Descent With Modification

Descent with Modification: A Darwinian View of Life

  • Illustrates the concept of descent with modification using a diagram showing the evolutionary relationships between various animals.
  • Examples include a lamprey, sunfish, newt, lizard, bear, and chimpanzee.
  • Highlights common ancestors such as the common mammal ancestor, common amniote ancestor, common tetrapod ancestor, common jawed vertebrate ancestor, and common vertebrate ancestor.

Organization of Life

  • Presents the organization of life from atoms to organisms and then to ecosystems.
  • Atoms to Organisms:
    • Atoms form small molecules (e.g., water, oxygen, methane, carbon dioxide).
    • Small molecules form large molecules (e.g., proteins, nucleic acids like DNA).
    • Large molecules are organized into cells.
    • Cells lead to specialized tissues (6000 specializations).
    • Tissues form organs.
    • Organs are organized into organ systems.
    • Organ systems create multicellular organisms (e.g., leopard frog).
    • Also includes unicellular organisms and colonial organisms.
  • Organisms to Ecosystems:
    • Organisms form populations.
    • Populations form communities.
    • Communities interact to form an ecosystem.
    • Ecosystems make up the biosphere.

Evolution

  • Defines evolution in two key aspects:
    • Observed patterns in nature.
    • Mechanisms that produce these observed patterns of change.

History of Evolutionary Thought

  • Early views saw life-forms as perfect and permanent, with species being immutable (unchanging).
  • Scala Naturae: Life forms arranged on a ladder or scale of increasing complexity, with humans at the top. Associated with Aristotle (384-322 BC).
  • References historical works:
    • Liber de ascensu et descensu intellectus (1305).
    • Traité d'insectologie (1745).

Linnean Classification

  • Carl Linnaeus (1707-1778):
    • Attributed as the founder of “modern” taxonomy.
    • Developed the Linnaean system, which uses binomial nomenclature to name species (e.g., Homo sapiens) and organizes them into hierarchical categories.
    • Nested vs. Linear Classification: Emphasizes the shift from Aristotle's linear classification to Linnaeus's nested classification.
    • Hierarchical Categories: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Lamarckism

  • Jean-Baptiste Lamarck (1744-1829):
    • Proposed the first process of evolution in 1809.
    • Viewed species as changing over time based on fossil record observations.
  • Key Idea: Changes in traits acquired during an individual's lifetime are passed on to their offspring.
    • Example: Increased muscle mass through exercise.

Modern Evolutionary Theory

  • Charles Darwin (1809-1882): A central figure in the development of modern evolutionary theory.

HMS Beagle

  • Darwin served as a naturalist aboard the HMS Beagle from 1831-1836.

HMS Beagle Voyage

  • Voyage Details: The map shows the journey of the HMS Beagle, including stops at the British Isles, Europe, Asia, North and South America, the Galápagos Islands, Tahiti, Africa, Australia, Tasmania, and New Zealand.
  • Galápagos Islands: Special attention is given to the Galápagos Islands, with specific islands like Pinta, Marchena, Genovesa, Santiago, Santa Cruz, Fernandina, Santa Fe, Isabela, Tortuga, San Cristobal, Santa Maria, and Española mentioned.

Observations from HMS Beagle

  • Darwin observed differences between species in South America versus Europe and on the Galápagos Islands.
  • Key Question: What accounted for these differences?

Influence of Geology/Paleontology

  • James Hutton (1726-1797) and Charles Lyell (1797-1875):
    • Proposed that Earth's geological processes are shaped by gradual mechanisms still at work today.
    • Supported the idea that Earth is much older than a few thousand years, challenging the common belief of the time.

Influence of Population Studies

  • Thomas Malthus (1766-1834):
    • Authored An Essay on the Principle of Population (1798).
    • Argued that human population size increases geometrically, while resources increase arithmetically.
    • Key Concept: There are not enough resources for all individuals to survive and reproduce.
    • Darwin read Malthus's essay in 1838, which influenced his thinking on natural selection.

Natural Selection and Adaptations

  • Natural Selection: Individuals with certain inherited traits tend to survive and reproduce at higher rates than others because of those traits.
  • Adaptations: Inherited traits of organisms that enhance survival and reproduction.

