Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 86 (8950 total)
29 online now:
Diomedes, jar, xongsmith (3 members, 26 visitors)
Newest Member: Mikee
Post Volume: Total: 867,191 Year: 22,227/19,786 Month: 790/1,834 Week: 290/500 Day: 53/65 Hour: 0/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Common Ancestor Terminology
Hideyoshi
Junior Member (Idle past 2554 days)
Posts: 5
From: Kobe, Japan
Joined: 08-16-2003


Message 1 of 15 (672893)
09-11-2012 9:42 PM


A special note to preface: The criticism contained herein is not intended to challenge the fact of biological evolution. However, the terminology often used by public proponents does seem to be lacking in consistency with the natural world.

When Charles Darwin entered the fray in the ongoing discussion about common descent, it was a discussion that already borrowed terminology from more mundane human geneaology. When social custom demanded worrying about property and violence and loyalty; a term like descendant and ancestor was intended to settle the matter once and for all. If Queen Bonnie owned Tulipsville in ye olden times and you could show the direct and real and sequential descendant of Queen Bonnie to all concerned; that was that, Tulipsville was yours. Transferred to evolutionary usage, if it could be determined and shown that the descendants of a small mammal that lived and loved in Cretaceous North America survived to present day as a human being living in Brooklyn, that would be that. Direct, Real, Sequential.

On the other hand, going in the reverse order doesn't seem so convenient with the terminology at hand. Specifically, "the Common Ancestor" of, say, a human living today in Brooklyn and an African Elephant named Mogri living in the Serengeti today. Much can be inferred toward that end on a very general trend, more primitive primates here, and more primitive proboscidean there. And yet this only gets you so far. In the case of a descendant, you can safely throw out a great majority of the individuals as unimportant (not unimportant on ethical grounds, but just for the bookkeeping) , say the various siblings and such. But for an ancestor, if you try to ignore any of the individuals, you lose all of your accuracy. The closest you may be able to get is a population of potentially breeding organisms. The genes shared in common between a human and elephant of today did not necessarily come from an individual in that population, but could have been contributed by distant relatives in that population who are not connected in any direct linear fashion. The individual elephant living today in the Serengeti and the human living in Brooklyn today may have never gotten any closer than a cousin of a cousin of a cousin of a cousin of a cousin and all separated in existence by a hundred years or more.

Despite all this, when was the last time anyone described to the public or expected the public to assume that the term "the Common Ancestor" was actually plural, not necessarily distinct, and possibly metaphorical in nature? Is there simply a weakness in the definitions of our language, and we need a new word? Or does the existing terminology need to be readdressed and properly defined to those outside the biological sciences?


Replies to this message:
 Message 3 by RAZD, posted 09-12-2012 9:59 AM Hideyoshi has not yet responded
 Message 4 by Dr Adequate, posted 09-12-2012 10:01 AM Hideyoshi has not yet responded

  
Admin
Director
Posts: 12653
From: EvC Forum
Joined: 06-14-2002
Member Rating: 3.0


Message 2 of 15 (672895)
09-12-2012 8:59 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the Common Ancestor Terminology thread in the Proposed New Topics forum.

  
RAZD
Member
Posts: 20329
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.6


Message 3 of 15 (672900)
09-12-2012 9:59 AM
Reply to: Message 1 by Hideyoshi
09-11-2012 9:42 PM


Hi Hideyoshi, and welcome to the fray,

On the other hand, going in the reverse order doesn't seem so convenient with the terminology at hand. Specifically, "the Common Ancestor" of, say, a human living today in Brooklyn and an African Elephant named Mogri living in the Serengeti today. Much can be inferred toward that end on a very general trend, more primitive primates here, and more primitive proboscidean there. And yet this only gets you so far. ...

That's why I like to talk about a common ancestral gene pool, or a common ancestor population, rather than an individual.

Despite all this, when was the last time anyone described to the public or expected the public to assume that the term "the Common Ancestor" was actually plural, not necessarily distinct, and possibly metaphorical in nature? Is there simply a weakness in the definitions of our language, and we need a new word? Or does the existing terminology need to be readdressed and properly defined to those outside the biological sciences?

It is always useful to be more specific and define the terms as well as can be done, for clarity of understanding is necessary to meaningful debate.

Enjoy

... as you are new here, some posting tips:

type [qs]quotes are easy[/qs] and it becomes:

quotes are easy

or type [quote]quotes are easy[/quote] and it becomes:

quote:
quotes are easy

also check out (help) links on any formatting questions when in the reply window.

