Evolution

1. Life changes over time… Evolution

2. A history of life on Earth Charles Darwin is the name most associated with evolution, but he did not publish his views on the subject until 1859. We need to understand the ideas of the time before we examine his radical new theories… 2 common ideas about life on Earth: • Earth was less than 10,000 years old • Fixed species – species do not change

3. The French Connection Buffon – French naturalist who, in the mid 1700’s examined fossils he believed to be more than a few thousand years old. Noted similarities between fossils and living creatures. Lamarck – French naturalist who, in the early 1800’s proposes to explain Buffon’s observations. Species are not permanent, life changes or evolves. Evolution explained as a process of adaptation. • “Inheritance of acquired characteristics”

4. Great Scots! Hutton – Scottish geologist who proposed in the late 1700’s, that Earth was formed much the same way that we see changes occurring today. Gradual change that can be immense over time. Uniformitarianism is born. Lyell –Another Scot geologist who furthered Hutton’s ideas in the early 1800’s. Erosion and earthquakes are examples that are attributed as geologic processes that can account for the changes in Earth’s physical features.

5. Can’t stop the pop. Malthus – British demographer, whose ideas on population growth in the early 1800’s had a large impact on scientific thought and ideas to come. His observation that populations grow geometrically while resources do not, led to the explanation of disease and competition as components of man’s “struggle for existence”.

6. The Beagle sets sail In 1831, the HMS Beagle embarks on a ‘round-the-world voyage. The mission? To chart the South American coastline for the British Navy. Along for the ride was a 22 year old biologist by the name of Charles Darwin. He wanted a chance to study the plants and animals on the trip. Through specimens he collected, pictures he sketched, and journals he kept, Darwin’s ideas began to change. He left with many of the beliefs common in his time. By the time he returned to England, he had seen things that began to make him question…

7. What did he see? Many species of South America. These were similar to European species, but quite distinct at the same time. Even fossils he found were different from what he was used to. Some fossils were similar to living creatures, but much larger than anything still alive. This led to the idea that the living species were descendants of those in the fossil record. The Galapagos Islands. Young volcanic islands that had many similar species to the mainland, but were different, even from island to island. His idea was similar to that of Lamarck’s … that the species must have adapted to the new environment.

8. More observations While in South America, Darwin found marine fossils high in the mountainous regions, and even experienced an earthquake while in harbor where he noticed an underwater landmass had been heaved up above the water level, exposing it to the environment for the first time. He concluded that this could be along the lines of what Hutton and Lyell had explained in their theories.

9. 5 years later… Upon returning home, Darwin had amassed a large collection of fossils, had volumes of journals, and had seen organisms that varied greatly from place to place. Due to the specimens he sent home while on his journey, he had gained quite a reputation back home as a respectable scientist. When he left, his ideas about life were on par with most others’. After his return, he had developed 2 new ideas based on his experience. • The Earth was old. • Species change.

10. Putting it all together So, if Darwin thought that species changed over the Earth’s long life, he had to come up with an explanation for how this occurred. If species change, it must be for a reason. What is the reason? Selective breeding of livestock and animals leads to a change, but that is not what happens in nature. Malthus’ ideas of competition strike a chord, and he proposes that this must be what drives the changes.

11. Darwin’s Idea He writes his ideas in 1844, but only tells a few close colleagues of his ideas. They encourage him to publish before someone else beats him to the same conclusions, but he sits on the writings until 1858, when another scientist by the name of Wallace has the same ideas. Darwin publishes his ideas a year later in On theOrigin of Species. In it he outlines two main points: • Descent with modification – based on evidence • Natural Selection – the mechanism for evolution

12. Observations and evidence Evolution II

13. Darwin’s Idea Descent with modification • Descendants spread into different habitats • New habitats necessitated adaptation • This accounts for diversity of life Natural Selection • Individuals inherit characteristics well-suited to their environment • Those individuals leave more offspring than others • Those offspring are more likely to have well-suited characteristics

