Chapter 22 Darwin Views of Life

Origin of Species Book published by Charles Darwin in 1859 began a new era in Biology Darwin made 2 major points: 1. Many species inhabiting the Earth were descendants of ancestral species different from modern form 2. Mechanism of natural selection – idea that population can change over generations

Natural Selection If individuals that possess certain heritable traits leave more offspring than others, then the population will change Evolutionary adaption – the result of natural selection – an accumulation of inherited characteristics that enhances organism’s ability to survive and reproduce Evolution - defined as the change over time in the genetic composition of a population

Traditional Views Darwin’s view of life contrasted with traditional beliefs and challenged a worldview that had been prevalent for centuries  Aristotle – believed that species as fixed or unchanging, but later observed that life forms could be arranged in order of increasing complexity (scala naturae) scale of nature  Linnaeus – founded taxonomy – branch of naming and classifying organisms -believed a pattern of creation explain similar species rather than evolution  Georges Cuvier – developer of Paleontology –study of fossils – noted strata layer in which species would appear and others disappear *Catastrophism – boundaries in strata represents a catastrophic event that destroyed many species living at that time

Traditional Views James Hutton- theory of Gradualism – idea that profound change can occur through a cumulative slow continuous process -proposed many gradual mechanisms currently operating in world i.e. river erosion Charles Lyell – proposed idea of uniformitarianism – in which same geologic processes operating today as in the past and at the same rate Jean-Baptiste de Lamarck – proposed incorrect but insightful observations into recognition of evolutionary change - use and disuse theory (use it or lose it) - inheritance of acquired characteristics (giraffe neck)

HMS Beagle Voyage around the world whose primary mission was to chart poorly known stretches of South American coastline. Darwin noted similarities among plants and animals between South America and Western Europe Noted uniqueness of organisms in Galapagos islands – new species appeared from ancestral form by gradual accumulation of adaptations

Natural Selection and Adaptation Ernst Mayr dissected and summarized Darwin’s views: Observation 1 – For any species, population sizes would increase with successful reproduction Observation 2 – Populations remain stable in size, except for seasonal fluctuations Observation 3 – Resources are limited Inference 1 – Producing more individuals than the environment can support leads to struggle for survival and only a fraction of offspring make it Observation 4 – Members of population vary in characteristics; no individuals alike Observation 5 – Most variation is heritable Inference 2 – Survival depends on heritable traits and those that pass them on will survive and reproduce while others will decline Inference 3 – Ability to survive and reproduce leads to gradual change and accumulation of favorable characteristics over generations

Artificial Selection Modification to a species- plant or animal- over many generations by selecting and breeding desired traits - result in little resemblance of wild ancestors. Darwin reasoned if it can be done in a short time artificial than gradually over time it can happen naturally

Points of Emphasis 3 important points of evolution through natural selection: 1. Individuals do not evolve; populations are the smallest unit 2. Natural selection can amplify or diminish only heritable traits 3. Because environmental factors vary natural selection is always occurring but which traits are favored depends on the environment.

Direct Observations Soapberry bugs in Florida with longer vs. shorter beak lengths based on vegetation Ex: long (balloon vine)vs. short (goldenrain tree) Methicillin-Resistant Staphylococcus aureus (MRSA) – growing resistance to multiple antibiotics 2 key points: 1. Natural selection does not create, it edits. 2. Natural selection depends on time and place.

Homology Homology – Similarity resulting from common ancestry – characteristics in related species have similarity even through they may have different functions a. Anatomy – homologous structures – similarities among organisms of different species *vestigial organs – structures of little importance that may have served more important function to the ancestors b. Molecular – all forms of life use same genetic machinery of DNA and RNA to pass traits and express genes *may have truly descended from one common ancestor

Homologous Structures

Biogeography Biogeography – geographic distribution of species -closely related species tend to be found in same region -same niches elsewhere in the world are occupied by different species -Organisms inhabiting islands resemble species from nearby mainland *Endemic – species of animals and plants that are found no where else in the world Ex. Galapagos inhabitants