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Many types of evidence support evolution. Chapter 6 Section 4 The Fossil Record • Preserved remains or traces of an organism that lived in the past What Is A Fossil? How Do MOST Fossils Form? • An organism dies and becomes buried in sediment How Most Fossils Form Then People Find Them! What Do Fossils Reveal? • Fossil record: millions of fossils that scientists have collected • Most of what we know about extinct species • Provides clues about how and when new groups of organisms evolved • Extinct: no members of the species are alive Fossils and Evolution Fossils! Elephant Evolution Elephant Evolution! Common Ancestor Evidence for Evolution Biological evidence supports evolution. • State evidence from modern-day organisms that scientists use to show evolutionary relationships among groups. • Describe how scientists classify organisms and place them on branching trees. Vestigial Structures Similarities in Body Structure • homologous structures: similar structures that related species have inherited from a common ancestor • Example: fish, amphibians, reptiles, birds & mammals all have an internal skeleton with a backbone Homologous Structures Similarities in Early Development • embryos suggest common ancestor • Similar organisms go through similar stages in early development • Who is a closer relative: chickens and rats or chickens and turtles????? Which Embryo Is Human? Guess The Embryo! Try Your Luck! Genetic Evidence: Similarities in DNA • Related Species have many of the same nitrogen bases in common • Compare order of amino acids in similar proteins • Elephant shrews – rodent or elephant???? Golden-rumped sengi Rhynchocyon chrysopygus Weight = 550 g. Gedi Ruins, Kenya • The new species, named the gray-faced sengi (Rhynchocyon udzungwensis), weighs about 1.5 pounds, 25 percent larger than any other member of the elephant-shrew family. It is known to exist in only two groups in a 115-square-mile area of this largely unexplored forest. • Scientists report that its relatives include elephants, manatees, and the aardvark. In recent years, a number of other new species have been discovered here, including the Udzungwa partridge, a monkey known as the kipunji, and several amphibians and reptiles. African Elephant ORDER: Proboscidea FAMILY: Elephantidae GENUS: Loxodonta SPECIES: africana The Clock Gene – Circadian Rhythms Our Family Tree Our Family Tree How Fast Does Evolution Occur? • Fossil record is incomplete • Fossils don’t always tell when something evolved • Some scientists think it occurs slow and steady • Some think it occurs in occasional rapid bursts Horses! How Fast Does Evolution Occur? • Usually find fossils unchanged for long periods of time • Fossils appear that are very different Explanation for lack of intermediate forms • Fossil record incomplete • Assume that more forms will eventually be discovered How Fast Does Evolution Occur? Gradualism • Slowly but steadily • Tiny changes gradually add up to major changes over very long periods of time • This is what Darwin thought • If correct, many intermediate forms for all species should exist How Fast Does Evolution Occur? Punctuated Equilibria • Evolution occurs during short periods of rapid • • • • • change Most new species form when small populations become isolated Small, isolated populations can evolve quickly and adapt to new environment Maybe as quick as a few hundred years Not many intermediate fossil forms would exist Both seemed to have occurred