1. SC B-5.4: Explain how genetic variability and environmental factors lead to biological evolution.
SPECIATION

2. Speciation: formation of a new species
Species: group of similar organisms that can successfully breed & their offspring are fertile
Individuals of same species share a common gene pool
genetic change in 1 member of species can spread thru the population
If that change increases fitness  many members of the species

4. Isolating Mechanisms
When a subset of a population becomes isolated & no longer breeds with original population   over time they will no longer be able to interbreed …..new species has formed

5. Behavioral Isolation
Occurs when 2 populations are capable of interbreeding BUT have differences in courtship rituals or reproductive strategies that involves behavior

6. Behavioral Isolation
Eastern & Western meadowlarks have overlapping ranges.
No interbreeding because they have different mating songs

7. Geographic Isolation
2 populations physically separated by geographic barriers
May separate some species (non-flying insects, small mammals) but not others (birds, flying insects)
Does not guarantee formation of new species

8. Geographic Isolation

9. Temporal Isolation
2 or more species reproduce at different times

10. Testing Natural Selection in Nature
Darwin’s Finches:
Once Darwin realized all the birds on the Galapagos were finches he hypothesized that they all had a common finch ancestor

11. Darwin’s Finches His hypothesis relied on 2 testable assumptions:
Must have enough heritable variation to provide raw material for natural selection
These variations must produce differences in fitness

12. Darwin’s Finches Variation studied by Peter & Rosemary Grant
Found lots of variation in a # of traits

13. Darwin’s Finches
Was there differences in their fitness?

14. Factors Leading to Speciation
Galapagos finches:
Small birds
Do not usually fly over open water

15. Factors Leading to Speciation
Founder Effect
a few finches from South America made it to one of the Galapagos islands
once there, they managed to survive & reproduce

16. Factors Leading to Speciation
2. Geographic Isolation once there, birds do not move from island to island

17. Factors Leading to Speciation
3. Changes in the Gene Pool over time populations on different islands natural selection forces acted on the different populations…which had slightly different variations among the population…leading to development of different adaptations suited to the available food sources on each island

18. 3. changes in the Gene Pool
Over time natural selection would have caused birds on islands with large seeds or nuts as food source to have larger and larger beaks… birds on islands with plentiful small seeds would still have small beaks

19. Factors Leading to Speciation
4. Reproductive Isolation
if finches return to original island after natural selection has changed their beak size they are not likely to interbreed with original population of finches
the finch is very particular about beak size when choosing a mate
So population with large beak will live in same community as small beaked finches but never interbreed

21. Factors Leading to Speciation
5. Ecological Competition
different populations of finch on same island will be competing for resources
during dry season when few seeds available those with more specialized beaks will have less competition from others so will be more successful ….over time differences between populations will increase

23. Factors Leading to Speciat
6. Continued Evolution
This process of geographic isolation..reproductive isolation…genetic change would have been repeated many times over the years on the Galapagos

24. Studying Evolution Since Darwin
Modern technology has confirmed Darwin’s hypothesis that living species descended with modification from common ancestors that lived in ancient past
DNA, RNA, proteins

25. Limitations of Research
There are “holes” in the evolutionary tree
intermediate fossils helpful

26. Why is Understanding Evolution Important?
Because it is still going on
Drug-resistance in bacteria
Understanding it helps respond to changes in ways that hopefully improve human life