1. Individuals do not evolve, populations do
IB Topic 5.4: Evolution
Individuals do not evolve, populations do

2. What is evolution? Evolution
Cumulative change in the heritable characteristics of a population
Change over time
Simpson’s couch gag

3. What’s the evidence for evolution?
Charles Darwin
Contributed more to our understanding of evolution than anyone else
Born 1809
Traveled on the H.M.S. Beagle
In 1831 set sail (at the age of 22!) from England for a voyage around the world
Made numerous observations and collected evidence that led him to propose a radical and revolutionary hypothesis about how life changes over time
Evolution
Evidence: fossil record, artificial selection, homologous structures

4. The Fossil Record
Life 500 million years ago is very different from life today
Fish fossils have only been found in rocks ~500 millions years old or younger (less than 15% of the history of life)
Top predators today did not exist at the time of dinosaurs (or before)
Many living organisms today have no identical form in the fossil record
Conclusion: life on Earth is constantly changing

5. Artificial Selection Breeding domesticated animals
Breeders choose the males and females with the most desirable genetic characteristics and breed them together
Examples?
Conclusion: Evidence that evolution is happening, but the driving force is human choice
Not the driving force of evolution in natural ecosystems

6. Homologous Structures
Similar in form and function, but found in dissimilar species
Example: 5 fingered limb
Humans, whales, and bats (see fig. 5.8 page 147)
Humerus, radius, ulna, carpals
Pentadactyl (penta – 5; dactyl – fingers)
The shape and number of bones may vary, but the general format is the same
Conclusion: evidence that the organisms in question have a common ancestor

7. Struggle for existence
Organisms produce many more offspring than survive to be mature individuals
Darwin did not coin the term ‘struggle for existence’ but it does sum up the point that over-production of offspring in the wild leads to their competition for resources

8. No. of eggs/seeds/young per brood or season
Some examples
Organism
No. of eggs/seeds/young per brood or season
Rabbit
8-12
Great tit 10
Cod
2-20 million
Honey bee (queen)
120,000
Poppy
6,000
Many of these offspring die before they reproduce

9. Darwin’s Observations
1st Observation
Populations tend to reproduce rapidly and if every individual survived, there would be exponential growth
Not the case
Seems to be a natural checks and balance system
There is a limit to the size of a population that the environment can support
Deduction
There is a struggle for existence
Some live and some die

10. Darwin’s Observations
2nd Observation
Organisms vary
There are differences between individuals of the same specie
These differences affect how well suited an organism is to its environment (fit or fitness)
This is called adaptation
Some individuals are better adapted to their environment than others because they have favorable variations
Deduction
In the struggle for existence, the less well-adapted individuals will tend to die
Natural selection

11. Darwin’s observations
3rd Observation
Much of the variation between offspring can be passed on to offspring
It is heritable
Deduction
Better adapted individuals reproduce & pass on their favorable characteristics
Over the generations the characteristics of the population gradually change
Evolution by natural selection

12. Why do individuals within a specie show variation?
Genetic variations arise from gamete formation and fertilization
Random assortment
Crossing over
Random fusion of male and female gametes during sex
Mutations
Not as powerful as sexual reproduction
Mutations by be advantageous, harmful, or neutral
Most mutations are neither harmful or useful
Does this sound familiar?

13. Evolution in Action Galapagos Finches
Darwin visited the Galapagos Islands in 1835 and collected specimens of small birds (finches)
Group of islands off the coast of Ecuador
14 species in all
Darwin observed that the size and shapes of the beaks varied, as did their diet
Further research from Peter and Rosemary Grant suggests a close relation between beak characteristic and diet

16. Examples of natural selection
Antibiotic resistance in bacteria
Pesticide resistance in rats

17. Antibiotic resistance in bacteria: more evidence for evolution
Antibiotics were one of the great triumphs of medicine in the 20th century
When they were first introduced, it was expected that they would offer a permanent method of controlling bacterial diseases
However, there have been increasing problems of antibiotic resistance in pathogenic bacteria.

18. The following trends have been established:
After an antibiotic is introduced and used on patients, bacteria showing resistance appear within a few years
Resistance spreads to more and more species of bacteria
Strains of bacteria appear that are resistant to more and more different antibiotics
Called multiple resistance

19. How?
Antibiotic resistance is due to genes in bacteria and so it can be inherited
Example of evolution by natural selection
The evolution of multiple resistance has occurred in just a few decades.
It is so important to finish all of your prescribed antibiotics
Due to:
Widespread use of antibiotics (humans and animals)
Bacteria reproduce quickly (less than 1 hour)
Populations of bacteria are HUGE, increasing the chance of a gene for resistance to form via a mutation
If you want more info:

20. Pesticide resistance in rats
What are pesticides?
Typically used by farmers
Due to natural variation, some rats are unaffected (resistant) to the toxin
They survive and reproduce, making a new population in which some or all members possess the genetic resistance
New pesticide must be used
The cycle continues …

21. Take away … Illustrates how a population can adapt to its environment
Illustrates how humans can be responsible for creating “super-resistant creatures”
Why is this not an example of artificial selection?

22. Flanders calls Homer an
ape and makes a case for evolution
revolution in THE SIMPSONS
episode "The Monkey Suit"

23. Exit Slip 3 multiple choice questions
1 minute to answer each question before screen changes.

24. Question1 What is natural selection?
The mechanism that increases the chance of certain individuals reproducing.
The mechanism that leads to increasing variation within a population.
The cumulative change in the heritable characteristics of a population.
D. The mechanism that explains why populations produce more offspring than the environment can support.

25. Question 2 Which factors promote evolution in a species?
I. Sexual reproduction
II. Environmental change
Overproduction of offspring
A. I and II only
B. II and III only
C. I and III only
D. I, II and III

26. Question 3 Natural selection is based on which of the following?
I. Variation exists within populations.
II. There is differential reproductive success within populations.
Individuals must adapt to their environment.
A. I only
B. I and II only
C. II and III only
D. I, II and III