[b]EDIT[/b] So the first true warm blooded fish has been discovered. http://m.livescience.com/50839-first-warm-blooded-fish-found.html Pretty awesome. Pic above. Its called an Opah, or moonfish. [b]OP:[/b]Since the issue is always a lack of understanding, and its often requested to be explained when people point out anothers lack of understanding on it, I'll lay it all out for everyone. [b]Evolution[/b], put simply, is descent with modification. So let's break down the basics of how that happens. [b]DNA[/b] or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms that resides in our cells. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell. Its during this replication process that is constantly happening, that errors or mutations can occur. If an error occurs you now have a cell that is different from the original, due to mutation. [b]Mutations[/b] or copying errors cause the copied DNA to be different from the original. These mutations can be passed to the next generation of organisms when the gametes and zygotes contain the mutated DNA. Evolution occurs when you have a change in gene frequency within a population over time. What affects gene frequency? It is the [b]mechanisms of change.[/b] These mechanisms are [b]mutation, migration, genetic drift, and natural selection.[/b] Since I already went over how mutation occurs next comes [b]migration[/b] or how geographic location of populations can affect the overall gene frequency of a species. An example will be best here. You have 2 population of beetle species X. Population 1 typically has spots, population 2 typically does not. If these two populations migrate farther apart, you will see that difference become more defined due to isolation. If they migrate closer and intermingle, you'll see much more variation in the two populations. Migration, whether it be by the animals itself, or caused by other events, like plate tectonics (on a scale of millions of years) can allow or prevent the genetic divergence of populations of animals, resulting in a new species. [b]Genetic Drift[/b] is more random chance affecting organisms. Let's say in our beetle species X, population 1, lives in the lower forests, and population 2 live higher in the mountains. Well the mountain is a volcano, it erupts, and wipes all of population 2 out. All the little differences it had that were unique to it out of beetle species X, are now gone, resulting in the populations 2 genes to be gone from the future generations of beetle species X. Basically genetic drift accidental selection. And finally we come to [b]natural selection[/b]. Natural selection is the gradual process by which heritable biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. Or, put simply, it is the process of how the selecting factors in an environment; predators, food sources, climate, etc make certain inheritable traits more or less likely to be passed on to future generations. All of these mechanisms acting in conjunction cause evolution, and create new species. How do differentiate between species? A [b]species[/b], is often defined as the largest group of organisms capable of interbreeding and producing [u]fertile[/u] offspring. When one species becomes two, this is called speciation. This event creates all kinds of new opportunities for more evolution to occur. Its important to look at the timeline of life, not as a ladder of organisms getting "better", but as a tree, where the father up you go the newer the branches are, not necessarily better. Old branches can last a long time, like the [url=http://vertebrates.si.edu/fishes/coelacanth/indonesia_coelacanth_2.jpg]coelacanth[/url], and new branches can have relatively short life spans, like any of the many now recently extinct plants and animals. The tree just shows the lines of ancestry. Evolution does [b][u]not[/u][/b] address the origin of life. Evolution is how life forms have changed over time as a result of their environment and genetics. Claiming not having an answer for life's origins affects evolution is patently false. Yes, there are still questions being investigated in regards to evolution. For example: -Does evolution tend to proceed slowly and steadily or in quick jumps? - Why are some [url=http://www.evolution.berkeley.edu/evolibrary/search/imagedetail.php?id=260&topic_id=&keywords=]clades[/url] very diverse and some unusually sparse? Among other things regarding the specifics. All available evidence supports the central conclusions of evolutionary theory, that life on Earth has evolved and that species share common ancestors. Biologists are not arguing about these conclusions. But they are trying to learn more about how evolution happens, and that's not an easy job. It involves collecting data, proposing hypotheses, creating models, and evaluating other scientists' work. These are all activities that we can, and should, hold up to our checklist and ask the question: are they doing science? All sciences ask questions about the natural world, propose explanations in terms of natural processes, and evaluate these explanations using evidence from the natural world. Evolutionary biology is no exception. Darwin's basic conception of evolutionary change and diversification explains many observations in terms of natural processes and is supported by evidence from the natural world. This is a summary in my own words of how it works, so its entirely possible I forgot something. I've really tried to keep this as short, and simple as possible, and I welcome any questions and any issues you see.