Ch22-1108

Chapter 22: Descent with Modification: A Darwinian View of Life

Introduction

  • Endless Forms Most Beautiful

    • The ways organisms are suited to life in their environments.

    • The shared characteristics (unity) of life.

    • The diversity of life.

Evolution: Descent with Modification

  • Definition of Evolution: Evolution is described as "descent with modification", which refers to how an entity changes through time. It encompasses both a pattern (observable changes in organisms and their traits) and a process (mechanisms of change).

Historical Context: The Voyage of HMS Beagle

  • Timeline: December 1831 - October 1836

    • Importantly, Charles Darwin's explorations during this expedition contributed significantly to his development of the theory of evolution.

The Galapagos Islands

  • The Galapagos Islands served as a crucial focal point for Darwin's observations and insights regarding species adaptation.

Darwin’s Focus on Adaptation

  • Adaptation: An inherited characteristic that enhances an organism's survival and reproductive success in a specific environment.

  • Natural Selection: The process that serves as the mechanism of evolution.

    • Mechanism of Natural Selection:

    • Individuals with favorable inherited traits are more likely to survive and reproduce.

  • Examples of Adaptation Types:

    • Cactus-eater, Seed-eater, Insect-eater exhibit adaptations relevant to their respective environments.

Alfred Russel Wallace

  • While studying species in the Malay Archipelago, Wallace sent Darwin his hypothesis of natural selection in 1858, showcasing the independent development of similar ideas regarding evolution.

  • Wallace's Line:

    • Initially proposed by Wallace in 1859, this line delineates the flora and fauna of Asia (west of the line) from Australasia (east of the line).

    • Modified later by T.H. Huxley to adjust the separation of the island of Palawan from the Philippines.

Artificial Selection

  • Definition: A process in which humans selectively breed organisms for desirable traits.

  • Examples in Agriculture:

    • Selection for apical (tip) bud leads to Brussels sprouts.

    • Selection for axillary (side) buds gives us Kale.

    • Selection for leaves results in Wild mustard.

    • Broccoli is selected for flowers and stems.

    • Modern corn was derived from Teosinte.

    • Kohlrabi was produced through selective breeding for stems.

Natural Selection and Population Variation

  • Population Varying Traits: Members of a population often vary in inherited traits, contributing to the natural variation observed in environments.

  • Overproduction: All species typically produce more offspring than the environment can support, resulting in competition among offspring for survival.

  • Natural Selection as a Driver of Adaptation:

    • Natural selection increases the frequency of favorable adaptations in a given environment.

    • Changes in the environment can lead to new adaptations and potentially the emergence of new species over time.

Evidence for Evolution

  • Types of Evidence:

    • Direct Observations:

    • Example: Natural selection observed in soapberry bugs with beak adaptations to balloon vine fruit.

    • Reference: S. P. Carroll & C. Boyd's study published in Evolution (1992).

    • Evolution of Drug-Resistant Bacteria: Documented cases demonstrate rapid evolutionary adaptations.

Homology

  • Definition of Homology: Similarity resulting from common ancestry.

  • Ontogeny Recapitulates Phylogeny: A phenomenon where the development of an organism (ontogeny) reflects the evolutionary history (phylogeny).

    • Organisms highlighted for comparison: human, mouse, bat, chicken, alligator.

Vestigial Structures

  • Vestigial structures are anatomical remnants that no longer serve a clear function in the current form of the organism.

Convergent Evolution

  • Definition of Convergent Evolution: The process through which unrelated organisms evolve similar traits or features in response to similar environmental challenges or opportunities.

The Fossil Record

  • Definition: The remains or traces of organisms from the past, typically found in sedimentary rock which is arranged in layers called strata.

  • Significance of Fossils: They provide evidence for the transitions between groups of organisms, including notable transitions such as land to sea in cetacean ancestors.

  • Examples of Cetacean Evolution:

    • Rodhocetus kasrani: Mentioned as a modern toothed whale with reduced hind limbs, adapted to swim with an up-and-down motion.

    • Ambulocetus natans: Likely walked on land similar to sea lions and swam like modern otters.

    • Pakicetus attocki: An early whale that lived on land and exhibited many head characteristics seen in contemporary whales.

Biogeography

  • Definition: The scientific study of the geographic distribution of species.

  • Observations: The existence of strikingly similar groups of plants and animals in geographically distant regions underlines the principles of adaptation and divergence in evolution.