1. 5.4 Evolution

2. 5.4.1 Define evolution
cumulative change in the heritable characteristics of a population.
‘heritable’ –
changes must be passed on genetically from one
generation to the next
implies that evolution doesn’t happen overnight
‘cumulative’ -
one change isn’t enough to have major impact on
the species
‘population’ -
changes do not affect just one individual

3. 5.4.2 Outline evidence for evolution.
Fossil record
transition species
Comparative Anatomy
homologous & vestigial structures
Comparative Embryology
embryonic development
Molecular record
protein & DNA sequence
Artificial selection
human-caused evolution

4. Fossil record Layers of sedimentary rock contain fossils
new layers cover older ones, creating a record over time
fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

5. Fossil record
A record showing us that today’s organisms descended from ancestral species
Millions of years ago 50
100
150
200
250
300
350
400
450
500
550 60 55 45 40 35 30 25 20 15 10 5
Equus
Hyracotherium
Mesohippus
Merychippus
Nannippus
Body size (kg)

6. Fossil record
A record showing us that today’s organisms descended from ancestral species

7. Comparative Anatomy Homologous structures Similar structure
Similar development
Different functions
Evidence of close evolutionary relationship
recent common ancestor

8. Comparative Anatomy Homologous structures
similarities in characteristics resulting from common ancestry
Results of adaptive radiation - emergence of many species from common ancestor
All vertebrates have similar bone structures in their limbs

9. Comparative Anatomy Separate evolution of structures
Analogous structures
Separate evolution of structures
similar functions
similar external form
different internal structure & development
different origin
no evolutionary relationship
Don’t be fooled by their looks!

10. Comparative Anatomy Analogous structures
Flight evolved in 3 separate animal groups
evolved similar “solution” to similar “problems”
may have developed as a result of convergent evolution – unrelated species share the same environment (similar environmental pressures) and independently evolve similar structures

11. Comparative Anatomy Analogous structures Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to life in the sea
not closely related
Those fins & tails
& sleek bodies are analogous structures!

12. Comparative Anatomy Homologous structures Analogous structures
Results from:
Adaptive radiation
Common ancestor
Similar origin
Different functions
Ex. wing of bat, human arm, dolphin flipper
Results from:
Convergent evolution
Different ancestors
Different origin
Similar functions
Ex. wings of bird, wings of insect
Remember:
Convergent
evolution
Adaptive
radiation

13. Comparative Anatomy Vestigial structures
Modern animals may have structures that serve little or no function
remnants of structures that were functional in ancestral species
deleterious mutations accumulate in genes for non-critical structures without reducing fitness
snakes & whales — remains of pelvis & leg bones of walking ancestors
eyes on blind cave fish
human tail bone, appendix

14. Comparative Anatomy Vestigial structures
PBS: Whales in the Making

15. Comparative embryology
Similar embryological development in closely related species
all vertebrate embryos have similar structures at different stages of development
gill pouch in fish, frog, snake, birds, human, etc.

16. Molecular record
DNA & proteins are a molecular record of evolutionary relationships
Closely related species have sequences that are more similar than distantly related species 25 50 75
100
125
Millions of years ago
Horse/
donkey
Sheep/
goat
Goat/cow
Llama/
cow
Pig/
Rabbit/
rodent
Horse/cow
Human/rodent
Dog/
Human/
Human/kangaroo
Nucleotide substitutions

17. Molecular record
Human
Macaque
Dog
Bird
Frog
Lamprey 32 45 67
125 20 30 40 50 60 70 80 90
100
110
120
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans

18. Artificial selection (selective breeding)
Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties”
line of evidence that supports evolution by natural selection
the breeding of domestic plants and animals to produce specific desirable traits (ex. different breeds of dogs)
people are doing the “selecting” rather than the environment

19. 5.4.3 State that populations tend to produce more offspring than the environment can support.
Natural populations (a population consists of
all the individuals of one species in a particular
area) of all organisms have the potential to
increase rapidly – organisms produce far more
offspring than can possibly survive

20. 5.4.3 State that populations tend to produce more offspring than the environment can support.
More than needed to keep species around
More than K (carrying capacity) can support, but limited resources
Intraspecific competition
Some have competitive advantage such as traits, behaviors, symbiosis)
More fit (competing for resources,
fighting disease, etc.) = More likely
to successfully reproduce
Freq of these alleles higher in next
generation

21. 5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

22. Some individuals selected FOR
5.4.4 Explain that the consequence of the potential overproduction of offspring is a struggle for survival.
Some individuals selected FOR
Some selected AGAINST
Survivors (selected FOR) form new breeding
population
Increases freq of advantageous alleles

23. 5.4.5 State that the members of a species show variation.
Individual members of a population differ from one another in their ability to obtain resources, withstand environmental extremes, escape predators etc. (Variation)

24. 5.4.5 State that the members of a species show variation.
At least some of the variation among individuals in traits that affect survival and reproduction is due to genetic differences that can be passed on from parent to offspring – natural selection
Over many generations, differential, or unequal, reproduction among individuals with different genetic makeup changes the overall genetic composition of the population – evolution
Evolution is the result of natural selection

25. 5.4.6 Explain how sexual reproduction promotes variation in a species.

26. 5.4.6 Explain how sexual reproduction promotes variation in a species.
MIXING IT UP w/MEIOSIS!
Random assortment of chromosomes in Metaphase I
2^n combinations of chroms in daughter cells
8,388,608 in humans!!
Crossing-over in
Prophase I
New combos of alleles
on a chromosomes
Random fertilization 
any gamete can fertilize any
gamete from the other individual

27. 5.4.7 Explain how natural selection leads to evolution.

28. Darwin’s Theory of Natural Selection:
Populations produce more offspring than can possibly survive. (overproduction)
Individuals in a population vary extensively from each other, mostly due to inheritance. (variation)
Struggle to survive: individuals whose inherited characteristics best fit to environment leave more offspring than less fit. (survival of the fittest)
Unequal ability of individuals to survive and reproduce leads to gradual change in population. (adaptation)
Favorable characteristics accumulate over generations – (descent with modification).

29. 5.4.7 Explain how natural selection leads to evolution.
Individuals with genetic characteristics that are WELL-adapted for environment
Tend to be MORE successful at accessing resources
And thus have BETTER chance of surviving to maturity
Since they survive to adulthood, these successful organisms have a better chance to reproduce and pass on their genetic characteristics to the next generation.
Over many generations, accumulation of changes in the heritable characteristics of a population results in evolution. THE GENE POOL HAS CHANGED!

30. 5.4.8 Explain 2 examples of evolution in response to environmental change. (one must be antibiotic resistance in bacteria)

31. 5.4.8 Explain 2 examples of evolution in response to environmental change. (one must be antibiotic resistance in bacteria)

32. 5.4.8 Explain 2 examples of evolution in response to environmental change – peppered moth melanism

33. 5.4.8 Explain 2 examples of evolution in response to environmental change – peppered moth melanism

34. 5.4.8 Explain 2 examples of evolution in response to environmental change – insecticide resistance
– evolution in action
Insecticide & drug resistance
insecticide didn’t kill all individuals
resistant survivors reproduce
resistance is inherited
insecticide becomes less & less effective