Life

[modest]

Originally Posted by HydrogenBond

What I am saying is simple single cell life either got stuck in evolution or formed after the original formation. It may be right on schedule if one assumes a more abbreviated evolutionary schedule. Those little guys make new cells all the time. Calculate the mutations for 1 billions years. How do they avoid this impulse for major change and stay simple?

All I am doing is using Darwinism and selective advantage. What is the advantage of staying close to the beginning of evolution? If there is an advantage to not evolving very far, selective advantage can also mean very slow evolution or no evolution at all.

One possible way to explain it, is evolution is a group event. In other words, there is always a bell curve of evolution with the sideline critters of the curve offering logistical support for life forms closer to the top of the curve. The simple stuff stays stuck so it can continue to offer logistical support for the money area of the evolutionary curve.

I see what you're saying.

I think the answer you're looking for is sex... er.. sexual reproduction.

For the first 2 or 3 billion years or so life got along developing quite slowly. It's a very long time for nothing much to happen - and indeed nothing much was happening as mother earth had not yet invented sex.

Single celled organisms reproduced via mitosis which means the cell splits into two exact copies of itself like Kirk on Star trek. This apparently isn't the most efficient way for evolution to advance life. Diversity isn't a quickly developing asset when everything is cloning itself. The circumstantial evidence of this is the 2 to 3 billion years of slow evolution.

Then God (or shall I say evolution) saw fit to endow these pathetic little lifeforms with a truly marvelous gift. Meiosis. Without getting into all the sticky details - let's just say its a new spin on reproduction. This happened some 1.2 to 2 billion years ago.

Shortly after the greatest invention of all biological history on earth - evolution took off. We soon had animals, plants, fungus, etc - all who evolved from one group of particularly randy little archaea that decided to be the progenitor of the entire eukaryote family.

Indeed, bacteria (and their like) that seem to be stuck in the evolutionary mud are mostly the lifeforms that evolved separate from those of us that have that key ingredient we love so much. Don't feel bad for them. All life was that way for at least 2 billion years. Besides....

Have you considered what we gave up for that key ingredient? Bacteria never die. They just divide. The stuff that's growing in your sink has been alive in one form or another since the genesis of life. We... well, we traded in immortality for a short life spent chasing Nikki around the dorms when I knew she was never gonna leave her boyfriend for me. I just loved the way she wore those cute little clips in her hair. I wonder what she's up to these days.

What was I talking about?

-modest

[raghu]

Originally Posted by Modest

Have you considered what we gave up for that key ingredient? Bacteria never die. They just divide. The stuff that's growing in your sink has been alive in one form or another since the genesis of life. We... well, we traded in immortality for a short life spent chasing Nikki around the dorms when I knew she was never gonna leave her boyfriend for me. I just loved the way she wore those cute little clips in her hair. I wonder what she's up to these days.

What was I talking about?

I think the last para explains the paradox posed by H-bond.

One can't really term multi-cellularity as evolutionary more advanced, & never
as evolutionarily more advantageous.

There are advantages, as well as disadvantages of multi-cellularity; one of which Modest has talked about, & many others, which are discussed in the paper given below.
So, there's sort of a trade-of between the two, at certain conditions, unicellularity might prove to be more advantageous than multi-cellularity, & at others, vice-versa!

An excellent example of this trade off is the dictyostelids:
a group of cellular slime moulds

When food (normally bacteria) is readily available they take the form of individual amoebae, which feed and divide normally. However, when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium or slug (not to be confused with the gastropod mollusc called a slug). The slug has a definite anterior and posterior, responds to light and temperature gradients, and has the ability to migrate. Under the correct circumstances the slug matures forming a fruiting body with a stalk supporting one or more balls of spores. These spores are inactive cells protected by resistant cell walls, and become new amoebae once food is available. -From Wiki

http://dictybase.org/tutorial/about_dictyostelium.htm

Dictyostelium amoebae grow as separate, independent cells but interact to form multicellular structures when challenged by adverse conditions such as starvation. Up to 100,000 cells signal each other by releasing the chemoattractant cAMP and aggregate together by chemotaxis to form a mound that is surrounded by an extracellular matrix. -From: dictybase

However, I'd like to point to a recent paper by Martin Willensdorfer, freely available at:

[0801.2610v1] On the evolution of differentiated multicellularity

On the evolution of differentiated multicellularity

Author: Martin Willensdorfer
(Submitted on 17 Jan 2008)

