Evidence for Evolution Biology 9

EVIDENCE FOR EVOLUTION What is the evidence that all species on earth are related to each other and share common ancestors? Overview: 4 Major Types of Evidence: Homologous Structures Embryos Gene Sequences Fossils

1. HOMOLOGOUS STRUCTURES – Similar body parts or bone structures due to sharing a common ancestor that had those structures Don’t necessarily have the same function now, but did in the common ancestor Ex: human arm, cat leg, whale flipper, bat wing all have same bones

Homologous Structures, continued: Vestigial Traits - Don’t have a function now, but suggest that they descended from an ancestor that did use them. Examples: human tailbone, human goose bumps, ostrich wings Ex: human tail bone, human goose www.toptenz.net animal.nationalgeographic.com

Don’t confuse Homologous Structures with Analogous Structures structures that have the same function but NOT the same skeletal structure This suggests these organisms did NOT descend from a common ancestor with that trait Ex: insect wing and bird wing Bird wing Insect wing bio.miami.edu

2. Embryos Similar characteristics appearing during specific embryonic/ developmental stages of development Example: Fish, reptile, bird, and human embryos all have gill slits and a tail (but some lose these features before birth)

3. Gene Sequences Similarities between DNA or amino acid sequences for different organisms Closer the similarities = Closer relationships

4. FOSSILS Fossils show… show species that are now extinct show transitions to new body forms Example: Tiktaalik (lived 375 million years ago) fish with legs and (maybe) primitive lungs… earliest amphibian? Artist Rendering Fossil Objectives for Class: Describe how fossils are used as evidence for evolution and give one example that illustrates this.

FOSSILS, cont. Example: Archaeopteryx (lived 150 million years ago) earliest bird… but has many dinosaur features www.ansp.org Objectives for Class: Describe how fossils are used as evidence for evolution and give one example that illustrates this.