So what's the problem? It's that science works by hypothesis and speculation but proposes all discoveries as definitive truths, time after time, until a new theory will replace it as another "truth". Maybe scientists should stop using expressions such as "X years ago the world was thus" and replace them with "It is speculated/it is a general opinion of the scientific community that X years ago the world was thus". That would make science maybe a little less credible, but surely more humble in its approach to the world.
OK. Then we should say, "it is speculated and is a general opinion of the scientific community that a molecule of water consists of two atoms of hydrogen and one atom of oxygen."
No, because you you CAN SEE experimentally how atoms and molecules are built, and the main three forces (electromagnetism, strong interaction and weak interaction) that govern it: the theories have made previsions, and the previsions have been up to now confirmed experimentally; the only certainty is that these theories describe very well reality, but they may be incomplete and need to be filled in with new discoveries (if you're used to physics, an example is the search for the boson of Higgs). What always surprises me is that we arrived at this conclusions in an incredibly easy way despite the many obstacles of looking into the "infinitely little" (including Heisemberg's principle of indetermination).
On the contrary, you can't say with accuracy which ape was an ancestor of modern man. There was a period when scientists taught with certainty that the Cro-magnon man and Neanderthals were son and father, but now the opinion is that they are cousins independently evolved from a common ancestor Homo Heidelbergensis, and that they walked on Earth simultaneously for a long period of their existence. A similar error was made when scientists assumed as obvious that - as reptiles - dinosaurs were cold-blooded. These things were taught as "scientific dogmas" in school books, in my country (I don't know of the US). Recent studies have shown that this certainty was an error, since there are solid hints that they were warm-blooded. Nevertheless, school books of the time gave cold-blooded dinosaurs and our supposed father Neanderthal as certainties, which has been clearly disproved. Proofs are necessary to sustain a theory.
The problem with paleontology is that the only known model for life exists on Earth, so that we can't verify experimentally the path of evolution from one species into another. An Italian physicist, former director of CERN Antonio Zichichi, has been largely criticized for having put in discussion the evolutionary theory as a strictly-speaking scientific theory. Of this theory he criticized the METHODS, since evolution is neither experimental nor mathematical.
I will invent a "visual" experiment, if you like, to explain how evolution is based on a weak scientific base. Let's assume we have a man in front of three different ladders who bring from a point A to a point B. We go away and give a look at this place after one hour, and we find out that the individual has already reached point B. We know that he somehow moved from point A to point B, and we might assume that he did so through the most direct and short of the three ladders, but how can we be sure? He could have taken the longer ladder and be there in an hour. He could have used a different means to reach point B. He could even have travelled as fast as light and have circled the entire Earth, reaching point B from the opposite direction, or he might have used a teleportation device. There are virtually an unlimited possible range of ways to reach point B from point A, and the most logical may be nevertheless wrong: it's only a GUESS, an hypothesis or theory which we could verify only asking to the individual directly or to an eyewitness who must have seen the entire travel of the individual. Even using alternated cameras along the possible paths from A to B doesn't grant us that, in the points from a camera to another, he might have used other means of travel then the ladders.
Bringing this to evolution, we can easily understand that men and apes are biologically linked (I mean in their DNAs) but:
1) We can't be sure of the evolutionary path of man, i.e. which steps of evolution man has really followed to become what it is.
2) We can't be sure by which means man evoluted from some primate, even if we can take pictures of man (i.e. find the missing links) at some points of his evolutionary process.
We could say this is a "principle of indetermination" applied to evolutionism: as the electrons move in a "cloud of probability", so that we can either calculate the position of an electron, but we can't know how fast it travels before its relevation, in the same way we can calculate the space-time coordinates of a fossil animal and compare with others, but we can't know for sure whence the animal evolved, or what he was going to evolve into.
In Christ, Alex