Evolution is based on anatomy, geology and genetics.
The geological record indicates that the further back in time you go, the simplier the organisms.
Go back far enough and you find only indications of bacteria- like organisms such as blue-green "algae" (really a bacteria with cholorphyll). As you progress through the geological record you find the remains of increasingly more complex organisms which have physical similarities to some organisms which preceeded them and some which succeeded them.
Organisms which have anatomical similarities are believed to be related - to have had common ancestors. When comparisons are done on the DNA of living organisms which are presumed to be related through evidence like this in the geological record, these relationships are generally substantiated. They are also substantiated through amino-acid studies on body fluids and tissues.
Look at snakes. Snakes have scales. So do lizards. Anatomically, they are very similar with some very significant difference. Snakes have no legs or pelvic or pectoral girdles in their skeletons. But SOME "prmitive" snakes like pythons, still retain very tiny remnants of rear legs. It is assumed, based on these factors that snakes evolved from lizards.
The earliest horse fossils are of small animals with several toes. As you move forward in the fossil record, you find the fossils of those horse are gradully replcaed with fossils of larger animals with reduced toes until the most recent horses have only a single one-hoofed toe.
Similar relationships have been observed in very many species of animals.
There is even embryological evidence. AS an embyo developes, it has certain features of a primitive nature which later disappear or altered into another form as the embryo grows larger.
Once it was thought that evolution preceeded in a rectilinear progression - a primitive species giving rise to a more advanced species, and so on until the final modern product was achieved. We now believe that evolution preceeds more like a growing bush. Some species evolve into current organisms, other became biological "dead ends". We don't really know for certain which of these primitive homids were our ancestors, but if they weren't directly ancestral to us, they most certainly were our genetic "cousins". A current debate along these lines involves Neaderthals and modern man. Most anthropologists believe Neanderthals were our gnetic cousins and di not evolve into modern man. They believe modern man evolved from some other ancestor which might have also been the ancestor of Neanderthals and later modern man exterminated or displaced Neanderthals. Some others believe that Neanderthals may have interbred with early Modern Man and contributed to our gene pool.
These studies are somewhat in a state of flux, but few if any serious biologists really question the basic premise that all living organisms are related and derived from some common ancestors.
Zulu you're not listening. Problem with many militant evolutionists is they talk when they should be listening. The problem we have is when you're use of the term "common ancestors". That “Common ancestor” has never been found. In fact study on Neanderthal man has shown that through DNA analysis that it was improbably we had a common ancestor.
http://www.accessexcellence.org/WN/SUA10/neander797.html
Were hominids present around the same time as modern man, absolutely. But many of the theorems on evolution from a common Eastern African ancestor are not agreed universally in the scientific community. All theories nailing Darwinian evolution as scientific fact to this date have been either disproven or are on shaky ground, see Piltdown man. How many transitional species have been found to date, let me help you, a fat goose egg '0'. No short neck giraffes found to this date. I have a better question for you, if you are serious about the truth, why do you want the evolution theory to be true? Think about my question and not fire back with the “Skeptic” magazine James Randy type philosophical mumbo jumbo word games answer.
When I was visiting my parents over T-Day, my mom mentioned that he had recently converted to Catholicism. My conclusion is that, as a leading scientist, he probably grew weary of these types of crevo debates and felt more comfortable in a church that fully embraces evolution.
Thomas Aquinas had it all figure out almost 1,000 years ago: over time, man may be able to explain natural law (eg DNA, evolution, el al) but who created natural law?
Believing the literal passages of texts written by goat herders roaming the desert over 2,000 years ago violates the very natural laws (ie our evolution into sentient/understanding beings) that enable mankind to perform such inquiries in the first place.