Abstract: Most conspicuous organisms are multicellular and most multicellular organisms develop somatic cells to perform specific, non-reproductive tasks. The ubiquity of this division of labor suggests that it is highly advantageous. In this paper, I present a model to study the evolution of specialized cells. The model allows for unicellular and multicellular organisms that may contain somatic (terminally differentiated) cells. Cells contribute additively to a quantitative trait. The fitness of the organism depends on this quantitative trait (via a benefit function), the size of the organism, and the number of somatic cells. This model allows one to determine when somatic cells are advantageous and to calculate the optimum number (or fraction) of reproductive cells. I show that the fraction of reproductive cells is always surprisingly high. If somatic cells are very small they can outnumber reproductive cells but their biomass is still less than the biomass of reproductive cells. Only for convex benefit functions can the biomass of somatic cell exceed the biomass of reproductive cells...

This paper talks about the trade-offs of multi-cellularity, in comparison with freelancer unicellular micro-organisms.
It discusses conditions where the multi-cellularity would confer an advantage to the organism, & those, where the unicellulars would have an edge over the multi-cellular organisms.

Hope that the paradox is resolved for now!

[coldcreation]

Originally Posted by modest

...
Then God (or shall I say evolution) saw fit to endow these pathetic little lifeforms with a truly marvelous gift...

Are you saying that god and evolution are interchangable? Let's put it this way: I don't understand your use of "god" in a discussion about biological evolution. It's almost like discussing evolution in a theology forum.

Or, are you just being provocative?

What gives...

[modest]

Originally Posted by coldcreation

Are you saying that god and evolution are interchangable? Let's put it this way: I don't understand your use of "god" in a discussion about biological evolution. It's almost like discussing evolution in a theology forum.

Or, are you just being provocative?

What gives...

That's rich CC.

You'll notice my entire reply above is layer upon layer of innuendo and double meaning. I wrote it that way intentionally. When I say Meiosis is the greatest gift ever given by god... or some such... well... I'm sure you understand what I mean.

I may not believe in god, but if Natalie Portman showed up at my door right now, I'd thank him till the day I die.

-modest

[modest]

Originally Posted by coldcreation

I don't understand your use of "god" in a discussion about biological evolution. It's almost like discussing evolution in a theology forum.

Or, are you just being provocative?

Off topic here, but I went on about this in applicability of deistic analogy and allegory

-modest

[Moontanman]

One more possible life bearing moon!

Could There Be Life On Saturn's Moon Enceladus?

[Thunderbird]

Originally Posted by HydrogenBond

What I am saying is simple single cell life either got stuck in evolution or formed after the original formation. It may be right on schedule if one assumes a more abbreviated evolutionary schedule. Those little guys make new cells all the time. Calculate the mutations for 1 billions years. How do they avoid this impulse for major change and stay simple?

All I am doing is using Darwinism and selective advantage. What is the advantage of staying close to the beginning of evolution? If there is an advantage to not evolving very far, selective advantage can also mean very slow evolution or no evolution at all.

One possible way to explain it, is evolution is a group event. In other words, there is always a bell curve of evolution with the sideline critters of the curve offering logistical support for life forms closer to the top of the curve. The simple stuff stays stuck so it can continue to offer logistical support for the money area of the evolutionary curve.

The boundary is one of functions. simple single cell inhabit a simple fitness space, or environments therefore stay simple. Cells that inhabit the complex fitness space, of the internal environment of an animal have adapted to a more complex symbioses. The environments are hierarchal and serve as structural foundations, and functional supports.

[Moontanman]

Originally Posted by HydrogenBond

What I am saying is simple single cell life either got stuck in evolution or formed after the original formation. It may be right on schedule if one assumes a more abbreviated evolutionary schedule. Those little guys make new cells all the time. Calculate the mutations for 1 billions years. How do they avoid this impulse for major change and stay simple?

All I am doing is using Darwinism and selective advantage. What is the advantage of staying close to the beginning of evolution? If there is an advantage to not evolving very far, selective advantage can also mean very slow evolution or no evolution at all.

One possible way to explain it, is evolution is a group event. In other words, there is always a bell curve of evolution with the sideline critters of the curve offering logistical support for life forms closer to the top of the curve. The simple stuff stays stuck so it can continue to offer logistical support for the money area of the evolutionary curve.

It could also be that environmental conditions stopped life from becoming more complex. Too hot or even too cold restricts complex life on the Earth. At long as tempertures stayed above (I think) about 45 degrees C complex life could not evolve. Only after cooling oceans, a slow down in impact events, and oxygen in the atmosphere could complex life develop.