The History of Life on Earth

1. The History of Life on Earth Chapter 25

2. Objectives • Conditions that led to origin of life on earth • The history of life as seen in fossils • Key events include origin of single-cellular and multi-cellular organisms and the development of terrestrial life • The effects of continental drift, mass extinctions, and adaptive radiation on groups of animals • Developmental genes can radically change body forms • Understand why evolution is NOT goal oriented.

3. Early earth • Abiotic synthesis of amino acids and nucleotides • Formation of macrocmolecules (proteins and nucleic acids) • Packaging these molecules into protobionts • Origin of self replicating molecules that led to inheritance

4. Synthesis of organic compounds • Oparin-Haldane hypothesis—Early earth was a reducing atmosphere that led to synthesis • Miller and Urey tested the hypothesis which yielded amino acids • Demonstrated that abiotic synthesis was possible • Analysis of meteorites show presence of AAs • Synthesis of macromolecules may have been initiated by formation of AA polymers

5. Protobionts • Protobionts are abiotically created molecules surrounded by a membrane. • They can engage in simple reproduction and metabolism • The can maintain an internal environment different than the external environment. • Liposomes can spontaneously organize in water from lipids and organic molecules

6. Self replicating RNA • RNA catalysts are called ribozymes • Protobionts with RNA were more successful • The development of DNA provided a more stable molecule for genetic information

7. Key events in earth’s history

8. The First Eukaryote

9. The First Eukaryote

10. Origin of multicellularity • First evidence of multicellular organisms (algae) ~1.2 billion years • The fossil record indicates that the first major diversification of multicellularity was after a thaw ~565 million years • Ediacaran biota • The Cambrian explosion

11. Colonization of land ~ 500 mya • Adaptations developed to live on land • Plants produced waterproof coating and a vascular system for internal transport • Early plants had no roots or leaves • Fungi followed plants • Arthropods are the most abundant land animals • Tetrapods arrived ~365mya • Our species arrived 195,000 years ago

12. Rise and fall of organisms • Continental drift • Formation of mountains • Oceanic plates usually slide below terrestrial plates

13. Continental drift • Alters habitats • Reroutes ocean currents • Changes weather patterns • Promotes allopatric speciation • Helps explain why fossils in two different regions can be the same

14. Mass Extinctions Permian extinction Cretaceous extinction

15. Cretaceous extinction

16. Consequences of mass extinctions • Evolutionary lineages disappear • Reduction in the diversity of an ecosystems • Increase in predators • Arising of adaptive radiations

17. Mass extinction and predators

18. Adaptive radiation • An organism’s movement into a variety of different environments or exploitation of a variety of different food sources leads to adaptive radiation. • The mass extinction of dinosaurs gave way to adaptive radiation of mammals 65 million years ago.

19. Mammalian adaptive radiation

20. The Silversword Alliance N Dubautia laxa 1.3 million years KAUAI 5.1 million years MOLOKAI MAUI OAHU 3.7 million years Argyroxiphium sandwicense LANAI HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis

21. Exaption • Using a trait that evolved for one purpose for another purpose. • The lightweight honeycombed bones of early non-flying birds were taken advantage of by birds that fly. • Feathers were initially developed for camouflage, courtship, or thermoregulation. Later they developed for flight. • Karel Liem, “Evolution is like modifying a machine while it is running.”

22. Evo-devo • Genes that control development have had a profound effect on evolution • Effect growth rates of particular body parts • Controls timing of the emergence of particular structures • Controls spatial pattern of particular structures

23. Evolution and development • Genes control the rate, timing, and spatial pattern of development.

24. Evolution and development • Varying the rate of growth of different body regions leads to morphological changes.

25. Heterochrony and salamanders • Foot growth gets turned off later in ground dwelling salamanders. • Paedomorphosis

26. Chicken leg bud Region of Hox gene expression Zebrafish fin bud Changes in spatial pattern • Homeotic genes, such as Hox genes control spatial organization of body features.

27. Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster First Hox duplication Hypothetical early vertebrates (jawless) with two Hox clusters Second Hox duplication Vertebrates (with jaws) with four Hox clusters

28. New developmental genes

29. Gene regulation

30. Evolved complexity Pigmented cells (photoreceptors) Pigmented cells Mollusc eye evolution Epithelium Nerve fibers Nerve fibers Eyecup Patch of pigmented cells Slit shell Pleurotomania Limpet Patella Cornea Fluid-filled cavity Cellular fluid (lens) Epithelium Optic nerve Pigmented layer (retina) Optic nerve Pinhole camera-type eye Eye with primitive lens Marine snail Murex Nautilus Cornea Lens Retina Squid Loligo Optic nerve Complex camera-type eye

31. Recent Equus Hippidion and other genera Pleistocene Nannippus Pliohippus Neohipparion Hipparion Pliocene Sinohippus Megahippus Callippus Archaeohippus Merychippus Miocene Anchitherium Hypohippus Parahippus Miohippus Oligocene Mesohippus Paleotherium Epihippus Propalaeotherium Pachynolophus Orohippus Eocene Key Grazers Hyracotherium Browsers