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

2/7/2011

Summary by Emily Pacetti

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

In order to fully appreciate the complexity of life, one must first acknowledge the multiple definitions and applications of the word. Dr. Tom Davis, having a biological background, led a discussion that revealed the diverse connotations of the word “life,” ultimately allowing us to interpret the different meanings and relate it to our being. The word “life” to one person could refer to the possibility of extraterrestrial life, while to another it could spark interest in life after death. As individuals, “life” could encompass numerous meanings, including synthetic life, the diversification of life, and its origin. Since the scope is so broad and can have multiple interpretations, there is the necessity for a universal definition to divide the broad range into general categories. There are two main definitions of life; life as a property and life as a category. Life as a property is specified as the unique or defining characteristics of living things. An example of life as a property could include telling someone they look lively for a Monday morning. This would suggest the person was energetic, or perhaps noticeably enthusiastic. In this sense, life or lively is used to better describe a characteristic or emotional quality of the noun, while life as a category is used to describe the actual physical state of the noun. To distinguish between these two definitions, one might want to consider the example of a classroom of students early on a Monday morning. Physically they are alive, but, at the moment, don’t exhibit emotional characteristics associated with being “lively”. Life as a category is divided into physically living and non-living. Although it may be easy to tell the students in the classroom are alive, the simplicity of differentiating between alive and dead in other situations can be deceiving. To attempt to eliminate or minimize the grey area between life and death, a list of six qualifications was devised for life as a category.

Life is extremely diverse and can range from the smallest microbes to the largest and most complex mammals. In order for organisms to function, they rely on the combination organic and inorganic molecules to carry out necessary functions for life. They also use elemental cations and anions for many vital processes. Although organisms can seem extremely different based on their external appearance or perhaps the habitat where they live, the fundamentals remain consistent throughout, ultimately deeming the organism as living. The first condition is a molecular structure, composed of an aqueous medium (H20) encompassing organic molecules. In addition, there must also be a cellular or subcellular structure. The third requirement is the ability to use metabolism, or the chemical reactions responsible for producing usable energy. This can either be in the form of catabolism, where organic molecules are broken down, or anabolism, where organic molecules are built. The fourth stipulation includes the demand for the organism to have a genetic system, where genes are expressed so it can carry out all functions and have a physical structure. The genes provide the genetic blueprints for the organism and are necessary for their day to day function, as well as their actual physical existence. The genetic information also allows the organism to maintain its identity, ultimately distinguishing between what becomes a whale, elephant, mouse, etc. Another important factor is the ability for the organism to reproduce. If the organism can’t reproduce, then there will be no progeny to replace the organism when it dies, and the species would die out. Reproductive ability allows for the long-term continuation of life. If organisms were unable to reproduce, the organism technically would never have existed itself, because there was no way for it to be produced without being birthed, or a product of its parents. The last condition states the organism must be able to change or evolve over time, according to Darwin’s evolution, in response to environmental stimuli.

At this point in the discussion, many questions were raised that criticized the necessity of all of these rules. Viruses were the first entity that presents a problem when trying to classify it as either living or non-living. Viruses contain nucleic acids, proteins, and sometimes a lipid membrane; however, they lack a cellular structure or metabolism. They are able to reproduce, but only if they infiltrate a host and use its cells and mechanisms for replication. They can also change and evolve as they become more resistant when exposed to different kinds of medication. To this day there are groups of scientists who argue viruses are living, while the opposing side argues they are non-living. Another example that fits some of the criteria but lacks essential qualities is that of organisms that are sterile and can’t reproduce. Mules (female donkey x male horse) and hinnies (female horse x male donkey) are quiet obviously living, however, most are unable to reproduce because they result from hybrid crosses between two different species of animals. In order to minimize the gray area, Dr. Davis emphasized metabolism, maintenance of structure, and genetic system as the most important characteristics of life.

