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Author Topic:   What IS reproduction?
RAZD
Member
Posts: 20156
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.9


Message 1 of 9 (560496)
05-15-2010 3:15 PM


I'd like to bring together parts of three current threads and look at one aspect that pertains to each of them.

First we have Are there evolutionary reasons for reproduction?:

quote:
MrQ Message 1
The question is in all texts of evolution life correlates to reproduction and reproduction is a key driving force in the evolution process. ... I mean, reproduction is very energy consuming process. ... if we assume the life came from organic molecules in the earth atmosphere or in a primordial soup, why on earth should a molecule suddenly decide to reproduce ...

Then from Definition of Life

quote:
RAZD Message 69
See wikipedia
http://en.wikipedia.org/wiki/Life
particularly the "conventional definition
http://en.wikipedia.org/wiki/Life#A_conventional_definition

While there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life exhibits the following phenomena:

1. Organization - Living things are composed of one or more cells, which are the basic units of life.
2. Metabolism - Metabolism produces energy by converting nonliving material into cellular components (synthesis) and decomposing organic matter (catalysis). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
3. Growth - Growth results from a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter. The particular species begins to multiply and expand as the evolution continues to flourish.
4. Adaptation - Adaptation is the accommodation of a living organism to its environment. It is fundamental to the process of evolution and is determined by the organism's heredity as well as the composition of metabolized substances, and external factors present.
5. Response to stimuli - A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. A response is often expressed by motion: the leaves of a plant turning toward the sun or an animal chasing its prey.
6. Reproduction - The division of one cell to form two new cells is reproduction. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from at least two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.

(bold in the original)

(note the second wiki link above works, but it takes you to the same place as the first wiki link and should be replaced by
http://en.wikipedia.org/wiki/Life#Biology)

and

quote:
Mr Jack Message 70
The trouble with any definition of life that includes reproduction is that excludes the many examples of things we'd call alive but don't reproduce: the sterile, the elderly and the unlucky. So you end up having to be rub in a side order of "potential to reproduce" or "from a class that reproduces" which again muddy the issue and, even then, reproduction is, itself, not exactly a trivial concept to clearly define.

And finally from Self-sustained Replication of an RNA Enzyme

quote:
dcarraher Message 39
A Living Cell, on the other hand, has ... information contained in its DNA - e.g. how to build a protein. The ability to build a copy of itself is not a characteristic of its physical binding chemistry, it is a process that requires messengers and translators. Replicating RNA replicates because of its chemical characteristics, not because of the information it contains that can be interpreted.

Noting that dcarraher apparently draws a distinction (whether it is valid or not) between DNA replication and RNA replication, it seems appropriate to delve into this in a little greater detail.

He also says:

quote:
Message 30
Because the experiment starts with something that is clearly non-life, and ends with more of something that is not significantly different. You started with the ability to replicate, and ended with the ability to replicate - you did not add the ability to replicate, nor did you add any other "life-like" characteristics. Ergo, irrelevant to the question of abiogenesis.

Now of course the point of the thread is that the RNA is self-replicating rather than just being replicated within a cell as part of the process of reproduction

Is this self-replication life? Without a clear definition of life it is difficult to say. Is a virus alive? This depends on your definition of life.

Is this self-replication a feature of life as we know it? Yes, it is common to all organisms during reproduction that all the elements of a cell are replicated.

Reproduction is commonly listed as an element of life, as seen in the wiki article above, and a critical part of reproduction is the replication of the material within a cell so that another cell is formed.

At its most basic level, cell reproduction occurs by:

  1. the accumulation of additional basic cell materials (the "structural" parts of the cell), and
  2. self-replication of the core molecules, the DNA, and
  3. division of material into two or more cells.

This holds for prokaryotes and eukaryotes, for single cell life and multi-cellular life, for asexual reproduction and the reproduction of cells within sexual organisms.

As such, I would propose that self-replication of the core molecules is a better defining feature of life than reproduction.

Enjoy.

Edited by RAZD, : added (c)


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 ...
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Replies to this message:
 Message 3 by Phage0070, posted 05-16-2010 12:27 AM RAZD has responded

  
AdminSlev
Member (Idle past 2931 days)
Posts: 113
Joined: 03-28-2010


Message 2 of 9 (560553)
05-16-2010 12:01 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the What IS reproduction? thread in the Proposed New Topics forum.

  
Phage0070
Inactive Member


Message 3 of 9 (560558)
05-16-2010 12:27 AM
Reply to: Message 1 by RAZD
05-15-2010 3:15 PM


RAZD writes:

As such, I would propose that self-replication of the core molecules is a better defining feature of life than reproduction.

Isn't that just another way of distinguishing number 6 "Reproduction" from number 3 "Growth"? It doesn't seem like a new concept, just another way of describing reproduction.

