Life As We Know It and Its Evolution
Lead: Thomas Davis

2/7/2011

Summary by Elora Demers

Life As We Know It and Its Evolution

Reading:

R. Dawkins "The selfish Gene", Ch. 2
E. Mayr "One long Argument", Ch. 4, 5
Stannard, God for the 21st Century, Part 2
Foreword of "Origins of Life

This discussion encompassed many topics relevant to the knowing of life, such as:
• What is life – by definition?
• What is alive?
• The existence of life
• The diversity of life
• The origin of life
• The significance of life

There are many ways that one can define life; the life we know can be compared to non-life, but there is also the possibility of life we don’t know. Life as a property can be considered a unique or defining characteristic of living organisms. Life as a category, however, can be considered as “Life on Earth” which classifies living versus non-living. Other manners of defining life are as having or being capable of these characteristics:
• Diversity – animals, plants, fungi and microbes
• Composition – H, O, N, C, S, P, etc.
• Molecular Structure – organic molecules in a aqueous solution
• Cellular and subcellular structure
• Metabolism – catabolism (digesting) and anabolism (building complex molecules)
• Growth and reproduction
• Genetic system – DNA --> RNA --> Proteins
• Capability of Darwinian Evolution.

It is by this definition that scientists generally classify viruses as non-living, because they are missing a few basic components of life – cellular structure, metabolism and growth. From these collective definitions we must realize that biological “living” things as we know them are structurally complex, physical entities that dynamically maintain their organic molecular structure via the internal use of chemical energy. And we think that the collective sum of life has arisen from living predecessors and diversified into species under the influence of Darwinian natural selection.

In the class discussion that arose from this, we considered that though this definition of life is adequate and understood, there is still a fine line between the actual death of a cell and the death of an organism, since in humans, we know that brain cells can die, causing a person to be clinically brain dead, but their body can be kept alive. Multiple members of the class brought up the issue of brain death versus being in a coma. When someone is brain dead there is extremely minimal brain activity, sometimes not even enough to sustain the body’s mandatory functions; someone in a coma has more measurable brain activity. In this way, in regards to humans, part of the organism (body) can survive even if the person (mind) is unresponsive/dead. The difference between brain dead and regular coma is that sometimes people awake from a coma and remember what happened around them while they were comatose; this shows that they were still conscious and aware of their surroundings even though they didn’t actively show it.

After this, the actual accounting of existence was discussed, because what good is discussing life if we don’t exist? In the same way that physicists have used the laws of nature to retrodict how the universe as we know it came from the Big Bang, biological scientists have used the principles of Darwinian Evolutionary Theory to retrodict how life as we know it is derived from the origin of life, but since Darwinian Theory depends on reproduction, we can only retrodict back to the origin of reproducing and evolving organisms. The issue with this is that it is not plausible that organisms sprung to life with the complex reproduction system we know of, so we can only trace reproducing organisms back so far before we hit a wall.

Our theory of how life evolved and diversified came from Darwin, but has been modified in recent years to become what is known as the Neo-Darwinian Paradigm. From Darwin we know that change over time, aka evolution, occurs gradually as new species arise from a common ancestor by the mechanism of natural selection. The Modern Synthesis added to this the genetic mechanism of evolution and the neutral theory, which says that evolution can happen by chance or natural selection.

Dr. Davis explained that mutations are inevitable within a population and are random with respect to need, but are required for evolution. With evolution comes natural selection, which selects for beneficial adaptations within a species due to changes in environmental circumstances. The Neo–Darwinian Theory tells us that mutations and genetic recombination continuously generate hereditary diversity, but that due to the limitations of environmental carrying capacity, natural selection is propelled by excess reproduction, differential fitness and environmental change. Natural selection is one way in which the Earth makes sure its carrying capacity is not exceeded. Evolution can be considered unpredictable, because of the occurrence of random mutations, but it can also be thought of as semi-predictable, because of the tendency of a species to better adapt to its environment. As with any theory, however, there are people who support it and then there are those that don’t. The proponents say that since we can witness evolution happening and it is consistent with the physical laws, it explains the appearance of design. The opponents question the validity of the fossil record, which has been used as proof of change over time, and say that organisms are too complex to have evolved and thus must have been the product of design, which is in essence the theory of intelligent design.

Despite controversy, the origin of biological life is believed, in the scientific community, to have been approximately 3.5-3.8 billion years ago. Since the exact origin is unknown, we discussed three of the popular theories on this topic: the emergence of life from nonliving matter on Earth (i.e., an RNA based origin), panspermia–meaning that life came to Earth from another place, and intelligent design, meaning that there is an intelligent designer who created life on Earth. What is known is that the oldest cellular fossil is about 3.5 billion years old, which means that life appeared quickly after we think the environment of the Earth became hospitable. This fact could show the resilience of life and that it happens whenever there is an opportunity and that it is inevitable; or it could mean that the existence of life is extremely rare, and the conditions just happened to be perfect here. Though resilience versus rarity was discussed, there really is no way to resolve that argument in any way, unless we discover life somewhere else in the universe. Some said that the presence of organisms in extreme environments, like thermal vents, shows the resilience of life, but the evolution from one common ancestor shows the rarity of life forming. These are both just possible explanations, it is also possible that life arose many times and that life as we know of was the strongest form and wiped out all others.

It was brought up by a few members of the class that even though there is a lot that is speculated about the origin of life, scientists have not yet been able to produce life from nonliving components in a laboratory setting. The synthetic “life” that was documented and popular in the news a few months back was actually a synthetic genome that was put into an already existing membrane, and thus the organism was not truly created from scratch. It is reasonable, however, that we have not yet created synthetic life, because the exact conditions at the moment of formation of life are still only speculated and even in those conditions it could have taken thousands or millions of years – we just don’t know. In regards to this idea of creating synthetic life, it was brought to the class’ attention that though the parts and pieces of a cell can be replicated in a lab individually, it is the actual dynamic “environment” and interaction of the cellular pieces within a cell that constitutes life.

From all this discussion, we know that life is complex, but we still don’t know how it could have arisen. Dr. Davis’s recipe for basic life is a compartment, so the inside and outside are distinguished, plus metabolic processes, as a means of self–maintenance, plus a genetic system, to provide an operational and developmental “blueprint”, and some means of reproduction to perpetuate the species. People are slowly coming to accept the possibility that both a cellular membrane and metabolic processes could have arisen from nonliving material, but many people are stumped by how a genetic replication system could have spontaneously developed. This is because DNA is a complex molecule, which gets transcribed into RNA, which then helps make proteins. This is a logical progression, but, unfortunately, to translate the RNA into proteins, proteins are required. Thus this becomes one of the ultimate chicken-or-the-egg problems, because, as we know it, RNA cannot create a protein without the help of proteins but we do not know of any other system that could have evolved into what we have now.

To wrap everything up, Dr. Davis quickly touched on the significance of life, and though that may mean many things to many different people, we touched on it in relation to the universe. This is where the importance of consciousness comes in, because as was quoted “without consciousness, there can be no meaning” – there is no life and no consciousness, how can the universe mean anything or even be acknowledged; thus is life a necessary part of the universe? And to end the class, Dr. Davis left us with this: If consciousness is a prerequisite for meaning, is life a prerequisite for consciousness, or is consciousness simply fundamental and irrevocable?