1. Outcomes of Evolution

2. Selection acts on Variation
Genetic variation
Directional Disruptive Stabilizing

3. Directional Selection
Favors one of the
extreme variations
of a trait
Can lead to rapid
evolution of a
population

4. Disruptive Selection Favors both extreme variations of a trait
Eventually results in no intermediate forms of the trait
Leads to the evolution of two new species

5. Stabilizing Selection
Favors average individuals
Reduces variation in a population

6. SPECIATION
The evolution of a new species from previously existing species
Isolating Mechanisms lead to speciation

7. Crash Course: Speciation

8. What can lead to speciation?
Geographic Isolation
A new species can evolve when a population has been GEOGRAPHICALLY ISOLATED.
Physical barriers divide a population

9. Reproductive Isolation
Occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring
Genetic information becomes too different (mutations)
Behaviors become too different (mating seasons)

10. On the Origin of Species
Darwin did not publish his ideas on evolution until 1859.
He published On the Origin of Species by Means of Natural Selection

11. Darwin’s ideas have been updated
Genes are responsible for inherited traits.

12. Darwin’s ideas have been updated
Isolation leads to species formation.
Isolation: the condition in which two populations of the same species cannot breed with one another.
Populations of the same species living in different locations tend to evolve differently.

13. Kaibab Squirrel
Aberts Squirrel

14. Species:
Group of organisms that are genetically similar and can produce fertile offspring.

15. 13: Processes and outcomes of evolution
Challenge: How do evolutionary processes lead to changes in biodiversity?
Vocab:
Adaptations
Macroevolution
Microevolution
Speciation

16. #1
Microevolution refers to the evolution of very small organisms, such as bacteria.
FALSE
Microevolution is evolution on a small scale that changes the gene pool of a population or species

17. Microevolution
Results in changes in the frequency of alleles (like we saw in the mice in activity 12)
Four main factors:
Mutations
Natural selection
Genetic drift
Gene flow

18. #2
The evolutionary fitness of an organism is related to its physical strength or size.
FALSE
Evolutionary fitness is related to the probability of survival and reproduction

19. #3 Adaptations result only from natural selection. TRUE
Adaptations are inherited characteristics that favor survival or reproduction and are the result of natural selection

20. Adaptations
Inherited traits that increase an organism’s fitness (survival and rate of reproduction)
Results from natural selection
Organisms cannot CHOOSE to adapt
Organisms don’t adapt out of NEED. Either they have traits that will help them survive, or they die!
INDIVIDUAL organisms cannot adapt in their lifetime

21. #4
Geographic Isolation results from either changes in the land or migration of a group of organisms to a distant location.
TRUE
Geographic Isolation can occur when rivers or canyons form, or if a population moves far away from others of the same species.

22. #5
When gene flow continues between two populations, they are likely to remain the same biological species.
TRUE
When populations share a common gene pool they exchange genes through sexual reproduction and share any genetic changes

23. #6
The evolution of many species from one ancestral species is proposed as a mechanism for the evolution of the 13 species of Galapagos finches.
TRUE
Scientists think that the different species of finches evolved from a small population that was blown off course from mainland South America

24. Speciation
If enough small changes accumulate in a population (microevolution), this could lead to speciation (macroevolution)
Occurs most often when gene flow is restricted or cut off
Examples:
adaptive radiation of Darwin’s finches
changes in birds seen in the computer simulation

25. #7
Until human populations grew and began to change the environment, there were very few extinctions.
FALSE
Extinctions have occurred throughout earth’s history for many reasons, including disease and natural disasters. Human activities have increased the rate of extinctions

26. #8
Macroevolution refers to any evolutionary changes at or above the species level.
TRUE
Macroevolution includes speciation and extinction, which change earth’s biodiversity. Most species that have lived on earth are now extinct, perhaps as high as 99%

27. Activity 10: What is a Species?
Challenge: How do new species separate from existing species?
Page Introduction

28. Background Information- pg 473
The biological species concept is a method of defining a species based on whether the organisms can breed with each other in nature to produce fertile offspring.
Gene flow results from this interbreeding, as genes move between populations
Members of the same species share a common group of genes called a gene pool
This method of classification does not always fit: (species that reproduce asexually, some plants that can crossbreed, extinct fossil organisms)

29. Part A: Procedure
Claims about the process of species separation:
Early means they are still one species or have just begun separation.
Mid means they are separating.
Late means they are at the end of separation, they are most likely two species.

30. Part A: Procedure Read the examples from the textbook, pages 475-479
Complete a chart for each of your assigned examples
Species Separation
Example number/ organism name
Claim
Evidence to support the claim
Reasoning

31. Ex. 1: Red and Purple Sea Urchins
Species Separation
Example number/ organism name
Example 1: Red and purple sea urchins
Claim
Late
Evidence to support the claim
Eggs can only be fertilized in a lab, embryos do not survive
Reasoning
Even though eggs can be artificially fertilized, the offspring don’t survive, so there is no exchange of genes or a common gene pool. They have most likely split into two different species

32. Procedures Example #1 as a class Group 1– examples 4, 5, 8

33. Part A: Procedure Dogs and wolves Midas cichlid Red sea urchins Horses
Orchids
Copper resistant/tolerant monkeyflowers
Eastern/Great Plains frogs
Northern & California Spotted owls Blue & red Cichlids green lacewings
Dogs and wolves
Arrow cichlid
Purple sea urchins
Donkeys
Orchids

34. Part B: Procedure Steps 13-15 (Scientific Groupings)
Analysis questions 2 & 3

35. Procedure Step 15– Reproductive Barriers
Behavioral Isolation- different mating signals/rituals
Meadowlarks, fireflies, blue/red cichlids
Habitat Isolation- same area, different habitat
Garter snakes, insects
Temporal Isolation- different breeding times
Lacewings, orchids
Mechanical Isolation- physically incompatible
Flowering plants, damselflies
Gametic Isolation- sperm and eggs can’t interact
Purple/White Sea urchins
Hybrid Sterility- offspring are infertile
Horses/donkeys
Reduced Hybrid Viability- offspring don’t live long
Frogs
Geographical Isolation- live in different locations
Lions/tigers, squirrels

36. So what happens next?
Reproductive barriers prevent gene flow between populations
Mutations and adaptations that evolve in one population can’t be shared with the other if there is no gene flow
Over time, populations can become so genetically different that they are no longer the same species (speciation)

37. Analysis Question 2
Explain how geographic isolation can lead to speciation.
If two populations do not meet in nature, than there is no gene flow between the populations. There genes will continue to mutate and evolve separately, since the populations will have different gene pools.

38. Analysis Question 3
Lions and tigers do not overlap in range and do not breed in nature. In captivity, a male lion may mate with a female tiger and produce offspring. Although more rare, a male tiger may also mate with a female lion to produce offspring. In both cases, the male offspring are sterile, while the females might or might not be fertile. Explain where lions and tigers are on the speciation continuum, according to the biological species concept. Support your answer with evidence and reasoning.
Very late in the process of speciation, but not totally separate, since male offspring are infertile but females might still be able to produce offspring of their own.

39. Human Species
DNA evidence suggests that modern humans (Homo sapiens) could interbreed with Homo neanderthalis
There is newly discovered evidence of another human ancestor, “Denisova” that might have bred with humans as well
One current hypothesis is that all three species evolved from Homo heidelbergensis along parallel paths at the same time. Denisovans and Neanderthals went extinct. Homo sapiens survived.