Evidence for Macroevolution

Fossil Record When fossils are arranged according to their age, a progressive series of changes are seen. By dating rocks, in which fossils occur, we can get a very accurate idea of how old the fossils are according to:

The Relative Positions of Sedimentary Rock Older rocks are lower than younger rocks. If you find fossils in deeper rock layers, they are older than those in upper layers.

Radioactive Dating Radioactive dating can tell us how old a rock (or a fossil) is. The T. rex lived 85 – 65 million years ago.

The fossil record shows the first horse was small, about the size of a dog. 55 million years ago – dog sized 24 – 17 million years ago – 3 toes but side toes are smaller Modern horses – fused toes 32 – 25 million years ago – look at the toes

Description of Molecular Record All organisms from bacteria to humans share many of the same biochemical details.

Evidence of Molecular Record All have DNA and RNA to carry genetic information All use ATP as an important energy carrier

How are the molecular and fossil records related? The longer organisms have been separated according to the fossil record, the more differences are seen in their DNA. Every evolutionary change involves the substitution of new versions of genes for old ones (the new versions coming from mutations).

Phylogenetic Trees or Cladograms These show relationships among organisms. Those on the same branches are more related than those who are not.

Homology Homologous structures are parts of different organisms, often quite dissimilar that develop from the same ancestral part.

Dog vs. Frog All vertebrates contain a similar pattern of organs, suggesting they are related to each other.

Homologous Structures The forelimbs of all mammals contain the same pattern of bones, although the bones now carry out a variety of functions.

Homologous Structures Human arm, cat leg, whale flipper, bat wing

Description of Development During development, organisms may exhibit characteristics of other organisms. This suggests that these organisms are related to other forms.

Evidence of Development (Embryology) The embryo of a human exhibits characteristics of the embryos of its ancestors.  Early - fetuses posses gill slits like those of fish  Later - the embryos develop a tail  During the 5 th month – human embryos are coated in a fine fur (called lanugo)

Human embryos at 4 and 9 weeks

Organisms that are more closely related look more similar throughout development.

Vestigial Structures Many organisms contain structures that have no function but that resemble functional structures of other organisms. This suggests that structures are inherited from a common ancestor.

Evidence of Vestigial Structures Humans  Web of muscles for wiggling ears (found in coyotes)  Appendix with no function (previously used for digestion?)

Evidence of Vestigial Structures Whales  Hip bones no function (ancestor had legs) Cave-dwelling organisms  Eyes can’t be used in complete darkness (ancestor used them outside of the cave)

Speciation Animations How Geographic Isolation can lead to speciation How Geographic Isolation can lead to speciation Anole Lizards