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From Citizendium, the Citizens' Compendium
The scientific discipline of biology has numerous sub-disciplines, including that of evolutionary biology, a sub-discipline, however, that practically subsumes biology, as many if not most biologists endorse the proposition of the 20th century's pioneering evolutionary biologist, Theodosius Dobzhansky, videlicet: "Nothing in biology makes sense except in the light of evolution." For evolutionary biologists, not surprisingly, evolution takes center stage, in particular as "the unifying theory of biology". 
Evolutionary biology concerns itself centrally with the history of evolutionary change — the changes in function and structure in populations of organisms through geological time — and with the mechanisms, or causes, of evolution — the processes operating that bring about those evolutionary changes. In pursuing those concerns, evolutionary biology informs us about ourselves and the living world that embeds us, rewards us with satisfactions to our instinctual curiosities, and, as will become evident, contributes critically to the research efforts of biologists in almost every discipline, from molecular and cell biology, genetics, physiology, medicine, mathematical biology, agriculture, ecology, anthropology, environmental conservation, and the philosophy of biology — to name a few.
This article endeavors to provide an overview of the concepts, principles and applications of evolutionary biology; the questions evolutionary biology tries to answer; the questions that arise from those answers; how evolutionary biology has changed, and continues to change, our worldview; and, how the discipline itself continues to evolve.
Evolution in brief
Typically the characteristics of populations of kindred (interbreeding) organisms (viz., species) differ one generation from another, the transgenerational changes occurring sometimes slowly, sometimes rapidly. Those transgenerational changes constitute the evolution of the population, a descent with modification, as Charles Darwin referred to it,  descent often accompanied by diversification into separate distinctive populations. The key to descent with modification: heritable variation operated on by natural selection.
|The hardest thing to understand about biology is the importance of variation. There are probably several reasons for this. One may be human psychology. It is easier for us to think in terms of homogeneous classes of things, rather than heterogeneous sets of things. If we count out three plastic yellow ducks for our toddler, then we are implicitly conveying the idea that they are the same thing, which is of course illusory. The yellow ducks are bound to be different from each other, at least in subtle ways.|
|Another problem is that the foundations of science were defined by physicists using mathematical representations of reality in which any type of variation or randomness was neglected. This is the metaphysics by which integral and differential calculus become cosmology.|
|But it turns out that these important tendencies of human thought, and the thought of modems particularly, are highly counterproductive in biology. Variation is not merely characteristic of living things, it is also essential to their very evolution.|
In a distinctive population of living systems (e.g., a species, similar to a population of humans speaking a distinctive language, individual members of the population vary from one another in their characteristics; not all infant male chimpanzees of similar age have identical charcteristics. Moreover, due to heredity, the characteristics of organisms in one generation show similarity with those of those of its parent or parents. Those two facts define the principles of variation and inheritance of characteristics.
As the generations of a species proceed, the proportions of members with differing variations in characteristics may change due to elimination of organisms less reproductively advantaged than their conspecifics — Darwin's descent with modification — a phenomenon that can lead to a population with a changed profile of characteristics better adapted to their environment, and depending on circumstances, to separate populations (speciation arising from a common ancestral population.
For example, the approximately one dozen and a half extant distinctive populations (species) of penguins descended, with modification, from a common ancestor population, that also incidentally gave rise to storks, the ancestral population living approximately 60 million years ago. 
For another example, chimpanzees and humans descended with modifications from a common ancestral population living some five to seven million years ago.
Among other factors, so-called 'mutations' in the determinants of heritable characteristics (e.g., genes) cause variations within a population. Natural processes of sorting among the variants, based in part on the 'fitness' of the variants in respect of reproductive success, as in natural selection, cause the changing proportions of different variants in successive generations. The sorting process of natural selection results in the adaptation of the population to changing environmental conditions affecting reproductive fitness.
