Descent With Modification: A Darwinian View of Life

Big Ideas Explored in this Unit: Big Idea 1: The process of evolution drives the diversity and unity of life. Big Idea 3: Living systems store, receive, transmit, and respond to information essential to life processes.

Defining Evolution Evolution is defined as the idea that living species are descendants of ancestral species that were different from the present day ones. Other ways of saying this are: Change in the genetic composition of a population from generation to generation. Descent with modification.

Syncholora aerata as a model for evolution Syncholora aerata (common names are wavy-lined emerald moth and camouflaged looper) This illustrates three major concepts about life: The ways in which organisms are suited for their environment The shared characteristics of life The large diversity of life

Timeline of Historic Events

Why Darwin’s Ideas Appeared Radical At the time the earth was considered by most to be relatively young (by comparison to its actual age) and Darwin challenged the preconceived notions of that time period.

Scala Naturae and Classification of species Greek philosophers were amongst the first to suggest that life changed over time. Aristotle being the most influential, suggested that organisms fit into certain “scale of complexity” which he called “scala naturae.” These ideas were quite consistent with the Old Testaments accounts of creation which all organisms are created individually by God in an unchanging world and thus were perfect. Many scientists believed that the organisms that did well in their environment were designed as such, and thus used it as evidence for a creator. One believer of this doctrine, Carolus Linnaeus, sought to classify these organisms based on their complexity. He called it “binomial nomenclature.” Scala naturae was a very linear approach to increasing complexity, whereas binomial nomenclature took to more of a netted approach and classified the organisms based on similar characteristics. It would not be until Darwin argued that relationships between organisms should be based on their evolutionary relationships.

Ideas about change over time The first suggestions that organisms were not static came in the form of fossils. Fossils are typically found in sedimentary rock, and as the layers of sedimentary rock slowly pile atop each other, they form what are called strata (stratum singular). Paleontology, which is the study of fossils, was partly developed by Georges Cuvier. While observing strata in Paris, Cuvier noticed that the lower to strata was in the ground, the more dissimilar the fossils were from current species. He also noticed that some species would disappear while ones not seen in older layers suddenly appeared.

Picking apart Cuvier’s merits and fault in his explanations Cuvier attempted to explain the sudden appearance and disappearance of certain organisms by suggesting that major cataclysmic events would wipe out one species, and then another would migrate there after that event. This is a logical thought process, but it was contrary to what other scientists of the time were suggesting. The scientist in particular that would have clearly rebuked this suggestion was James Hutton. Hutton suggested that processes that occurred that shaped the different strata were not sudden, but gradually changed, like a valley being formed by a river. Incorporating Hutton’s work, Charles Lyell stated that processes that occurred in the past operate at the same speed then as they do today.

Lamarck’s Hypothesis on Evolution Jeane Baptiste Lamarck, was one of the first to attempt to explain the gradual process by which organisms changed over time. He would not be remember for his revolutionary thought process, but rather by the blunders made in mechanisms to his approach.

Problems associated with Lamarck’s Theory of Evolution Lamarck had a few major holes in his theory. They are: Organisms don’t have the inborn desire to become perfect. Evolution does not mean a species becomes better in some way. Evolution does not proceed in a predetermined direction. Traits acquired in an organism’s lifetime cannot be passed on to future generations.