Evolution: Encyclopedia II - Evolution - Science of evolution

Evolution - Science of evolution

The word "evolution" has been used to refer both to a fact and a theory, and it is important to understand both these different meanings of evolution, and the relationship between fact and theory in science.

When "evolution" is used to describe a fact, it refers to the observations that populations of one species of organism do, over time, change into new species. In this sense, evolution occurs whenever a new species of bacterium evolves that is resistant to antibodies that had been lethal to prior strains.

Another clear case of evolution as fact involves the hawthorn fly, Rhagoletis pomonella. Different populations of hawthorn fly feed on different fruits. A new population spontaneously emerged in North America in the 19th century some time after apples, a non-native species, were introduced. The apple feeding population normally feeds only on apples and not on the historically preferred fruit of hawthorns. Likewise the current hawthorn feeding population does not normally feed on apples. A current area of scientific research is the investigation of whether or not the apple feeding race may further evolve into a new species. Some evidence, such as the fact that six out of thirteen alozyme loci are different, that hawthorn flies mature later in the season, and take longer to mature, than apple flies, and that there is little evidence of interbreeding (researchers have documented a 4-6%hybridization rate) suggests that this is indeed occurring.^[8] (see Berlocher and Bush 1982, Berlocher and Feder 2002, Bush 1969, McPheron et. al. 1988, Prokopy et. al. 1988, Smith 1988)

When "evolution" is used to describe a theory, it refers to an explanation for why and how evolution (for example, in the sense of "speciation") occurs. An example of evolution as theory is the modern synthesis of Darwin and Wallace's theory of natural selection and Mendel's principles of genetics. This theory has three major aspects:

1. Common descent of all organisms from a single ancestor or ancestral gene pool.
2. Manifestation of novel traits in a lineage.
3. Mechanisms that cause some traits to persist while others perish.

When people provide evidence for evolution, in some cases they are providing evidence that evolution occurs; in other cases they are providing evidence that a given theory is the best explanation yet as to why and how evolution occurs.

The modern synthesis, like its Mendelian and Darwinian antecedents, is a scientific theory. In plain English, people use the word "theory" to signify "conjecture", "speculation", or "opinion." [9] In this sense, "theories" are opposed to "facts" — parts of the world, or claims about the world, that are real or true regardless of what people think. In scientific terminology however, a theory is a model of the world (or some portion of it) from which falsifiable hypotheses can be generated and tested through controlled experiments, or be verified through empirical observation. In this scientific sense, "facts" are parts of theories – they are things, or relationships between things, that theories must take for granted in order to make predictions, or that theories predict. In other words, for scientists "theory" and "fact" do not stand in opposition, but rather exist in a reciprocal relationship – for example, it is a "fact" that every apple ever dropped on earth (under normal, controlled conditions) has been observed to fall towards the center of the planet in a straight line, and the "theory" which explains these observations is the current theory of gravitation. In this same sense evolution is an observed fact and the modern synthesis is currently the most powerful theory explaining evolution. Within the science of biology, modern synthesis has completely replaced earlier accepted explanations for the origin of species, including Lamarckism and creationism.

Evolution - Academic disciplines

Scholars in a number of academic disciplines and subdisciplines document the fact of evolution, and contribute to the theory of evolution. Every subdiscipline within biology both informs and is informed by knowledge of the theory and details of evolution (examples: population genetics, ecological genetics, human evolution, molecular evolution, phylogenetics, systematics, evo-devo). Mathematics (example bioinformatics), physics, chemistry and others all make important foundational contributions. Even disciplines as far-removed as geology and sociology play a part, since the process of biological evolution has coincided in time and space with the development of both the Earth itself and human civilization upon it.

Physical anthropology emerged in the late 1800s as the study of human osteology, and the fossilized skeletal remains of other hominids. At that time anthropologists debated whether their evidence supported Darwin's claims, because skeletal remains revealed temporal and spacial variation among hominids, but Darwin had not offered an explanation of the mechanisms that produce variation. With the recognition of Mendelian genetics and the rise of the modern synthesis, however, evolution became both the fundamental conceptual framework for, and object of study of, physical anthropologists. In addition to studying skeletal remains, they began to study genetic variation among human populations (i.e. population genetics); thus, some physical anthropologists began calling themselves biological anthropologists.

Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change over time.

At first it was an interdisciplinarity field including scientists from many traditional taxonomically oriented disciplines. For example, it generally includes scientists who may have a specialist training in particular organisms such as mammalogy, ornithology, or herpetology but use those organisms as systems to answer general questions in evolution.

Evolutionary biology as an academic discipline in its own right emerged as a result of the modern evolutionary synthesis in the 1930s and 1940s. It was not until the 1970s and 1980s, however, that a significant number of universities had departments that specifically included the term evolutionary biology in their titles.

Evolutionary developmental biology is an emergent subfield of evolutionary biology that looks at genes of related and unrelated organisms. By comparing the explicit nucleotide sequences of DNA/RNA, it is possible to experimentally determine and trace timelines of species development. For example, gene sequences support the conclusion that chimpanzees are the closest primate ancestor to humans, and that arthropods (e.g., insects) and vertebrates (e.g., humans) have a common biological ancestor.

Adapted from the Wikipedia article "Science of evolution", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki