Thursday, January 24, 2008


Archaeology studies the contemporary distribution and form of artifacts (materials modified by past human activities), with the intent of understanding distribution and movement of ancient populations, development of human social organization, and relationships among contemporary populations; it also contributes significantly to the work of population geneticists, historical linguists, and many historians. Archaeology involves a wide variety of field techniques (remote sensing, survey, geophysical studies, coring, excavation) and laboratory procedures (compositional analyses, dating studies (radiocarbon, optically stimulated luminescence dating), measures of formal variability, examination of wear patterns, residue analyses, etc.). Archaeologists predominantly study materials produced by prehistoric groups but also includes modern, historical and ethnographic populations.

Wednesday, January 16, 2008


The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.

There are two types of chromatin. Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell. The other type, heterochromatin, is the more compact form, and contains DNA that are infrequently transcribed.

Tuesday, January 08, 2008


Genetic variation comes from random mutations that occur in the genomes of organisms. Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. These mutagens produce several different types of change in DNA sequences; these can either have no effect, alter the product of a gene, or prevent the gene from functioning. Studies in the fly Drosophila melanogaster suggest that about 70 percent of mutations are deleterious, and the remainder are either neutral or have a weak beneficial effect. Due to the damaging effects that mutations can have on cells, organisms have evolved mechanisms such as DNA repair to remove mutations. Therefore, the optimal mutation rate for a species is a trade-off between short-term costs, such as the risk of cancer, and the long-term benefits of advantageous mutations.

Thursday, January 03, 2008

Metaphysical naturalism

Metaphysical naturalism is any worldview in which the world is amenable to a unified study that includes the natural sciences and in this sense the world is a unity. According to such a view, nature is all there is, and all things supernatural (which stipulatively includes spirits and souls, non-natural values, and universals as they are commonly conceived) do not exist. It is often simply referred to as naturalism, and occasionally as philosophical naturalism or ontological naturalism, though all those terms have other meanings as well, with naturalism often referring to methodological naturalism. This article presents only a basic outline of the definition and history of metaphysical naturalism and the major arguments for and against it.