1. Lesson # 2: Evolution “Evidence for Evolution”

2. We will look at major evidence supporting theories of evolution: 1.Fossil Record 2.Comparative Anatomy 3.Biogeography 4.Biochemistry Evidence Supporting Theories of Evolution

3. Fossil Record Fossil Definition  Any ancient remains, impressions, or traces of an organism or traces of its activity that have been preserved in rocks or other mineral deposits in Earth’s crust  Hard impressions in solid rock and leave little doubt as to what they represent Fossil Formation  Fossils are formed when the remains of a buried organism are gradually replaced by mineral deposits  Once a body dies the body usually decomposes  When sediments accumulate over time the body becomes compressed, and gradual chemical changes occur that result in the body being mineralized  Only organisms that die in low – oxygen locations will fossilize

4. How fossils are formed

5.  Organisms with hard body parts (shells, bones, teeth) are more likely to be preserved  Fossils of aquatic organisms are very common rather than fossils of land animals and plants  Dinosaur fossils are well known but very rare compared to those of aquatic organisms  Fossils can also be formed from footprints and burrows  Organisms can also become trapped in materials that preserve its chemical remains i.e. tree sap, volcanic ash, permafrost, acidic bogs Fossil Record Continued

6. Reading the Fossil Record  Paleontology  The scientific investigation of prehistoric life through the study of fossils  Discoveries about fossils: 1)Many fossils appear to be of unusual and unknown organisms 2)There are no fossils of most living species 3)Fossils are often buried very deep within rock formations 4)Fossils are often found in unexpected locations (i.e. fossils of sea life are found high in mountain formations in present – day deserts)  These contradicted prior views that fossils were nothing more than organisms that had become trapped in muddy deposits and then hardened

7. Georges Cuvier  Conducted the first detailed studies of fossils  Noted the following:  Fossils are very simple organisms are found in all depths of fossil deposits  Fossils of more complex organisms are found only at shallower depths, in younger rock  Fossils in the shallower depths are more likely to resemble living species  Rock layers contain fossils of many species that do not occur in layers above or below them

8. How Fossils Support Theory of Evolution  Life had evolved from simple to more complex forms over time  Species themselves do not change, instead theory of catastrophism  Catastrophism  The theory that the pattern of fossils could be accounted for by a series of global catastrophes that wiped out most species on Earth  Cuvier discovered that different groups of species get more complex in each younger layer but not why this happened  Recall Lyell  Proposed that Earth’s geological features can be explained by very slow changes occurring over very long periods of time

9. Darwin’s Hypothesis  Theory that species evolved  Hypothesized that remote oceanic islands became populated by species that arrived by water or air  After the species became established, many evolved into new species over time  “Tree Thinking”  Implies that all organisms are related  According to the principle of common descent, all species living or extinct are descended from common ancestors

10. Darwin’s Hypothesis Regarding Remote Islands Observations on Galapagos IslandsDarwin’s Hypothesis Many species of plants, birds, insects and in some cases reptiles Only these kinds of organisms are able to reach remote islands by crossing large expanses of open ocean No native amphibians and very few land mammals Amphibians and most mammals are unable to cross open ocean and will not be found on remote islands Many unique species found nowhere else on Earth Over time, ancestral species have evolved into new geographically isolated species Unique species most closely resemble species on the nearest continental land mass Unique species are descendants of ancestral species from the nearest continental land masses and will exhibit some similarities

11. Comparative Anatomy (Homologous Features)  Homologous Feature  A structure with a common evolutionary origin that may serve different functions in modern species  i.e. bat wing and human arm  Similar structures of two organisms could have entirely different functions  Similar in origin  Different in function  May appear in embryonic development and disappear before birth  Existence of homologous structures adapted to different purposes as a result of descent with modification from a common ancestor

12. Comparative Anatomy (Analogous Features)  Analogous Feature  A structure that performs the same function as another but is not similar in origin or anatomical structure  i.e. wing of bee and wing of bird  Different in origin  Similar in function  May appear in embryonic development and disappear before birth

13. Comparative Anatomy (Vestigial Features)  Vestigial Features  A rudimentary and non – functioning, or only marginally functioning, structure that is homologous to a fully functioning structure in closely related species  i.e. hipbones of bottleneck dolphins  Relation to Evolution  Features that in an ancestor had once served a useful purpose had become useless or greatly distorted as the species evolved

14. Biogeography  Biogeography  The scientific study of the geographic distribution of organisms based on both living species and fossils  Darwin’s Discoveries  Looked at finches on the Galapagos islands  Populations on islands evolved from mainland species  Natural selection on islands produced variations among populations (resulting in different but closely related island species)  Beak depth, and the ability to crack larger seeds, varies according to drought conditions, which produce fewer, harder seeds in dry years and more and softer seeds in wet years  Consistent environmental differences in different habitats on different islands in the Galapagos, as well as the availability of different foods sources, have produced more than a dozen distinct species of finches, all unique to the archipelago.

15.  Natural selection shaped beaks as became adapted to eat different foods

16. Biochemistry  Genetic and Molecular Biology  Some of the most crucial evidence comes from genetics  At the molecular level, universal genetic code and homologous molecules provide evidence of common descent  Also, mutations and reshuffling of genes during sexual reproduction produce heritable variation on which natural selection operates

17. THE END!!