Post on 24-Dec-2015
What affects the Rate of Evolution?
What can The Cambrian Explosion and Mass Extinction
Events teach us about the rate of the Evolution of life?
Two Factors affect the rate of Evolution: Variation and Selection
• Variation: The differences among
members of the same species. Due to
differences in genetics caused by
mutations
• Selection: How strongly the
environment is selecting for of against
a specific characteristic
What was the Cambrian Explosion and what caused it?
The Cambrian Explosion is used to define the boundary
between the Precambrian and the Cambrian (544 MYA),
Before this time life on earth was mostly single cellular
Prokaryotic and Eukaryotic, some simple colonial species
present.
• During the Cambrian we see a sudden increase in
the number, types, and complexity of life on earth
• What caused the sudden increase?– A type of
mutation called Gene duplication occurred to a group
of genes called homeotic genes.
• What do Homeotic genes do?– They are active during
embryonic development and determine body segment
identity.
Tree of Multicellular life according to Number and type of Homeotic Genes
The embryos highlighted show the region
where that Homeotic gene is turned on to
regulate development of segment identity
In Summary, Gene duplication of the
Homeotic Genes that regulate embryonic
development and body segment identity
dramatically increased the variety of
forms that life could produce. This
occurred shortly before and during the
Cambrian explosion, producing all the
major body plans that are present on earth
today.
How do Mass Extinctions lead to new diversity oon earth?
• Mass Extinctions are events that cause a
massive die-off of a large percentage of the
species on earth
• Most often caused by cataclysmic volcanic
activity, asteroid impacts, and climate
change.
• Mass Extinctions increase the rate of
selection
• They open up previously occupied niches
• Organisms that are able to survive diversify
to occupy the niches left available in a
process called adaptive radiation
Example: Cretaceous-Tertiary Mass Extinction65 mya
• This was most likely caused by an asteroid
impact followed by climate change
• The dinosaurs, except for the ancestors of
birds, became extinct.
• Mammals were small and able to survive this
period of upheaval.
• After Climate normalized, mammals
expanded and diversified to take the niches
once occupied by dinosaurs