Ashwin on Common Descent

(George) #61


Speciation is, by definition, a subset of Common Descent operations. We have all heard about the moths in the UK that demonstrated adaptation by NATURAL Selection.

Ratios of color alleles shifted back and forth due to predation and shifting environmental factors (low soot levels, followed by high levels and then low soot levels again).

And we also know that these events did NOT lead to Speciation, right?

But the principles of Common Descent were nevertheless IN ACTION… unless someone was going to suggest that God created, de novo, the adaptive changes demonstrated in subsequent generations of moths.

If you accept the MICRO-EVOLUTION of the UK moths… that is accepting the general principles of Common Descent … up to - - but NOT including - - speciation!

(George) #62


This sentence of yours [as quoted above] ONLY makes sense if Common Descent is ALWAYS about Speciation. And you (and @JoeG) seem to be the only one(s) saying this.

Speciation is an EXTENSION of the logic of Common Descent… not a REQUIREMENT of Common Descent.

This has to be true… otherwise, the only way you could say two related but separate sub-populations of squirrels (or finches or fish) - - that still belong to the same species - - were not yet eligible for the principles of common descent.

Common “Descent” comes into play the very MOMENT there are “descendants”… and does not pause simply because Speciation has not yet happened!

(Ashwin S) #63

I don’t have any problems with “micro evolution”.

Having said that, your example of the pepper moth was unfortunate. That study was marred by dubious methodology (I don’t want to call it a fraud). The observation was that these moths rest on tree barks and hence color helped them to find camouflage. Pollution supported the darker versions while the presence of lichen helped the lighter versions of the moth. The only problem is that moths don’t naturally rest on tree barks (they rest higher up in the branches and they actively find a place that hides them well irrespective of their color). The biologist who first reported this seems to have fudged his data, even going to the extent of faking photographs (he stuck dead moths on tree barks and took their picture). Currently, there is no evidence that natural selection or industrial pollution had anything to do with this. The entire story is debatable and possibly false.

I am telling you this so that you don’t use this example in the future. It will put you at a disadvantage and turn the discussion into other directions.

(T J Runyon) #64

Wow. I’ve never seen someone misunderstand what i said so badly

(Ashwin S) #65

Help me understand. I would love to listen.
You said common descent is more probably than design.
How did I misunderstand?

(T J Runyon) #66

I did not say that. I said certain observations are more probable on common ancestry than design (I’m using design to mean special, separate creation). @Ashwin_s

(Ashwin S) #67

Ok. Fair enough. Have you calculated the probability?
Is there a scientific foundation to do this?
If it only an intuition… I have been told recently by someone that science is often not intuitive.

(T J Runyon) #68

And please tell why design predicts a common blueprint

(T J Runyon) #69

I’m a Bayesian. If common ancestry is true we would expect the patterns of similarities we see. Design, while Compatitable with the pattern of similarities, doesn’t necessarily predict them. Design could still be true if these patterns didn’t exist. So it follows Observstion E is more probable on C than D

(Ashwin S) #70

What exactly do you mean by that.
I am interested in this because I have been told science cannot test for design… do you disagree with this? If so, why not publish calculation proving special creation did not happen?

(Ashwin S) #71

The basic prediction of design would be a complexity that natural processes cannot achieve.

This needs foundational work to be done on the nature of design vis a vis natural stochastic processes… and mathematical models to distinguish between the two.
To be honest, I don’t know if it is possible. We will know as and when someone designs a method.

What intrigues me is how scientists, recognise that complex biomachinery are the handiwork of nature and not design. Is there a scientific/mathematical way to do it? Some mathematically grounded method perhaps?

(T J Runyon) #72

Heres a decent overview of Bayes’

And I’m not sure science can detect design either. It’s something I’m Certainly open to and will continue to explore @Ashwin_s

(Ashwin S) #73

That’s the only point I wish to make. We can’t have it both ways…
If design can be detected, then science can either prove or disprove it. Else science is silent on design.
And statements like common descent being more probable than design and vice versa are opinions.

I don’t claim there exists scientific proof for design. However, it’s worth investigating whether we can develop reliable scientific methods to distinguish between stochastic natural processes and design.

(T J Runyon) #74

My statements didnt have anything to do with detectability. There are just certain lines of evidence that favor one hypothesis over another. I think the fine-tuning data supports design over no design. Why? Because I think you would expect something like fine-tuning on design and not necessarily so on the hypothesis on non design. But I’m not “detecting” design. Just making a modest claim that this data point makes more sense on design. @Ashwin_s

(Ashwin S) #75

That’s fair enough…
Words like “probability” have a different connotation. May I suggest you add “in my opinion” to such statements for the purpose of clarity?
I understand where you are coming from in this and all of us make such inferences.
I appreciate the clarification.


