Ashwin on Common Descent


Certainty is never possible. There is no fool-proof, empirical means of distinguishing which of two sets of hypothesis that can potentially produce indistinguishable outcomes is correct. However, practical experience gained from at least a couple hundreds years seems to provide some some guidelines. No certainties for sure, but to invoke another, unprecedented mechanism to research definitely requires making a case that can lead to a positive research program.


Engineering also uses Occam’s Razor when assessing explanations.

I started off as a chemist in college and used to scoff at the lack of stringent details I perceived in biology. But I was fascinated with the subject and later moved into the field of biochemistry and biological regulation. I learned that actually, biologists worked quite hard and were no less rigorous in studying what they could about the systems they researched. I work in the early stages of cancer drug discovery today, dealing with very real life and death issues. This is hard and complex, and we definitely keep working towards improving our understanding of cell and organismal biology.

I don’t see ‘historical’ issues as a defining difference in science or engineering. First, there are branches within engineering that perform forensic analysis where the specific history of a system or component matters. Second, insofar as historical information can be discerned (in biology, such from comparison with related groups, and sequences retained), hypotheses can be compared, tested and validated. Inferences and comparisons from similar systems for which we have stronger understanding is also a common method in engineering and the sciences.

The problem with time, not history per se, is that entropic mechanisms often introduce noise.

All I am advocating is a through knowledge of the limitations of scientific claims… I think science as a body should welcome such an approach.

It does. We confront the limits of knowledge and evaluate scientific claims daily in my area. Most people studying evolutionary biology do as well. This is a topic that has been continuously pondered since the formalization of modern science (circa 1700’s?). It’s part of epistemology, which has roots going back at least to the early Greeks. However, none of this makes ‘design’ a better or worse scientific research area or explanation for biological evolution.

Researchers in ‘design’ need to develop a consistent, focused, research direction that provides positive (testable) statements. It must add to our systematic understanding. This has been attempted many times in the past – You can see it in Linnaeus’ work from the 1700s. A case for design cannot simply be made as: “Design can also explain that.” or “Evolutionary theory doesn’t explain ‘X’”. That gives science nothing to work with. A biological design theory can’t be argued for on the basis that it hasn’t been refuted (Related to the the general impossibility of refuting a negative).

With regard to evolution, epistemology, and science, I think there are a number of excellent articles and books by philosophers of science. Elliot Sober is one philosopher who covers this area and I thought his book, Philosophy of Biology was a good read.


Recent work on guppy tail lengths in streams and even Galapagos finches seem to provide pretty rigorous analyses of selective effects on traits.

(Ashwin S) #83

Yes and it is a controversial example…
His purposes would be far better served if he chose a better example… why get into a tangent about the particular example?
That was my larger point. I don’t know why you feel the need to refute that?
Look at the time we wasted disputing a relatively trivial issue when both of us agree on the larger point - micro evolution!

(Blogging Graduate Student) #84

I’d also highly reccomend his book “Evidence and Evolution” if you get the chance. It’s a tour de force of the philosophy of science on the subject of evolution and ID. I’ve learned a lot about how to weigh evidence and compare models from it.

(Blogging Graduate Student) #85

My point is that it’s not really a “controversial” example at all. Having a few loose ends to tie up doesn’t mean it’s controversial. I particularly took umbrage with your comment about “dead moths stuck to trees”, as it’s a such a common objection that just holds no water at all.

(Ashwin S) #86

It is the truth… his test involved dead moths stuck to trees. And even scientists have criticized his methodology as faulty.
Having a few loose ends to tie up is one way of putting it…
Be practical. If you presented this example to anyone who doesn’t believe in evolution, you would end up spending the next couple of hours debating about dead moths and the intentions of scientists who died long ago… why split off into tangents.

I won’t be replying on this particular topic of moths anymore. You are welcome to have the last word.

(Blogging Graduate Student) #87

That’s something different, you first mentioned the photos of moths that had been stuck to trees, and suggested these photos were fraudulent because moths don’t land on tree trunks. I explained why this was an objection that was doubly wrong: not only do moths land on tree trunks, but those photos were never supposed to be used as proof of that claim, they were used to illustrate differences in camouflage.

(George) #88


If you haven’t already been corrected in this point by now… then let me point out that this work has been reviewed and re-verified thoroughly.

The only controversy is that some misconstrue the work as evidence for Speciation… when it is really a grand study for so-called micro-evolution, and NATURAL selection in general.

But rather than insist on the point… if you already acknowledge the reality of micro-evolution (a position which I happily expected from you) we dont have to quibble about the moths.

The point is Common Descent … prior to the cusp of Speciation… IS THE story of micro-evolution.

