1. The Origin of Species Mom, Dad… There’s something you need to know…
I’m a MAMMAL!

2. So…what is a species? Biological species concept defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark

3. How and why do new species originate?
Species are created by a series of evolutionary processes
populations become isolated
geographically isolated
reproductively isolated
isolated populations evolve independently
In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
The definition of barrier depends on the ability of a population to disperse
Separate populations may evolve independently through mutation, natural selection, and genetic drift
Regions with many geographic barriers typically have more species than do regions with fewer barriers
In allopatric speciation, geographic isolation restricts gene flow between populations
Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
Even if contact is restored between populations, interbreeding is prevented
In sympatric speciation, speciation takes place in geographically overlapping populations
In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species
Sympatric speciation can result from polyploidy, natural selection, or sexual selection

4. Sexual Selection Sympatric speciation
Sexual selection can drive speciation
Video
Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

5. Building “family” trees
Closely related species (branches) share same line of descent until their divergence from a common ancestor

6. Speciation
When new species are formed, they share some characteristics with their ancestors and with other organisms that have the same ancestor. Phylogenetic trees do show patterns of descent

7. Homologous structures
Similar structure
Similar development
Different functions
Evidence of close evolutionary relationship
recent common ancestor
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Whale
Cat
Bat
Figure Mammalian forelimbs: homologous structures
Homology is similarity resulting from common ancestry

8. Homologous characteristic
Fig
Branch point
(common ancestor)
Lungfishes 1
Amphibians
Tetrapods 2
Mammals
Tetrapod limbs
Amniotes 3
Lizards
and snakes
Amnion 4
Crocodiles
Figure Tree thinking: information provided in an evolutionary tree
The Darwinian concept of an evolutionary tree of life can explain homologies
Evolutionary trees are hypotheses about the relationships among different groups
Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
Homologous
characteristic 5
Ostriches
Birds 6
Feathers
Hawks and
other birds

9. Homologous Structures in Embryos
Comparing embryos can reveal anatomical homologies not visible in adult organisms

10. 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!
Solving a similar problem with a similar solution

11. Convergent evolution Flight evolved in 3 separate animal groups
analogous structures
Does this mean they have a recent common ancestor?

12. Convergent evolution Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to life in the sea
not closely related
Those fins & tails
& sleek bodies are analogous structures!

13. Vestigial organs Structures that serve little or no function
remnants of structures that were functional in ancestral species
snakes & whales — remains of pelvis & leg bones of walking ancestors
eyes on blind cave fish
human tail bone
Vestigial structures are remnants of features that served important functions in the organism’s ancestors
Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

14. Vestigial organs
Hind leg bones on whale fossils

15. Molecular record
Comparing DNA & protein structure
universal genetic code!
DNA & RNA
compare common genes
cytochrome C (respiration)
hemoglobin (gas exchange) 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
Closely related species have sequences that are more similar than distantly related species
A molecular record of evolutionary relationships

16. Comparison of a protein found in diverse vertebrates
Species
Human
Rhesus monkey
Mouse
Chicken
Frog
Lamprey
14%
54%
69%
87%
95%
100%
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide

17. Comparative hemoglobin structure
Human
Macaque
Dog
Bird
Frog
Lamprey
Why does comparing amino acid sequence measure evolutionary relationships? 8 32 45 67
125 10 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. What Is Theoretical About Darwin’s View of Life?
In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions
Ongoing research adds to our understanding of evolution