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Evolution: Change Over Time

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1 Evolution: Change Over Time
Chapter 15 Evolution: Change Over Time

2 CHARLES DARWIN Founder of modern evolutionary theory
1831 Darwin became a naturalist on the HMS Beagle Studied animal and plant life on mapping expedition to South America and South Pacific

3 Darwin's Voyage

4 Galapagos Islands Darwin studied anatomy of insects, reptiles, birds and flowering plants

5 Galapagos Tortoises The inhabitants...state that they can distinguish the tortoise from different islands; and that they differ not only in size, but in other characters. Captain Porter has described those from Charles and from the nearest island to it, namely Hood Island, as having their shells in front thick and turned up like a Spanish saddle, whilst the tortoises from James Island are rounder, blacker, and have a better taste when cooked.---Charles Darwin 1845

6 Species Change Over Time
Darwin was convinced that evolution occurs Species Change Over Time

7 Darwin Concluded... That there must be a struggle for existence among all individuals Organisms must struggle for Food Space Prey

8 Ideas that shaped Darwin's thinking
From ancient times, most people believed all living things were created by a divine being at the same time and remained unchanged. By the time Darwin set sail, numerous discoveries, including a rich fossil record, had turned up importance evidence that caused some scientists to question these ideas.

9 Ideas that shaped Darwin's thinking
Geologists James Hutton and Charles Lyell After examining Earth in great detail, recognized that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present. Ex: volcanoes, earthquakes, erosion, continental drift, etc. The Grand Canyon, with its many layers of rock, was formed over millions of years by the Colorado River (erosion).

10 Ideas that shaped Darwin's thinking
Jean-Baptiste Lamarck - French naturalist Published hypothesis of Inheritance of Acquired Characteristics same year Darwin was born Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. Traits could then be passed on to offspring Over time would lead to change in species



13 Ideas that shaped Darwin's thinking
Thomas Malthus - English economist Reasoned that if the human population continued to grow unchecked, eventually there would not be enough space and food for everyone Forces such as war, famine and disease work against the growth Darwin realized this was even more true for plants and animals because humans produce far fewer offspring

14 Upon returning to England, Darwin began studying his specimens and filling notebooks with ideas.
Shared ideas with friends but reluctant to publish -- understood his ideas challenged scientific and religious beliefs of his day After more than 25 years -- published On the Origin of Species in 1859

15 Charles Darwin Published: “On the Origin of Species”

16 Survival of the fittest

17 Survival of the Fittest
Only some of the population survive long enough to produce offspring Survival of the Fittest

18 Which ones survive? Darwin’s observations led to the conclusion that individuals have different variations of traits that can be inherited Darwin bred pigeons with desirable variations and he was able to produce offspring with the same features

19 Artificial Selection Breeder selects the particular traits
Darwin wondered if there was some force in nature similar to artificial selection

20 Darwin's Explanation for Change...

21 Natural Selection Mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce and pass variations on to the next generation Organisms with less favorable variations are less likely to survive and pass on traits to the next generation

22 Summary of Natural Selection

23 Tendency toward Overproduction
For example: Fish lay thousands of eggs Most of these eggs will not survive

24 Individuals Exhibit Variations
Example: Fishes may differ slightly in color, fin and tail size and speed

25 Individuals with favorable traits survive and pass on those genes
Ex: A fast fish with camouflaged skin will be more likely to survive and reproduce. Thus, passing along the more desirable traits to future offspring.

26 Populations evolve, or change over time
Gradually, the offspring of the survivors make up a larger portion of the population. After many generations the population may look entirely different.

27 Natural Selection and Adaptations

28 Changes in structure or body parts that aide in survival
Adaptation Changes in structure or body parts that aide in survival

29 To copy the appearance of another species
Mimicry To copy the appearance of another species

30 CAMOUFLAGE Color adaptation so organism blends with its surroundings

31 Adaptations.... May take millions of years to develop or they may be rapid Ex: Slow---Sightless mole rat Fast: Antibiotic resistance

32 Evidence for Evolution
The Fossil Record Fossils show change over time

33 Geographical Distribution
Organisms live in different areas of the world, but have similar adaptations Different ancestors, but similar environmental pressures acting against it Descent with modification

34 Homologous Structures
Modified structure that is seen among different groups of descendants Limbs and Wings

35 Analogous Structure Similar in function, but different in structure
Ex: Bird Wing/Butterfly Wing

36 Vestigial Structure Appendix Eyes of a sightless mole rat
Any body structure that is reduced in function in a living organism but may have been used in an ancestor Appendix Eyes of a sightless mole rat

37 Embryological Development
Fish, reptiles, birds and mammals look similar during embryological development

38 Mechanisms for Evolution

39 Populations Evolve; Individuals Do Not
If you know the genotypes of all the organisms in a population, you can calculate the allelic frequency. A population in which the frequency of alleles does not change is in genetic equilibrium.

40 Populations Evolve; Individuals Do Not

41 Mutations Result in changes in the gene pool

42 Stabilizing Selection
Favors Average Individuals in a population

43 Directional Selection
Favors either of the extreme forms of a trait

44 Disruptive Selection Both extreme forms of a trait are favored

45 Evolution of a Species Speciation, or the formation of new species, can only occur when either interbreeding or the production of fertile offspring is somehow prevented: Reproductive Isolation Geographic isolation Temporal isolation Behavioral Isolation

46 Behavioral Isolation Occurs when two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior. Ex. Eastern and Western Meadowlarks Habitat overlaps, but will not mate with each other because they do not respond to each others song!

47 Geographic Isolation Two populations are separated by geographic barriers such as rivers, mountains, or bodies of water. Ex. Colorado River separating the Abert squirrel and the Kaibab squirrel (about 10,000 years ago).

48 Temporal Isolation Two or more species reproduce at different times.
Example: Orchids. Release pollen on different days, so they cannot pollinate each other.

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