The Theory of Evolution

1. The Theory of Evolution

2. How did the animal on the next slide get his amazing camouflage?

4. Evolution sometimes has a bad rep… • But it’s really simple. • THINGS CHANGE! Animals, plants, algae, pond scum, bacteria, viruses, and even humans! Every SPECIES has the potential to evolve (change over time) and everything has evolved. Individuals can’t change, but the species as a whole can. • How do we know evolution is real? • Just by looking at the world around us! (All living things are made of the same building materials, DNA is DNA is DNA, similar looking organisms have similar DNA, different species use the exact same proteins, the fossil record shows that things looked different…)

5. Things Change. Life does too!

6. Before Darwin Everybody believed that the world never changed. Every plant, animal, and organism was made in the beginning exactly as it exists now. But nature said differently…

7. Darwin and the Voyage of the Beagle Charles Darwin- the scientist given credit for the discovery of evolution through natural selection. Traveled the world on the HMS Beagle. Made observations as he went.

8. Darwin’s Observations • Changing Geography – The Earth is many millions of years old and has changed a lot over time. It is still changing. • If the earth changes, shouldn’t life change too?

9. Darwin’s Observations • The Fossil Record – we have evidence underground of animals and plants that no longer exist (e.g. dinosaurs) and sometimes we find fossils that look like earlier versions of modern species • If nothing ever changes, then why did they go away? Why do they sometimes look similar but different to existing species? Could they be an earlier version?

10. Darwin’s Observations • Patterns of Diversity – populations show variety even among individuals • Even identical twins can be a little different! If nothing ever changes, why aren’t we all exactly the same?

11. Natural Variation These differences in individuals is called natural variation. New traits can even be added through genetic mutations. Could these small tweaks lead to big changes over time?

12. Darwin’s Observations • Artificial Selection – humans have been exploiting the variations and changing animals and plants drastically for hundreds of years for our own use (e.g. wolves to dogs) • If we can make changes, why can’t nature?

13. Darwin’s Breakthrough • Darwin’s big break came on a group of islands called The Galapagos Islands. This island chain contained different (but VERY similar) species on different islands. Could they all have come from the same original species?

14. Can you see what Darwin saw? What do these two islands have such different tortoise shells? Hint: Check the backgrounds!

15. “Natural” Selection of the Galapagos Tortoises • An ancestral group of tortoises ended up on the Galapagos islands. They contained variation among the individuals. Some had dome and some had saddle shells. The domes could not survive on the harsh islands because they could not lift their head to get food from shrubs. The saddles had a harder time protecting their neck from predators on the greener islands. Overtime, all of the unsuited tortoises on each island died, leaving behind only the tortoises that best “fit”. In the end, the tortoises are selected by nature for their environment.

16. Evolution • A change in the available genetics in a population’s gene pool. Over long periods of time, good genes become more common and bad genes become less common in the group. Occasionally new genes will arise (good or bad) through mutation • Population = all the animals of the same species living within an area • Remember: Populations (groups) evolve. Individuals cannot.

17. Evolution is driven by Natural Selection Organisms best suited for their surroundings will survive and reproduce more, producing even more individuals in the next generation with the good genes. Overtime, only the best genes will remain. 

18. PROOF: The Evolution of the Peppered Moth In England a species of moth called the Peppered Moth had two available, inheritable wing colors- a light color and a dark color. (Through genetics, dark colored moths had dark colored babies, and vice versa.) Prior to the industrial revolution, the light color dominated with 99% of the moths displaying this phenotype. (See below to find out why.) However, after the factories opened, the light phenotype became almost extinct and the darker color began to dominate. What changed? Why do you think this happened?

19. Problem… Evolution can take a really long time. How can we know it’s actually happening if we can’t directly see it?

20. Evidence of Evolution While we can’t watch evolution directly, we CAN see the results of it. Darwin argued that living things have been evolving on Earth for millions of years. Evidence can be found in the fossil record, the geography of living species, homology between different species, and similarities in early development.

21. Evidence of Evolution The Fossil Record shows how species have changed. It also enables us to create an evolution timeline through radioactive or relative dating. It’s a way to peek into the past and see what things *used* to look like.

22. How old is this fossil? • Relative Dating: A fossil found deeper in the ground is older than a fossil found near the surface; can’t give an exact age, only “older” or “younger”; can also be used for the same fossil found in different locations

23. How old is this fossil? • Radioactive dating: using the decay of special chemicals called isotopes can determine an exact age of a fossil • Half life: the time it takes for half of the isotope to decay; after 1 half-life, 50% remains. After 2 half-lives, 25% remains. After 3 half-lives, 12.5% remains…

24. Evidence of Evolution Geographic Distribution- different regions have their own variations of similar organisms due to different environments working on common ancestry. All of these giant rodents came from a common ancestor. They look different now because they live in different areas. Just like the Galapagos tortoises!

25. Evidence of Evolution Homologous Body Structures – organisms descended from the same ancestor will have similarly built traits; they may work differently, but they are built the same (e.g. bat wings and human hands)

26. Evidence of Evolution Molecular Homology – Since genetic relatives (like siblings) have similar DNA, species related through evolution will also have similar DNA. Can compare DNA or protein sequence. Similar proteins = similar DNA

27. Careful! • Sometimes two species look a lot alike, but they are not related. This is still evidence for natural selection, because their similarities came from living in the same environment/ability BUT they do NOT have a common ancestor. • Analogous structures – structures that work the same way, but they are built differently; these species are NOT related! (e.g. butterfly wings and bird wings)

28. Evidence for EvolutionVestigial Structures- traits that were used in an ancestor, but are not used anymore (ex: whale pelvis)Whale ancestors used to have legs!

29. Evidence of Evolution Embryology – related species develop in similar ways and the embryo can show evidence of past traits; sometimes watching an embryo grow is kind of like watching evolution in fast forward!