Biology Homework Chapter 15: Evolution - Macroevolution
Textbook assignment: Chapter 15: Tracing Evolutionary History, sections 1 -13.
- 15.1 Astronomy and geology provide theories for the age of the universe (around 13 BY) and for the age of the earth (4.5 BY), as well as for the earth's early atmosphere (hydrogen, then gasses expelled by volcanic activity). Rocks dated at 3.5 BY show structures identified as prokaryotic (bacterial) fossils. From the fossil evidence, it would appear that life arose between 4.1 and 3.5 BYA from nonorganic molecules. Synthesis of amino acids, formation of proteins and nucleic acids, protobiont structures, and self-replicating molecules are requirements for single-celled life as we know it.
- 15.2 The Miller-Urey experiments show that amino acids will form spontaneously from inorganic components under the right conditions. The experiments cannot prove that amino acids now found in all life forms actually did spontaneously form from nonorganic molecules in the atmosphere at some point in the earth's history, but scientific evidence supports this possibility. Energy conditions would favor formation near deep-sea vents.
- 15.3 Polymers such as polypeptides have been formed in the lab by dripping dilute solutions of monomers on hot clay surfaces. Some experiments demonstrate that strands of RNA can form spontaneously from existing monomer nucleotides, then self-replicate. Some experiments demonstrate that mixes of polypeptides (which will form proteins) and lipids will self-assemble into cooperatives that grow by absorbing polypeptides and lipids from the environment, dividing when they reach a certain size.
- 15.4 Now we get to macroevolution: the theory that mutation of the genetic code leads to species that cannot interbreed, with radical changes in phenotypical traits. Again, one of the fundamental principles of evolution is that mutations create diversity: more species develop over time and these later species have more characteristics than their predecessors. We move from the simple to the complex, from simple single-compartment prokaryote cells to multiple compartment but still single-cell eukaryotes, then to multicellular eukaryotes with specialized tissues (all in aquatic environments). Survival on land requires the ability to exist and provide structure without a constant water source.
- 15.5 A "half-life" is the time estimated for half of a sample of radioactive material to decay. This is a prediction based on statistical behavior for large groups of radioactive atoms. We cannot predict the time-to-decay of an individual atom, only the likelihood that so many radioactive atoms of an element in a sample will decay in a given period. Radioactive half-life determinations for elements are supported by a century of observations of different elements.
- 15.6 On the basis of rock strata and fossils, geologists have broken down the history of earth into eras and further divided eras into periods. Those periods of the Cenozoic era have further divisions into epochs: there is more evidence for recent periods which suggest ways for geologists to distinguish particular events. [Whether you agree with the conclusions of the geologists and evolutionists about the age of the earth or not, these terms are the vocabulary of the debate....so learn them!]
- 15.7 Continental drift is based on Wegener's theory of plate tectonics, that different sections of the earth's surface float on the liquid mantle, shoved about by convection currents. The continents of the earth-as-we-know-it had different relative positions and orientations in the past, and these can be discovered by comparing geological formations that spread across now widely-separated contents, or looking at magnetic fields fixed in rock. Modern Earth-orbit satellite measurements of continental positions show that the contents are moving relative to one another.
- 15.8 Earthquakes and volcanic activity occur along the edges of plates, threatening life (and occasionally wiping out species).
- 15.9 Mass extinction is the elimination of many species during a single geological period, sometimes by a single catastrophic event. The fossil record supports the idea that up to six mass extinctions occurred during the last 600 MY, since fossils of species found before each event do not occur in later formations. As the competition is wiped out, surviving species move into newly-available niches, and diversify, becoming specially adapted to their own niche.
- 15.10 Adaptive radiation is the term applied when descendents of a common ancestor appear to diverge into different species by developing different adaptations to a diverse environment.
- 15.11 Homeotic genes and differentiation govern the development of an individual through embryonic, juvenile, and adult forms. Paedomorphosis occurs when the normal differentiation schedule is interrupted, leaving an individual in a juvenile or partially juvenile form. If a sex-gene mutation caused the paedomorphosis and the individual is viable, it may survive to pass the new characteristic and form to its offspring.
- 15.12 New structures can appear through mutations that provide a particular function (adaptations), and over time some of these structures are co-opted to provide a different function (exaptations).
- 15.13 The ancient Greek "Great Chain of Being" and the evolutionary theories of the French Enlightenment philosophers assumed that nature pursued processes that improved on the past, and that new species would be better than earlier species, a goal-directed view that spilled over into their perception of human beings and was fundamental to the theories of humanism. Darwinian evolution is not goal-directed: there is no over-arching purpose. Even when a trend is noticeable (increasing size of a species), it results from natural selection processes at a particular time and place. Sudden changes in habitat can make a previously favorable adaptation become a liability.
Read the following weblecture before chat: Tracing Evolutionary History
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Check out the Evolution Lab at the PBS Nova site. Watch the video intro, read the "About this lab" instructions, then play the game.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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