Life as We Know it and its Evolution, Lead: Thomas Davis

1/31/2005

Summary by Ed Bourbeau:

Life as We Know it and its Evolution

Readings:
"God for the 21st Century" Part 2, by Russell Stannard ed.
Foreword of “Origins of Life”
R. Dawkins “The Selfish Gene”, Ch. 2
E. Mayr “One Long Argument”, Ch. 4 & 5

The third meeting started with Dr. Davis stating that "the universe is meaningful because there are beings that can experience it".  Humans are the ones who give our universe meaning because we are the ones experiencing it.  This concept was the basis of a very discussion-based session, indeed.

            The first question posed in the discussion was, plainly put, "How did we get here?"  In order to come up with a plausible answer as it relates biologically, we have to start about 3.8 billion years ago.  This number is based on fossil evidence of the oldest forms of life.  We can compare this number to the time of the "Big Bang" (about 13.7 billion years ago) and the age of the earth itself (about 4.5 billion years old).  In order to draw parallels between life now and life 3.8 billion years ago, we have to observe how life functions now and assume that the processes that govern life have remained largely unchanged throughout time. 

            Gaining an understanding of what the earth was like billions of years ago is also a key to furthering our understanding of life.  We have to turn to evidence from our solar system to get an idea of what Earth was like before it could support life (also referred to as the prebiotic world).  At some point the earth was too hot and dry but then it cooled off and life could begin to thrive.  In the grand scheme of things, it did not take long for life to begin once the world was able to foster such endeavors.  That is not to say, however, that life may not have had several so-called false starts before finally staying on the planet for keeps.  That is to say it is possible that several geological events have wiped out several versions of life on earth before life finally prevailed. 

            Simply because there is life on Earth today does not mean it originated here.  It was to deal with this notion that Dr. Davis introduced the concept of panspermia.  Panspermia is, simply put, the theory that life on Earth came from extraterrestrial sources.  The idea is fascinating but a criticism of it is that it doesn't get us any closer knowing where or how life was created.  This theory sparked the first question from the class in what turned out to be a rather discussion-oriented evening.

           Mark: How probable is it for an organism to survive space travel?

Dr. Davis: Bacterial spores can survive for millions of years and if reasonably protected, could travel through space.  So it is reasonably probable.

           Dr. Davis went on to say that most of life traveling through space is probably some sort of spore as opposed to some complex organism.  There are even amino acids and sugars found in outer space.  However, if the form of life that may have come to Earth several billion years ago came today, it would probably die due to changes in the environment.  For instance, initially life was anaerobic but the oxygen level in the atmosphere continued to rise, causing many organisms to become aerobic.  Also, as Dr. Davis pointed out, organisms that arrive from outer space today would probably be eaten by terrestrial life forms.  Another question was asked relating to the beginnings of life.

            Steve: What parameters made life possible in the beginning?

            Dr. Davis: Liquid water and cool enough temperatures allowed life to develop.

After all the talk about lineages and origins Dr. Davis thought it would be helpful to define the idea of the transformations of life with an analogy.  The Cake Analogy was used to demonstrate that transitions of life were not sudden; they started out on some low level, like cake batter as it goes into the oven, and continuously evolved into some recognizable form of life, which would be like the fully-cooked cake.

            At this point, Dr. Davis set out to define life by giving the following list of characteristics life should possess.

1.     Ordered Structure.

2.     Cellular Structure

3.     Sensitivity

4.     Regulation

5.     Homeostasis

6.     Metabolism

7.     Growth (growing larger), Development (growing more complex), and Reproduction

This list was not meant to be the defining line of what characteristics all life must possess. For example, elderly women lose the ability to reproduce but they are still living beings.  On the other hand entities such as viruses, which are nothing more than inert matter, could not be defined as living creatures because their means of existing are based entirely upon surviving off a host organism that is alive.

Dr. Davis then presented the astrobiology definition of life:
"Life is a self-sustaining chemical system, capable of undergoing Darwinian evolution."

It was at this point that the group really began to get involved in the discussion.  The following are some of the questions and comments that were made:

            Beth: Where do parasites fit into the definition of life?

            Dr. Davis: "Self-sustaining" applies to its environment.  If we have access to food, we can sustain ourselves.  Viruses, on the other hand, are host-specific and are nothing more than inert matter.  They provide the host with blueprints to produce more of the virus.  Living things must have chemical involvement with their environment in order to support themselves.

            Dr. Möbius: Are we blurring the mechanical/biological boundary?  Nanotechnology has the ability to arrange itself like organisms in a host, for example.

            Dr. Davis: Getting back to the cake metaphor, this may be a case of "half- baked life".  Robots do not constitute a chemical system.  They are engaging in a mechanical system.  Can consciousness come from a machine?

            Dr. Möbius then briefly discussed a computer program that could simulate Darwinian evolution.  He talked about how the program evolved and how the machine could figure ways around having parts of its programming deactivated.

            Beth: Isn't the criteria of life that it can fight entropy?

            Dr. Davis: "Life" is maintaining a complex structure by using energy.  Materials are taken from the environment in order to maintain itself and reproduce.

            Alicia: Why does the definition of life include "Darwinian evolution?"

            Dr. Davis: In order for life as a general phenomenon to get past "half-baked",Darwinian evolution needs to kick in.  It is the only plausible naturalistic way that life may have taken off to create what we see now.

            After that discussion, another one started up concerning the difference between "alive" and "dead."  Steve mentioned that he had heard of some frozen frogs in the Antarctic that stayed in stasis for months at a time and wondered if they could be considered "alive" even though they did absolutely nothing.  Dr. Davis responded by saying if the frog could be reanimated then it was never dead.  When a cell dies, its structure falls apart rapidly and does not recover from that.  There is a loss of order and metabolism.

            Mark: Wouldn't the breakdown of DNA cause death?

            Dr. Davis: DNA could be removed and put back in, and life will go on.  DNA is a key part to evolution and self-sustaining, but if is removed from a cell, no one would know how to take DNA and make it into a cell.  When a cell dies, nothing can be done; it's dead.  DNA can be removed and the cell doesn't necessarily die immediately.

            Dr. Davis explained the notion of reproduction by saying that there are individuals that lose the ability to reproduce or never had it to begin with.  Darwinian evolution requires reproduction.  Reproduction should not be an initial requirement to life, but rather something that Darwinian evolution reinforced upon the first organism that acquired this ability.  The possession of life may be determined without knowledge of the Darwinian evolution of that organism, however.

            Dr. Davis went on to say that the origins of life had to have structure, and furthermore, that there were three main steps in the transition of life:

1.     The structure needs a compartment (a cell).

2.     Metabolism has to happen (involving catalyst enzymes in cells).

3.     There eventually needs to be some hereditary material present (genetic material).

Dr. Davis then told this class about a man named Guenter Wächtershauser, who studied how various metabolic systems could have originated.  He noted that iron and sulfur ions acted as catalysts in a number of simple reactions.  In the early years of life on Earth, there was water and rocks which held sulfur, iron, and other elements and minerals that could act as chemical catalysts.  Negatively charged minerals present on the rocks reacted with the positively charged catalysts in the water to form larger organic molecules, polymers, and perhaps initially simple RNA molecules.

The session was concluded with a brief overview to try and tie up a few loose ends.  He stated that somewhere in the prebiotic world there were RNA molecules that had catalytic properties and could do some of the things proteins can do now. This scenario is called the "RNA world". Also, the prebiotic world experienced Darwinian evolution, before there was actually cellular life.  Life and Darwinian evolution can exist independently of each other, but when they come together things can really take off.