Chapter 17 --Darwin and Evolution “The Origin of Species” Question: How did the giraffe get its long neck? Why are there 9 subspecies of giraffes?

History of Evolutionary Thought In 1831, Charles Darwin, a 22-year-old naturalist, accepted a position aboard the ship HMS Beagle that began a voyage around the world; it provided Darwin with many observations.

Pre-Darwinian world-view was determined by theological beliefs. 1) The earth is young; ~10,000 years old 2) Each species was specially created and did not change 3) Observations are to substantiate the prevailing worldview. Rothchilds Giraffe How would this worldview explain the giraffe’s neck? How would it explain the 9 subspecies?

Mid-Eighteenth-Century Contributions Carolus Linnaeus and Taxonomy Taxonomy is the science of classifying organisms;. Linnaeus developed a binomial system of nomenclature - two-part names for each species Homo sapiens Canis lupus Giraffa camelopardalis * with 9 subspecies

Masai Giraffe (Giraffa camelopardalis tippelskirchi) Thornicroft Giraffee Giraffa camelopardalis thornicrofti

Biogeography study of the distribution of species and ecosystems in geographic space and through geological time

Erasmus Darwin suggested the possibility of common descent. The idea that species could change was not Charles Darwin’s original idea. No one could propose a MECHANISM for how these changes could occur. Paleontology was a new field, uncovering fossils of organisms that no longer exist.

Lamarck's Acquired Characteristics Lamarck mistakenly saw "a desire for perfection" as inherent in all living things. His view of giraffe evolution would have looked like this:

Experiments fail to uphold Lamarck's inheritance of acquired characteristics          

So…. if that was wrong. How did giraffes come about So….if that was wrong. How did giraffes come about? Also, why are there so many subspecies of giraffes?

What We Know So Far 1.  Taxonomy and classification emphasize similarities among species  (common descent) 2.  Fossils show extinct species (paleontology) 3.  Isolated species are distinct (biogeography) 4.  Organisms have adaptations to help them survive .........Enter Charles Darwin..........

The Voyage of the Beagle

Galapagos Islands off S. America Island species varied from mainland species Finches resembled mainland finches, but with more variation Tortoise Variations Shells that flare up, long necks - feed on tall plants

Figure 17.7a

Figure 17.7b

Darwin's Finches a. Finches on the Galápagos Islands resembled a mainland finch but there were more types. b.  Galápagos finch species varied by nesting site, beak size, and eating habits.

Did the animals on the islands descend from one mainland ancestor? Questions to Ponder: Did the animals on the islands descend from one mainland ancestor? What were the variations found on the finches? Why were the island finches so different from mainland finches?

Natural Selection and Adaptation Natural selection was proposed by both Alfred Russel Wallace and Darwin. It is the MECHANISM by which evolution occurs. It would explain how giraffes got their long necks, why finches have different beaks, and why there are two different varieties of tortoises.

There are three preconditions for natural selection. 1. The members of a population have random but heritable variations. 2. In a population, many more individuals are produced each generation than the environment can support. 3. Individuals have adaptive characteristics that enable some to survive and reproduce better.

There are two consequences of natural selection. 1. An increasing proportion of individuals in succeeding generations will have the adaptive characteristics. 2. The result of natural selection is a population adapted to its local environment.

Natural selection can only utilize variations that are randomly provided; therefore there is no directedness or anticipation of future needs.

Pause and think: Thinking that evolution has a direction is a common misconception. Can you think of any statements you may have heard that suggest people think that evolution is directional? Why didn’t chimpanzees evolve the ability to talk? Why aren’t other animals as intelligent as humans? Why didn’t giraffes evolve in other places?

Extinction occurs when previous adaptations are no longer suitable to a changed  environment.

How Evolution by Natural Selection Works 1. Variations exist in a population.

2. Every individual struggles to exist.

3. Individuals differ in FITNESS a) fitness measures an organism’s reproductive success b) it does not necessarily mean stronger. Fully armored stickleback (ocean) Low armor (freshwater)

4. Survivors pass traits to offspring Over time, the traits that provide the best chance of survival and reproduction are the ones most prevalent in the population - these are ADAPTATIONS

Apply these principles to the giraffes. Procamelus (ancestor)

Be careful with that word….. Adaptation is a trait, a noun. It is dangerous to use it in verb form because it suggests that an individual can choose to adapt. They cannot. ***** POPULATIONS EVOLVE ***** Fix this sentence: This Aye Aye has adapted to a life of eating insects. Its long digit is used to probe wood.

Dogs breeds were developed by years of breeding wolves ARTIFICIAL SELECTION Dogs breeds were developed by years of breeding wolves We chose the traits most desirable, then bred the dogs with those traits. Nature does the same with “natural selection”

“On the Origin of Species” by Darwin 1. After the HMS Beagle returned to England in 1836, Darwin waited over 20 years to publish. 2. He used the time to test his hypothesis that life forms arose by descent from a common ancestor and that natural selection is a mechanism by which species can change and new species arise. 3. Darwin was forced to publish  Origin of Species after reading a  similar hypothesis by  Alfred Russel Wallace.

The Definition of Evolution Evolution is the change in allele frequencies, or a change in the gene pool, of a population. Mythbuster: “No one has ever seen one animal change into another, therefore evolution isn’t true.” How would you respond to this statement?

Imagine a Scenario of Evolution..... 1.  Create a real or imagined organism 2.  Describe 2-3 variations 3.  Show how evolution would act on this population given a change in the environment (climate, predators, food change..) 4.  Pay attention to which variations are beneficial, which are harmful. 5.  Show how reproduction changes the overall population (with regard to these variations) 6. Be creative!   You can map your organism through a few generations...  You will present your scenario to the class!