For other formatting tips see Posting Tips
For a quick overview see EvC Forum Primer
If you have problems with replies see Report Discussion Problems Here 3.0


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 1 by Hideyoshi, posted 09-11-2012 9:42 PM Hideyoshi has not yet responded

  
Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 4 of 15 (672901)
09-12-2012 10:01 AM
Reply to: Message 1 by Hideyoshi
09-11-2012 9:42 PM


The individual elephant living today in the Serengeti and the human living in Brooklyn today may have never gotten any closer than a cousin of a cousin of a cousin of a cousin of a cousin and all separated in existence by a hundred years or more.

I'm not sure how this is meant to work. If you and I are related by being descended from two people who were cousins, then those two cousins must have had a common grandfather, and who is our common ancestor. Or if they were second cousins, they had a common great-grandfather, who was our common ancestor. Or if they were third cousins twice removed, then someone was the great-great-grandfather of one of them and the great-great-great-great-grandfather of the other ... and so on.

In general, I don't see how you could have a scenario where two people (or elephants, or whatever) are related but don't have a common ancestor. What else is relatedness, when you get down to it?

(Obviously for the purposes of this discussion, being "related by marriage" doesn't count.)

So my brother and I have a common ancestor (my mother, to name but one); my father and I have a common ancestor (his father) my aunt and I have a common ancestor (my grandfather). My niece and I have a common ancestor (my grandfather again). My great-aunt and I have a common ancestor (my great-grandmother) ... and so on. You seem to be imagining that there's some degree of consanguinity by which two people (or elephants, or whatever) could be blood relatives but not have a common ancestor. Well, what is it?

Edited by Dr Adequate, : No reason given.


This message is a reply to:
 Message 1 by Hideyoshi, posted 09-11-2012 9:42 PM Hideyoshi has not yet responded

Replies to this message:
 Message 5 by Taq, posted 09-12-2012 10:45 AM Dr Adequate has responded

  
Taq
Member
Posts: 8207
Joined: 03-06-2009
Member Rating: 3.9


Message 5 of 15 (672911)
09-12-2012 10:45 AM
Reply to: Message 4 by Dr Adequate
09-12-2012 10:01 AM


I'm not sure how this is meant to work. If you and I are related by being descended from two people who were cousins, then those two cousins must have had a common grandfather, and who is our common ancestor.

Each cousin will also carry DNA from a set of grandparents that is NOT shared between the cousins. That DNA can be passed on to the next generation. An ancestral gene pool or population is a much, much better model.

Let's stay with these cousins as our example. Let's say that a mutation occurs in one set of grandparents that is not shared. This mutation would end up in one of the cousins, and this potentially important genetic marker would not be the result of common ancestry between the cousins.

Edited by Taq, : No reason given.


This message is a reply to:
 Message 4 by Dr Adequate, posted 09-12-2012 10:01 AM Dr Adequate has responded

Replies to this message:
 Message 6 by Dr Adequate, posted 09-12-2012 12:17 PM Taq has responded
 Message 7 by Straggler, posted 09-12-2012 4:02 PM Taq has responded

  
Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 6 of 15 (672923)
09-12-2012 12:17 PM
Reply to: Message 5 by Taq
09-12-2012 10:45 AM


Yes, but that's another question.

My question is, how can two people (or organisms) be related without having some individual who is their common ancestor? So far as I can see, they must do so simply by definition of "related" There has to be some point --- some individual --- at which their family trees meet, or they aren't related.

The author of the OP seems to be suggesting otherwise. He says: "The individual elephant living today in the Serengeti and the human living in Brooklyn today may have never gotten any closer than a cousin of a cousin of a cousin of a cousin of a cousin and all separated in existence by a hundred years or more." But surely he's wrong --- the closest that two organisms' family trees can get can never be distant cousinship, 'cos if they get that close then there must also actually be an individual common to both.

Edited by Dr Adequate, : No reason given.


This message is a reply to:
 Message 5 by Taq, posted 09-12-2012 10:45 AM Taq has responded

Replies to this message:
 Message 8 by Taq, posted 09-13-2012 11:52 AM Dr Adequate has responded

  
Straggler
Member
Posts: 10285
From: London England
Joined: 09-30-2006


Message 7 of 15 (672947)
09-12-2012 4:02 PM
Reply to: Message 5 by Taq
09-12-2012 10:45 AM


But the cousins in your example still share a common ancestor. If they didn't they wouldn't be related in any biological sense at all would they?

