Darwin s Theory of Evolution. The Puzzle of Life s Diversity

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1 Darwin s Theory of Evolution The Puzzle of Life s Diversity

2 Evolutionary Theory A scientific explanation that can illustrate the diversity of life on Earth Theory A well-supported, testable explanation of phenomena (unexplained event) that have occurred in the natural world

3 Evolution Change over time A process by which modern organisms have descended from ancient organisms

4 The Voyage of the Beagle Charles Darwin ( ) In 1831 he sailed around the world for 5 years Made observations and collected evidence that led to a revolutionary hypothesis Proposed how life changes over time This hypothesis has become known as the Theory of Evolution

5 Patterns of Diversity Darwin noticed that organisms were well-suited to their environments He began collecting fossils and noted that some looked completely different from the species of the time, while others resembled species alive at the time

6 The Galapagos Islands Darwin noted that traits of organisms varied depending upon which island they were found

7 Ideas that shaped Darwin s thinking James Hutton 1785 Proposed Earth is shaped by geological changes over long periods of time Charles Lyell Principles of Geology 1833 Explained that processes that occur now have shaped Earth s geological features over long periods of time

8 Ideas that shaped Darwin s thinking (continued) Together, Hutton and Lyell helped scientists recognize that Earth is many millions of years old Influenced Darwin in 2 ways If Earth can change over time, life can change over time, too It would have taken many years for life to change, and it s only possible if Earth is very old

9 Ideas that shaped Darwin s thinking (continued) Jean-Baptist Lamarck Proposed that by selective use and disuse of organs, organisms acquired or lost certain traits during their lifetimes These traits can be passed on to offspring His hypothesis was later proven to be incorrect, but he was the first person to suggest a method for evolutionary change

10 Ideas that shaped Darwin s thinking (continued) Thomas Malthus - On the Principle of Population 1798 Reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone Darwin read Malthus work and realized it applied more strongly to plants and animals than humans because humans produce far fewer offspring than other species. Alfred Wallace 1858 Studied the distribution of plants and animals Wrote a letter to Darwin, speculating on evolution by natural selection

11 Darwin Presents His Case 1859 Darwin published a collection of his observations Included ideas about species diversity Also included ideas about the process that would later be referred to as evolution

12 On the Origin of Species The book containing Darwin s ideas Proposed the theory of natural selection

13 On the Origin of Species Further presented evidence of evolution occurring for millions of years Stated that evolution was still happening

14 Inherited Variation Darwin noticed that members of each species differed from one another Example: some plants of a particular species beared larger fruit than others Differences were due to heritable variation Passed from parent to offspring Due to variations in genes

15 Artificial Selection Breeders of organisms began choosing which organisms to breed This produced offspring with the most desirable traits Example: the domestication of animals

16 Evolution by Natural Selection The Struggle for Existence A direct result of competition for necessary resources Examples: food, living space, and other necessities

17 Survival of the Fittest A key factor in the struggle for existence How well suited an organism is to its environment Fitness The ability to survive long enough to reproduce

18 Survival of the Fittest (continued) Adaptation Any inherited characteristic that increases an organism s chance of survival Can include anatomical or structural characteristics Examples: a porcupine s quills, thick fur on deer

19 Survival of the Fittest (continued) This mechanism can also include physiological processes or functions Example: the efficiency of a plant s photosynthetic process

20 Survival of the Fittest (continued) Can also include behaviors

21 Survival of the Fittest (continued) States that individuals that are better suited to their environment have increased chances of survival and reproduction Natural selection results in changes in the characteristics of a population Organisms of a particular species living in the same place at the same time

22 Natural Selection Can only be measured by observing the changes in a specific population over many generations

23 Summary of Darwin s Theory Individual organisms differ from one another and some of this variation is heritable Organisms produce more offspring than can survive The ones that die do not have a chance to reproduce

24 Summary of Darwin s Theory (continued) Organisms in a particular population compete for limited resources Each individual organism has advantages and disadvantages in their struggle for existence Species today are descended from common ancestral species that existed in the distant past