Bellringer-5/11/15 What is evolution? Explain what you know.

EXPLORING CHANGE OVER TIME Evolution EXPLORING CHANGE OVER TIME

The Theory of Evolution HOW DID ORGANISMS EVOLVE?

What is Evolution? Evolution is the change in heritable traits through generations CHANGE OVER TIME Occurs in populations, not individual organisms

How Have Organisms Changed? At the time life emerged on earth (about 3.8 billion years ago), the atmosphere is thought to have contained very little oxygen! First cells were thought to be anaerobic Recall that “anaerobic” means “without oxygen” As the atmosphere of the Earth changed, so did the development of organisms

How Have Organisms Changed? These prokaryotic (simple), anaerobic cells were able to exist in Earth’s early atmosphere As Earth’s atmosphere and conditions changed, photosynthetic prokaryotes evolved, using sunlight to produce food What molecule do photosynthetic organisms produce as byproduct (waste)?

How Have Organisms Changed? Eventually, Earth’s atmosphere became filled with oxygen Aerobic organisms evolved This resulted in the evolution of eukaryotic complex multicellular organisms we have on Earth today!

The Endosymbiotic Theory The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.

Endosymbiotic Theory ~2 billion years ago: Evolution of internal membranes in prokaryotes The result was the ancestor of all eukaryotic cells. Endosymbiotic theory: Eukaryotic cells formed from a symbiotic relationship among several different prokaryotic organisms Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria. Prokaryotes that carried out photosynthesis evolved into chloroplasts.

But what evidence supports the theory of evolution…?

Fossil Evidence Fossils show us the similarities between organisms of the past and present 220 Million Years Ago 190 Million Years Ago Today

Similar Structures (Homologies) Homologies describe similarities between the anatomical structures of species

Vestigial Structures Vestigial structures are anatomical structures that still appear, but are no longer used! Examples: Tails in humans, legs in snakes Suggests that these structures may have existed at a previous time or in an ancestor; organisms evolved and structures not needed

Comparative Embryology Insects and animals often have very similar embryonic development Ex. All vertebrates (have a backbone) have similar development Suggests a common ancestor

Biochemical (Molecular) Evidence Comparison of DNA and macromolecules between organisms Through gel electrophoresis Tells us what organisms are closely related

NEW Evidence