The theory of evolution is not, as is commonly assumed, equivalent to Darwinism; it is not a process, nor something to believe in. Evolution is not something that only happened in the past, it does not deny the theories of Creationism or Intelligent Design, but it is an alternative explanation. The theory of evolution is an interrelated set of now well-confirmed hypotheses, and theories, including descent with modification, natural selection, genetic drift, and genetics as the mechanisms behind the evolutionary process itself.
The mechanism for how evolution happens has been largely explained by natural selection. Natural selection is observed constantly, and its role as the main driving force of evolution (the Theory of Evolution by Natural Selection, essentially as Charles Darwin proposed) has been observed, tested and challenged many times and in many ways, and has survived largely intact. There are also many independent lines of evidence that are consistent with natural selection as the main mechanism of evolution. There is no observed evidence against this as a working process for evolution. Efforts by some to point out "evidence against evolution" always turn out, under critical examination, to be without merit. The Theory of Evolution by Natural Selection (or, more accurately, the Theory of Natural Selection), therefore, holds the high status of near certainty: it is a scientific fact.
By extension, as this process of speciation proceeds with time, an increasing numbers of species appear, becoming increasingly different. The pattern of natural selection looks like a branching tree; all the species we see today are like the growing tips of that tree, close clusters of tips have most recently branched (evolved); more distant tips can be traced to much lower (earlier) branches in the tree.
The recognition of this pattern of change in life forms over time was developed from many observations. It has even been...