1. Chapter 15-17
Evolution

2. What is evolution? Evolution is change over time
Theory of evolution – process by which modern organisms have descended from ancient organisms
Remember that a scientific theory is a well- supported testable explanation of phenomena that have occurred in the natural world

3. Where did the idea of evolution come from?
Charles Darwin made numerous observations and collected evidence that led him to propose his hypothesis about the way life changes over time
Collected plant/animal specimens where ship anchored
Learned that an enormous number of species exist
Noticed how well suited organisms are to their environment

4. Galapagos Tortoises

5. Lamarck and Evolution
In 1809 Lamarck proposed that by selective use or disuse of organs, organisms acquire or lose certain traits
These traits can then be passed to offspring
This could lead to a change in the species

6. Lamarck and Evolution

7. Darwin and Evolution
“On the Origin of Species” was published in by Charles Darwin
Darwin proposed natural selection as a mechanism for evolution
Competition for resources leads to survival of the fittest
Successful adaptation means the organism has and advantage to survival and reproduction
Adaptation – any inherited characteristic that increases an organism’s chance of survival
Over time natural selection results in the inherited characteristics of a population

8. Darwin and Evolution
Darwin proposed that each species has descended, with changes, from other species over time (descent with modification)
The principle of common descent states that all species (living and extinct) were derived from common ancestors (single “tree of life”)
Darwin hypothesized that living things have been evolving for millions of years
Evidence found in fossil record, geographical distribution of species, homologous structures of organisms, similarities in early development

9. Darwin and Evolution

10. Types of Evolution
Micro-evolution – change in a population’s gene frequencies
Macro-evolution – when a new species emerges
Species – group of organisms that can reproduce with fertile offspring in nature
Variation in the population provides the material for natural selection. Sexual reproduction (the shuffling of alleles and, thus, uniqueness) provides for this variation

11. Evidence for Evolution
The fossil record - Strata of fossilized remains of organisms extinct for many years. The oldest layers have the oldest fossils beginning with bacteria.
Biogeography – the presence of organisms in areas of the world correlates with the movement of land masses over time
Australia has a unique abundance of marsupials found no where else in the world
Comparative anatomy – Organisms share many characteristics called homologous structures
Vestigial structures are parts reduced in size or no longer used by a more recent organism, ex. hip bones of whales

12. Geographic Distribution of Species

13. Homologous Body Structures

14. Evidence for Evolution
Comparative embryology – Similarities exist between many animals as they are developing
DNA or molecular similarities – All organisms share the same genetic code, ATCG’s. Most of the codons match the same amino acids.
Population studies – We can see bacterial populations change over time
Bacteria exposed to antibiotics will die except for the resistant few
The resistant ones live and reproduce, creating a population of bacteria resistant to the antibiotic.

15. Similarities in Embryology

16. Evolution and Isolation
Geographic isolation – when populations are split by geographic barriers, they sometimes change so that when brought back together, they can’t have offspring together
Reproductive isolation – when organisms in a population do not interbreed for some reason and become distinctly different groups.
In plants this can occur as a mistake in meiosis, and the new plant will not have the correct chromosome number for successful zygote formation. ex. salamander ring species

17. Genetics and Evolution
Gene pool- all genes, including the different alleles, in a population
Relative frequency- number of times that an allele occurs in a gene pool
Genetically, evolution is any change in the relative frequency of alleles in a population
Mouse fur frequencies begin B is 40%, b is 60% (B=black, b=brown)
If it changes to B=30%, then the population is evolving

18. Sources of Genetic Variation
Mutations are a change to the sequence of DNA, which may result in a phenotype change
Can be caused by mistake in replication or radiation/chemicals
During gamete productions gene shuffling occurs (independent assortment and crossing over)
Can produce a huge variety in phenotypes
Does not change relative frequency
Can result in unique phenotypes that could be an advantage

19. Genetics and Evolution
Evolutionary fitness is an organism’s success at passing genes to the next generation
However, natural selection never acts on genes only on the organism as a whole
In addition, evolution is about the frequency of alleles for an entire population, not and individual organism

20. Genetics and Evolution
Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution
The red lizards are more visible; black lizards warm faster, which allows them to be more active sooner

21. Genetics and Evolution
Natural selection can affect polygenic traits (trait controlled by 2 or more genes) in 3 ways:
Directional selection occurs when individuals on one end of a phenotype curve have higher fitness
Low mortality,
high fitness
High mortality,
low fitness

22. Genetics and Evolution
Stabilizing selection occurs when higher fitness at the center of the curve than the ends
Weight of
human infants
Low mortality, high fitness
High mortality, low fitness
Brightness of
Feather Color
Selection against both extremes keep curve narrow and in same place.
Percentage of Population

23. Genetics and Evolution
Disruptive selection occurs when the ends of the phenotype curve have higher fitness than the middle
Can cause it to split into 2
Medium sized seeds become less common

24. Genetics and Evolution
Genetic equilibrium occurs when allele frequencies remain constant; 5 requirements
Random mating (not true in organisms like elk)
Large population
No movement into or out of the population
No mutations
No natural selection

25. History of Life Biogenesis – Life comes only from life.
Abiogenesis – spontaneous generation, life can come from the nonliving
Louis Pasteur – disproved spontaneous generation by sterilizing broth solutions.
Stanley Miller and Harold Urey (1950’s) simulated early earth in the lab. By making amino acids in the lab.

26. Pasteur’s Experiment

27. Miller and Urey Experiment