The Origin of Life, Lead: Thomas Davis

2/6/2007

Summary by Sam Meehan

The Origin of Life

This discussion during this class period was led by Professor Tom Davis of the Department of Plant Biology. Professor Davis began by briefly touching upon the origin of the universe as the main starting point of the class. He said that there are difficulties in this area of study arising from the main problem; that we are constituents of the universe, and thus it is hard to study it from an outside view. This stretches the capacity of imagination and from it arise many unanswered questions. However, beyond the scope of the origins of our universe, the next major question that follows is, “How did we come to be here?” In the discussion that ensued, Professor Davis wished to touch upon the topics of what life truly is, the origins of life, and the “emergence” of life in our universe.

To begin, the discussion of how life began and how we as beings came about, it is important that we understand what life actually is. To do this, it is logical to first define “life”. However, this is not a simple task and so rather than creating a single definition, we first give a piecewise description through comparison to other entities. This description began by saying that we can look at life as we know it and ask, “With respect to what is this life distinct?” Two possible comparisons for this description of life would be saying that life is distinct from non-life as well as death. The difference between life and non-life is straight forward. Entities of life include everything that is covered in our definition of life while non-life is anything else that does not fall under this same definition. The distinctness from death is better understood through transitions. To be alive, an object (being, body, thing, etc.) had to go through some transition to be considered such and has to go through a similar transition to be considered death. Thus, because there is a distinct transition for each, the same being cannot be both alive and dead at the same time.

A second platform to which life can be compared to is life as we may not know it. This description considers the possibility that life may exist elsewhere and that this life may be radically different from that which we presently know. This “life”, if found, may prove very difficult to study. It would not be encompassed in our normal definition of what life is because our definition applies to life as we know it through observation. Such new forms, if recognized as a new type of life, would force the definition of life to be broadened in order to include them. At this point, Davida H. brought up the point that there are things observed on Earth that are difficult to classify as being distinctly life or non-life. She cited viruses and spores as two examples. In response to this, Professor Davis suggested that in a more general sense, life can be classified as such by the conditions of reproduction, growth, and development. However, then the question might arise whether an individual that cannot perform one or more of these functions at the time of observation, is alive or not. The answer to this question should be kept flexible so as to allow for special cases. Viruses and spores serve as an example of a special case. These can be frozen for extended periods of time and although they are not actively pursuing reproduction, growth, or development, they still have the capacity to do such. Thus, it would seem as though they can still be considered life. Professor Davis suggested that viruses are not considered life when studied independent from everything else but when taken in the context of existence as a whole, they can be considered life because they participate in a “life cycle”. As far as spores and viruses are concerned, it was agreed that it is not appropriate to say that they are not alive solely because they sometimes are inactive for long periods of time. This is not appropriate because they may eventually show metabolic processes or reproduce. However, a conclusion concerning the definition of life formed by studying the viruses and spores was not made at this point.

Returning to the topic of life as we do not know it, Professor Davis suggested that there may be multiple possibilities for its type of existence. This would result from the discovery of entities that are not yet included in our definition of life but would seem to be a new form of life. First, this new life may be carbon based in a way similar to life as we presently know it but be different in its genetic code. Thus, it may possess certain similarities but great differences in some ways. Second, it may be possible that this new life would be a non carbon based structure and in this sense be very different from what we presently know life to be. From this idea arises the question as to what type of environment would be needed to sustain such a type of life. It may be very similar to our own with exceptions that distinguish it from Earth that would explain the different traits of the new life found there. However, there is also the possibility that it may be radically different from any type of life sustaining environment we presently know. The third possibility suggested is that life as we do not know it may be “non biological” life. The term “non-biological”, when applied to life, can be very difficult to understand. This difficulty is partially alleviated when the possibility is opened that machines may constitute life as we do not know it and thus fall under this category of non biological life. At this point, Professor Moebius asserted the NASA definition that, “life is a self-sustained chemical system capable of undergoing Darwinian evolution”. Using this definition, one can imagine a society of robots built by mankind who operate independently of man. These robots can build themselves (reproduce) and can maintain themselves and regenerate their power supplies through various mechanical and chemical processes (metabolism). Although they do not contain DNA as we understand it, this component of life would be contained within the software with which they are programmed. This begs the question as to whether this engineered society could be considered life. This suggestion showed how comparing natural and artificial life is beneficial provides another way to view the entity of life as we do not know it.
A final view would be to consider existence after death. It is necessary to say existence after death because if it were stated as life after death, it may seem as though this new existence is classified as a form of life. This is also made difficult because it would contradict our original observation that life is distinct from death through the transition to each. However, if it were thought of as such, it would seem that life after death may constitute another form of non biological life.

