2. La nuova biologia.blu Le cellule e i viventi David Sadava, David M. Hillis, H. Craig Heller, May R. Berenbaum

3. Evolution of Life

4. What Is the Relationship between Fact and Theory in Evolution? Evolution is the change in genetic composition of populations over time. These genetic changes drive the origin and extinction of species and the diversification of life. Evolutionary theory is the understanding of the mechanisms of evolutionary change.

5. What Is the Relationship between Fact and Theory in Evolution? The young Charles Darwin was passionately interested in geology and natural history. In 1831 he was recommended for a position on the HMS Beagle, for a five-year survey voyage around the world.

6. What Is the Relationship between Fact and Theory in Evolution? In the Galápagos Islands he observed that species were similar to, but not the same as, species on the mainland of South America. He also realized that species varied from island to island.

7. What Is the Relationship between Fact and Theory in Evolution? These observations, and many others, led Darwin to propose an explanatory theory for evolutionary change based on three propositions: Species change over time. Divergent species share a common ancestor, and species have diverged gradually through time (descent with modification). The mechanism that produces the change is natural selection. Darwin published his book, The Origin of Species, in 1859.

8. Artificial Selection Artificial selection is the purposeful selection of specific phenotypes by humans.

9. How Do Scientists Date Ancient Events? Earth’s history is recorded in rocks. Layers of rocks are called strata. Relative ages of rocks can be determined by looking at strata of undisturbed sedimentary rock. The oldest layers are at the bottom, youngest at the top.

10. How Do Scientists Date Ancient Events? Earth formed 4.6 to 4.5 billion years ago but it was 600 million years or more before life evolved. The history of Earth can be pictured as a 30-day month.

11. How Do Scientists Date Ancient Events? The history of life is divided into four eons. Precambrian (4 billion years) Phanerozoic eon—diversification of eukaryotes

12. What Are the Major Events in Life’s History? By the late Precambrian (630–542 mya) and early Cambrian, many kinds of multicellular soft-bodied animals had evolved.

13. What Are the Major Events in Life’s History? Cambrian period: beginning of the Paleozoic era. A rapid diversification of life took place called the Cambrian explosion.

14. What Are the Major Events in Life’s History? Ordovician period A great radiation of marine organisms occurred. Silurian period The first vascular plants appeared, as well as some terrestrial arthropods—scorpions and millipedes.

15. What Are the Major Events in Life’s History? Devonian period Rates of evolutionary change accelerated in many groups. An extinction at the end of the Devonian resulted in loss of 75% of marine species. Two meteorite impacts may have contributed to this extinction.

16. What Are the Major Events in Life’s History? Carboniferous period Great swamp forests of horsetails and tree ferns grew on the tropical continents. These swamp plants became fossilized as coal. Diversity of terrestrial animals increased and insects evolved wings.

17. What Are the Major Events in Life’s History? Permian period The continents came together to form the supercontinent Pangaea. Differentiation of two lineages: reptiles and mammals. Near the end of the Permian about 96% of all species became extinct.

18. What Are the Major Events in Life’s History? At the start of the Mesozoic era, the surviving organisms inhabited a relatively empty world. Triassic period Pangaea began to break apart. On land, conifers and seed plants became dominant. A great radiation of reptiles began. A mass extinction at the end eliminated about 65% of species.

19. What Are the Major Events in Life’s History? Jurassic period Pangaea divided into Laurasia, which drifted northward, and Gondwana, which drifted southward. First lizards and flying reptiles (pterosaurs) appeared; most large terrestrial animals were dinosaurs. Several groups of mammals first appeared. Flowering plants appeared late in this period.

20. What Are the Major Events in Life’s History? Cretaceous period Dinosaurs continued to diversify and snakes appeared. Flowering plants began the radiation. By the end of the period, many mammal groups had evolved. Another mass extinction at the end of the Cretaceous was caused by a meteorite.

21. Tertiary period Grasslands spread. Birds and Mammals began the radiation. Cenozoic era The positions of the continents resembled those of today. What Are the Major Events in Life’s History? Quaternary period Many large mammal species became extinct in Australia and the Americas when Homo sapiens arrived—possibly due to hunting pressure.

24. Adapted from Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014 Inc. All rights reserved