Evidence for Evolution  Review (what we’ve learned so far) Mutations provide variability within a population of organisms Some traits give individuals within a species an advantage - those organisms live longer and/or reproduce more = natural selection Over time, the population shifts so the all (or most) individuals have this trait = adaptation Evolution of a whole new species (speciation) takes long periods of time

Main evidence for evolution Fossils Geographic distribution of organisms around the world Artificial selection Homologous structures Vestigial structures Embryology Comparative analysis of DNA

Fossils  The bulk of our understanding about ancient life  Bacterial cells to complete T. rex skeletons  How are fossils formed? (Short video) watch?v=c_DCP4cLVNg watch?v=c_DCP4cLVNg

Fossil Questions 1. How are fossils formed? Organism covered by sediments (mud, sand, silt, clay, ash) Organism covered by sediments (mud, sand, silt, clay, ash) Calcium replaced by minerals in the sediments over time Calcium replaced by minerals in the sediments over time Sometimes imprints can also be preserved (tracks, leaf impressions, etc.) Sometimes imprints can also be preserved (tracks, leaf impressions, etc.)

Fossil Questions, cont. 2. Why do most living things not leave fossils behind?  Organism was eaten  Didn’t die in correct environment to be preserved  Body has no ‘hard parts’ (shell, skeleton) Virtually absent from fossil record: amoebae, flatworms, jellyfish, sea slugs, etc.) Virtually absent from fossil record: amoebae, flatworms, jellyfish, sea slugs, etc.)

Fossil Questions, cont. 3. How are fossils uncovered?  Erosion brings fossils back to surface  Humans dig to find fossils Determine specific locations that are likely spots to hold fossilsDetermine specific locations that are likely spots to hold fossils

Fossil Questions, cont. 4. How do scientists determine the age of fossils? Technique 1: Relative dating Compare the unknown fossil’s position in rock layer with placement of other known fossils in that layer, or layers just above and below Compare the unknown fossil’s position in rock layer with placement of other known fossils in that layer, or layers just above and below

Fossil Questions, cont. 4. How do scientists determine the age of fossils? Technique 2: Radioactive Dating: - Calculate amount of remaining radioactive isotopes the rock contains = age of rock

Transitional Fossils  A.k.a. Intermediate fossils  Importance: provide a link between past forms of an organism

Transitional Fossils: Orca example  We’ve believed for a long time that whales (and seals, otters, etc) were mammals because they share COMMON FEATURES with land mammals 1. Warm-blooded (endothermic) 2. Give live birth and provide milk for young 3. Have hair 4. Similar respiratory, circulatory, nervous, and digestive systems

Transitional Fossils - Whales Modern whale – totally aquatic  Nostrils on top of head = blowhole  Tail evolved into flipper  Ears modified directional hearing underwater Basilosaurus – clearly aquatic  Sturdy flippers & long, flexible body  Still has small, weak hind legs  Nostrils on top of head Ambulocetus – amphibious (both land and water)  Forelimbs equipped with fingers/small hooves  Hind feet and tail adapted for swimming  Nostrils on top of snout Mesocynids– terrestrial   Tetrapod – limbs adapted to moving on land   Ears adapted to hearing in air  Nostrils in front of snout

Gaps in Fossil Record  Fossils for 350,000 species of ancient organisms 0nly a tiny fraction of total! 0nly a tiny fraction of total! Recall that estimates put extinct species at Recall that estimates put extinct species at 10 trillion!  Fill in the ‘gaps’ using logical reasoning as well as other lines of evidence

Comparative Embryology of Vertebrates

Embryology  Early stages of related animals are very similar  Similarity in the development from egg to adult form (ontogeny) is evidence of common ancestry More similarity in ontogeny = more recent common ancestor (more closely related) More similarity in ontogeny = more recent common ancestor (more closely related)

Geographic Distribution on Organisms around the world  Convergent evolution Similar selective pressures lead to common structures and behaviors that aid survival and reproduction = Example: prairie dogs & meerkats  Similar environments around the world contain organisms that are DIFFERENT species but have similar anatomies and/or behaviors Prairie dogs live in the open grassland prairies of the North America Meerkats live in the open grassland plains in Africa (savannahs)

Another example of similar geography resulting in similar structure in unrelated organisms: beavers, muskrats, coypus, & capybaras Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capabara

Geographic Distribution, cont. Additionally, organisms from a common ancestor will change in structure and function to adapt to a new, specific environment Prime example: islands! –the more isolated the island, the more distinct its organisms

Artificial Selection  When humans breed organisms with desired trait repeatedly until desired characteristic is obtained  Plant and animal breeders have long taken advantage of the heritability of traits to improve crops and livestock and pets  Humans use the same mechanisms to change organisms that nature uses Artificial – humans ‘select’ the best traits Artificial – humans ‘select’ the best traits Natural – nature ‘selects’ most best, or ‘most fit’ traits Natural – nature ‘selects’ most best, or ‘most fit’ traits

Artificial Selection Examples Hundreds of varieties of peppers – all originated from an initial species Different breeds of dogs and cats ‘created’ by man by selecting for desirable traits (fast, sociable, good smell, short fur, etc.)

Homologous Structures  Similar structures in a variety of different organisms  Shared trait provides evidence that the organisms had a shared common ancestor with that trait Homologous bone structure in forelimbs of all mammals

Homologous Vs. Analogous Homologous Structures: Inherited from common ancestor, Similar structure, different function. Analogous Structures: Similar function, different structure.

Vestigial Structures  As species evolve over time… some structures become unnecessary to survival of organism  Over time become reduced (vestiges)  Eventually disappear  Pelvis in whale  Human appendix, tail bone, wisdom teeth  Second lung in snakes

Comparative Analysis of DNA = Comparing the amount of DNA that is similar  Greater similarity between 2 species = more recent common ancestor  Note: allowing us to more accurately determine not only ‘closeness’ but also an approximately WHEN the 2 groups diverged from a common ancestor