This message is a reply to:
 Message 5 by Taq, posted 09-12-2012 10:45 AM Taq has responded

Replies to this message:
 Message 9 by Taq, posted 09-13-2012 11:54 AM Straggler has not yet responded

  
Taq
Member
Posts: 8207
Joined: 03-06-2009
Member Rating: 3.9


Message 8 of 15 (673036)
09-13-2012 11:52 AM
Reply to: Message 6 by Dr Adequate
09-12-2012 12:17 PM


The author of the OP seems to be suggesting otherwise. He says: "The individual elephant living today in the Serengeti and the human living in Brooklyn today may have never gotten any closer than a cousin of a cousin of a cousin of a cousin of a cousin and all separated in existence by a hundred years or more." But surely he's wrong --- the closest that two organisms' family trees can get can never be distant cousinship, 'cos if they get that close then there must also actually be an individual common to both.

The author of the OP also said:

"Despite all this, when was the last time anyone described to the public or expected the public to assume that the term "the Common Ancestor" was actually plural, not necessarily distinct, and possibly metaphorical in nature? Is there simply a weakness in the definitions of our language, and we need a new word? Or does the existing terminology need to be readdressed and properly defined to those outside the biological sciences?"

So this is really about how scientists use the term. What scientists are ultimately concerned with is how a species got the DNA that they have. For cousins, they share DNA from multiple common ancestors, not just one. Each mutation and gene will have it's own lineage within the population, and each could coalesce to a different common ancestor. With sexually reproducing species it makes no sense to talk about an individual as a common ancestor, at least from a genetic standpoint. We could also talk about incomplete lineage sorting and the impact it has on determining common ancestry.

Ultimately, evolution comes back to genetics, and in genetics the common ancestor is a gene pool, not an individual.


This message is a reply to:
 Message 6 by Dr Adequate, posted 09-12-2012 12:17 PM Dr Adequate has responded

Replies to this message:
 Message 10 by Dr Adequate, posted 09-13-2012 12:11 PM Taq has responded

  
Taq
Member
Posts: 8207
Joined: 03-06-2009
Member Rating: 3.9


Message 9 of 15 (673038)
09-13-2012 11:54 AM
Reply to: Message 7 by Straggler
09-12-2012 4:02 PM


But the cousins in your example still share a common ancestor.

They share multiple common ancestors from multiple generations, each of which made different contributions to their genome.


This message is a reply to:
 Message 7 by Straggler, posted 09-12-2012 4:02 PM Straggler has not yet responded

  
Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 10 of 15 (673046)
09-13-2012 12:11 PM
Reply to: Message 8 by Taq
09-13-2012 11:52 AM


Yeah, but he's still wrong.

With sexually reproducing species it makes no sense to talk about an individual as a common ancestor, at least from a genetic standpoint.

No, not really. It would, of course be wrong to suggest that such an individual was unique, which I didn't. But they did exist. If humans and chimps (for example) have a species that is our common ancestor, then necessarily there was at least one individual in that species which was our common ancestor, because two individuals can't be related unless they have at least one common ancestor.


This message is a reply to:
 Message 8 by Taq, posted 09-13-2012 11:52 AM Taq has responded

Replies to this message:
 Message 11 by Taq, posted 09-13-2012 12:51 PM Dr Adequate has responded
 Message 15 by Hideyoshi, posted 09-15-2012 12:25 PM Dr Adequate has not yet responded

  
Taq
Member
Posts: 8207
Joined: 03-06-2009
Member Rating: 3.9


(1)
Message 11 of 15 (673060)
09-13-2012 12:51 PM
Reply to: Message 10 by Dr Adequate
09-13-2012 12:11 PM


It would, of course be wrong to suggest that such an individual was unique, which I didn't. But they did exist. If humans and chimps (for example) have a species that is our common ancestor, then necessarily there was at least one individual in that species which was our common ancestor, because two individuals can't be related unless they have at least one common ancestor.

I fully agree that there would be such an individual, and probably more than one.

But is that really what we are talking about when we reference a common ancestor? I would say no. That is not what we mean. When we say that humans and chimps share a common ancestor what are we really trying to describe? Well, we are ultimately talking about a speciation event where a single population split into two populations. The common ancestor would be the ancestral population that spawned the two separate lineages.

When we look at the fossil record we are forced to use the same concept. We have no way of determining direct ancestor/descendant relationships between fossils, barring the discovery of DNA in those fossils. We are forced to describe relationships through common ancestry, and once again these relationships are referencing an ancestral population.

