Bill Nye, the “Science Guy,” was recently speaking about the debate in Texas over whether to include creationism in the science curriculum in addition to Darwinian evolution.

Nye, as you can guess, is against teaching creationism, calling it “an outrageous notion” and “inane or silly.”

Like many notably atheist science advocates, Nye opposes teaching anything that might be seen as counter to the theory of evolution, which he regards as “fact.” Or, as he might put it, he’s open to teaching other theories, he just isn’t aware of any that meet his scientific criteria.

But you always have to watch out when supposed advocates for science start insisting that evolution is fact. To be a scientist means to ask questions and to be open to new ideas, even if they don’t fit into current belief. Evolution “fact” often seems to have more to do with the religious beliefs of atheists than with verifiable science.

People like Nye would have you accept that there is no valid scientific challenge to Darwinian evolution. They certainly won’t accept anything like “young-Earth” creationism or intelligent design theory, which they consistently try to lump together, dismissing them as “mere” religious belief. But what about challenges to evolution that originate in their own camp?

University of Georgia geneticist Eugene McCarthy has published a new theory on his own website that some people are seeing as a serious challenge to evolution.

Brace yourselves for this one.

Because Darwinian evolution does not adequately explain many of the traits of humans that chimpanzees, our supposed closest ancestor in evolution theory, do not have in common, McCarthy has come to the conclusion that humans can only be some sort of a hybrid between chimps and another animal.

His candidate for the “other” animal? Pigs.

Pigs share a number of traits with humans that chimpanzees lack, such as almost hairless skin, fatty tissue under our skin, prominent noses, eyelashes and light-colored eyes. Pig heart valves can even be used in human hearts because of their similarity.

“What is this other animal that has all these traits?” McCarthy asks. “The answer is Sus scrofa, the ordinary pig.”

McCarthy believes that the historic pig-chimp hook-up was followed by several generations of “back-crossing,” in which the proto-human hybrids mated with their chimp clan relatives and became more apelike.

In other evolution-shaking news, you might recall North Carolina State University molecular paleontologist Mary Schweitzer, who in 2005 discovered the seemingly impossible, soft tissue belonging to a Tyrannosaurus rex.

Many people dismissed her findings, and Schweitzer has sort of lain low for several years while she did what real scientists do and tried to verify her research.

Now she has come out with the news that she and her team of researchers have found a method that might explain the extended survival of soft tissues. In the course of their research, the team looked for signs of soft tissues in other fossil samples.

They found them. A lot.

According to a Discovery News article, soft tissues were discovered in half of the fossil samples the team examined.

“The problem is, for 300 years, we thought, ‘Well, the organics are all gone, so why should we look for something that’s not going to be there?’ and nobody looks,” Schweizer said.

That’s the scientific process in action, and it illustrates what’s wrong with the “evolution is fact” crowd’s insistence that nothing besides evolution should be taught.

Regardless of what you think of McCarthy’s or Schweizer’s ideas, they are doing what scientists are supposed to do: notice things that current theories don’t explain and proposing new hypotheses.

Some people are dismissing McCarthy’s pig-ape hypothesis, others are calling it paradigm-shifting. It certainly challenges evolution theory.

Schweizer’s findings pose a different sort of challenge. Although she’s focused on longevity of tissues, her incidental discovery of soft tissues that scientists hadn’t noticed over the course of three centuries seems bound to challenge some timelines of prehistoric life and will inevitably change the picture we have of dinosaurs.

The “evolution is fact” dogma of Nye and other self-styled science advocates would lock out the possibility of any new ideas. It also works against the professed goal of science education, to make children learn to think critically.

How can children learn to think critically, if no one is allowed to criticize existing ideas?