Principia

Hi guys,

I heard this argument today during a discussion of evo-cre with my fellow Christian colleagues. They claim that most Christian biologists find no conflict between the Bible and their work because inevitably they believe that certain questions cannot be tested scientifically. For example, they asked me why almost all life have a capacity to reproduce in a manner that attempts to replicate their genetic information. I admitted that I had no good explanation. It dawned on me that evolution and natural selection implicitly assumes that any form of life must reproduce.

Has anybody here heard this kind of argument as an implication for some Creator (or IDer)? In the end, it seemed like this question was begging a meaning-of-life debate. Is there a good way to respond to this kind of idea?

Thanks,
SC

Mageth

For example, they asked me why almost all life have a capacity to reproduce in a manner that attempts to replicate their genetic information.

I can't think of any kind of life that doesn't attempt to pass on ("replicate") at least some of its genetic information during reproduction.

It dawned on me that evolution and natural selection implicitly assumes that any form of life must reproduce.

Any form of life that doesn't reproduce wouldn't stick around very long, would it? And since "reproduction" in life as we know it requires genetic information, it's no surprise that the reproducing organism passes on its own genetic information to its progeny.

Read "The Selfish Gene" by Richard Dawkins if you haven't. There it's posited that reproduction is genetic information (genes) using "life" (the organism) to replicate itself.

NialScorva

You kinda have this backwards. Evolution explicitely applies only to forms of life that reproduce. A hypothetical form of life that didn't reproduce in any way wouldn't be affected by evolution, and you wouldn't expect to see anything beyond the first "generation". It's not an assumption, it's a requirement. Remember too that evolution is a *description* of what we see. Since we only see reproducing life around us, there's no need to explain non-reproducing life.

Principia

Good point guys,

But the question put before me was why 'genetic reproduction.' In other words, why not a membranous bag of chemical substances that could replicate its contents from raw material (e.g. water, oxygen, etc.)? Or maybe even a membranous bag of enzymes that function to replicate its contents?

My imagination is limited, but I suppose the question I felt was being asked was why DNA? I know there are theories about auto-catalytic RNA, but RNA by itself does not reproduce.

SC

theyeti

That's pretty much what living things are. Membranous bags of enzymes that function to replicate themselves.

Quote:

My imagination is limited, but I suppose the question I felt was being asked was why DNA? I know there are theories about auto-catalytic RNA, but RNA by itself does not reproduce.

If you want chemical reasons, protein and RNA are too unstable to make for good permanent storage of information. Proteins function according to their 3-dimentional shape, but that can be easily disrupted by changes in temperature and/or pH. They also get damaged. That's why there is a fair ammount of turnover when it comes to cellular proteins. Most importantly though, proteins don't act as a template for their own replication (except for some rare small peptides). They don't have the base-pairing complementation that nucleic acids do.

RNA, on the other hand, can serve as a template for its own replication. It's quite probable that life originated from an "RNA world" in which self-replicating, catalytic RNAs were abundant. But RNA's problem is that it lacks chemical stability. The 2' OH group on the ribose does a nucleophilic attack on the phosphate to disrupt the polymer. Given the rate of spontaneous decay, RNA life is impossible with all but the smallest of genomes (like retroviruses). DNA, on the other hand, lacks that 2' OH group (hence the name, 2' deoxyribonucleic acid), so it is much more stable than RNA. DNA probably evolved afterward, or what pressed into service at some point, as a permanent storage facility for the information contained in RNA.

theyeti

mac_philo

Well, I wouldn't call it an assumption. You have to be clear on the order.

Natural selection can only arise in the context of differential replication. The 'winning' traits become dominant because they get duplicated.

Dawkins says that, if there is any one thing that unites all forms of life (terrestrial or otherwise) is the differential replication of information. For us, DNA.

mac_philo

Now that I've read the thread I see my point was made several times already. Ho-hum.

Anyway; why not a membraneous sack? Why not, indeed!

Because your sac has no 'syntax', no information, no directions.

Genetic replication is not special because of the double helix, or the ACTG code, or any other physical fact. It is special because its structure contains information.

Describe a sac that contains information and then we'll all agree it could be the basis for replication.

Principia

I am in danger of making arguments for the opposing case... I guess the question is whether life could exist in the absence of nucleic acids. For instance, scrapies is a disease in which a diseased enzyme changes the conformation of the native enzyme to its diseased state. Of course, in this example, DNA is already involved in churning out the enzyme.

I guess it is difficult to imagine life other than DNA/RNA/proteins. But that lack of imagination was the problem I had. Did 'evolution' select for nucleic acids for reproduction (even though it makes little sense to speak of evolution in the absence of life)? What reproductive advantage was conferred specifically to an enzyme/RNA system that any other organic compounds could not achieve?

But, then once we get answers to the above questions, comes the real conundrum for me. Is a self-reproducing system inevitable? In other words, in an energetically favorable system with adequate resources, would some form of self-reproducing mechanism *always* develop? Of course once a reproducing system is in place, then it makes sense to have a mechanism like natural selection to improve upon the system.

I am reminded of Conway's game of life. The analogy to this question seems to be a random process of throwing dots onto the playing field while the game is continously evolving. What is the probability that the right combination of dots appear to generate a pattern that is either persistent or reproduces?

I'm getting a mild headache, but I appreciate any additional thoughts.

SC

tronvillain

Scientiae:
Actually, I think it's entirely possible that such replicating systems preceeded the use of nucleic acids as a genetic material. Sort of a progression from analogue to digital.

Quetzal

Scientiae: I'm with tron on this. What you've described lies at the heart of Cairns-Smith's clay abiogenesis hypothesis (and no, gang, before you jump all over me, I don't find the argument that compelling - it's just that the question keeps coming up and Cairns-Smith is the best analogy my poor brain can come up with).

Anyway, the idea is that crystals exhibit some properties that are normally attributed to life. They self-replicate, using chemicals in the environment, by a preferential layering (i.e., each layer of crystal is identical to the one below). There's an analogy for heritable variation, since flaws in one layer tend to propagate into subsequent layers. There's something like reproduction, where a piece can break off and provide a seed for the growth of an identical crystal. There might even be something akin to natural selection, where certain arrangements of crystals are more "successful" in capturing chemicals to add to their matrix than others because of chemical composition - meaning that they would be more likely to continue growing.

I guess your friends would need to define "life", before you could argue one way or the other. Just some food for thought.