1. Change in Populations over time
Evolution
Change in Populations over time

2. History- Ideas that Shaped our Understanding
James Hutton (1785)- proposes that Earth is shaped by geological forces that took place over extremely long periods of time
Scientists now believe Earth is 4.5 BILLION years old
Thomas Malthus (1798)- predicts that human populations outgrow food supply and that Death and famine are inevitable
Organisms must COMPETE to live
History- Ideas that Shaped our Understanding

3. History- Ideas that Shaped our Understanding
Jean-Baptiste Lamarck (1809)- Theory of the Inheritance of Acquired (developed) traits
Organisms changed due to the demands of their environments
Use or Disuse Principal- Organisms can gain or lose features if they were overused or not used at all, and that these traits could be passed on to offspring
(this theory was Wrong)
Proposed that organisms change over time (the only accurate part of his theory)
History- Ideas that Shaped our Understanding

4. Use or Disuse Principal

5. History- Ideas that Shaped the Current Theory
Charles Lyell (1833)- geological processes occurring now (weathering, erosion, volcanic activity) shaped Earth over millions of years
Charles Darwin (1859)- After years of traveling around the world, he published “On the Origin of Species” explaining his theory of evolution by Natural Selection
From 1831 to 1836 , Darwin served as naturalist aboard the H.M.S Beagle on a British science expedition
Observed that fossils of extinct species were similar to modern species
Noticed variations of similar plants and animals around the world
History- Ideas that Shaped the Current Theory

6. Natural Variations (differences among individuals) exist in all organisms. These differences are called adaptations.
An adaptation is a trait that helps an organism be more suited to its environment.
Many more individuals are produced in each generation than will survive
Natural Selection

7. Some individuals are better adapted to their environment so they survive and reproduce.
Their traits are passed on to the next generation so that the gene pool of a population changes in favor of the “best” or “fittest” phenotype and genotype
Organisms with traits that don’t help them survive will die and will NOT be able to pass these traits on.
Over time, the frequency of the “bad” traits will decrease
Natural Selection

8. Members of a population compete for resources (food, territory, mates)
Only the organisms best suited to their environment (or “fittest”) will survive and reproduce.
This is called “Survival of the Fittest”
Natural Selection

9. Descent with Modification
Another term for Evolution is “Descent with Modification”
ALL organisms are related through a common ancestor
Ancestors accumulate diverse (varying) modifications or adaptations that make them “Fit” for specific ways of life
To explain Natural Selection, Darwin compared it to Selective breeding, or Artificial Selection
Descent with Modification

11. Results of Natural Selection
Directional Selection
Environmental changes occur, causing one phenotype to replace another. As a result, there can be a rapid shift in allele frequencies
Examples: peppered moth, antibiotic resistance
Peppered Moth Video
Results of Natural Selection

12. Results of Natural Selection
Diversifying (Disruptive) Selection
When individuals at the extremes have a higher fitness than the most common individuals in the population
If the selection is strong and lasts long enough, the population can split into 2 different populations
Results of Natural Selection

13. Results of Natural Selection
Stabilizing Selection
When the most common individuals in a population have a higher fitness than individuals in the extreme
Intermediate forms increase and extreme forms decrease in the population
Results of Natural Selection

14. Evidence for Evolution
Fossil Record
Darwin saw fossils as a record of the evolution of life on Earth
By comparing fossils from younger layers with fossils from older rock layers, scientists can document that life on Earth has changed over time.
Fossils can be used to trace the history of modern life
Evidence for Evolution

15. Evidence for Evolution- Geographic Distribution
Darwin’s theory was that current living species descended from a common ancestor
Over time, these species shared similarities, but each had adapted to their environments
Adaptive Radiation- the evolution of many different species from a common ancestor
Occurs when a population moves into an area with diverse conditions
Many species become so different they can no longer breed with each other
Evidence for Evolution- Geographic Distribution

17. Similarities in Early Development
The same groups of embryonic cells develop in all vertebrates to produce the tissues and organs
Similarities in Early Development

18. Evidence for Evolution- Genetics
All species of life have the same basic genetic machinery of RNA and DNA and the genetic code is essentially universal
Sources of genetic variation in species:
Mutations
Gene Flow- movement of genes between populations
Sexual Reproduction- introduces new gene combinations
Evidence for Evolution- Genetics

19. Evidence for Evolution- Comparative Morphology
Study of body forms and structures in an organism
Homologous Structures- structures have different forms, but come from same tissue
Evidence that organisms descended from a Common Ancestor
Evidence for Evolution- Comparative Morphology

20. Evidence for Evolution- Comparative Morphology
Analogous Structures- structures that have similar function but different anatomy
Similarities are due to similar function, but do not necessarily show common ancestry
Evidence for Evolution- Comparative Morphology

21. Evidence for Evolution- Comparative Morphology
Vestigial Organs- organs that are reduced in size, but are traces of homologous structures
Structures have no current function, but can provide evidence for common ancestry
Evidence for Evolution- Comparative Morphology

22. The process of two or more species becoming more and more different
Organisms who share a common ancestor evolved into different species through divergent evolution
Over millions of years, similar species become dissimilar as they adjust to their environment
Divergent Evolution

23. The emergence of biological structures or species that have similar functions or appearance
Organisms with analogous structures evolved independently of each other
Convergent Evolution

24. The joint evolution of two or more species that closely interacted
Example: Bumblebees and the flowers they pollinate have coevolved so they depend on each other for survival
Coevolution

25. Microevolution Refers to evolution that occurs within a population
Example: peppered moths (black or white) experience directional selection
Causes
Lead to changes in allele frequencies
Asks WHY some characteristics are more common in specific populations
Microevolution

26. Causes of Microevolution
Genetic Mutations- some white moth genes mutate into black moth genes
Very rare
Gene Flow: some moths with black genes migrate from another population, some white moths leave the population
Genetic Drift: When the moths reproduced, just by chance, more black moth genes ended up in the offspring
Natural Selection- moths with black genes escaped predation and reproduced more frequently than moths with white genes, so that more black genes were passed on
Causes of Microevolution

27. Macroevolution Refers to evolution that occurs on a large scale
Speciation- produces a unique population of organisms
Gene flow between the two populations is minimal
Genetic differences gradually accumulate between populations
Reproductive isolation develops as a consequence
Macroevolution

28. Causes of Speciation Geographic Isolation
Separation by geographic differences
Temporal Isolation
Reproduction takes place at different times of the year
Behavioral Isolation
Populations are capable of interbreeding, but have different courtship rituals
Causes of Speciation

29. Gradualism- organisms descend from a common ancestor and evolve slowly over a long period of time
Punctuated Equilibrium-new species appear suddenly after long periods of little change
Rates of Evolution