Evidence of Evolution

As scientists we must review all of the evidence before confirming a theory There is a tremendous amount of evidence to support Darwin’s Theory of Evolution –Fossils –Similarities in embryos –Similarities in Body Structure

Fossils are used as Clues… Preserved remains or traces of an organism that lived in the past. They form when orgs. die and become buried. Usually its bones, teeth, shells, etc.. Plants can be preserved too – their leaves, stems, roots, seeds, etc.

Evidence from fossils… Most of the fossils recovered by geologists are of species that are extinct: –No members of that species are still alive Geologists collect fossils to form the fossil record The fossil record provides CLUES about HOW and WHEN new groups of organisms evolved –The rocks the fossils are found in can be dated

Observe the fossils of these relatives of the modern horse. Dating the rocks that these fossils were found in allows scientists to understand HOW the modern horse has changed over time and WHEN its ancestors roamed the Earth.

Types of Fossils - Petrified Fossil Remains changed to rock.

Types of Fossils - MOLD Hollow space in sediment in the shape of an organism or part of an organism.

Types of Fossils - Cast The mold becomes filled IN with hardened minerals. Trilobite – extinct arthropod

Evidence from similarities in embryos Scientists look at the early development of an organism. –They will look at the formation of the embryos –One can hypothesize that similar looking embryos can be related to each other

Evidence from Similarities in Body Structures Homologous structure: similar structures that related species have inherited from a common ancestor.

Sometimes, organisms have body structures that remain long after they are no longer needed by the organism. These “evolutionary left-overs” are called VESTIGIAL ORGANS. –Scientists can use vestigial organs as evidence that organisms can share common ancestors. –Ex. Pelvis bones found in whales?

Do Humans Have Vestigial Organs? Appendix Wisdom Teeth Coccyx Bone Goose Bumps

Nictitating Membrane The owl, like other birds, closes its haw when flying at high speeds because the additional moisture improves their vision. Certain kinds of sharks also use nictitating membranes to keep from being stabbed by thrashing prey. Amphibious creatures such as alligators, crocodiles, and other reptiles use their third eyelid while hunting, or while not underwater.

Nictitating Membrane Harbor seals benefit from their nictitating membrane because they live in and out of the water. Aardvarks close their nictitating membrane when they are eating termites to keep from getting bitten. For the polar bear, the membrane actually filters ultraviolet light and reduces snow blindness. The nictitating membrane of other mammals, like cats, dogs, and horses, only protrudes if they are ill.

With today’s technology and the discovery of DNA, scientists can make much more accurate inferences about how species are related to each other –In most cases, DNA evidence has SUPPORTED what scientists had already inferred from fossils, embryos and similar body structures. Ex. Dogs are more closely related to wolves, than coyotes. –In other cases, DNA evidence has CONTRADICTED what scientists had previous thought. Ex. The elephant shrew once thought to be closely related to mice and other rodents is actually more closely related to elephants!

How similar is the human DNA sequence to other living things?

Tracing Species Similarities Branching tree: a diagram that shows how scientists think different groups of organisms are related.

How do new species form? Isolation – complete separation. Could be isolated by a river, volcano, or mountain range. Even an ocean wave can separate some from the rest of their species. A new species can form when a group of individuals remain separated from the rest of its species long enough to evolve different traits. Kaibab squirrel Alberts squirrel

Does Evolution Ever End? There are two theories that hypothesize how rapidly species change. –Gradualism – proposes that evolution occurs slowly but steadily. Tiny changes in a species gradually add up to major changes over very long periods of time. The fossil record SHOULD show many intermediate stages if this were true.

Punctuated Equilibria –Punctuated Equilibrium – species evolve quickly during relatively short periods of time. These periods of rapid change are separated by periods of little or no change.

Today, scientists think that evolution can occur by both means.