Professor Davis then brought the attention of the discussion to the topic of life as we do know it by saying that in introductory biology classes, and even for many professional biologists, it is difficult to say what life itself is. Rather, it is more feasible to list a set of characteristics inherent to observed life. The list presented by Professor Davis was:
- Complex Systems – cellular components
- Metabolism
- Genetic Systems
- Growth, Reproduction, and Life Cycle
- Darwinian Evolution?
This list brought about much discussion. By this type of classification it seems as though we must decide on the set of things that are being observed and characterized before we design a definition of life that will describe these things. This would seem to be an infinitely recursive process. However, Professor Moebius commented that for all we do, we always list components of the system and create distinguishing factors in hindsight of the situation. This allows us to find what is common among a group of beings that we do not find in others. Following this, Professor DeVries observed that some of the components on the list, such as metabolism and genetic systems, are recent developments in science. Furthermore, he said that the Greeks defined life as being the internal principle of motion. From this basic idea, we had a basic definition from which to build. Professor Davis opened the idea that there has been a historical evolution of the definition of life and that its scope of inclusion has increased over time. A final comment pertaining to the list came from Professor Moebius. He asserted that if we narrow the list too much and we base our distinction on only a few conditions, there is the possibility that things may be considered life that would normally not be classified as such. He cited the water cycle as an example because in a sense it fulfills the requirement of Growth, Reproduction, and Lifecycle but is not recognized by society as being life as we know it.

Professor Davis then went forward to say that at the heart of the question of what is life are the characteristics that life is cellular in nature and that these cells are maintained by some sort of metabolism. If there is no metabolism then there is no life. Professor DeVries contested that if we abide by this description, then before 1800 there was no life because we had not yet discovered metabolism or the cellular structure. He then posed the question as to whether we are redefining life by what we presently know. No definite answer came from this point, and the discussion shifted focus.

Professor Davis then presented several examples of life (strawberries and fungus) and prompted all to consider what these things have in common. He then presented something that he said he, “may or may not have gotten from the MIT advanced robotics laboratory.” When first revealed, what he was holding appeared to be a cockroach. However, there was skepticism because of his previous comment. Furthermore, he asked whether the creature he was holding would be considered living or not.

To this question, he responded that it could be said to be alive if it fulfilled the three requirements of life; growth, reproduction, and life cycle. However, this three part descriptive definition breaks down if only a single cockroach is considered, because under this condition, reproduction can not occur and therefore the single cockroach is not considered life. However, by this argument, it would seem that one can find limiting factors on anything that is to be considered life.

Professor Moebius then suggested that the definition of life itself changes due to the context within which it is used. This was followed with a comment from Professor DeVries. He said that the reason the definition of life changes is because our methods of observation change over time. Thus, the apparent complexity of something changes over time and so must the definition. Professor DeVries used the classification of the element gold (Au) as an example for how our understanding changed from a macroscopic definition in terms of malleability and density to the microscopic properties of specific weight and atomic number.

Propelling the discussion, Professor Davis posed the question as to whether it is possible to create life in a laboratory setting. He said that he would consider life to be successfully created in a lab if cells were to be made from scratch. This is something that has not been done but new discoveries lead science ever closer to having the capability to create such entities. Professor Davis then commented on the effects of the involvement of prizes in scientific discovery. If such prizes were to exist for the creation of life in a laboratory, then it would be necessary to define life so that it can be known when life is created. The first step in the creation of a life form would be to engineer a cellular structure in which life could exist. Following this advancement would be creating a system of metabolism by which the cell maintains its structure. In addition to this metabolism, an associated genetic structure would need to be created so that the metabolism could function properly. However, unlike previously, this life that is created would not have to reproduce. Sam Meehan then commented by asking, “If to be considered life, a being has to reproduce, then is reproduction a requisite of living?” Using this logic, it would seem that if a human spans their entire life without procreating, then they have never lived. This does not fit with what seems to hold that all humans are indeed alive and so causes for confusion when viewing human beings as a natural example of life. However, Professor DeVries quickly asserted that the distinction must be made between actual reproduction that occurs and the classification of being of the type that has the ability to reproduce.

After discussing what life is and how we can attempt to define life and thus classify different forms of existence as such, Professor Davis began the discussion of the origin of life. There were two main distinctions of thought with respect to this subject. One question is, “Did life get started?” and the other question is, “Has life always existed in the universe as we know it?” If in our thought we obey what Professor Moebius presented as the origin of the universe, then life had to start at some point. This idea arises because in the early universe, there was no carbon and because life as we know it is carbon based, there could be no life. Professor Moebius then spoke on the topic of how heavy elements required for life (carbon, iron, etc.) formed in the early universe as the result of fusion of hydrogen and helium in heavy stars. Mike Dunn then commented that the heaviest element that could be formed from this process was iron but that there are many more elements we presently observe past iron in the periodic table. Professor Moebius agreed with Mike but said that during a supernova, high enough energies are attained to form heavier elements and so explain the elements beyond iron.

