17.2 Clues About Evolution

Mr. Perez

Important Vocabulary

Review vocabulary Epoch Sedimentary

rock Radioactive

element

New Vocabulary Embryology Vestigial

structure Homologous

Clues from Fossils (recap) Most of the evidence for evolution comes

from fossils. Most fossils are found in sedimentary rocks The fossil record provides evidence that living

organisms have evolved Relative dating vs. Radiometric dating

Relative dating uses the principle of superposition to figure out the age of fossils (does not give absolute age, only relative)

Radiometric dating uses an estimate age of the rock by comparing the amount of radioactive element with the amount of nonradioactive element in the rock. (absolute age)

Fossils and Evolution (recap) Fossils provide a

record of evidence of organisms that live in the past, however, the fossil record is incomplete because some animals do not become fossils

More Clues about Evolution Embryology Homologous

structures Vestigial

structures DNA

Embryology The study of embryos and their development

An embryo is the earliest growth stage of an organism • A tail and pharyngeal pouches are found in the

embryos of:• Fish• Reptiles• Birds• Mammals

• Fish develop gills• Tails remain in:

• Reptiles• Birds• Some mammals

• These similarities suggest an evolutionary relationship among all vertebrates (animals with backbones)

Embryology

Homologous structures Body parts that are similar in structure and origin

Can also be similar in function Often indicate that two or more species share

common ancestors

Vestigial structures Structures that don’t seem to have a function

Example: manatees, snakes and whales no longer have back legs, but still have a pelvic bone

Example: the appendix in the human body serves no purpose

Scientists hypothesize that these structures once served a function in an ancestral species

DNA (deoxyribosenucleic acid) The molecule that controls heredity and directs

the development of every organism Found in chromosomes in the nucleus

Scientists can use DNA to: Compare the similarities with other species (similar

ancestry) Determine how closely related organisms are

Classwork questions1. Compare and contrast relative dating and

radiometric dating.2. Explain how DNA can provide some evidence of

evolution.3. Compare and contrast the five types of evidence

that support the theory of evolution.

Videos http://www.pbs.org/wgbh/evolution/educators/tea

chstuds/svideos.html

Resources Florida Science Grade 8

Glencoe Science & McGraw Hill Publishing Google Images