The Evidence for Evolution Flashcards
Charles Darwin on Beagle
(1831-1836)
Age 22, ships naturalist
- lot of time in South America
- Observations of fossils, flora and fauna of oceanic islands, geographical distribution of plants and animals
FOSSILS
Wonder - over evolutionary time there is this big gap
- Transitional fossils found 20 years ago - evolving from a fish (living in water) to starting living on land
Goes onto phylogenetic tree - probably a common ancestor to people living on land
Evolutionary trajectories
- Fossils provide lots of information (dinosaurs and their extinction)
Fossils are the singular direct evidence we have of evolutionary trajectories over time
- Birds are intermediates
Fossil record provided Darwin with a good reference of evolutionary change
EXAMPLE
- Fossil record of dolphins and whales, evolved from land mammals
- Fascinating forms from being on land to the water
- We can see some of the resemblance to mammals living on the land
Lessons from Geology
Geology was key for Darwin
- Very difficult to explain any other way
- Deep age of the earth allows for immense time to have occurred
- Evolution could be occurring even If we can’t see it over our lifetime
Organisms today are just a tiny subset
- Evidence for common ancestors linking features of living and extinct organisms
There were these strata (layers in the earth) the further up you go, the more the organisms resemble modern day organisms, vice vera when you go down (Exactly what we expect
Loss of Flight on Oceanic Islands
Key observation -
Flightless cormorant
Clearly are birds but they do not fly
- Provided Darwin with the question “why are they birds but don’t fly”
- It used to be able to fly because of decent and modification
- There are many hypothesis - could’ve been favoured to not fly
- Flying is costly, environment could’ve been a factor
- Favoured to lose flight now - then it will be lost
VEGESTIAL TRAIT
Blind cavefish
Fish that have evolved in caves - they used to be able to see, relics of eyes
Not pigmented at all
This are clearly fish, have some similar properties that show they used to be able to see
- Vegesital character that only makes since from evolution
Vestigial Characters in Humans
Ear muscles used to flex In the direction of the sound
Tailbone - descended from mammals with tails, human babies have tails
Animals that responded to a threat - raising hair in order to become bigger, also helps with thermoregulation
Appendix - might be an important thing for some good bacteria in our body
Evidence for Vestigial Characters in Genomes
Genes that allow us to smell (many different genes)
- Some of our mammalian relatives rely a lot more on smell (navigating etc)
- A lot are no longer functional
- Quite a high percentage of dead genes
What do we share with our close relatives?
We evolved trichromatic color vision - we can detect many more colours then other
- Still a lot of genetic variation between what who can smell
Howler Monkey that independently has trichromatic colour vision - decent by modification
HOMOLOGY
HOMOLOGY - similarity because of shared ancestry
Bats vs. Birds - modification of flight has happened in very different ways, did not evolve because of common ancestor, they evolved independently
The similarity provides evidence - provides key evidence were related to these organsimc
Galapagos Islands
Really young islands
- Incubators of evolutionary experiments
15 main islands of volcanic origin
– Oldest seamounts from 5-10 million years ago
– Youngest islands 700 kya to 1 Mya
* Flora and fauna colonized from mainland South
America
– Species capable of long-distance dispersal
– Distinct forms and species on different islands
provide evidence of early stages of speciation
* Darwin spent only 5 weeks on the islands but his
observations formed the foundation for his theory of
evolution
Where did organisms come form?
The organisms resemble the species in mainland south america
Subset of species on mainland
Darwin’s Observations on the
Galapagos
Less diversity than on the mainland,
only organisms capable of long-
distance dispersal
2) Species on these young islands
resemble the mainland, but are
different from them
3) Many similar-looking, but not identical
types on different islands
Adaptive radiation
The evolution of ecological and phenotypic diversity
within a rapidly multiplying lineage as a result of
speciation
– Originates from a single common ancestor
– The process results in an array of many species
– The species differ in traits allowing exploitation of a
range of habitats and resources
* Three features commonly identify an adaptive radiation
1) Recent common ancestry from a single species
2) Phenotype-environment correlation
3) Rapid speciation
Australia
Distinct flora and fauna with high endemism
and many unique adaptations
– Biological uniqueness is a result of its long
history of isolation from other land masses
* Although a continent, Australia also is an island
– Hence, shows many island characteristics:
* Endemism, radiations, & unique adaptations
Evidence From Biogeography
Geographically close organisms resemble each other
* Different groups of organisms adapt to similar environments
in different parts of the world
* Geographically isolated regions have unusual organisms
Evidence From
Domestication
Vast amounts of heritable variation
found within species
* This variation can be selected on,
leading to dramatic changes over generations
– Artificial selection as the human imposed analog
to natural selection in the wild
Evidence For Evolution:
165 years on
Abundant evidence for evolution in action
– e.g. antibiotic resistance, herbicide resistance,
adaptation to pollution, experimental evolution
* Strength of natural selection measured in the wild
– Evolutionary responses can be faster than Darwin
realized
* Genomic DNA evidence for vestigial traits,
homology, descent with modification, rapid
evolution
– Population and evolutionary genomics
* Advances in geology to estimate age of rock strata
