Darwin Presents His Case 15-3 Evolution Darwin Presents His Case 15-3

Inherited Variation and Artificial Selection Members of each species differ from each in important ways Darwin argued that variation mattered and was inherited Darwin states that humans drive “evolution” through artificial selection =Nature provides the variation, but humans select the desirable trait (ex: fast horses, cows that produce more milk, large fruit)

Natural Selection When populations change in response to their environment Including competition for food, shelter, and mates Also includes climate and vegetation conditions Do only animals evolve? {Anything living thing with DNA}

The Struggle For Existence Variation in genes exist within the genes of every population Individuals over-reproduce with differences in organisms that are better suited to survive Over time, the traits that make that organism successful are passed on to the population Evidence can be seen in the fossil record

Application to Natural Selection Secret Life of Marine Iguanas What kinds of natural variations could exist in saltwater iguana populations? When over reproduction occurs, which variations would make them more successful? Why? - Reptile, Herbivore - Life Span: 5 to 12 years - Size: 4 to 5 ft (1.2 to 1.5 -Weight: 1 to 3.3 lbs (.5 to 1.5 kg) -Protection Status: Threatened -Fun Fact: Marine iguanas sneeze frequently to expel salt from glands near their noses. The salt often lands on their heads, giving them a distinctive white wig.

Survival of the Fittest Fitness: the ability to survive and reproduce in their environment Adaptation: any inherited characteristic that increases chance for survival Darwin termed this natural selection b/c of it’s similarities to artificial selection

Over time, Species Change B/c of the environmental changes and the struggle to survive, species look different now than they did then! Descent with Modification

Things you may not know about evolution

How do we know evolution really happens?

All living things are related

Evidence of Evolution Living things have been evolving for years We all came from common ancestors= common descent Giving us a tree of life! Most common ancestor at the bottom

Evidence Fossil Record Comparative Anatomy Comparative Biochemistry Homologous Body Structures Vestigial Organs Comparative Embryology Comparative Biochemistry Geographical Distribution of Living Species (Plate Tectonics)

FOSSILS -Remains of once living organisms provide evidence of change over time -Limited- incomplete record, break down easily *disadv -Can be dated (carbon or superposition) *adv

Comparative Anatomy (3 kinds) -Structural similarities link related species a. Homologous Body Structures: same underlying structures, different function (based on different environments)

Comparative Anatomy b. Vestigial Structures- Structures that are present in an organism but are reduced in size and either have no use or have a less important function than they do in other related organisms.

Can you think of 2 human examples of vestigial structures?

Comparative Anatomy Cont. c. Comparative Embryology: similar embryo development in closely related species

Comparative Biochemistry -Examples include DNA, RNA, and other molecules -Similar DNA sequences code for similar traits “Vital proteins, such as the ribosome, DNA polymerase, and RNA polymerase, are found in everything from the most primitive bacteria to the most complex mammals”

What Percent of Their DNA Matches Yours?? Another human? 100% - All humans have the same genes, but some of these genes contain sequence differences that make each person unique. A Chimp? 98% - Chimps are the closest living species to humans. A Mouse? 92% - All mammals are quite similar genetically. A Fruit fly? 44% - Studies of fruit flies have shown how shared genes govern the growth and structure of both insects and mammals. Yeast? 26% - Yeasts are single-celled organisms, but they have many housekeeping genes that are the same as the genes in humans, such as those that enable energy to be derived from the breakdown of sugars. A weed? 18% - Plants have many metabolic differences from humans. For example, they use sunlight to convert carbon dioxide gas to sugars. But they also have similarities in their housekeeping genes.

Other Examples of Biochemistry Similar proteins example: Cytochrome c “Cytochrome c is an ancient molecule, and it has evolved very slowly. Even after more than 2 billion years, one-third of its amino acids are unchanged. This conservatism is a great help in working out the evolutionary relationships between distantly-related creatures like fish and humans”

Using only Cytochrome c as a marker,eukaryote evolution would look something like this!

Geographical Distribution of Living Species -Continents were once one land mass, animals roam freely -Closely related species have ancestors now on separate continents

Geographical Distribution of Species