Evidence for Evolution  Review (what we’ve learned so far) Mutations and sexual reproduction/ crossing over provide variability within species. 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 that 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) 8/sci/life/div/becfossil/index.html 8/sci/life/div/becfossil/index.html 8/sci/life/div/becfossil/index.html 8/sci/life/div/becfossil/index.html resource/tdc02.sci.life.evo.becfos sil/becoming-a-fossil/ resource/tdc02.sci.life.evo.becfos sil/becoming-a-fossil/ resource/tdc02.sci.life.evo.becfos sil/becoming-a-fossil/ resource/tdc02.sci.life.evo.becfos sil/becoming-a-fossil/

Fossil Questions How are fossils formed? Organism dies and is covered by sediments (mud, sand, silt, clay, ash) Organism dies and is covered by sediments (mud, sand, silt, clay, ash) Calcium in bones replaced by minerals in the sediments over time Calcium in bones 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.)

It’s a pretty rare event to find complete fossils in good condition. After millions of years any number of things could happen to destroy fossils before they are discovered and documented by scientists, if the animal even fossilizes at all. Finding well preserved baby animals is particularly hard, since they are more likely to have gotten trampled or eaten after their death. Phillip Currie from the University of Alberta has recently uncovered a juvenile Chasmosaurus belli that was so complete and intact, he was actually able to speculate about the cause of death. The fossil was found in what used to be a riverbed. This has led Currie and his research team to believe that the baby didn’t die at the hands of a larger creature. It most likely wandered out too far into the water and got caught in the current. Unable to save itself, it drowned and settled at the bottom of the river, where it would eventually become fossilized in the sediment. The body was so well preserved, Currie was actually able to see impressions from the baby’s skin in the surrounding rock.the baby didn’t die at the hands of a larger creature

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: flatworms, jellyfish, sea slugs, etc.Virtually absent from fossil record: flatworms, jellyfish, sea slugs, etc.

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

How do scientists determine the age of fossils? Technique known as: Radiometric Dating dating/

Transitional Fossils  a.k.a. Intermediate fossils Important because they:  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 evolution example: Modern whale – totally aquatic  Nostrils on top of head = blowhole  Tail evolved into flipper  Ears modified directional hearing underwater Basilosaurus – aquatic  flippers & long, flexible body  small, weak hind legs  Nostrils on top of head Ambulocetus – amphibious (both land and water)  Forelimbs equipped with fingers/small hooves  Hind feet & 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

What is this picture of??  Are you 100% sure?

What is this picture of??  Are you still 100% sure?  Can we ever truly fill in all of the gaps??

Gaps in Fossil Record  We have fossils for 350,000 species of ancient organisms… That’s only a tiny fraction of total number of species that have ever lived!!!!! That’s only a tiny fraction of total number of species that have ever lived!!!!!  We fill in the ‘gaps’ using logical reasoning as well as other lines of evidence

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)

Comparative Embryology of Vertebrates Which one is the human? The rabbit? The fish? The salamander? The tortoise? The hog? The calf?

Comparative Embryology of Vertebrates So when do organisms begin to look different? During _______? HUMAN

Comparative Embryology of Vertebrates Which two seem more genetically related/separate from the others?? How do you know?

Geographic Distribution on Organisms around the world  Similar environments around the world contain organisms that are DIFFERENT species but have similar anatomies and/or behaviors because…  similar selective pressures lead to common structures and or behaviors that aid survival and/or reproduction  Example: meerkats and prairie dogs

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 (niche)  Prime example: islands! the more isolated the island, the more distinct its organisms 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’ best, or ‘most fit’ traits Natural – nature ‘selects’ 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(structure) provides evidence that the organisms had a shared common ancestor with that trait Example: Homologous bone structure in forelimbs of all mammals

Vestigial Structures  As species evolve over time… some structures become unnecessary to survival of organism  Over time become reduced (vestiges)  Eventually disappear Examples: Human Tailbone (coccyx) Human Tailbone (coccyx) - These fused vertebrae are the only vestiges that are left of the tail that other mammals still use for balance, communication, and in some primates, as a prehensile limb. As our ancestors were learning to walk upright, their tail became useless, and it slowly disappeared. Hind Leg Bones in Whales

Comparative Analysis of DNA If all organisms evolved from same original ancestors (3.5 bya), then all should share some common DNA  YES! all life shares same general machinery for regulation of cell division, building cell parts, etc.  Greater DNA similarity between 2 species = more recent common ancestor