The OP asked, "Despite all this, when was the last time anyone described to the public or expected the public to assume that the term "the Common Ancestor" was actually plural, not necessarily distinct, and possibly metaphorical in nature?". That is a great question. Perhaps we SHOULD stress what we really mean by common ancestry. It is trivially true that we can trace the lineages of any two organisms back to an individual who is a common ancestor, but that is not really what we are describing. I think it also causes confusion when we talk about mitochondrial DNA and y-chromosome MRCA's. It can cause people to think that ALL of our DNA came from those two individuals.

So should we be using something like "common ancestral population" instead of "common ancestor"? Perhaps we should consider it.


This message is a reply to:
 Message 10 by Dr Adequate, posted 09-13-2012 12:11 PM Dr Adequate has responded

Replies to this message:
 Message 12 by Dr Adequate, posted 09-13-2012 2:51 PM Taq has responded

  
Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 12 of 15 (673076)
09-13-2012 2:51 PM
Reply to: Message 11 by Taq
09-13-2012 12:51 PM


I fully agree that there would be such an individual, and probably more than one.

But is that really what we are talking about when we reference a common ancestor?

Well, we mean both. When we say that chimps and humans had a common ancestor, then we mean that there was some individual who was a common ancestor of both. And, of course, vice versa. We cannot say one without meaning (as a matter of logical necessity) the other.

And this is the only point that I'm trying to clear up. Admit that I'm right, which I clearly am, and we have no quarrel.


This message is a reply to:
 Message 11 by Taq, posted 09-13-2012 12:51 PM Taq has responded

Replies to this message:
 Message 13 by Taq, posted 09-13-2012 4:06 PM Dr Adequate has responded

  
Taq
Member
Posts: 8207
Joined: 03-06-2009
Member Rating: 3.9


Message 13 of 15 (673084)
09-13-2012 4:06 PM
Reply to: Message 12 by Dr Adequate
09-13-2012 2:51 PM


Well, we mean both.

My problem is my own biases in how I view it, so I would be happy to agree with that. I tend to stress the population over the individual common ancestor, but that doesn't necessarily have to be the case.

Admit that I'm right, which I clearly am, and we have no quarrel.

You are mostly right.


This message is a reply to:
 Message 12 by Dr Adequate, posted 09-13-2012 2:51 PM Dr Adequate has responded

Replies to this message:
 Message 14 by Dr Adequate, posted 09-14-2012 6:07 AM Taq has not yet responded

  
Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006
Member Rating: 8.3


Message 14 of 15 (673123)
09-14-2012 6:07 AM
Reply to: Message 13 by Taq
09-13-2012 4:06 PM


My problem is my own biases in how I view it, so I would be happy to agree with that. I tend to stress the population over the individual common ancestor ...

And so would I, but not to the point of denying the individual common ancestor. That's all that I'm trying to clear up.

You are mostly right.

Yeah, I mostly am.


This message is a reply to:
 Message 13 by Taq, posted 09-13-2012 4:06 PM Taq has not yet responded

  
Hideyoshi
Junior Member (Idle past 2554 days)
Posts: 5
From: Kobe, Japan
Joined: 08-16-2003


Message 15 of 15 (673178)
09-15-2012 12:25 PM
Reply to: Message 10 by Dr Adequate
09-13-2012 12:11 PM


I did not say they did not exist; but it's rather more like how we say a proton really and truly exists....but assure ourselves that a proton is not what we thought it was. Less a singular thing, and more a plurality of phenomena with a metaphorical center and boundaries.

One of the problems with the terminology of human geneaology is that it is meant to track things like a last name...singular, distinct, either yes or no; and you object to it being treated any other way. But in the biological sense, these gene sequences are not that way. Organisms have offspring and those offspring have offspring...but many of the gene sequences they had do not, in fact, pass along. Moreover, a gene sequence may be present in both mating partners, but will only have been contributed to an offspring by one of the mating partners. Random gene sequence that allows for multiple muscle cell division in the snout; that was a mutation within a population of cretaceous mammals and not shared by the population, say.

Again, this is not to say that common descent is not real; but rather that relatedness is not singular and distinct and literal to the individual as you intuitively think when you hear the term Common Ancestor.


This message is a reply to:
 Message 10 by Dr Adequate, posted 09-13-2012 12:11 PM Dr Adequate has not yet responded

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019