
characteristic?
A: Hair