Chapter 22 Evidence for Evolution

Evolution occurs by natural selection…  Darwin’s finches  Found on Galapagos  Descent with modification

Natural selection has 3 conditions that must be met:  1.) variation within the population  2.) variation must lead to differences among individuals in survival and reproductive success  3.) variation must be genetically inheritable

Found with finches:  variation is within the population  changed from one year to the next depending on the weather and plant seed production  drought = fewer seeds, birds with large beaks survived b/c could eat bigger seeds  wet = many more small seeds, birds with small beaks survived ok  Traits were passed down according to those who survived – fluctuated within the population

Peppered moths and industrial melanism  Industrial melanism is the darkening of a species due to industry  Two main forms: peppered and melanic  In areas of industry, the tree bark is darker – the dark moths do better  Non-industrial areas, the light moths do better

 Kettlewell –did experiment with industrial melanism  Raised both colors of moths  Marked their abdomens and released equal amounts of each color into an area of industry and a rural area.  Waited a a few weeks and recaptured as many moths as possible in each area.  Results:  light moths more in rural area  dark moths more in industrial area

Artificial Selection  Lab experiments:  Used to test if selection can produce evolutionary change…  Used fruit flies  Chose flies with many bristles - Only bred the ones with the most  Over 86 generations, increased the bristle # from 9 to over 40!!

In Agriculture…  Only allow the plants that produce the best seeds to breed  Ex: corn, wheat, strawberries

Domestication…  Taking a once wild animal and breeding those with desirable traits to eventually spawn a desirable offspring  Has been done with wolves, foxes, cats and more!

The fossil record…  Most direct evidence for evolution  Can get from rock, amber, permafrost, dry caves or deserts  Problem: fossilization does not occur easily!  Must have very specific conditions  Usually the remains are scavenged or eroded before the process can be completed

 Must have very specific conditions  Usually the remains are scavenged or eroded before the process can be completed  Here’s a bird in the process of being fossilized!

Dating fossils  Date the rocks in which they are preserved:  Absolute dating – uses U 238  Relative dating – uses rock layers in respect to one another

Gaps in the record  Even though gaps exist, links have been found between:  Reptiles and birds  Ex: Archaeopteryx

Snakes and lizards - pelvic girdles still visible in snakes Whales and land mammals - flippers with homologous structures, pelvic girdle

Anatomical record  Homology – homologous structures are structures with different appearances and functions that are all derived from the same body part in a common ancestor  Ex: forelimbs of mammals

Vestigial Organs - Rudimentary structures of marginal, if any, use. Vestigial Organs - Rudimentary structures of marginal, if any, use.

Human Example

Evolution Viewpoint  Remodeling of ancestral structures as their functions or adaptations changed.

Comparative Embryology  Problem - closely related organisms go through similar stages in their embryonic development.  Ex: Gill pouches in vertebrates

Molecular Biology  Study of Evolution at the DNA or protein levels.  Problem - related species have similar DNA sequences.

Evolution Viewpoint  Related species share a common ancestrial DNA. The closer the relationship, the more similar the DNA sequences should be.

Convergent evolution

Horse evolution…  For example, we can trace the evolution of the modern horse through fossils.  First horses:  small, short legs, broad feet  lived in woods and ate leaves and berries We will look at the changes in these animals…

Size  First horses were the size of dogs or smaller  Now they weigh on average about 1000 lbs!  Let’s see the fossils for this change…  on/HorseEvolution.htm on/HorseEvolution.htm on/HorseEvolution.htm

Toe reduction  Primitive horses had 4 toes with fleshy pads like a dog’s  Modern horses have one toe encased in bone and keratin  This allowed the horse to run faster for longer distances  First row = forefoot  Bottom row = hindfoot

Tooth size and shape  Primitive horses had small and simple teeth for the vegetation of the time  Modern horses now have more complex teeth that are longer and have ridges for chewing grasses which evolved along with the horse  The grasses are tough and the teeth need to tough to withstand the chewing of these materials

 Only one genus of horse still exists today…Equus  All others died out long ago – naturally selected against in the changing environment

Summary  Know Darwin’s “facts” and “inferences”.  Be able to discuss the various evidences of Darwinian evolution.