Evidences of Evolution (Clues) Darwin stated that all organisms descended from a common ancestor Darwin based his theory of Natural Selection on observations of: Traits, geographical distribution, selective breeding and fossils
Evidences of Evolution Today, we use all the tools that Darwin used, and some others, to help us understand how different organisms have a common evolutionary history and could descend from the same once living creature.
Phylogeny or Phylogenesis Phylogeny is the evolutionary history of a species.
Phylogenetic Tree A phylogenetic tree is a diagram that represents evolutionary relationships among organisms. It reflects how different organisms evolved from common ancestors.
Evidences of Evolution Fossils Embryology (or Similarities in Development) Homologous Structures (or Comparative Anatomy) Vestigial Structures Similarities in the DNA of different organisms (or Molecular Biology) Biogeography or geographic distribution not in the handout
The Fossil Record The collection of fossils and their placement in chronological order is known as the fossil record. The fossil record documents the existence, diversity, the changes and the extinction of many organisms throughout the history of life on Earth.
Why are fossils important evidences of evolution? Fossils show when life first appeared When plants and animals first moved to land When certain organisms became extinct When, where and how organisms once lived How the anatomy of a species changed over time
Other evidences of evolution - read handout and complete the worksheet
Conditions for fossil formation Usually formed in sedimentary rocks, due to the quick deposit of sediments on top of the dead organism, Quick deposit of sediments protect the fossil from scavengers and agents of physical destruction such as wind Sedimentary rocks are not form with heat and pressure such as igneous and metamorphic rocks Remains have to have hard parts. The hard parts of an organism's body will then become fossilized and included in the sedimentary rock
Dating Fossils - handout Relative dating or Principle of Superposition Radiometric dating
Principle of superposition Only valid in undisturbed layers of rock, the rocks at the bottom are older and the younger on top. The fossils will be from the same period of the rock.
Relative Dating of Fossils or Principle of Superposition - The position of the fossil in the rock strata is a clue to when the organism lived and its age
**Relative age Relative age of a rock is its age compared to the age of the layers in an undisturbed rock. Relative age does not give the age in years.
**Absolute Age It is the age in years To determine the age in years of a rock or a fossil scientists will use Radiometric or Radioactive Dating
Radioactive or Radiometric dating Radioactive dating is a technique that analyzes the amount of radioactive material present in an artifact or fossil. Scientists know the rate of decay of radioactive materials, so they can infer the age of the fossil by the amount of radioactive material compared to the amount of non-radioactive material found in the fossil or ancient artifact.
Embryology or Similarities in Early Development Embryos of different species of vertebrates show similar stages during their development, suggesting evolution from a common ancestry. Ex: all vertebrates frogs, snakes, fishes, birds and mammals have a similar embryonic development, reinforcing the idea that all vertebrates have a common ancestor.
Early Development of Vertebrates
Homologous Structures or Comparative Anatomy Different species have similar body structures suggesting that these species share a common ancestor. During their evolutionary history, these structures developed into structures used for different functions, according to the organisms environment.
Vertebrates: The number and position of bones are the same, suggesting a common ancestry, but the shape and size changed over time depending on the function of the structure
Vestigial Structures- Structures found in the body of organisms that are not in use anymore. Usually they are reduced in size because they have no anatomical or physiological importance. EX of vestigial structures in humans: Muscles of the ear, wisdom teeth, the appendix, body hair, goose bumps, tailbone.
Similarities in the DNA or Molecular Biology Similarities in the genes and in the amino acid sequence in the proteins, are clues to how related different species of organisms can be. species that have similar DNA and proteins could have evolved from the same ancestor. The DNA of a human is more similar to a DNA of a gorilla than to the DNA of a frog.
***Biogeography the study of the distribution of different species of organisms around the planet today and in the past It helps us understand that similar species inhabited the same area long time ago this can be a clue to common ancestry
There are 2 factors that affect Biogeography or the distribution of the organisms on Earth: Migration Continental Drift
I-Migration: Organisms migrate for different reasons and start inhabiting different areas Organisms have to adapt to the new environment generating new species over time EX: the cases of the finches in the Galapagos islands, all descendant from a common ancestor that lived in the mainland.
II - Continental Drift - separation of continents resulting in species geographical isolation This theory suggests that organisms that lived in the same area developed into different species when separated by the continental drift When the continents separated, local conditions changed and the populations living in the area had to adapt, generating new species
Worksheets All these rodents live in different parts of the world They have very similar characteristics, which suggests that they have a common ancestor. Maybe, they all lived in the samne area in the past, and turned into different species due to continental drift and geographic isolation.