The discussion of the origin of life then moved to another pressing topic concerning life. By our understanding of cosmology, life could not have existed forever inside out universe and on Earth because of the conditions at and prior to the big bang. One theory that addresses how life came to exist on Earth is panspermia. Panspermia is the theory that life originated somewhere inside our universe but not on Earth and through processes such as meteor strikes, migrated through the universe and came to Earth. If this theory is correct then many people would wonder why we are searching for the origins of life on Earth instead. Professor Davis and Professor Moebius described this through the story of the man who was searching for a set of keys under a street light one night. When asked where he last saw his keys, the man responded, “In the dark alley over there.” Then when asked why he was searching under the street lamp and not near the alley, the man responded, “Because this is where the light is.” In the same manner, the origins of life may be found somewhere else but we study the Earth because it is where the “light” is.

Professor Davis then presented a timeline of our universe. The age of our known universe is 13.5 billion years old and the Earth is 4.5 billion years old. The first fossil evidence we have, and thus the point of earliest observable life is 3.6 billion years old. However, it is believed that the Earth was inhospitable until 3.8 billion years ago. This is only a 200 million year delay between the origin of Earth and the origin of life. Comparing this to the age of the Earth, it seems as though life “began” quite quickly. Furthermore, it makes it seem as though “life just happens” under the right conditions. It also leaves open the possibility that life may have previously begun but was destroyed by an outside force and so the origin of life that we know is that which evolved to the present state of life.

In the timeline of life, the gap between the first cellular life observed and the present condition of life has been bridged to a great extent by Darwinian evolution. However, there is the giant step from the state of non-life to life that still looms over this timeline. What is known is that in the early age of the hospitable Earth, there was a very rich environment containing a large amount of prebiotic soup. It is surmised that in this early age of the Earth, the conditions were conducive to the beginning of life. Indeed, it spontaneously occurred at some point. Chris Rothschild then asked, “If we were able to create the exact same initial conditions today in a laboratory that were present in the distant past, could we just wait and allow life to happen?” Professor Davis answered by saying that there was a very large volume of prebiotic soup on the early Earth and this contributed to a better opportunity for the creation of life. Sam Meehan then asked if the origin of life in the prebiotic soup was spontaneous, then would it be possible to calculate the probability of it occurring under the same conditions. Professor Davis extended his last answer by saying that there were so many conditions that it would be extremely hard to take into consideration all factors that contributed to life to make this calculation.

The discussion of the origin of life on a very basic level continued as Professor Davis listed three characteristics that life, when coming into existence from non-life would need to have. In order of increasing difficulty, these three components are (1) cellular compartments, (2) metabolism, and (3) a genetic system.

The easiest of these three characteristics to create, and thus the simplest to be created naturally are cellular compartments. The reason this is a key characteristic of life is because all cells that make up living things have cell membranes to separate them from the outside world. To demonstrate the formation of an analogous membrane, Professor Davis mixed water and oil in a test tube and gently shook the mixture. Because these are two different substances, the physical interactions between the individual molecules cause the oil to form into many small spheres whose surface resembles a membrane. Something similar may have happened at the beginning of life when the first cell membrane bi-layer was formed. Professor Moebius asked whether this would be possible in the case of performing the same experiment using ammonia. It was agreed that this could be possible because ammonia, like water, is a polar molecule.

Now that there are membranes in which life can reside, it is necessary for a type of metabolism to be created by which the membrane is preserved and energy is supplied. The form of metabolism common to all life is glycosis in which processes involved are catalyzed by enzymes. However, it has been observed that some forms of metabolism are catalyzed by minerals, of which there were many on the early Earth.

The focus of the discussion then moved on to the topic of genetic systems that would need to be present in early life for it to be considered life. The manner in which DNA works causes for a recursive cycle that can be fairly confusing. DNA produces RNA from which proteins are formed. These proteins do the catalytic work involved in the metabolic processes of cells to provide energy and maintain the structure of the cell. Some of the processes involved in the work are carried out by DNA. Although the DNA reproduces itself in a cyclic process, the difficulty arises in starting the production process so as to enter the cycle. This is the “big black box” of life as we know it. When this topic was presented, Chris Rothschild suggested that one possibility is the RNA world theory. This theory for the beginning of life suggests that in the pre-biotic soup, some RNA species were created that had limited capabilities to reproduce. If there are instances of self-replication then the Darwinian theory of evolution can come into play and the strongest and most capable strands of RNA would survive and reproduce. This theory is based on contemporary observations of some RNA molecules that have catalytic properties. These catalytic properties allow for some RNA to carry out tasks that are usually performed exclusively by proteins.

This led us to the end of discussion around the fundamental question, “How did life begin?” Although we never were fully able to answer this question, we began by describing, as best we could, what life is in a fundamental sense. After finding key components of life, we studied how the type of life we described may have been able to form from a natural point of view. Finding answers to these questions, however incomplete they were, was very difficult. It raised the question as to whether life began from totally natural processes or if there were components involved that would qualify as intelligent design. This left the door open at the end of the class to further discussions on more focused topics concerning the vastness of life and existence.