14. 5 areas of support • Fossil Record • Geographic Distribution • Structural Similarities • Developmental Similarities • Molecular Biology Let’s examine each of these more in depth…

15. Fossil Record Most fossils found in sedimentary rock • Due to aquatic preservation, fossils remain largely intact and fossilize in layers Rock forms in layers, or strata • Often sand or silt is deposited on top of existing layer, compacting it into rock Fossil Record is formed due to the layering • Older rock is “lower” than younger rocks Helps put the puzzle of life together • Fossils help show what organisms have as similarities or dissimilarities

16. Geographic Distribution Another way to understand the similarities Is to see how they are spread out around the globe Some animals in South American tropics share similarities with African desert animals rather than African tropical animals Australia is home to more marsupial animals than anywhere else in the world, and had relatively few placental animals.

17. Structural Similarities Skeletal structures are very similar in parts of different animals. Analogous structures • Bees and Birds can fly, but not in the same way • Similar jobs do not indicate common ancestry Homologous structures • Human, Feline, Whale, and Bat limbs are similar • structures that indicate common ancestry Vestigial structures • structures that have a major function in one organism, but less in another

18. Developmental Similarities • Developing embryos of different organisms appear similar during maturation. • Organisms start differentiating at different times, with more closely related organisms differentiating later in the process. • Distinctive differences occur later in the process

19. Molecular Biology • In the era of DNA, why don’t we just use the ultimate similarity of life and compare DNA sequences to see how closely organisms resemble one another? • The closer the DNA sequences, the more closely related • The less the sequences match, the further relationship

20. Microevolution Evolution III

21. Microevolution This is a change in the gene pool over time. • Within a single population Hardy-Weinberg equilibrium equation p2 + 2pq + q2 = 1 • Large population • Random Mating • No Mutation • No Migration • No Selection For/Against

22. How does change happen Only the gene pool has to change, which means individuals that make it up must be different than in the past. • Natural Selection – “good” genes survive • Mutation - random • Gene Flow – more diversity • Genetic Drift – less diversity

23. Gene Flow Transfer of alleles from one population to another Migration • Immigration • Emmigration

24. Genetic Drift Change in allele frequency due to “chance” Bottleneck effect due to “disaster” Founder effect due to “pioneers”

25. Origin of Species Evolution IV

26. More than microevolution… • Natural Selection allows for adaptation • Adaptation over time is microevolution • If microevolution were the “end”, we would only have adaptations of one species • How do other species come to exist?

27. Microevolution to Macroevolution Speciation – the development of new species through evolution Taxonomy is the science of classifying different species Binomial Nomenclature – Scientific Naming Eg: Homo sapiens, Pantera Leo, Helianthus annuus

28. Back to the Galapagos Grant study – Peter and Rosemary Grant • Daphne Major – size of football stadium • 2 finch species living on same island • Medium ground finch • Cactus finch • Seasons affect diet choices

29. Speciation • Speciation takes time • Changes in species occur over millions of years • Fossil record indicates this • Punctuated equilibria • Long periods of stability (equilibrium), and “sudden” speciation

30. How species separate Prezygotic Barriers • Temporal Isolation • Habitat Isolation • Behavioral Isolation • Mechanical Isolation Postzygotic Barriers • Hybrid Infertility • Hybrid Inviability • Hybrid Breakdown

31. Adaptive Radiation • Many species evolve from a common ancestor • This is what the branching diagrams illustrate • This is the idea behind how microevolution can lead to speciation, and that can lead to many diverse species if given enough time…

32. Some questions Why do species exist? They fit their habitat. Why can evolution occur and still leave “less evolved” life forms? “Less evolved” implies “not as good”. Good means they fit their environment. How can we get so much variation? Sexual reproduction has a large part of this, but random mutation and natural selection account for some of it as well.