In fact I take it back; it doesn't really distinguish reproduction from growth at all. Growth for many organisms involves the reproduction of the core molecules, so that definition would be a subset of both growth and reproduction.

Depending on how you viewed things, reproduction wouldn't necessarily require the duplication of the core molecules. If you view reproduction as when organisms split into individuals you could get really technical and mark the point when the DNA itself is split. The reproduction of the other half would then simply be growth; after all it is simply building on the core molecules that already existed in the new individual. A half-split DNA strand then could be half-individual, and growing.

In any case, I view the definition of life as largely irrelevant. "Life" isn't an inherent quality of any organism, it is an emergent property we choose to define (very poorly). A proper definition is not required to understand anything about the organisms, etc.


This message is a reply to:
 Message 1 by RAZD, posted 05-15-2010 3:15 PM RAZD has responded

Replies to this message:
 Message 4 by RAZD, posted 05-16-2010 9:53 AM Phage0070 has responded

  
RAZD
Member
Posts: 20156
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.9


Message 4 of 9 (560593)
05-16-2010 9:53 AM
Reply to: Message 3 by Phage0070
05-16-2010 12:27 AM


Hi Phage0070, thanks.

Isn't that just another way of distinguishing number 6 "Reproduction" from number 3 "Growth"?

In fact I take it back; it doesn't really distinguish reproduction from growth at all. Growth for many organisms involves the reproduction of the core molecules, so that definition would be a subset of both growth and reproduction.

Perhaps you are confusing the growth of a multicellular organism (by adding cells) with the growth of individual cells.

quote:
Growth results from a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter.

The cells increase in size.

Growth can occur without the replication of the core molecules.

A virus replicates without itself exhibiting growth - it hijacks the materials from another system\biology.

quote:
Reproduction is commonly listed as an element of life, as seen in the wiki article above, and a critical part of reproduction is the replication of the material within a cell so that another cell is formed.

At its most basic level, cell reproduction occurs by:

  1. the accumulation of additional basic cell materials (the "structural" parts of the cell), and
  2. self-replication of the core molecules, the DNA.

This holds for prokaryotes and eukaryotes, for single cell life and multi-cellular life, for asexual reproduction and the reproduction of cells within sexual organisms.


Part (a) can be viewed as growth, while part (b) would a part of reproduction that is different from growth.

I should add (c): division of material into two or more discrete units. This division is also a critical element of life that is not exhibited by other things that grow (crystals for instance).

Depending on how you viewed things, reproduction wouldn't necessarily require the duplication of the core molecules. If you view reproduction as when organisms split into individuals you could get really technical and mark the point when the DNA itself is split. The reproduction of the other half would then simply be growth; after all it is simply building on the core molecules that already existed in the new individual. A half-split DNA strand then could be half-individual, and growing.

And yet a cell that is undergoing the process from replication of the core molecules to division, is distinguishable from other cells that are only exhibiting growth.

Or you end up with two kinds of growth, and you need to distinguish one from the other ...

In any case, I view the definition of life as largely irrelevant. "Life" isn't an inherent quality of any organism, it is an emergent property we choose to define (very poorly). A proper definition is not required to understand anything about the organisms, etc.

So at what point does this property emerge during the development of life from chemical precursors?

Enjoy.


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 3 by Phage0070, posted 05-16-2010 12:27 AM Phage0070 has responded

Replies to this message:
 Message 5 by Phage0070, posted 05-16-2010 11:08 AM RAZD has responded

  
Phage0070
Inactive Member


(1)
Message 5 of 9 (560604)
05-16-2010 11:08 AM
Reply to: Message 4 by RAZD
05-16-2010 9:53 AM


RAZD writes:

Perhaps you are confusing the growth of a multicellular organism (by adding cells) with the growth of individual cells.

It is both. For a single-celled organism it is simply the cell increasing in size/mass, but for a multicellular organism it includes the addition of new cells.

RAZD writes:

And yet a cell that is undergoing the process from replication of the core molecules to division, is distinguishable from other cells that are only exhibiting growth.

You missed my point; you could technically view a reproducing cell halfway through copying DNA as half-individual, with an extraordinary level of resource sharing between those individuals. The purpose of doing that would be to distinguish growth from reproduction, by making the definition so particular that it turns normal cell reproduction into a nearly inextricable combination of reproduction and growth.

Simplification of the terms then complicates our interpretation of the event. This leads into my last point...

RAZD writes:

So at what point does this property emerge during the development of life from chemical precursors?

Whenever we decide it qualifies.

Think of it like the colors red and yellow; at what point does red become yellow as you move up the spectrum? There are certain points where almost everyone will agree that it is red, or yellow, but in the middle it gets fuzzy. We might even subdivide it into the uncertain range being called orange, but then where does the transition between yellow and orange, or red and orange occur?

