Textbook Notes (290,000)
CA (170,000)
UTSG (10,000)
BIO (600)
BIO120H1 (300)
Chapter 2

Lecture/ Chapter 2 Study Notes

Course Code
Benjamin Wright

of 4
Lecture 2
What Darwin Saw: The Evidence for Evolution
Key Concepts/ Terms:
Adaptive Radiation
Convergent Evolution
1)The Fossil Record:
a.Provides lots of evidence for evolution through time
b.Fossils found in geological strata (layers of rock) are similar to each other, more distant
layers show differences, suggesting evolutionary change
c.Younger fossils similar to living organisms living in area while older are increasingly different
d.Since Darwin more evidence for transitional forms between species have been found: feathered
dinosaurs (evolution of birds from dinosaurs), detailed insights into whale evolution
Lessons from Geology:
1)The earth is very old, allows immense amount of time for biological evolution
2)Intermediate forms provide evidence for common ancestors linking features of living organisms
3)Fossils in younger strata increasingly resemble modern species in same region, while older strata
show increasing differences
4)Earth has to be old in order for these changes to exsist
2)Homology: (vestigial characters)
a.Descent with modification implies organisms should show similarities to each other to varying
amounts that reflect their common ancestry
b.Homology term is used to describe shared characteristics of organism that reflect shared
c.This contrasts with features that evolved through convergent evolution
d.There is abundant evidence for hierarchical patterns of homology at many levels of biological
organization including:
e.Vestigial traits show evidence of homology but have no evidence for current function in
organism, provides good evidence
f.DNA evidence provides important means of examining homology
g.Homologous features provide basis for reconstructing relationships among organism using
phylogenetic methods
h.Amphibians and Human digits are similar- evidence
i. Approximately 500 genes are shared across all forms of life- evidence
3)Biogeography: (islands)
a.The geographic distributions for species provide strong evidence
b.Species found in geographically similar regions are more similar
c.Organism show discontinuities across geographic barriers
d.Island species tend to resemble nearby continental form
e.Similar ecological niches are occupied by very different groups of organisms in different parts
of the world
f.Different groups of organism adapt to similar environments in different parts of the world-
4)Evolution in Action:
a.Experimental work with micro-organisms
b.Field observations of natural populations (Grants work on Darwins finches)
c.Field experiments and pathogen evolution
d.Antibiotic resistance, herbicide resistance, adaptation to pollution, experimental evolution-
e.Discovery of Tikaalik Roseae (fishapod), 375 million years old on Ellesmere Island, Nunavut-
shows us evolutionary line:
i.390 million years- fish
ii.375 million years- new found fishapod
iii.360 million years- amphibians
iv.From the sea to the land
Evidence from Domestication:
1) Maize (sweet corn) and Teosinte (ancestor)
a. teosinte to sweet corn in matter of thousands of years, not that long
b.early people crushed seeds and ate them
2)vast amounts of heritable variation found in species
3)this variation can be selected on, leading to dramatic changes over generations
4)Darwin didnt exactly understand heritable variation
Darwins Voyage:
1)Age 22, ships naturalist
2) Most time spent in South America
3)Observed fossils, geographical distribution of plants and animals, flora and fauna of oceanic
4)From England the Beagle went to Brazil
5)Darwin finds a fossil line of extinct mammals in brazil that look like large armadillos
6)From Brazil, they sail to Galapagos Islands which are a series of islands 1000km off Ecuador
7)At first he wasnt impressed with the islands
8)Observed interesting things about vestigial characters:
a.First found flightless birds with wings that were good swimmers
b.Why would they have wings? Didnt need to because they were good swimmers?
c.Then found blind cave fish (not on Galapagos Islands) that still had eyes.
d.Why would they have eyes?
e.Similar fish that lived outside the cave had eyes and were not blind, makes sense if they
evolved from those fishes
Vestigial Characters in Humans:
1)Ear muscles- mammals move their eyes for sound
2)Appendix- monkey uses it to break down leaves
3)Tailbone-evolved from fish (humans have gills in the fetus)
4)Goosebumps-animals raise their fur when scared
Current evidence that Darwin couldnt know about is about our olfactory genes (sense of smell). Over half
of our factory receptor genes for smelling have become inactive because we rely much more on sight.
9)He found cacti which are early colonizers on land, they have a fruit which the birds eat and poop
out to spread seeds
10)Found tortoises on different islands that had different shells (shell morphology), they were similar
besides that- theory that they arrived on island then adapted to environment
11)Darwins Finches:
a.All 14 speacies of Darwins finches are closely related, derived from a common ancestor 2-3
million years ago
b.None has become extinct as a
result of human activity
c.Key factors in their evolutionary diversity:
i.Environmental change
ii.Natural selection
iii.Cultural evolution
d.Evolution occurred by natural
selection when the finches food
supply changes during droughts
e.Specification and diversification of finches throughout history:
i.Number of islands has increased
ii.Climate is colder
iii.Vegetation and food supply has changed
f. The Darwin's Finches diagram below illustrates the way the finch has adapted to take
advantage of feeding in different ecological niche's
g.Their beaks have evolved over time to be best suited to their function
h.Finches who eat grubs have a thin extended beak to poke into holes in the ground and
extract the grubs
i.Finches who eat buds and fruit would be less successful at doing this, while their claw like
beaks can grind down their food and thus give them a selective advantage in circumstances
where buds are the only real food source for finches
12)Find that the flora and fauna resemble those from South America mainland