If you keep on attempting to refute Common Descent in general… you are also attempting to refute the process you say you already accept!:

(Ashwin S) #89

Lets just agree to disagree on the level to which natural selection had a role to play in the moth story… There are factors such as migration which make it debatable.

As to micro evolution or adaptation within the species level. It happens… There are good case studies for it.

(George) #90

@Ashwin_s… good. We can agree on that much.

Now… can you follow the logic that, as general principles, Common Descent is NOT identical to Speciation ?

The most simple reason is that a great deal of the history of two separate sub-populations (derived from a common ancestral population) regards their unique genetic changes - within each sub-group - while their members are STILL viable members of the same species!

In fact, some sub-populations end up re-merging … once again freely exchanging the alleles that had been, for a time, denied free exchange within the entire species.

If you have a problem with speciation… it is best to specifically state that… rather than to allow your readers to think you are daftly rejecting ANY kind of natural selection shaping micro-evolutionary trends within sub-populations!

(Ashwin S) #91

I dont know any body who rejects adaption within the species level… All ID guys accept it… and most YECs accept it too. I doubt many will misunderstand that.

(George) #92


I see an unnecessarily phobic stance by you. If you accept micro-evolution, then you do not reject Common Descent per se… you are rejecting speciation.

Conceding agreement with Common Descent up to, but NOT, INCLUDING Speciation is the precise description of your objection!

Your refusal to accept the plain meaning of these words suggests an unwillingnesd to follow where the logic of your own terminology leads you … pretty much making you unfit for further discussions at PeacefulScience.Org.

You might as well return to BioLogis where they are used to contributors who are logically inconsistent.

I have demonstrated that Common Descent applies just as much to diverging sub-groups THAT ARE STILL members of the same species… as to two or more species that are ALLEGED to have come from the same ancestral population.

The common element to both applications of the phrase “Common Descent” is that Mutation + NATURAL Selection (+ any applicable non genetic factors) causes sub-populations to drift apart genetically.

The difference is that one is the Non-Speciation Scenario (since you say Speciation is impossible, and so the non-speciation scenario is the ONLY outcome)
- - vs. - -
the Speciation Scenario … which even Evolutionists say is not the universal outcome, nor is it inevitable! I believe @swamidass would back me up on these conclusions.

(Ashwin S) #93


You have asked me about 10 times whether i accept common descent within species… and i have replied yes every single time. I have also added that pretty much every one including ID and YEC people accept this…

You are wrong here… The only thing required for common descent within a species is reproduction… yes different different traits can be concentrated in different populations.
Why would anyone feel insecure to admitting to species reproducing?

Why do you keep bringing up an issue i have already agreed about?

(George) #94


Ahhh… perfect! Why? Because you refuse to admit it is ONLY SPECIATION that you object to…

… NOT the other principles which Common Descent has in common with all sorts of accepted FACTS about genetics.

Or have you had a change in heart? And you can see Common Descent per se is NOT the problem… that the problem is JUST Speciation?

2nd PS
Where there is reproduction… there is ALWAYS genetic change… which most academics define as inescapably meaning Evolution of one kind or another!

(Ashwin S) #95

People never talk about common descent as restricted to the species level… its always above the level of species. We always discuss this subject within such a context even in this blog. Whether It is the Common descent of homo sapiens from a primate ancestor… or Universal common ancestry.
And i have always questioned it within this context. You are raising a non issue.
In a theological context, i have said that i don’t see any reason to reject special creation by God.
In the scientific context, i have said that common descent is an assumption and i doubt it can be formally tested. There are some interesting discussions going on about this… Why not pay attention to that… perhaps we will learn something new.
If you are going to keep on talking about common descent within species… i will not reply as i don’t see any point in doing so.

(George) #96


Huh? By “people” you mean CREATIONISTS. Scientists know that the principles of Common Descent do not sit and wait until Speciation has finally occurred.

If they did, Ash, they would almost never use it in the present tense, because it is so rare when Speciation happens during the life of an individual Scientist… or even within the single span of existence of all human civilization.

Your objections are not logical… and show how emotionally invested you are in “the struggle” … rather than in “the solution”! - an observation about you that even @swamidass was able to see in you within the last few days. exists to put together The Solution… not to keep the dispute going in perpetuity.

(George) #97


I look forward to you showing the readers how wrong I am about your motives…if you are able to.

(Intelligent Design Deist) #98

Umm, the difference is between common descent, humans giving rise to humans, and universal Common Descent, the untestable concept that life’s diversity has a common ancestor.

(George) #99

@JoeG (& @Ashwin_s )

And what do you call differential micro-evolution of two groups that demonstrate differences… but continue to belong to the same species?

(Intelligent Design Deist) #100

That is still common descent- the body plans have not changed. You do realize that even YECs accept speciation? Speciation is just microevolution