Evolution and Taxonomy Laboratory 1 Introduction Evolution refers to the process by which forms of life have changed through time by what is described as descent with modification. Evolution explains the wonderful diversity of living things on earth and also represents the primary unifying concept in biology; all organisms can trace their ancestry (and therefore, their unity) to the first cells (basic unit of life). In a broad sense, evolution can be seen at the population level of biological organization as populations change in response to dynamic environmental conditions. Adaptations, traits which enhance survival, allow for organisms to be suited to their environment. The process of natural selection is the mechanism which drives evolution and new species are created while others go extinct. Extinction and evolution are closely related. There are three major categories of scientific data used to support evolution. 1.) Fossils are the remains of once living organisms. Fossils may be preserved remnants of actual body parts or impressions left behind by prehistoric life forms. The fossil record relates these fossils in a standardized geologic time scale. 2.) Comparative anatomy studies similar patterns of development and anatomical features among organisms. These comparative studies often examine embryological structures as well as adult forms. Similar developmental patterns relate directly to ancestry in many instances. Structures that are homologous represent shared ancestry. Homologous structures are also supported by embryological similarity. Analogous structures, while similar in form and function, are not supported by common ancestry and are often the result of convergent evolution (similar environmental pressures produce similar anatomical features without common ancestry). 3.) Biochemical evidence is becoming a more important source of evolutionary data. We know from our studies of the cell that molecules of DNA for the basis for inheritance. The genes which are encrypted on these DNA molecules are responsible for the structure and function of the cells in a living thing. 1
These data are used to construct the phylogeny of a given species. The phylogeny refers to the evolutionary history of a given species. Phylogenetic trees can be constructed to illustrate relationships among different groups of organisms. These phylogentic relationships are reflected in the taxonomy of living things. Taxonomy is the science of naming and classifying living things. Classification refers to the process of grouping organisms based on characteristics shared with other groups of organisms. Modern taxonomy uses categories called taxa (singular, taxon) to classify living things. These taxa form a hierarchy which is very similar to the taxonomic hierarchy developed by Carolus Linnaeus in the 18 th century. Taxonomic hierarchy: Broad, most inclusive Domain Kingdom Phylum Class Order Family Genus Species Narrow, most specific Linnaeus also developed the system of binomial nomenclature whereby each species is given a unique, two-part scientific name. The first part of the scientific name is the genus to which the organism belongs. The second part is known as the specific epithet and is usually a Latinized descriptive term. The genus is always printed in italics (or underlined if written) and capitalized, while the specific epithet is in lower case italics. Currently there are three listed domains: Archea, Bacteria (both prokaryotic) and Eukarya (includes all eukaryotic life). Taxonomy is a dynamic science due to the nature of discovery; science constantly uncovers more and more relationships among living things using increasingly complex technology and genetic analysis. What appears in a textbook today might be quite different from textbooks in the near future!! 2
We are going to compare several animals today to help illustrate the concepts of evolution and phylogeny. Taxon/common name Mudpuppy Pigeon Cat Human Domain Kingdom Phylum Class Order Family Genus Species Eukarya Eukarya Eukarya Eukarya Animalia Animalia Animalia Animalia Chordata Chordata Chordata Chordata Amphibia Aves Mammalia Mammalia Caudata Columbiformes Carnivora Primates Protiedae Columbidae Felidae Hominidae Necturus Columba Felis Homo N. maculosus C. livia F. catus H. sapiens 1. Based on what you know about taxonomy and phylogeny, from the table above: a. Which two organisms appear to be most closely related? b. Which organisms are composed of eukaryotic cells? c. What is the scientific name of a domestic cat? d. Which of the organisms above is most closely related to a i. Bullfrog - ii. Canada Goose - iii. Striped skunk - e. Chimpanzees (Pan troglodytes) belong to the family pongidae. Can you construct the taxonomic hierarchy below of a chimpanzee? 3
Examine the skeletons (to illustrate comparative anatomy) of the mudpuppy, pigeon, cat and human. 2. List several skeletal features that all the skeletons have in common. 3. Look at the shapes and sizes of the vertebrae (backbones). How do the mudpuppy skeleton s vertebrae differ from the: Pigeon Cat Human 4. Which of the skeletons appears to have the most flexible neck (cervical) vertebrae? Why do you suppose the skeleton evolved that way? 5. Notice the posture of the two mammal skeletons. Can you describe why the human skeleton s vertebral column appears recurved (shaped like an S ) and the cat s appears arched? 4
Now carefully examine the appendages (or limbs) of each skeleton. See forelimb drawings on p.6 6. How many limbs on each? 7. Can you identify the bones of the forelimb of a human? (humerus, radius, ulna, carpels, metacarpals, phalanges) 8. Do you notice a similar pattern of bones in all of the skeletal appendages? Describe below. 9. List one adaptation to the forelimb skeleton for each specimen that allows for a particular lifestyle 10. The wing of a bird is homologous / analogous to the wing of a bat. 11. the wing of a bird is homologous / analogous to the wing of a butterfly. 5
Label each forelimb: Cat, Mudpuppy, Pigeon, and Human. Be sure you can identify the major bones on each forelimb. Humerus, radius, ulna, carpals, metacarpals and phalanges 6