What can be considered evidence for evolution?

Answer 1

Virtually all species can be arranged into a nested hierarchy highly evocative of common ancestry. That was probably the pivotal piece of evidence launching the theory of evolution as the foundational science of Biology.

There is also the fossil record which shows us that single celled organisms populated earth's oceans billions of years before the first multicellular organisms appeared. Multicellular organisms themselves dwelled solely in marine environments hundreds of millions of years before the first terrestrial forms gained ground. Fossils of plants and insects are common before any known terrestrial vertebrates. The first of these bear uncanny resemblance to sarcopterygian lungfish of the Devonian. The fossil evidence for evolution continues to mount from there--dinosaurs and birds dominating the mesozoic, mammals and flowering plants running rampant in the cenozoic.

In addition to the nested hierarchy and the fossil record there is substantial evidence from molecular biology in support of evolution. DNA sequences in eukaryotes accrue mutations at varying rates that help establish genetic clocks timing diversification events between species.

Embryological development is another key piece of evidence indicating common ancestry between species. There are numerous other substantial and significant pieces of evidence, but this small handful is a good start.