We examine possible mechanisms in nature. We’ve observed that life on Earth has changed over time in patterns that tend to similarly track along temporal, biochemical, genetic and morphological characteristics. That, coupled with our understanding of reproduction & genetics, provides very strong support for the conclusion of common descent via modification of existing organisms.

We have not independently confirmed the existence of a cosmic or biological designer. While it’s possible that some ‘intelligence’ intervened in the development of life, it’s not clear that it’s necessary to invoke such an unprecedented mechanism (scientifically-speaking) with indeterminate capabilities. Granted, there is no perfect, fool-proof way of knowing when to consider alternate explanations. However, scientists tend toward favoring the more parsimonious models (related to Occam’s Razor).

We do know that historically, design explanations were proposed for the patterns of life observed. In fact, they were the default explanation for millennia. However, they were generally seen as leading to dead-ends, or unresolvable, or indeterminable hypotheses, particularly as our understanding of nature increased. Consequently, evolutionary models (descent with modification at their core), were seen to be much more tractable and capable of evaluation. It provided a positive research direction that also seems to have borne out over time. This doesn’t mean that it’s ultimately 100% correct or that a ‘designer’ may not have directed the path of life over time. Our understanding definitely has a long ways to go. However scientists have pretty good ideas about where additional knowledge must be extended.

At this time, ‘design’ interactions aren’t known to be necessary mechanisms. We have little agreement within science about whether a designer was present on Earth over the course of the past few billion years. Overall it’s not seen among scientists as likely to be a fruitful research program at this time.

It’s not that much different from how research proceeds in engineering.

(Ashwin S) #77

Except that we can’t say for sure whether a super powered nature is more parsimonious than an intelligent creator. I hope you realise this is a philosophical choice and not empirical.
I think it’s important to not forget such distinctions.

This is fair to an extent. However, I have also seen a lot of just so stories posing as science even in peer reviewed papers. There is a certain risk to this approach and possibilities of finding false positives.

That’s true. However engineering does not deal with historical issues… and we have much more stringent ways to test our ideas. (And of course real world consequences of failure that can lead to people dying). There are areas of science (especially when dealing with things that cannot be tested in a lab) which is a little more nebulous. 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.

(Blogging Graduate Student) #78

I think you’ve been reading too much Jonathan Wells. The moths certainly do rest on tree bark, and the claims about Kettlewell “fudging data” have been thoroughly discredited by the work of Michael Majerus e.g. this posthumusly published paper. Yes, some of the photos undoubtedly depicted dead moths that had been stuck to the trees, but that’s how you get illustrative photos. The photos weren’t touted as proof that the moths rested on trees, they were made to illustrate the difference in camouflage between the 2 colour morphs on different coloured trees.

(Ashwin S) #79

They rested far more often higher up in the trees among branches. Natural selection due to being more or less visible to predators is contested. It’s far from a settled issue and the truth is more nuanced than public accounts of it.
You might find the below summary interesting.

With respect to the moth settling issue… the observation is as below-

" Another variable about which too little was known was the pattern and strength of visual selection. In Kettlewell’s experiments, melanic and typical moths were at relatively high densities. There was a massive difference in relative visibility of the forms to the human eye between industrial and rural locations, and a corresponding difference in selective removal by birds. Experiments by others gave comparable results. But what matters is avian rather than human vision. To improve the estimates, it is critical to know how birds react to moths settled at the density and in the locations they adopt under their own volition. These aspects were investigated by Mikkola (1979, 1984), Howlett and Majerus (1987) and Liebert and Brakefield (1987). Although some rest on trunks (36 per cent; Majerus, 2007; Cook et al., 2012), most moths are higher in trees under horizontal branches or in the crooks of smaller branches, where they are better protected from predation (Mikkola, 1979). Howlett and Majerus (1987) compared individuals in the two types of resting position and found the disadvantage of melanics was halved by being in the better place."

Anyway, I had conceded George’s larger point and gave him this info out of good will… there are far better case studies to show the impact of natural selection/micro evolution out there.

(Blogging Graduate Student) #80

52% versus 35% isn’t a particularly large difference, but the relative proportions themselves don’t really matter, it only matters if the moths spend enough time on tree trunks to be vulnerable to predation, causing the different colour moths to be selected for in different environments. Even the paper you cited described the data showing that there is about a 10-15% selection coefficient that can mostly be attributed to predation.

Of course, the story is always more complicated than the accounts widely understood by the public, that’s trivally true of basically anything in science. The point is that while there may be other factors playing a role besides just predation, it’s pretty clear that predation is heavily involved. @gbrooks9 just used it as an example where micro-evolution took place, he didn’t even specify the causes. As an example of microevolution it serves its purpose, regardless of what the selection forces involved were.