Evidence of Evolution

I. The Fossil Record fossils of animals show a pattern of development from early ancestors to modern descendants fossils offer the most direct evidence that evolution takes place

fossils provide an actual record of Earth’s past life-forms however, the fossil record and thus the record of the evolution of life, is not complete because many species have lived in environments where fossils do not form

Horse Fossil Record

Fossil Layers Most Primitive

Which layer gave rise to the fossils in layer B Which layer gave rise to the fossils in layer B? Which layer is the most primitive?

II. Anatomy & Development Comparisons of the anatomy of different types of organisms often reveal basic similarities in body structures even though the structure’s functions may differ between organisms

vestigial structures – a structure in an organism that is reduced in size and function and that may have been complete and functional in the organism’s ancestor ex: hind limbs of whales, tailbone of human homologous structures – anatomical structures that share a common ancestry; same structure but different function ex: forelimbs of certain animals

Vestigial Structures A structure that has been reduced in size and function but may once have been complete and functional. leg bones tailbone Whale Human

Homologous Structures The bones in a human’s arm, cat’s arm, whale’s arm, and bat’s arm are the same (homologous), but the function is different.

Embryological Development Similarities seen are pharyngeal pouches (gills), tail, and buds that become limbs; this suggests a common ancestor

III. Biological Molecules similarities in amino acid sequences suggest that organisms are related, and may indicate the degree of relatedness differences in amino acid sequences suggest that mutations have introduced genetic variation into populations of organisms that eventually result in evolution

Questions: 1. List 3 types of evidence that show evolution has occurred. 2. Of the three types of evidences that evolution has occurred, which gives the strongest evidence that evolution has occurred? 3. What is the difference between homologous and vestigial structures?