Common ancestry: Assumption or conclusion

Tomk80 · #1 5th July 2005, 09:14 PM

It is sometimes asserted on this board that common ancestry in general, and of humans and chimpanzees in particular, is assumed rather than concluded. My aim in this thread is to address that criticism. I will do this by looking at the reasons why common ancestry is concluded and what assumptions lie at the basis of this conclusion. I will try to do this bit by bit, because there is a lot of ground to be covered on this subject. I'm not sure about the format yet, I might try to address the complete topic in a single thread, or make a seperate thread on different related subjects depending on how the thread develops.

I will address a piece of evidence and it’s underlying assumptions, allow time for discussion and then move on to the next piece of evidence. I hope to show that common ancestry of humans and chimpanzees is a conclusion based on the evidence, not an assumption, and that this conclusion can be reached regardless of the mechanism responsible for the divergence.

But to start this of I think it is important to say something on assumptions and how they are used in science. Science makes a number of very basic assumptions. For example, science assumes that the observations we make on the world are real, that we are not living in an imaginary world (cue in the matrix).

But I really don’t want to go too much into that, because than we will land in a discussion on the philosophical underpinnings of science, which I think has been done enough on this board already.

What I do want to talk about is that all methods in science are based on certain assumptions. For example, if I do a statistical analysis for my research, I usually start out by assuming that the data that I analyze has a certain distribution, that the variables I introduce in my analysis are independent from each other and that the error terms in my analysis (how much my observations differ from the mean value) also have a certain distribution. But the beauty of many statistical methods is that I can actually test these assumptions before and after I have done the analysis. And the same is the case with other methods in science. We can test whether an assumption is holds or not. By testing them, they stop being assumptions and are in fact tested hypothesis. So making assumptions isn’t necessarily a bad thing, as long as we have ways to test these assumptions. Ultimately, I’m not going to look at which assumptions are made, but which assumptions are made that cannot be tested or cannot be countered. If an assumption is made but can be tested, I will explain how it can be tested and what the results of these tests is.

I hope to finish and post the first part of the topic tomorrow. Meanwhile, feel free to comment on the above. I hope this thread will give rise to some enjoyable discussions.

Lilandra · #2 5th July 2005, 11:50 PM

Alchemist is looking for material about Evolution to teach at his church camp. Maybe this will give him some ideas.

Originally Posted by Tomk80

It is sometimes asserted on this board that common ancestry in general, and of humans and chimpanzees in particular, is assumed rather than concluded. My aim in this thread is to address that criticism. I will do this by looking at the reasons why common ancestry is concluded and what assumptions lie at the basis of this conclusion. I will try to do this bit by bit, because there is a lot of ground to be covered on this subject. I'm not sure about the format yet, I might try to address the complete topic in a single thread, or make a seperate thread on different related subjects depending on how the thread develops.

I will address a piece of evidence and it’s underlying assumptions, allow time for discussion and then move on to the next piece of evidence. I hope to show that common ancestry of humans and chimpanzees is a conclusion based on the evidence, not an assumption, and that this conclusion can be reached regardless of the mechanism responsible for the divergence.

But to start this of I think it is important to say something on assumptions and how they are used in science. Science makes a number of very basic assumptions. For example, science assumes that the observations we make on the world are real, that we are not living in an imaginary world (cue in the matrix).

But I really don’t want to go too much into that, because than we will land in a discussion on the philosophical underpinnings of science, which I think has been done enough on this board already.

What I do want to talk about is that all methods in science are based on certain assumptions. For example, if I do a statistical analysis for my research, I usually start out by assuming that the data that I analyze has a certain distribution, that the variables I introduce in my analysis are independent from each other and that the error terms in my analysis (how much my observations differ from the mean value) also have a certain distribution. But the beauty of many statistical methods is that I can actually test these assumptions before and after I have done the analysis. And the same is the case with other methods in science. We can test whether an assumption is holds or not. By testing them, they stop being assumptions and are in fact tested hypothesis. So making assumptions isn’t necessarily a bad thing, as long as we have ways to test these assumptions. Ultimately, I’m not going to look at which assumptions are made, but which assumptions are made that cannot be tested or cannot be countered. If an assumption is made but can be tested, I will explain how it can be tested and what the results of these tests is.

I hope to finish and post the first part of the topic tomorrow. Meanwhile, feel free to comment on the above. I hope this thread will give rise to some enjoyable discussions.

Tomk80 · #3 11th July 2005, 07:13 PM

Post II

Okay, so it’s been a while since I could return to this thread. This is for several reasons, most important amongst them being time constraints and the question of how I want to construct my arguments and in which order. Since I’m no expert on this subject matter, doing the research on it takes some time. Because of this, I will also proceed one step at the time for each piece of evidence. In this case, I will first turn to the philogenetic tree and nested hierarchies. I will give a basic description of what it is in this post. I will describe it's history in the next post, which I hope to be able to put up tomorrow. Then I hope to look at how it is arrived at and investigate the assumptions surrounding it in a third post, which I also hope to finish this week.

The phylogenetic tree

For the first piece of evidence, I will turn to the phylogenetic tree. What it comes down to is this. When we try to order animals into groups, we notice that we can order all organisms in a branching structure of groups within groups within groups. We call this a nested hierarchy. This picture is an example of such a structure for beetles:

Now, what is the significance of this? Well, we can’t produce an objective nested hierarchy for everything. The term objective forms the key here. We can produce a subjective nested hierarchy for everything. For example, we can classify Chryslers and BMWs in nested hierarchies:

http://www.clausenbilar.com/Chrysler%20Firepower%201.jpg

http://www.jumy.de/suv/chrysler/chsuv.jpg

http://vea.qc.ca/vea/v/bmwM181.jpg

http://www.csi-auto.nl/carshopping/0033/x5.3.jpg

Now, I could classify the cars above as being Chryslers and BMW’s, and then subdivide them in sportscars and cruisers. But I come across a problem that causes this classification to be subjective. The problem is that I can just as well classify the cars as being sportscars and SUVs, and subdivide both those groups into Chryslers and BMWs.

Now, this does not hold true for classifying organisms. Suppose want to classify dolphins, ichthyosaurs, turtles and otters.

http://www.scuba-works.com/images/Tutle2%203-14-03Copy.jpg

http://www.jyi.org/volumes/volume2/issue1/images/patyten_seaOttersSwim.jpg

http://www.museum.fm/2D_Web/MarineReptile/img/Ichthyosaurs.jpg

http://www.joanocean.com/joan0204/HappyDolphinWC.jpg

Now, there is only one valid classification. Namely, ichthyosaurs and turtles are both subgroups of the group reptiles and dolphins and otters are both subgroups of mammals. Because there is only one valid classification, we call this an objective nested hierarchy.

Now, as I already wrote, very few things actually produce objective nested hierarchy. But common ancestry is one of the things that does produce a nested hierarchy. So if we can devide the current biodiversity in an objective nested hierarchy, we can than conclude that one of the reasons for this nested hierarchy is common ancestry.

So, how is this nested hierarchy arrived at? What are the assumptions made to arrive at it and what does it tell us when we construct one? For this, the first thing we'll have to do is investigate the history and methods of the science which makes phylogenies, namely cladistics.