Although life is evident on Earth today, the condition of the planet wasn’t always able to sustain life, sparking the question of when it emerged. Using the qualifications of life today, scientists can make inferences based on laws, properties, and explanatory paradigm as to the origin of life. Darwin’s Evolutionary Theory offers a compelling explanation of most of what we know about the diversification of life. However, when one goes back to a certain point eventually his theory will not be applicable. According to Darwin’s theory, species change in response to environmental stimuli and also have the ability to branch off and form new species. All organisms also have a common ancestor called LUCA, or the last universal common ancestor. Species evolution also exhibits gradualism, or small incremental changes over a large span of time. According to classical Darwinism, organisms are the product of chance and necessity. Mutation and natural selection are the major driving forces and are unavoidable. Mutation can happen in many ways, but is random and doesn’t arise based on the organisms’ need. Mutations can be detrimental or beneficial to the organism. Organisms are also subject to natural selection, or adaptation in response to the environment. Although one might be able to predict favorable traits in a specific environment, there is no overall direction of natural selection other than to maintain or enhance fitness, so its outcome is unpredictable. Neo-Darwinism is the modern synthesis, incorporating and stressing the influential role genetics and stochastic processes plays in diversity and genetic drift. Integrating Mendelian genetics into Darwin’s theory of evolution highlights the important role of the genetic system in relation to natural selection and mutation in organismal diversification.

Using information available today, it has been estimated life originated on Earth between 3.5-3.8 billion years ago. Life can be traced back to LUCA through three major kingdoms including bacteria, eukarya, and archaebacteria. The three major explanations for the start of life on Earth discussed in class were earthly origins, panspermia, and designed origin. Some believe that life had to begin on Earth because we haven’t found any other life in the universe, so therefore it had to start here. People who support the idea of panspermia believe life originated and formed elsewhere and then came to this planet. This means they believe life is extraterrestrial in origin. People who believe life was designed think it is too complex and can’t be accounted for by natural causes. This group concludes life is evidence of intelligent design.
Whether life originated here on Earth, or elsewhere, it does spark the question of how new life can be created in a lab. Since life arose relatively quickly after the formation of the Earth, it suggests life is resilient. If life arose so quickly, is it a common occurrence and has it happened more than once? In reality, the time available to create and research life in a lab doesn’t come close to the amount of time and opportunity available during its actual creation. 100 million years can’t be approximated by the amount of time available in lab, especially since we can’t recreate or be sure of the environment that prompted the response. When it comes to recreating this phenomenon in a lab, Dr. Davis brought up how a laboratory successfully synthesized some genetic constituents of a particular cell. The individual parts were then inserted into a new cell, providing the ability to function as a whole. Some interpreters of the lab’s work suggested this was the synthesis of new life, while Dr. Davis along with others question if a synthetic genome is equivalent to synthetic life. Dr. Davis brought up the fact that all parts of the cell could be replaced, but it wouldn’t be able to function as a whole if the cell wasn’t already living. In order to understand when an organism is considered alive, one must also understand when it is dead. It was brought up how it is more difficult to mark the death of an organism than to determine death on a cellular level. A person can have brain damage and be alive, while there was obviously considerable cellular death. This concept must be taken into account when determining if a synthetic life has been created on the cellular level opposed to at an organismal level. This sparked some debate over cloning, and whether this was the creation of new life. Dr. Davis as well as many students in the class believed this isn’t the creation of life, but rather just the replication or copying, easily separating it from creating something new.

Although there wasn’t much debate during the class period, many good points were raised, especially towards the end of class. I brought up the point that in order for metabolism to occur, genes must be expressed, so wouldn’t DNA or nucleic acids need to be present on Earth before actual organisms? Unfortunately, the class period finished before this question could be answered, but it did continue to make me wonder if DNA was being transcribed and translated in some sort of process before our definition of life could be applied. Although the discussion did continue when the class period was over, the lecture portion did highlight the complexity of life, its origin, and future applications of its properties.