My AP Biology Thoughts Episode 7 Welcome to My AP Biology Thoughts podcast, my name is Victoria and I am your host for episode #7 called Unit 7 Evolution: Evidence of Evolution. Today we will be defining the 4 Pieces of Evidence for Evolution, giving examples of each, and making connections to the unit of evolution.  Segment 1: Introduction to Evidence of EvolutionWhat is evolution? A change in the allelic frequencies of a gene pool  Continuous 

4 Pieces of Evidence of Evolution -  Fossil Record the preserved remains of traces of any organisms from the remote past, included both discovered and undiscovered Only the hard parts of an organism are preserved  Fossil evidence can be either  Direct (body fossils): bones, teeth shells, leaves Indirect (trace fossils): footprints, tooth marks, tracks, burrows Like timeline, different kinds of organisms do not occur randomly but are found in rocks in a consistent order, this is known as the law of fossil succession  It is incomplete, and requires an unusual combination of specific circumstances for it to occur, creating many gaps in the fossil record  Biogeography: Organisms located in one area of the planet are closely related than those found in other parts of the planet It describes the distribution of organisms, over geographical areas, both in the past and present Comparative Anatomy: The comparison of the anatomic features of different species 2 Key types of structures that support this Homologous structures Demonstrate a similar underlying anatomy due to shared evolutionary origin, but have evolved into a variety of distinct forms or speciation due to the presence of different selective pressures The more similar the homologous structures between the two species are, the more closely related they are likely to be Adaptive radiation through divergent evolution, as similar basic organisms have been adapted to suit various environmental niches  Analogous structures  Adaptations that have similar features and functions as a result of exposure to a common selective pressure, but have different underlying anatomies due to having unrelated evolutionary origins  Shows convergent evolution as unrelated species have become structurally more alike due to exposure to shared selection pressures  Vestigial organs Homologous features that still remain in organisms, but serve no function or purpose in that organism but were once present and functional in their ancestors Changes in the environment have caused these organs to be useless and as a result over they have lost their functionality, they show the evolutionary divergence of a species from a past behavior/activity  Comparative embryology Studying the growing embryo in animals and plants show that closely related organisms go through similar stages of development Molecular Evidence:

Identifying conservation in DNA and protein sequences as a basis for determining evolutionary relationships, the comparison of DNA sequences can show how different species are related

Segment 2: Example of Evidence of EvolutionEvolution of the modern day horse (fossil record)

Distribution of marsupials around the earth (biogeography)

Biogeography the distribution of species around the world. It all started with a supercontinent called Pangaea. Over millions of years, Pangaea drifted apart into separate continents in a phenomenon called continental drift. Different species were separated on different continents. In particular, a majority of the marsupial population stayed on the continent known as Australia. Here’s how it went… The blue line illustrates the distribution of marsupials around the world. The highest concentration today is in Australia. The marsupial species that migrated there was free to breed, causing their populations to proliferate and diverge into new species. However, the marsupials on the rest of the planet could not...