Additional specifics of evolutionary processes will emerge in context in the discussion of topics to follow. The undisputed primer: Charles Darwin's, On the Origin of Species.  An informative website primer: 
Examples of questions asked by evolutionary biologists
In the first chapter of his 1998 book on evolutionary biology, Douglas Futuyma extols evolutionary biology as the "most sweeping and comprehensive" of all of the biological sciences. By way of justification, he illustrates the kinds of questions asked by evolutionary biologists. Many echo questions asked some thirty years earlier by Theodosius Dobzhansky.
- Why so many different kinds of organisms living today?
- Why do they share some common characteristics but differ in others?
- Why do the countless different species of organisms have the particular features they have?
- Why do almost all species of organisms have the same genetic code for specifying protein structures?
- Why the difference in life spans among species?
- Why do they differ in what they can learn?
- Why chromosomal crossing over?
- What brought about the immense variety of enzymes in cells?
- Why do men have nipples?
- Why menopause so nearly in the life span of a woman? 
- Why does swallowing risk choking in humans?
- Why the particular geographic distribution of species on Earth?
- How did human cognition arise?
- How did humans become bipedal?
- Why did humans become nearly hairless?
One might add many other questions asked by evolutionary biologists not specifically addressed by Professor Futuyma in Chapter One:
- Why do humans develop chronic degenerative diseases?
- Why do we have an obesity epidemic?
- Why sexual reproduction?
- Why a limited rather than indefinite life span?
- Why autoimmune diseases?
- Why breast cancer?
- Why mental illnesses?
- Why do we have the particular instincts we have?
- Why murder, war?
- Why do living things exist at all?
- How does novelty arise in living things?
All of the above questions give some sense of the sweep and importance of evolutionary biology.
Citations and notes
- ↑ 1.0 1.1 Dobzhansky T (1973). "Nothing in biology makes sense except in the light of evolution". Am Biol Teach: 125-9.
- ↑ 2.0 2.1 Futuyma DJ. (1998) Evolutionary Biology. Sinauer Associates, Inc. Sunderland. ISBN 0-87893-189-9
- ↑ Introduction to Evolutionary Biology
- ↑ 4.0 4.1 Darwin C (1982; originally 1859) The Origin of Species By Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. London: Penguin Books ISBN 9780140432053
- ↑ >Rose MR. (1998) Darwin's spectre: evolutionary biology in the modern world. Princeton, N.J.: Princeton University Press. ISBN 0691012172 [hb]; ISBN 1-4008-0675-5 [eISBN]. Adobe Digital Edition | Google Books preview.
- From book description: ...provides the general reader with an introduction to the theory of evolution...explains how evolutionary biology has been used to support both valuable applied research, particularly in agriculture, and truly frightening objectives, such as Nazi eugenics.</li>
- ↑ Shepherd LD, Lambert DM. (2005) Mutational bias in penguin microsatellite DNA. J. Hered. 96:566-571. PMID 15994417</li>
- ↑ The basics of how natural selection works to produce adaptations</li>
- ↑ Understanding Evolution</li>
- ↑ Reiber C. (2010) Female gamete competition: A new evolutionary perspective on menopause. Journal of Social, Evolutionary, and Cultural Psychology. 4(4):215-240.
- Abstract: Menopause has long perplexed evolutionists because it is hard to see how a trait that precludes reproduction for a large portion of a woman’s adult life could have spread evolutionarily. Neither of the two common explanations is scientifically satisfying. The Extended Lifespan Hypothesis–that menopause is simply a byproduct of the modern expansion of human lifespans– is plagued by its inability to account for gender differences and the fact that many non-human animals also cease reproducing well before the end of life, among other problems. The Grandmother Hypothesis argues that women net more genes in future generations by assisting their descendants.than they would by continuing to reproduce directly, but gains large enough to offset a woman’s direct reproductive potential have never been demonstrated. Approaching the phenomenon from the perspective of the gamete rather than the individual suggests a new hypothesis: Female gametes are competing to achieve ovulation, and the high rate of gamete loss that results leads directly to the follicular depletion that triggers menopause. Thus, menopause is a cost imposed upon individuals by gametes that are behaving in their own evolutionary best interest.</li>
- ↑ Evolution of Menopause, by Chris Reiber. The Evolution and Medicine Review.</li></ol>