Darwin s Theory of Evolution Chapter 16

Transcription

1 Darwin s Theory of Evolution Chapter 16

2 Darwin & Natural Selection

3 Darwin s journey

4 Darwin s Observations On his voyage, Darwin read Lyell s book As he visited different places, he began to see evidence that change occurs slowly. In 1835, the Beagle landed on the Galapagos Islands He collected specimens of birds & animals Finches, mockingbirds Observed slight differences in birds from each island Also observed animals looked similar to those on the mainland nearby

5 Evolution by Natural Selection Darwin read essay about human population growth controlled by war, famine, disease. Now we use population to describe all individuals of a species in a geographical area that can interbreed. He started thinking about the species he observed while on the Beagle. Natural Selection Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits

6 Evolution The process of change within a population over time This process occurs over time and will vary with the environment Organisms differ from place to place because the habitats vary and present different challenges to the organsisms. Each organism has evolved in response to their environment. An adaptation is an inherited trait that becomes common in a population because of it s advantage.

7 Pinta Island Intermediate shell Fernandina Pinta Marchena James Tower Isabela Santa Fe Santa Cruz Floreana Hood Hood Island Saddle-backed shell Isabela Island Dome-shaped shell

8 Darwin s Theory 1. Inherited variation exists within the genes of every population or species 2. Some individuals of a population are better suited to survive and have more offspring 3. Over time, the traits that make certain individuals able to survive and reproduce tend to spread in that population. 4. There is overwhelming evidence from fossils and other sources that living species evolved from organisms that are extinct

9 Ideas that Shaped Darwin s Thinking 1830s and before, most Europeans believed: the Earth was only several 1,000 years old since their creation, neither plants nor animals had changed Geology findings Hutton proposed layers of rock form over millions of years Lyell explained how geological phenomena (volcanoes, earthquakes) build up or tear down the Earth over millions of years Explains how marine fossils can end up on mountain tops

10 Ideas that Shaped Darwin s Thinking Lamark s Hypothesis he proposed that by use or disuse an individual acquires or loses organs during their lifetime, passing this to their offspring

11 Population Growth Thomas Malthus noted that humans were being born faster than people were dying.

12 Darwin Updated Species formation Different populations of the same species tend to evolve differently to adapt to their surroundings. Reproductive Isolation occurs when two populations are prevented from interbreeding Geographic isolation Temporal isolation Behavioral isolation

13 Formation of New Species The process by which new species form is called speciation The first step is divergence accumulating adaptations to fit it s environment. A population will first become a subspecies still able to interbreed but have adaptations that fit it s environment

14 Factors in Natural Selection 1. All populations have genetic variation 2. The environment presents challenges to successful reproduction 3. Individuals tend to produce more offspring than the environment can support 4. Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment do.

15 Tempo of Evolution Gradualism In most cases, evolution occurs slowly, a gradual process that occurs over time Fossil records show that some species change slowly, gradually becoming new species. Punctuated Equilibrium In some cases, evolution occurs during periods of rapid change. Galapagos Island finches they rapidly evolved to fill the available niches.

16 Evidence of Evolution Most scientists agree on the following three points 1. The Earth is ~4.5 billion years old 2. Organisms have inhabited the Earth for most of its history 3. All organisms living today share common ancestry with earlier, simpler life-forms Fossils provide us with a record of Earth s previous life forms

17 Formation of Fossils In order for an organism to leave a fossil record of it s existence, it had to live a specific environment Wet lowlands, slow-moving streams, lakes, near volcanoes that spew ash not lava Even then, it must be covered in sediment before it could decay Result the fossil record is far from complete

18 Baby mammoth found frozen in Russia in 2007

19 Iceman found frozen in the Alps, Italy in 1991

20 Archaeoptryx Archaeoptryx model

21 Comparative Anatomy Homologous Structures related organisms share similarities that are derived from common ancestors homologous structures = different mature forms developed from the same embryonic tissues

22 ex: limbs differ greatly in form and function (wings, arms, legs, flippers), yet they are all constructed from the same basic bones vestigial structure = structure inherited from an ancestor that now has less or no function ex: human appendix, hind limbs in snakes, pelvis in whales, male nipples, wisdom teeth in humans, wings of flightless birds

23 Elephant Evolution

24 Examples of Evolution Tuberculosis TB is caused by the bacterium Mycobacterium tuberculosis Kills more adults than any other infectious disease worldwide In 1950 s two antibiotics were developed to treat TB In late 1980 s, new strains of TB were discovered that are resistant or immune to these antibiotics. These strains developed through natural selection

25 Examples of Evolution Darwin s finches Darwin collected 9 species of finches Difference was in the bills of the birds. The food varied seeds, insects, fruit, even blood from other birds He suggested they all evolved from one species they changed as they adapted to different food sources. David Lack studied the finches for 5 months in 1938 He determined that there was little evidence to support Darwin s theory

26 Examples of Evolution Peter & Rosemary Grant studied the finches for 25 years They saw changes in finch beaks over time. Dry seasons saw an increase in beak size so that the birds are able to eat the seeds. Wet seasons saw a decrease in beak size so that the birds are able to eat the insects.