Our subjective definition of colors is irrelevant to being able to get from one color to another through increasing or decreasing the frequency of the light. It is such an issue because creationists are making what amounts to an argument from incredulity, saying that life cannot come from unlife. This is tantamount to saying that red cannot come from yellow; the dividing line, or lines between subdivisions between those points, can be placed anywhere by the individual observer. In every case the separating point of that distinction would be overcome by an extremely slight modification of frequency.

Coming up with a universal definition of colors so that definition can be made would be useless, as the color-creationists would simply reject it so that they could hang on to their belief that you cannot get from red to yellow. Instead we should point out that wherever you draw the line it is a very slight modification to get to the next step, so they will have to show a reasonably large void in the steps. If there was some large gap of light frequencies between red and yellow that could not exist, then they might have a point. The same holds true for creationist claims, if they could produce such a gap.

Instead they cling to an unknown subjective definition of life which will travel like a greased-up deaf guy to avoid being nailed down, where the argument from incredulity can be destroyed. It is just a waste of time and we are better off doing something else.


This message is a reply to:
 Message 4 by RAZD, posted 05-16-2010 9:53 AM RAZD has responded

Replies to this message:
 Message 6 by RAZD, posted 05-16-2010 3:30 PM Phage0070 has not yet responded

  
RAZD
Member
Posts: 20156
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.9


Message 6 of 9 (560628)
05-16-2010 3:30 PM
Reply to: Message 5 by Phage0070
05-16-2010 11:08 AM


Hi Phage0070,

It is both. For a single-celled organism it is simply the cell increasing in size/mass, but for a multicellular organism it includes the addition of new cells.

In other words yes, you are lumping them together. As I said, however, if you include reproduction in growth then you have to define two kinds of growth, reproductive growth and non-reproductive growth.

If we define life at the cellular level, then organisms that are multicellular are still included, and the only issue for multi-cellular life then is whether it is a colony or a single organism.

You missed my point; you could technically view a reproducing cell halfway through copying DNA as half-individual, with an extraordinary level of resource sharing between those individuals. The purpose of doing that would be to distinguish growth from reproduction, by making the definition so particular that it turns normal cell reproduction into a nearly inextricable combination of reproduction and growth.

No, because I think your conflation of reproductive growth with non-reproductive growth is muddying the waters and that this is what leads to your problems.

In the context of defining life there is no need to have reproductive growth and reproduction in the definition, so a parsimonious definition should just stick to non-reproductive growth as an element of life.

Likewise, when we discuss reproduction, we should not include the elements that are part of normal (non-reproductive) growth: the self-replication of core molecules and cell division into new cells.

Whenever we decide it qualifies.

Think of it like the colors red and yellow; at what point does red become yellow as you move up the spectrum? There are certain points where almost everyone will agree that it is red, or yellow, but in the middle it gets fuzzy. We might even subdivide it into the uncertain range being called orange, but then where does the transition between yellow and orange, or red and orange occur?

Our subjective definition of colors is irrelevant to being able to get from one color to another through increasing or decreasing the frequency of the light. It is such an issue because creationists are making what amounts to an argument from incredulity, saying that life cannot come from unlife. This is tantamount to saying that red cannot come from yellow; the dividing line, or lines between subdivisions between those points, can be placed anywhere by the individual observer. In every case the separating point of that distinction would be overcome by an extremely slight modification of frequency.

Coming up with a universal definition of colors so that definition can be made would be useless, as the color-creationists would simply reject it so that they could hang on to their belief that you cannot get from red to yellow. Instead we should point out that wherever you draw the line it is a very slight modification to get to the next step, so they will have to show a reasonably large void in the steps. If there was some large gap of light frequencies between red and yellow that could not exist, then they might have a point. The same holds true for creationist claims, if they could produce such a gap.

Instead they cling to an unknown subjective definition of life which will travel like a greased-up deaf guy to avoid being nailed down, where the argument from incredulity can be destroyed. It is just a waste of time and we are better off doing something else.

Agreed, however this has little to do with what reproduction is or isn't.


 a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z 
_|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|__|_

In the context of reproduction as an element of life, we can say that having self-replicating molecules is somewhere in the orange sector: it is something that rocks, water, crystals and other non-living (inorganic) chemical objects do not have, and so it is no longer in the red zone, but somewhere between (a) and (i).

Likewise fission, the division of a cell (which is also poorly defined, and somewhat circular in the above definition of life re organization) into two or more similar functional units.

Uranium may fission into two distinct elements, but neither of the product elements is uranium.

Crystals can fracture into smaller crystals, however this fracturing is not caused by the crystal itself.

So again, the elements of reproduction that are critical to the definition\existence of life is that self-replication of core molecules occurs and cell division occurs.

