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Darwin and Speciation Notes
Meet Charles Darwin
• 1809-1882
• Published On the Origin of
Species in 1859
• Fun fact! Darwin dropped
out of medical school after
seeing his first cadaver
Darwin’s Findings
• Darwin observed many species during his voyage
on the HMS Beagle
• In the Galapagos, Darwin observed the variations
of animals and plants from island to island.
• This eventually led to his theory of evolution by
natural selection
Building on Earlier Science
• Darwin built his theory off the work of JeanBaptiste Lamarck
• Lamarck wrote that living things change over time
• Lamarck thought that organisms passed on their
most-used traits to their offspring
– Is this true? No!
What is a Species?
A species is a group of similar individuals capable
of interbreeding to produce fertile offspring.
How Many Species Are There?
We don’t know
Estimates range from 4 to 100 million
~2 million species have been described
How Do Species Arise?
Speciation- evolutionary process by which
reproductively isolated biological populations
evolve to become distinct species.
Let’s break that down, shall we?
First things first: Evolution = ?
Change over time!
How Do Species Arise?
The key to
speciation is
reproductive
isolation of
populations.
Geographic
isolation is
most common
Process of speciation:
Parent
species
I. Barrier
2 separate species
II. Diverge
and Mutate
III. No Longer
Able to interbreed
Two Types of Speciation
1. Allopatric
speciation:
geographic
isolation creates
a reproductive
barrier (an
extrinsic
mechanism).
Allopatric Speciation Example
Harris’ antelope squirrel White-tailed antelope squirrel
Two species of ground squirrel are thought to have descended
from a common ancestral population that was separated by
formation of the Grand Canyon.
Two Types of Speciation
Sympatric
speciation:
reproductive
barrier is created
by something
other than
geographic
isolation
(intrinsic
mechanism).
Sympatric Speciation Example
Ancestors of apple maggot flies laid their eggs
on hawthorns, a plant species native to North
America.
When immigrants came from Europe,
they brought apple seeds.
Apple maggot flies now had a choice of where
to lay their eggs—hawthorns or apples.
Flies hatched on apples only mate with applehatched flies, while flies hatched in hawthorns
only mate with hawthorn-hatched flies.
How Fast Does Speciation Occur?
It depends! Speciation relies on many factors
Examples: A slow rate of speciation evidenced by a living
horseshoe crab (13 extant species) and a 300 million year-old
fossil species.
In contrast, Galapagos finches have diversified into 13 species
within the last 100,000 years.
Does Evolution Create the Perfect Organism?
No, only better organisms
as evolution is constrained
by history and buffeted by
random events.
What do we mean by
“better?”
Better for survival and
reproduction