Evidence of Evolution

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Evidence of Evolution
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By the end of this class you should understand

• That prevailing scientific thought has changed
  throughout history
• The essential concepts of artificial and natural
  selection
• The geological evidence for a changing Earth
• The essential geological history of the Earth

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Categories of Life

• There have always been nerds, and nerds like to
  organize things
• Aristotle was a well-respected thinker (nerd) who
  attempted to categorize living things
• For millennia afterwards, nerds attempted to
  categorize all living things the way he did
• Words like flora and fauna used to be the height
  of biological wisdom

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Religion and Science

• During the middle ages, the most learned people
  (who had access to Greek writings) were religious
  figures
• The notion of categorizing all living things
  became a form of worship, to understand Gods
  plan for the world
• This had the unfortunate side effect of also
  creating the belief that each group of animals
  (species) was a sacred, eternal creation
• Gods plan doesnt change, etc.

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Problems with Species

• These different birds live on different
  continents yet are physically very similar
• How do you categorize them?
• What about butterflies that seem very similar and
  live in the same environment but never actually
  mate?
• Are they one species or two?

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Morphology

• Morphology is the study of shape (body plans and
  structures)
• Comparative morphology only made the state of
  species more confusing due to finding body parts
  with no function
• Snakes and whales have tiny leg bones, but
  clearly have no legs

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Homology

• Additionally, many structures are found to be
  similar throughout living things
• Animal limb bones follow the same general pattern
  even though they have vastly different purposes
• This is known as homology in general and the
  parts can be referred to as homologous parts

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Fossil Evidence

• Scientists had also started finding more rocks
  that seemed to have rock bones inside them
• It was eventually determined that these were
  fossils, which are bones that are trapped in mud,
  so when the mud turns to rock the bones turn to
  rock also
• A lot of these fossils didnt match any living
  things!
• Perhaps they went extinct (complete death of all
  members of a species)!

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Where Are They Now?

• This new fossil evidence ran counter to the idea
  that all species were eternal unchanging
  creations of God
• Many were suggested to be creatures that drowned
  in the Great Flood
• The story of Noahs Ark was starting to look less
  plausible, however
• Extinction was unheard of until the Dodo went
  extinct in the 1600s, and it was not immediately
  realized what happened

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A Radical Theory

• A radical new school of thought was forming by
  the 1800s that species were not special and in
  fact could change over time
• The seminal publication on this topic was On the
  Origin of Species by Charles Darwin but he had
  collaborated with many other scientists
• Alfred Wallace had actually sent Darwin a paper
  outlining ideas Darwin had already written down!

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Breeding

• A large portion of On The Origin of Species is
  devoted to analyzing breeding of domestic animals
  and plant
• Dogs, pigeons, farm crops
• This has been going on for millennia and is very
  well understood
• How does it work??

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Artificial Selection

• The essential core of breeding is artificial
  selection, where humans decide what
  animals/plants should make more children
• These animals/plants are chosen for particular
  desirable characteristics
• The desired characteristics become amplified over
  time due to genetics

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Examples of Artificial Selection
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Natural Selection

• Darwins concept was radically simple if humans
  choose what animals breed and that creates new
  breeds, when nature chooses what animals breed,
  it creates new species!
• Note Nature is not an intention or a conscious
  force, but a name for what occurs naturally
• Some people interpret nature as a supernatural
  force or God
• Maybe it is!

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How Does Nature Choose?

• The process of organisms being selected for the
  next generation is called natural selection
• There are three primary aspects Getting food,
  not getting eaten, and reproducing
• Sex and violence!
• An organisms fitness in a given environment is
  evaluated based on how many offspring it has

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Nuances of Fitness

• The expression survival of the fittest is often
  used to refer to having more fitness (success) in
  a challenging world
• Fitness is much more complex than simply
  getting the most food and mating the most!
• In ant colonies, none of the workers reproduce
  but they can be considered fit because their
  sisters become new queens!
• More on this next week

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Geological Time

• Until the 20th century it was widely believed
  that the Earths continents have always been the
  way they have been
• Africa and South America just happen to look like
  they used to fit together
• In the 20th century the theory of continental
  drift finally had more evidence than just Africa
  and South America look like they fit together

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Geological Evidence

• Geology (the study of Earth) revealed that
  erosion occurs due to wind and water wearing away
  rock bit by bit
• So where is the new rock coming from?
• Volcanoes release molten rock that hardens into
  new rock
• Wouldnt the Earth fill up with rock eventually?
• Hardened rock with a lot of iron can be
  magnetized by the Earths magnetic field but
  older rocks are magnetized in different
  directions
• The Earths field has been changing!

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Current Model of Geology

• The eventual realization that the Earths core is
  molten rock validated the continental drift
  theory
• This is now taken as basic fact!
• The continents are literally floating on the
  liquid core into each other
• The Earths crust is only 30 miles thick at the
  most!

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Fossil Evidence for Continental Drift
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Fossil Age

• The age of different rocks can be established
  with radiometric dating
• Certain rocks have particular amounts of
  radioactive particles like uranium when they are
  formed
• How much remains after a given time can be
  precisely measured
• Space rocks give the oldest ages since they dont
  have volcanoes
• The Earth is much older than previously thought!

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Earths Timeline

• The Earth and other planets were formed around
  4.5 billion years ago
• Life probably started around 3.8 billion years
  ago, when there first started to be liquid water
• First life was probably made mostly of RNA
• Multicellular life didnt show up until around 1
  billion years ago
• Dinosaurs lived from 200 to 65 million years ago
• Humans appeared around 2 million years ago

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Earths Timeline

• Most of the interesting life has happened in the
  last 500 million years
• The first 3 billion years was molecules slowly
  becoming more efficient at coiling
• Development of DNA, ribosomes, etc.

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Major Events in Life

• 500 Mya the Cambrian explosion, the oldest
  fossils from most major groups of animals
• Arthropods, Mollusks, Echinoderms, etc.
• 250 Mya the Permian extinction, the biggest mass
  extinction in the fossil record
• Cleared the way for the dinosaurs to take over
• 65 Mya the Cretaceous extinction, a massive
  comet or meteor hit the Earth, and the dust
  clouds that covered the Earth prevented plants
  from growing for years
• All large animals with large dietary needs
  (including dinosaurs) went extinct way before
  humans existed
• Sorry, the Flintstones is fake!

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Note on Dinosaurs

• All large dinosaurs went extinct at the
  Cretaceous extinction
• The smallest dinosaurs survived! Birds are part
  of the dinosaur family
• The distinctive hip structure is a giveaway

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See you in lab!

• Next weeks lab will include studying the
  timeline of life!