I was making a separate unrelated point, that even the evolutionary leaders in their fields can't agree on how descent among organisms progressed. Their discussions are free-for-alls at times, even deteriorating into verbal insults hurled at each other. These "pillars of science" fail to establish a solid ground on which to build a unified platform. The tree of life is a thorny bush.
That's not the way science work.
Nothing in science, whether it be physics, chemistry or biology, or any combination, are never set in absolute and never unchanging.
Science is knowledge (i.e. theory), is the ability to explain a natural or man-made phenomena (examples of man-made phenomena, computers, automotive engine, etc), but its acceptance is dependent on evidences.
New evidences discovered can possibly -
(A) reinforce and verify existing theory,
(B) update the existing theory,
(C) correcting errors in existing theory,
(D) discovering better alternative theory,
(E) and lastly debunk the existing theory.
Science don't remain static and unchanging, so any theory can be changed or replaced by better theory.
And the only way any theory can be accepted, is through empirical and verifiable evidences, or through rigorous and repeated testings.
So nothing in science is absolute and unchangeable.
In all of my above points, it mean that science is essentially dependent upon on "probability". So a theory is only determined as -
(A) probable true,
(B) probable false,
(C) or undetermined.
So any theory can be questioned or challenged...BUT, scientists who questioned or challenged, MUST BE ABLE TO PROVIDE EVIDENCES to support their challenges, otherwise their alternative theories are rejected.
Scientists can disagree with any current and existing theory, but their hypotheses must be testable, and new hypotheses can only be accepted or rejected, with testings an/ or with evidences.
And it is only accepted when evidences have been found and verified.
To give you an example of competing hypotheses or theories, where scientists may challenge existing and older explanation, let me demonstrate with history of cosmology.
People used to believe and accept the 6-day creation literally, and it has been unchallenged for millennia, and that the Earth was centre of the known universe, while the sun, moon, 5 planets and the stars revolve around Earth, hence the "geocentric planetary motion model" (let shortened this to "geocentric model" or even geocentrism).
All geocentric model is, is that the sun and planets revolve around the Earth in its orbits.
Before the invention of a telescope, geocentric model has only be challenged a few time in history, by the (3rd century BCE) Greek (Aristomachos of Samos) and Indian astronomers, and even by one Muslim astronomer (I can't remember if he was an Arab or Persian astronomer, though this Muslim retracted his claim, when he was unable to prove it) with the heliocentric model.
The heliocentric model is a model that say the planets, including the Earth, orbited around the Sun.
This (heliocentric) model would not reappear again, until the renaissance with first, Nicolaus Copernicus (1473-1543) - the Copernican heliocentrism, and then supported by Johannes Kepler (1571-1630), but confirmed by Galileo Galilei (1564-1642) with his invention of the telescope.
It was the works done by Kepler, who influenced Isaac Newton (1642-1727) to develop his theory on gravity. And Newton's theory went unchallenged though the succeeding couple of centuries, until Albert Einstein (1879-1955) published his theory on General Relativity, in 1916.
His theory didn't make Newton's theory on gravity completely obsolete, but it does reveal Newton's theory have serious limitations, as it doesn't work in deep space, where gravity operates differently.
But General Relativity (GR) did more than just push Newton's law into the background; GR provide the framework of future works on the physical cosmology.
Two astrophysicists, Alexander Friedmann (in 1922) and Georges Lemaître (in 1927) have independently provide their hypotheses that the universe have a beginning, and it (universe) have been expanding ever since. It was known as expanding universe model or the inflationary universe model, back then, before the more popular Big Bang model was coined in 1948, by Fred Hoyle.
Hoyle wasn't a supporter of the Big Bang theory. He challenged the BB model with his own hypothesis - the Steady State model in 1948.
Hoyle was actually being interviewed on BBC radio, when he coined the Big Bang, but he was actually trying to promote his own Steady State model.
But there has already been evidence to support the Big Bang model, as early as 1929, when Edwin Hubble discovered how to measure galaxies are moving away from each other, by noticing the red-shift. If galaxies are moving away from each other than it is red-shifting in the spectrum, suggesting the universe is expanding, while blue-shifting on the side of scale of visible spectrum, the galaxies are moving towards each other, hence universe would be contracting.
On the same year (1948), Hoyle was promoting his hypothesis in public, George Gamow predicted Big Bang Nucleosynthesis (BBN), and Gamow's former pupil but now colleague, Ralph Alpher, with Robert Herman, predicted the Cosmic Microwave Background Radiation (CMBR).
CMBR wasn't discovered until in 1964, by other astronomers, Arno Penzias and Robert Wilson. The CMBR was recently mapped by space telescopes WMAP and the Planck space probe.
CMBR discovery was the final nail needed to nail the coffin for Hoyle's Steady State model.
As you can see in my history lesson on cosmology, some challenges earlier cosmology that began with Aristomachos' with heliocentric model was scientifically true, but was generally unpopular, only to succeed over 1500 years later. While other challenged the current theory, like with Hoyle against the expanding universe model (or the Big Bang) have failed.
All of which, demonstrate that the only way anything can be true, is through evidences, not faith and belief.
Evolution has been challenged by other biologists, but have failed. Evolution have also been challenged by some religions, like with young earth creationism (YEC) and by intelligent design (ID), but neither of these two are science, and they have failed.
Evolutionary biology and its theory can be questioned and challenged, Hockeycowboy, but without evidences, neither creationism, nor ID, can ever be called science.
Darwin's original theory on Natural Selection, have already been corrected and amended after his death by 20th century biologists, so it is still a very valid theory. Even new mechanisms that have been discovered, like mutation, gene flow and genetic drift, doesn't make natural selection obsolete.
One day, there may be better alternative explanation for biodiversity, but it looked like the 20th century biology did a thorough job in covering many of the basis.
