1. Speciation Evolution creates (and destroys) new species, but …
Macroevolution
5/9/2019
Speciation
Evolution creates (and destroys) new species, but …
What is a species?
Its not as straightforward a question as most believe.
G. Podgorski, Biol. 1010

2. Macroevolution
5/9/2019
What is a Species?
The definition we’ll use is this: A species is a group of individuals capable of interbreeding to produce fertile offspring.
G. Podgorski, Biol. 1010

3. How Many Species Are There?
Macroevolution
5/9/2019
How Many Species Are There?
We don’t know.
About 2 million species have been described.
Estimates of existing species number range from 4 million to 100 million (with million being a more commonly considered upper estimate).
G. Podgorski, Biol. 1010

4. How did this diversity of life come to be?
Macroevolution
5/9/2019
How did this diversity of life come to be?
Speciation is an event that produces two or more separate species from an original species.
Species = basic unit
Continuous lineage - information
passed through genes
Speciation - rise of new species
G. Podgorski, Biol. 1010

5. The key to speciation is reproductive isolation of populations.
Macroevolution
5/9/2019
How Do Species Arise?
The key to speciation is reproductive isolation of populations.
There are extrinsic and intrinsic reproductive isolating mechanisms.
Geographic isolation is the primary extrinsic reproductive isolating mechanism.
G. Podgorski, Biol. 1010

6. Geographic isolation is the primary extrinsic isolating mechanism.
Macroevolution
5/9/2019
Geographic Isolation
Geographic isolation is the physical separation of members of a population.
Geographic isolation is the primary extrinsic isolating mechanism.
G. Podgorski, Biol. 1010

7. Allopatric Speciation
Allopatric (different home lands) speciation occurs when geographic isolation creates a reproductive barrier (an extrinsic mechanism).
Once a populations have
been separated, Natural
Selection cause the two new
Populations to genetically
Diverge.

8. Allopatric Speciation
Macroevolution
5/9/2019
Allopatric Speciation
Harris’ antelope squirrel
White-tailed antelope squirrel
Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon.
G. Podgorski, Biol. 1010

9. Sympatric Speciation
Sympatric speciation occurs when a reproductive barrier is created by something other than geographic isolation (intrinsic mechanisms).
Intrinsic mechanisms involve changes to organisms that prevent interbreeding.
There are many different causes for intrinsic speciation.

10. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
Macroevolution
5/9/2019
Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
(different habits within an overlapping range)
G. Podgorski, Biol. 1010

11. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
Macroevolution
5/9/2019
Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species.
G. Podgorski, Biol. 1010

12. Behavioral Isolation Mechanisms
Macroevolution
5/9/2019
Behavioral Isolation Mechanisms
Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species.
G. Podgorski, Biol. 1010

13. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
Macroevolution
5/9/2019
Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
G. Podgorski, Biol. 1010

14. Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
Macroevolution
5/9/2019
Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation
G. Podgorski, Biol. 1010

15. Hybrid Infertility Was the reeson for Cloning Mules
Macroevolution
5/9/2019
Hybrid Infertility Was the reeson for Cloning Mules
G. Podgorski, Biol. 1010

16. Speciation Occurs at Widely Differing Rates
Macroevolution
5/9/2019
Speciation Occurs at Widely Differing Rates
A slow rate of speciation evidenced by a living horseshoe crab (13 extant species) and a 300 million year-old fossil species
A rapid rate of speciation evidenced by Galapagos finches which have diversified into 13 species within the last 100,000 years.
G. Podgorski, Biol. 1010

17. Speciation Dynamics - Gradualism or Punctuated Equilibrium?
Macroevolution
5/9/2019
Speciation Dynamics - Gradualism or Punctuated Equilibrium?
Gradualism states that speciation
Occurs at a regular gradual rate.
Punctuated equilibrium states that organisms evolved in a relatively short period of time. Short bursts.
Scientists still argue over this one!
G. Podgorski, Biol. 1010

18. Macroevolution
5/9/2019
G. Podgorski, Biol. 1010

19. A typical “lifetime” for a species is about 1 million years.
Macroevolution
5/9/2019
Species Come and Go
Best estimates from the fossil record indicate that greater than 99% of species that have exited are now extinct.
A typical “lifetime” for a species is about 1 million years.
G. Podgorski, Biol. 1010

20. Classifying Life’s Rich Diversity
Macroevolution
5/9/2019
Classifying Life’s Rich Diversity
Why bother?
An intrinsic reason is that modern classification systems tell who’s related to whom and how we all came to be.
G. Podgorski, Biol. 1010

21. Classifying Life’s Rich Diversity
Macroevolution
5/9/2019
Classifying Life’s Rich Diversity
Why bother?
A practical reason is that if we want to preserve an environment compatible with human life, we’d better know what’s out there.
G. Podgorski, Biol. 1010

22. The Linnaean Hierarchical Classification System
Macroevolution
5/9/2019
The Linnaean Hierarchical Classification System
G. Podgorski, Biol. 1010

23. How Do We Classify Organisms?
Macroevolution
5/9/2019
How Do We Classify Organisms?
Ideally, classification is based on establishing the evolutionary relationships between organisms.
The evolutionary relationship between organisms is their phylogeny.
Cladistics is the method of classification based on establishing phylogenies (i.e. getting at evolutionary relationships.
Cladistics proceeds by comparing shared ancestral and shared derived characters between sets of organisms.
G. Podgorski, Biol. 1010

24. Macroevolution
Cladistics
5/9/2019
A phylogeny (cladogram) for vertebrates.
each node indicates a common ancestor
The greater the number of derived characters shared by a pair of organisms, the closer their degree of relationship.
The closer the degree of relationship, the closer the most recent common ancestor.
G. Podgorski, Biol. 1010

25. Macroevolution
It’s Critical (and often difficult) To Distinguish Homology from Analogy
5/9/2019
Homologous structures, like the bat wing and gorilla arm, are similar because they are derived by modification of a shared ancestral structure.
Homology is the key to establishing phylogenies.
G. Podgorski, Biol. 1010

26. Another Set of Analogies Created by Convergent Evolution
Macroevolution
Another Set of Analogies Created by Convergent Evolution
5/9/2019
Ocotillo of the US southwest
Allauidia of Madagascar
G. Podgorski, Biol. 1010

27. Macroevolution
Results of Cladistic Analyses Sometimes Run Counter to Classical Classification Schemes
5/9/2019
Which pair is more closely related? A lizard/crocodile or bird/crocodile?
Cladistic analysis indicates that the bird/crocodile pair is more closely related.
G. Podgorski, Biol. 1010

28. DNA Hybridization: uses DNA similarity between species
Macroevolution
5/9/2019
DNA Hybridization: uses DNA similarity between species
G. Podgorski, Biol. 1010

29. Macroevolution
5/9/2019
G. Podgorski, Biol. 1010

30. Which species are the closest living relatives of modern humans?
Macroevolution
5/9/2019
Which species are the closest living relatives of modern humans?
Humans
Gorillas
Chimpanzees
Chimpanzees
Bonobos
Bonobos
Gorillas
Orangutans
Orangutans
Humans 14
15-30
MYA
MYA
The pre-molecular view was that the great apes (chimpanzees, gorillas and orangutans) formed a clade separate from humans, and that humans diverged from the apes at least MYA.
Mitochondrial DNA, most nuclear DNA-encoded genes, and DNA/DNA hybridization all show that bonobos and chimpanzees are related more closely to humans than either are to gorillas.
G. Podgorski, Biol. 1010