A General Comment

Many of the assignments do not have a unique right answer. We look instead for effective marshalling of relevant evidence, logical connections between parts of an argument, answers to possible counterarguments, appropriate recognition of limitations on the evidence, anticipation of possible future evidence, absence of irrelevancies, and general coherence. Of course it is entirely possible to come up with a wrong answer, i.e., one for which it is impossible to meet the criteria above. Please use plain language whenever possible. The famous book Elements of Style, by Strunk and White, may help guide you.

The range of lengths specified for written assignments gives approximate maxima as well as approximate minima. It's important to make your argument concisely, so each sentence should serve a function in the logical structure. Therefore, don't pad the essay to meet a pre-set length.

Sample Homework Essay

There is an 'exemplary' essay from a previous semester posted on Compass; here, we provide a parallel example from outside physics. This short essay resembles those expected on the first assignment, in that it lacks references, since there are not class notes and texts immediately available to me on the topic. It may also be a bit long.

Q: Two of the most prominent accounts of the origin the variety of life on Earth are the Darwinian explanation (descent via natural selection from a common ancestor) and the creationist explanation (supernatural creation of different kinds in parallel). Give an argument for one of these as opposed to the other. If you wish, you may instead advocate hybrid views, e.g. gradual evolution with supernatural guidance.

A. Evolution or Creation?

In this country, the two most widely held clear-cut accounts of the origins of species are the one based in Biblical literalism and the one which has developed from Darwin's theory of evolution by natural selection. It is often alleged that the choice between these cannot be made on scientific grounds, either because the creationist account can be ruled out ahead of time as non-scientific or because the Darwinian theory is an empty tautology devoid of testable predictions. In arguing for the Darwinian account, I will avoid the common claim that creationism should be rejected a priori as a non-scientific claim, since the real question of how life acquired its present form cannot be answered merely by defining one answer as illegitimate. Any sufficiently definite account should have observational implications, allowing actual tests. I shall argue here that in fact the Darwinian theory has made a wide variety of testable predictions, which have been remarkably successful, while the creationist account fits very poorly with observed data.

Darwin proposed that, starting from some ancestor in remote antiquity, all life evolved by the action of natural selection (including sexual selection) on random heritable changes. In order for that account to be true, several requirements must be met. Most obviously, there must have been ancestors forming continuous links between various species, groups of species, etc. Although this claim was a statement about the past, it was also a prediction about what would be found in the future. Needless to say, the fossil record has been found to be filled with intermediate forms, whether they be small-brained upright hominids, whale-like creatures with small legs, mammal-like reptiles, or small feathered reptiles. Obviously, the fossil record will never be complete, but one could hardly ask for more vivid confirmation of the evolutionary hypothesis than has been found. From the creationist viewpoint, these intermediate forms are about as welcome as the moons of Jupiter were to followers of Ptolemy.

In order to allow the great diversification shown by modern life, a very long history is required. A variety of isotopic dating techniques, based on the highly reliable and reproducible physical processes of radioactive decay, show that the Earth is more than 4 billion years old. Furthermore, these techniques allow reliable dating of fossils. The dated fossil record does indeed make sense, e.g. simple organisms flourished for a long time before more complex ones, the mammal-like reptiles flourished before the earliest mammals, etc. At least the most literal versions of creationism deny the antiquity of the Earth, and lack any coherent account of the isotopic evidence.

One early objection to the idea of evolution via natural selection was that blending inheritance would dilute the effect of any beneficial random heritable change before it could be established in a population. Darwin conceded that something must prevent full blending of heritable traits, i.e. he predicted that there must be discrete heritable units. Mendel's discovery of genes can be viewed as a confirmation of Darwin's prediction. Modern molecular biology has provided a full molecular picture (via DNA) of all the features required for the Darwinian account- heritability, random mutation, and random shuffling of combinations of traits. While these features do not contradict the creationist account, it is striking that they were more or less explicitly predicted by Darwinian theory.

Furthermore, the DNA evidence provides an independent check of the evolutionary history, which can then be compared with the fossil record. Many changes in DNA have no effect on phenotype, so evolutionary theory predicts they will gradually accumulate randomly. Thus, comparisons of DNA sequences in different organisms provide a way of estimating when they shared a common ancestor. The dated family tree obtained from this DNA clock agrees nicely with that inferred from the fossil record. It is extremely hard to see why a designer would carefully design non-coding, apparently random, differences in the DNA of different organisms specifically to mimic the relationships expected from the fossil record on the basis of evolution.

Rather than further belabor the overwhelming evidence for evolution, I would like to briefly address the question of whether the mechanism of evolution has indeed been natural selection. Perhaps the strongest argument is that once mechanisms of heredity and random mutation are established, it is simply impossible to avoid evolution by natural selection, unless all genomes were miraculously to be equally good at reproducing. The question then becomes whether this mechanism is sufficient to account for the varieties that we find.

All the key ingredients of Darwinian evolution have been established by observation. Large phenotypic variations can be induced by selection, as was known to Darwin from the experience of animal breeders. Populations evolve, sometimes very rapidly, in response to changing selective pressure, explaining why antibiotics and antivirals quickly lose much of their effectiveness if they are overused. New species do indeed form spontaneously when small populations become isolated, as insect experiments have confirmed. It is hard to see how these observed processes could fail to give rise to new species in a changing natural environment. It is not possible to rigorously rule out the role of non-random genetic changes, but Occam's razor would suggest that such processes should not be postulated unless the known random processes decisively fail.

Finally, life as we know it is full of ugly little quirks which make perfect sense within the Darwinian framework but which would seem inexplicable within a framework embued with more purpose. For example, the prevalence of diabetes among pregnant women has been coherently explained as a result of competing selection on fetal genes (favoring higher blood sugar levels) and maternal genes (favoring lower levels), leading to dangerously high levels of competing chemical signals released by the fetus and the mother. Any rational designer would have simply set the blood sugar at a compromise level, with low and safe levels of the competing signals. Likewise any rational designer would have given vertebrates optic nerves attached to the back of retinas, as in squids, rather than ones delicately attached to the front through blind spots. Unfortunately, evolution proceeds in a way which only sometimes mimics rational design, much less comprehensible higher purpose.