EK 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics. Describe how the following example provides morphological evidence for evolution. 1.Vertebrate front limbs allow have the same 1bone, 2 bones, many bones, digits pattern. This is an example of a homologous structure. How does the variation of this same basic pattern indicate evidence for evolution? homologous structure 2.The ancestor of the cavefish has eyesight, but the cavefish does not. How does the loss of eyesight provide morphological evidence for evolution?loss of eyesight 3.Whales have an ancestor that was a tetrapod and could walk on land. Whales still have hip bones which is a vestigial structure. How do vestigial structures like the hip bones in whales provide morphological evidence for evolution?vestigial structures Describe how the following example provides molecular evidence for evolution. 1.All organisms have the same 4 nucleotides that are used to build DNA molecules. How is this evidence of evolution?DNA 2.All organisms have amino acids which are used as building blocks of protein. How is this evidence of evolution?amino acids Describe how the following example provides genetic evidence for evolution. 1.How can differences in DNA sequences be used as genetic evidence for evolution?DNA sequences 2.How can differences in proteins be used as molecular evidence for evolution?differences in proteins Describe how the following example provides evidence for evolution. 1.What is stratigraphy? How is it used to date fossils?date fossils 2.What is radiometric dating? How is the rate of decay of isotopes used to date fossils?rate of decay of isotopes date fossils What are cladograms and phylogenetic trees used to show?cladograms and phylogenetic

Evolution of blindness in cavefish If a mutation disrupts a gene that is not being used, natural selection will have no restoring effect. This is why fish that adapt to a lifestyle of darkness in a cave tend to lose their eyes. There is no longer any advantage to having eyes, and so the deleterious mutations that creep in are no longer being weeded out. Think of it as the ‘use it or lose it’ school of evolution.** A world without light is quite an alien place. There are many examples of fish that live in completely dark caves. Remarkably, if you compare these fish to their relatives that live in rivers or in the ocean, you find that the cavefish often undergo a similar set of changes. Their eyes do not fully develop, rendering them essentially blind. They lose pigmentation in their skin, and their jaws and teeth tend to develop in particular ways. This is an example of what is known as convergent evolution, where different organisms faced with similar ecological challenges also stumble upon similar evolutionary solutions.

Hippos are large and aquatic, like whales, but the two groups evolved those features separately from each other. We know this because the ancient relatives of hippos called anthracotheres (not shown here) were not large or aquatic. Nor were the ancient relatives of whales that you see pictured on this tree — such as Pakicetus. Hippos likely evolved from a group of anthracotheres about 15 million years ago, the first whales evolved over 50 million years ago, and the ancestor of both these groups was terrestrial.evolved The picture below shows the vestigial remnants of a pelvis in the whale, which provides a link to an ancestor that walked on land.

Molecular Evidence The DNA in living things is highly conserved. DNA has only four nitrogenous bases that code for all differences in living things on Earth. Adenine, Cytosine, Guanine, and Thymine line up in a specific order and a group of three, or a codon, code for one of 20 amino acids found on Earth. The order of those amino acids determines what protein is made.nitrogenous bases20 amino acids The more closely species are related on the phylogenetic tree of life, the more closely their DNA sequences will overlap. Even very distantly related species will have some degree of DNA sequence overlap. Certain proteins are needed for even the most basic processes of life, so those selected parts of the sequence that codes for those proteins will be conserved in all species on Earth. phylogenetic tree of life

DNA sequence and evolutionary relationships

Protein sequence and evolutionary relationship

Fossil Dating Figure 2. How relative dating of events and radiometric (numeric) dates are combined to produce a calibrated geological time scale. In this example, the data demonstrates that "fossil B time" was somewhere between 151 and 140 million years ago, and that "fossil A time" is older than 151 million years ago. Note that because of the position of the dated beds, there is room for improvement in the time constraints on these fossil-bearing intervals (e.g., you could look for a datable volcanic ash at 40-45m to better constrain the time of first appearance of fossil B).

Radiometric dating techniques to calculate the ages of living and dead organims Isotopes decay at an exponential rate that that can be described in terms of half-life. One half-life is the time it takes for ½ of the parent isotopes present in a rock or bone or shell to decay to daughter isotopes. Parent isotopes decay to daughter isotopes at a steady, exponential rate that is constant for each pair.

Reading trees: A quick review A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa (singular: taxon). The tips of the tree represent groups of descendent taxa (often species) and the nodes on the tree represent the common ancestors of those descendants. Two descendants that split from the same node are called sister groups. In the tree below, species A & B are sister groups — they are each other's closest relatives.phylogenytaxaspecies nodescommon ancestorssister groups Many phylogenies also include an outgroup — a taxon outside the group of interest. All the members of the group of interest are more closely related to each other than they are to the outgroup. Hence, the outgroup stems from the base of the tree. An outgroup can give you a sense of where on the bigger tree of life the main group of organisms falls. It is also useful when constructing evolutionary trees.outgroup