Evolution of Life

Lead: Nathan Battey

3/28/2013

Summary by Matthew Graef

How did Life Evolve?

Reading:

P. Shaver "Cosmic Heritage" Ch. 12, 13
R. Holmes III. "Three Big Bangs", p. 48-56

Nathan Battey led the first class discussion after spring break. It covered, as Nathan put it, “everything that happened since we don’t know what happened” – that is to say, the story of life after it first developed. He started the discussion by asking the class a question: what exactly is evolution?

Joshua Skersey first answered, stating that to him, evolution was the morphing of life. Life evolves when it changes and picks up useful traits. Justin Ykema offered an answer from a more philosophical point of view. He claimed that evolution was the reduction of evil, which he later clarified by adding that evil was the presence of negative effects, so-called ‘natural evil’.

This viewpoint was quickly challenged by much of the class. Professor deVries was uncomfortable with the definition, saying that the word ‘evil’ implied a value statement. Others cited examples of things that, on the surface, might seem evil but really aid in evolution. One such example was that of a forest fire, without which some kinds of pinecones cannot grow. The class teetered on the edge of a full-blown discussion of the nature of evil until the student withdrew his definition of evolution.

Nathan then proceeded to discuss various theories of evolution, from its earliest roots up to modern day theories. The group discussed the theories of Lamarck, as well as traditional Judeo-Christian ideas, and the modern take of Intelligent Design. With the exception of Lamarck, all of these were shown to be at odds with the current idea of natural selection, in that none of the theories held that species changed over time. It was discussed that some of the ideas of Lamarck (e.g. that actions or events during a creature’s lifetime can cause changes that are passed to its offspring) are now understood to have some merit. In particular, the field of epigenetics finds that genes can change the way they are expressed due to external influences, and that the change in expression can have immediate effects on future offspring. It was discussed that these are still relatively new findings and should be taken with a grain of salt.

The discussion then turned to the generally canonical interpretation of natural selection, the so-called modern synthesis. At its core, the theory of natural selection says that the strong will live while the weak will die. This is buttressed by caveats regarding natural pressures, such as natural disasters, and ‘neutral selection’, in which random mutations that do not directly influence fitness are responsible for much of the evolution of a species.  The modern synthesis also identifies DNA as the mechanism behind inheritance, and that evolution acts upon DNA. This theory holds that evolution is something that acts upon populations, but not on individuals.

At this point, the class reengaged in a discussion of epigenetics. In particular, the topic itself was defined as the study of how genes are expressed, and how this process may appear Lamarckian. Some of these changes include how immunity to certain diseases can be passed from a mother to a child. Another example is how certain enzymes in insects will respond to an insecticide. Even if the enzymes (and the production thereof) are expressed at low levels, their use in combatting the insecticide will increase their rate of production. Because this section of the insect’s DNA is being accessed more, this section of its genome is more susceptible to mutation. In this way, Lamarckian methods are playing a role in the evolution of a species.

The discourse then turned to discussion of the history of life on the planet. The last common universal ancestor existed between 3.5 and 3.8 billion years ago. Multicellular life emerged much more recently. A graph of species diversity over time was discussed, with particular interest on the various mass extinctions that have occurred throughout history. One student inquired into how biologists knew that such extinctions took place, and how certain they were as to biological diversity. It was explained that the level of diversity and knowledge of large-scale die-offs was found through the fossil record. The fact that certain fossils were not found above certain layers is indicative of extinction. When many species disappear at once, a mass die-off is inferred. In some cases, the external cause can be determined. In the geological layer between the K and T epochs, a thin layer of iridium is found. This element is usually only found in asteroids – indicating an asteroid impact. This layer is called the K-T boundary, and marks the mass extinction that killed off the dinosaurs. Some students voiced concerns that we may be entering into another mass-extinction event, driven by human actions. Opinions were varied, with some concluding that a mass extinction was already occurring, while others felt that the level of die-offs was overhyped.

From here, the discussion segued into a conversation about humans and human evolution. Several students mentioned that they felt that humans had removed themselves from the gene pool by saving those who would otherwise die. Some went as far as to say that humans were weakening themselves by allowing ‘flaws’ to enter the genetic code. Others pointed out that this was, in fact, evolution in action. Some discussed how these ‘flaws’ didn’t really matter, as we already had ways to overcome them.

From there, the discussion turned to recent human evolution. In particular, it was noted that human brain sizes have actually been shrinking in the last several thousand years, with much of that loss occurring in areas associated with aggression. It was hypothesized that this was due to humans ‘domesticating’ themselves in much the same way that dogs were domesticated. Others pointed to the removal of violent individuals from society in a regular manner, either by execution or imprisonment.

The class concluded with a discussion of the future of evolution on Earth. The danger of overpopulation was mentioned, especially in the context of a possible modern mass extinction. The ability for humans to wipe out life through nuclear war was discussed, especially in the wider context of humans as important caretakers of diversity. Some felt that humans had an obligation to protect diversity. It was mentioned that humans might play the role of a species that carried life to new places through the use of space travel. John Heavisides mentioned the fact that the Earth will only be habitable for 800 million more years, meaning that most of life’s time on Earth was already over. The final consensus was that humans were now a species of critical importance for the future of life – not only on Earth, but in the universe at large.