Biol 100 - Lecture 30 Evol IV PDF

Species concept: Horse x Donkey = Mule Professor Farnsworth “Grelbers and Ruffers” Phyletic evolution = Sympatric speciation Gradual evolution of one species into another – Waxy Grelbers Allopatric speciation Geographic isolation – thin-furred vs thickfurred Ruffers Adaptive Radiation...

Species concept: Horse x Donkey = Mule Professor Farnsworth “Grelbers and Ruffers” Phyletic evolution = Sympatric speciation Gradual evolution of one species into another – Waxy Grelbers Allopatric speciation Geographic isolation – thin-furred vs thickfurred Ruffers Adaptive Radiation Darwin’s Finches In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species Sympatric speciation can result from the appearance of new ecological niches For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees Convergent Evolution: Where two species evolve similar adaptations (INDEPENDENTLY) to the same kind of environment. This leads to analogous (e.g., wings) characters. Good example is marsupial and placental mammals Note: Characteristics are NOT homologous and two species CANNOT evolve into one! Homologous structures Homology versus Analogy A character state is homologous in two species ONLY when it has been inherited by both species from a common ancestor A character state is analogous (homoplasy) in two species when it was not inherited from their most common ancestor. That is, the character state evolved more than once. An example of this is convergent evolution Co-evolution: Where the direction of evolution in one species is strongly influenced by evolutionary changes in another. This often occurs when species “depend” on each other. For example bat echolocation and moth ears Rate of Evolution A hypothesis termed “punctuated equilibrium” contradicts the idea of gradualism. Based on observations by Gould and Eldredge that new species or even higher taxa appear abruptly in the fossil record. Evolution as a “theory” The statement that “through time organisms have descended with modifications from common ancestors” (= changed) is true. It is as much of a hypothesis as gravity or the earth revolves around the sun. What remains are questions about mechanisms, rates, and interrelationships among ancestors. In review then: Natural Selection is simply: “The differential reproductive success of individual organisms” Natural Selection has NO purpose or goal and is not directed towards the survival of any species, especially Homo sapiens. Requirement: 1. Variation exists 2. Differences can be inherited 3. Different environments have different effects on different phenotypes 4. Genotypes which produce favoured phenotypes, will be selected for by the environment