Evolution

Evolution is the stand-on ground of all biological sciences. Evolution stems its knowledge from comparative anatomy, palaeontology, archaeology, ecology and most recently and importantly, genetics and genomics. Scientists cannot 'think' much about evolution as you seem to suggest as though they have an opinion of it.

Scientists do not have an opinion on gravity or electronics or photosynthesis for example, as though they were supposed to weigh up the moral rights and wrongs of such things.

Scientists may be excited by breakthroughs of course. The unravelling of DNA structure of the emerging of natural selection as a means for species-change, or the structure of atoms revealed through encounters with gold foil, or the discovery that gene traits are expressed in pairs called alleles, or the discovery that spacetime might end, are all thrilling when stumbled upon as new insight into the world and can thus be cherished that we know a little more, but to have an opinion is not what science is all about. Thus scientists do not 'think about' science, nor of evolution. Science is about the dispassionate description of the world, however ghastly or beautiful that description may turn out to be.

The world is an unconscious babbling of atoms and their subatomic mass-energy constituents all dancing on space-time. Scientists dispassionately listen and record and try to understand the babble and try to watch the dance. They describe the babble and the dance. They do not prescribe their moral values fabricated by their own species to it. They describe the dances and leapings on the stage of space-time whether or not they think they are good are bad. Of course the unconscous, never-conscious Brownian motion leapings of atoms, whether causing embryo development or fatal cancer cannot be bad at all, or else the Universe may not even be here. But members of the public with no knowledge of science try to paste their moral values and opinions on the Universe.

Relatively educated people tend to agree there is credence in the Theory of Evolution, while less educated people often dismiss the Theory of Evolution on religious grounds. This is a pasting of one's own (maybe indoctrinated) moral values on the Universe. Some may like to prescribe these notions to the behaviour of the Universe itself. Some refuse to see credence in the Theory of Evolution or the ungodguided development of the world by the big bang or abiogenesis from a religious viewpoint. These people have no knowledge of science at all. Science is an honest description of the world which may yield alarming results.

The notion that apes and humans developed ungodguided and that there is no benevolent dominance hanging over the heads of the peoples, that all is in the vacant emptiness of the lonely Universe among randomly prancing atoms that have no knowledge of human-indoctrinated morality and can randomly prance to instigate the stirrings of embryonic life or randomly cease life carcinogenically, is a very frightening notion to some. Thus the notions of ungodguidedness or randomness in the Universe is often frowned upon and people develop opinions, and perhaps prescriptions on the truths uncovered about the Universe. Particularly, the apparent randomness, the waiting for a genetic mutation in the Theory of Evolution is frowned upon by the public. In fact Evolution is under unnecessary attack, mainly by religious objectors. Science is not a place to have opinions of the Universe, whether evolution or big bangs or DNA. Morality is a place for opinions.

A disinterested scientific picture of the Universe need not be prescribed upon. When we settle into our societies we can have the morality-opinions and the thinking-about things, but they will be based around science whose objective description need not be quibbled with. But science still seems to leave us in a vacant, random Universe full of horrible little random atoms that one cannot trust from one moment to the next. In the lonely, empty Universe, one can at least, on the curtain of space-time, be comforted by the presence of these atoms and the delicious facts delineated and expiscated by science, all swirling around one like little rainbows. You need not have opinions, or pity morality, when at least you know what the Universe is about, described by the disinterest of science.

Geographic isolation refers to a situation where a species, or a population of a species, becomes separated by a physical barrier (a lake, ocean, mountains, etc.), allowing each group to diverge along separate evolutionary paths.

The effect of geographic isolation is that the two populations are subjected to different selection pressures, since the conditions in the two areas will be different. So different alleles will be selected for, and genetic differences will gradually accumulate between, the populations.

In time, enough genetic differences will occur so that the two populations will no longer interbreed. Then, by definition, they have become different species.

More Information:

Geographic isolation is the separation of two (or more) groups of organisms by a geographical feature eg. a river, mountain range, ocean, desert etc. It is the chief mechanism for allopatric speciation, still regarded by some as a theory.

Well, first of all, the correct term is venomous, but that is not that important. All spiders are venomous. Some very dangerous ones native to Maryland are the brown recluse and the black widow (yes, it does live around here, but you will most likely not see one around the house). So to answer your question, all Maryland spiders are venomous, just some are more dangerous than others. Most that you would see around here or in your house are relatively harmless (it might hurt to be bitten by one, but it probably won't do any significant damage).

Black widows, and brown recluse' are the only spiders in Maryland, and America that are fetal to humans. all the other spiders are either harmless to humans or a little dangerous

The classification of lines of evidence into four different types is quite arbitrary. One could as easily distinguish two types, or five, or ten, depending on the criteria used.

For instance: one might distinguish between evidence stemming from research in extant lifeforms on one hand, and from extinct lifeforms on the other. One might distinguish between genetic data and morphological data.

For information on various lines of evidence supporting evolutionary theory, see links below.
1. We have seen species change, and have even caused species to change by our own practices of animal breeding. In recent times we have seen the appearance of such things as antibiotic resistant bacteria and insecticide resistant insects; clearly, they have evolved. They were not always here.

2. In the development of the human embryo (or the embryo of another species) we see that the organism, as it grows from a single celled zygote to a fully developed fetus, goes through what appear to be evolutionary stages. At one point the embryo resembles a fish, having a tail and gills. This is a clear indication that earlier forms from which we evolved are still a part of human genetics.

3. Many species, including humans, have vestigial organs. We have the vermiform appendix, an organ which serves no purpose. More dramatically, whales have very tiny leg bones embedded within their bodies even though they never grow legs. We can find all sorts of residual features left over from earlier stages of evolution.

4. We can trace all sorts of connections, both physiological and biochemical, among different species. The various families and groups which species form, and the similarities within those groups, speak of shared descent and the process of evolution.