Note that I find the element of organization to be poorly defined:

quote:
1. Organization - Living things are composed of one or more cells, which are the basic units of life.

This is circular if we say life has organization and organization means things are built with bits of life.

IMH(ysa)o it would be better to say

1. Organization - Living things are are organized into one or more discrete units composed of different functional elements that work as a unit to accomplish metabolism, growth and reproduction.

This also helps to draw the distinction between growth and reproduction.

Enjoy.


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 5 by Phage0070, posted 05-16-2010 11:08 AM Phage0070 has not yet responded

Replies to this message:
 Message 7 by Modulous, posted 05-16-2010 5:49 PM RAZD has responded

  
Modulous
Member (Idle past 395 days)
Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 7 of 9 (560637)
05-16-2010 5:49 PM
Reply to: Message 6 by RAZD
05-16-2010 3:30 PM


In other words yes, you are lumping them together. As I said, however, if you include reproduction in growth then you have to define two kinds of growth, reproductive growth and non-reproductive growth.

If we define life at the cellular level, then organisms that are multicellular are still included, and the only issue for multi-cellular life then is whether it is a colony or a single organism.

I appreciate for theoretical discussion it is useful to differentiate these - but this is usually within the context of a certain kind of life where a universal method for discriminating between 'somatic' reproduction and 'germline' reproduction (for lack of better terms) might be available. I'm not sure this has much utility (or feasability) when considering the entirety of life.

Though maybe I'm wrong. Do you think it is possible to describe a working understanding of the processes so that in each case we could differentiate between (mere) somatic reproduction of a single cell from germline reproduction leading to a new 'individual'?

This might require being able to strictly identify 'individual' which may prove to be interesting...

Is there some key difference between a bunch of bacteria engaging in binary fission and human skin cells? I honestly don't know.

Edited by Modulous, : No reason given.


This message is a reply to:
 Message 6 by RAZD, posted 05-16-2010 3:30 PM RAZD has responded

Replies to this message:
 Message 8 by RAZD, posted 05-17-2010 7:36 PM Modulous has acknowledged this reply

  
RAZD
Member
Posts: 20156
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 3.9


Message 8 of 9 (560808)
05-17-2010 7:36 PM
Reply to: Message 7 by Modulous
05-16-2010 5:49 PM


Hi Modulus, thanks.

I appreciate for theoretical discussion it is useful to differentiate these - but this is usually within the context of a certain kind of life where a universal method for discriminating between 'somatic' reproduction and 'germline' reproduction (for lack of better terms) might be available. I'm not sure this has much utility (or feasability) when considering the entirety of life.

Though maybe I'm wrong. Do you think it is possible to describe a working understanding of the processes so that in each case we could differentiate between (mere) somatic reproduction of a single cell from germline reproduction leading to a new 'individual'?

I'm not sure we need to do this as yet. I'm thinking (a) in the context of the definition of life, a minimal and basic form of reproduction, at the cellular level, and (b) about the original process of reproduction at the early stages of life, and looking to establish what that consists of: the kind of reproduction that would be useful in determining whether abiogenesis has occurred.

Perhaps later on we can get to the application of reproduction to multicellular life (and what distinguishes it from colonies of cells).

This might require being able to strictly identify 'individual' which may prove to be interesting...

Indeed. As an example we all think of ourselves as individual organisms, and yet we rely heavily on many different kinds of bacteria to help break down and digest food and to protect our skin, etc. so that we are really a colony of many organisms.

Is there some key difference between a bunch of bacteria engaging in binary fission and human skin cells? I honestly don't know.

My understanding is that the (eukaryotic) cell reproduction is the same process in these two cases. There is a slight difference (simpler system) for the prokaryotes (no nucleus, no mitochondria).

If we take reproduction in prokaryotes first, as an initial simple system, then we can break it down into three basic elements:

  1. the accumulation of additional basic cell materials (the "structural" parts of the cell), and
  2. self-replication of the core molecules, the DNA, and
  3. division of material into two or more cells.

As noted above, element (a) is cell growth, and elements (b) and (c) are the elements specific to reproduction.

Enjoy


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 7 by Modulous, posted 05-16-2010 5:49 PM Modulous has acknowledged this reply

  
Dr Jack
Member (Idle past 396 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 9 of 9 (561386)
05-20-2010 9:33 AM


Abiogenesis vs. the generic
It occurs to me that the question of abiogenesis isn't really about the development of life from non-life. What abiogenesis needs to explain is how we get from "mere" chemicals to a self-replicator capable of surviving, multiplying and crucially evolving.

Although I suspect the first such replicators would be nothing we would recognise as life, evolution can then bridge the gap between there and organisms such as cyanobacteria we do recognise as life.


  
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