1. Bellwork: What were Darwin’s 3 key observations?

2. Darwin presents his case
Section 16.3

3. Why did it take Darwin so long to publish his work?
It took Darwin 20 years to publish his Ideas on Evolution
He was scared of being ridiculed
Radical idea
Revolutionary ground breaking research
He knew he would face a lot of opposition
He received a letter from Alfred Russel Wallace
English naturalist in Malaysia
Wallace’s thought were very similair to Darwin’s
Darwin didn’t want to get scooped and published his work

4. Evolution by natural selection
He described a process in nature that operated like artificial selection
He used ideas proposed by Malthus and Lamarck in on the origin of species.
Malthus
If more individuals are produced than survive, there will be competition for food, space and other necessities for life
Struggle for existence
Which species come out on top?
Variation and Adaption
Darwin knew that individuals have natural variations
He proposed that some of these variants are better suited to life in their environment than others
Faster predators, or those with longer claws, or sharper teeth might catch more prey
Prey who are better camouflaged are less likely to be caught
Any heritable characteristic that increases and organisms ability to survive and reproduce is called an adaptation

5. Examples of adaptations

6. Survival of the fittest
Darwin recognized a connection between the way an organism ‘makes a living’ and the environment that it lives in
Differences in adaptations affect an organisms fitness
Fitness refers to how well an organism survives and can reproduce in it’s environment
Individuals which flourish – and do well in their environment have a high fitness
Individuals which have characteristics not suited to their environment have a low fitness,
Die without reproducing or have a low fitness
Survival in evolutionary terms refers to reproducing and passing adaptations on to the next generation

7. Natural selection The name for Darwin’s mechanism for evolution
Organisms with variation most suited to their local environment survive and leave more offspring
Difference to artificial selection is that nature, rather than a farmer or breeder makes the choice!
It will occur whenever:
more individuals are born than can survive
There is natural heritable variation
There is variable ‘fitness’ amongst individuals

8. Natural selection explained

9. Natural selection….
Natural selection does not make an organism “better”
It doesn’t make the organism perfect
It just means that the organism is able to pass on their genes to the environment
It does not move in a fixed direction – it will depend on the local environment
If the local environment conditions change, some traits that were once adaptive may no longer be useful, and different traits may become adaptive

10. Peppered moths

11. Common descent
Natural selection relies on the ability to leave descendants
There are different scales of natural selection
Well adapted individuals in a species survive and reproduce
Well adapted species will survive over time
Darwin proposed that over time, and many generations, adaptation could cause successful species to evolve into a new species
He also proposed that living species are descended from common ancestors
Descent with modification
This requires a large amount of time – only possible with deep time, and Hutton and Lyell’s view of the Earth

12. Evolutionary trees
Darwin based his explanation for the diversity of life on the idea that species change over time
Evolutionary trees suggest that all organisms are related
Looking back in time you can find common ancestors shared by tigers, panthers and cheetahs
If you go further back there will be common ancestors with dogs, horses ,bats
If you keep heading back there will be a common ancestor for all living things
A tree of life exists for all living things

13. Evidence of Evolution
Section 16.4

14. Support for Darwin’s work
Darwin’s work over 150 years ago occurred before our undersatnding of certain fields of science was capable of testing the theory
Related fields are:
Geology
Physics
Paleontology
Chemistry
Embryology
Molecular biology
Genetics
Since his work was published, every scientific test has supported evolution

15. Biogeography
Study of where organisms live now, and where their ancestors lived in the past
Patterns in both living and fossil species provide a wealth of information
Show how modern species descend from ancestors
Two patterns relate to Darwin’s theory
Closely related species differentiate in slightly different climates
Galapagos species suggested descent from common ancestors
Natural selection on each island lead to different but related species
Very distantly related species develop similarities in similar environments
Emu, Rhea and Ostrich
Body structures show they are only distantly related
Similar selection pressures results in similar adaptations

16. Fossils
The age of the earth and the fossil record caused problems for Darwin
The Earth is now a lot older than previously thought – 4.6 billion years!
Gaps in the fossil record in have been infilled
Allow the trace of modern species from extinct ancestors

17. Anatomy and Embryology
By Darwin’s time, it had been shown that all vertebrate limbs share the same basic bone structure
But they have different uses
Some used for crawling
Some used for climbing
Some used for running
Some used for flying
Why do they all have the same bone structure?

18. Homologous structures
Darwin proposed that animals with similar structures evolved from a common ancestor
This ancestor will have had a basic version of this structure
Evolutionary theory explains how homologous structures can be adapted to different purposes through descent with modification form a common ancestor
Anatomical details are studied, alongside stages of embryo development and when they appeared in evolutionary history
Common appearances are used to link certain animals
Reptiles and birds share a common front limb suggesting they share a common ancestor
This common ancestor is more recent than the common ancestor of reptiles, birds and mammals
Common ancestor for all four legged animals was an ancient lobe-finned fish that lived over 380 million years ago

19. Analogous and vestigial structures
Analogous structures
When we talk about common descent, we talk about common structure not common function
Body parts that share common function but not structure are analogous
Example – wing of a bee and the wing of a bat
Vestigial Structures
Not all homologous structures have important functions
Vestigial structures are inherited from a common ancestor but have lost most or all of their original function

20. Embryology
Researchers have known for a long time that the early developmental stages of many animals with backbones look very similar
Groups of embryonic cells grow in the same order,
Similar patterns of embryonic development provide further evidence that organisms have descended from a common ancestor

21. Genetics and Molecular Biology
Darwin had no idea how heredity worked
Work on genetics has gone to support Darwin’s theory
The universal genetic code and homologous molecules provide evidence of common descent
We understand how mutation and reshuffling of genes during sexual reproduction produces variation that leads to natural selection

22. Common Genetic code
All living things use DNA and RNA to carry information an direct protein synthesis
This is nearly identical in all organisms including bacteria, yeast, plants, fungi and animals
Powerful evidence that all living things share a common ancestor

23. Homologous molecules Homology is not limited to physical structures
Homologous proteins have been found in a number of places
Cytochrome c which functions in cellular respiration is found in almost all living cells
Hox genes are found in almost all vertebrates
Determine the order of body parts

24. Testing natural selection
As most kinds of evolution have occurred over millions of years, it makes it hard to test….
Some however have been observed and studied repeatedly in labs, and controlled in outdoor environments
Best evidence comes from observations on the Galapagos islands and Darwin’s finches

25. Testing Darwin’s hypothesis
Peter and Rosemary grant tested Darwin’s hypothesis
They have studied Galapagos finches for more than 35 years
Recognised that Darwin’s hypothesis depended on two assumptions
For beak size and shape to evolve, there must be enough natural heritable variation
Differences in beak size and shape must produce differences in fitness
Tested on the small island of Daphne Major
All finches were caught, tagged and identified
Periodically re-caught and anatomical features like wing length were measured,
Their data showed a lot of variation in heritable traits in Galapagos finches

26. Testing natural selection
The Grant’s showed that individual finches with different sized beaks have better or worse chances of surviving both seasonal drought and longer dry spells
Birds with larger beaks are more likely to survive during dry spells
Natural selection can take place in finch populations both frequently and rapidly
They also showed that competition and environmental change drive natural selection