Darwin's Postulates

  • Observation #1: Members of a population often vary in their inherited traits.
  • Observation #2: All species can produce more offspring than their environment can support, and many of these offspring fail to survive and reproduce.
  • Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.
  • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Key Points of Natural Selection

  • Natural selection acts on individuals within a population; however, individuals do not evolve, populations do.
  • Only applies to inherited traits that differ between individuals in a population.
  • Environments are not static; a favorable trait in one place or time may not be in another.

Publication of "On the Origin of Species"

  • "On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Existence" was published on November 24, 1859.
  • This was 23 years after Darwin's return from the voyage of The Beagle.

Alfred Russel Wallace

  • Alfred Russel Wallace (1823-1913):
    • In 1858, Darwin received a manuscript from Wallace, another naturalist.
    • Wallace independently arrived at the same hypothesis as Darwin.

Modern Theory of Evolution

  • Definition: Change in the genetic composition (gene pool) of populations over time (generations).
  • Central Idea: Life originated from a single common ancestor.

Evidence of Evolution

  • Darwin recognized shortcomings in his hypothesis.
  • His hypothesis was testable.
  • Evidence has since appeared to support his hypothesis and explain some of its shortcomings.

Artificial Selection

  • Example: Dandyora

Observations in Nature

  • References Cuvier (1829).
  • Mentions natural selection on a major armor gene in threespine stickleback.
  • Cites research articles:
    • Barrett, R. D. H., Rogers, S. M., & Schluter, D.
    • Bell, M. A., Aguirre, W. E., & Buck, N. J.

Homology

  • Homologous Traits: Shared traits derived from a common ancestor.
  • Divergent Evolution: The process by which homologous traits diverge.
  • Example: Bones in the front limbs of various vertebrates (rhipidistian lobe-finned fish, primitive tetrapod, bird, dog, human, bat, whale) showing common bone structure (humerus, radius, ulna, wrist, and hand).

Homology and Evolutionary Relationships

  • Homologous traits provide information on evolutionary relationships.
  • Phylogenetic Tree Example: Shows the evolutionary relationships among lamprey, perch, salamander, lizard, crocodile, pigeon, mouse, and chimpanzee, highlighting the development of jaws, lungs, keratinous scales, claws/nails, fur/mammary glands, gizzard, and feathers.

Homology in Development

  • Developmental Homology: Similarities in embryonic development indicating shared ancestry.
  • Examples include urochordate larva, amphioxus larva, and ammocoete (larval lamprey), showing similar structures such as the neural tube, notochord, pharyngeal slits, and branchial skeleton.

Vestigial Structures: Homology

  • Vestigial structures are remnants of features that served a function in the organism's ancestors but have reduced or no function in the current organism.

Convergent Evolution

  • Analogous Traits: Traits that have a similar function but do not share common ancestry.
  • Convergent Evolution: The independent evolution of similar features in different lineages.
  • Example: Wing structure in birds and insects.

Examples of Convergent Evolution

  • New world knifefishes (Gymnotiformes) and old world knifefishes (Notopteridae).
  • Smilodon (sabre-toothed tiger) and Thylacosmilus (sabre-toothed marsupial).

Fossil Record

  • Fossils document the pattern of evolution.
  • Example: Evolution of digits in tetrapods, showing a transition from 8 digits to 5 digits in crown-group tetrapods.
  • Illustrates the evolution of the humerus, radius, ulna, and distal elements in various species, including ray-finned fish, lungfish, Eusthenopteron, Panderichthys, Ichthyostega, Acanthostega, Tulerpeton, and Greererpeton.

More Examples in Fossil Record

  • Examples with Pappochelys, Odontochelys, Proganochelys (Journal of Systematic Paleontology, Schoch and Sues 2017).

Key Takeaways

  • Understand the modern theory of evolution and be able to define evolution.
  • Be aware of the contributions of Aristotle, Carl Linnaeus, Lamarck, Darwin, and Wallace to our understanding of evolution and classification.
  • Understand natural selection, adaptations, and Darwin’s four postulates.
  • Be aware of different forms of evidence for evolution (e.g., artificial selection, observations in nature, homology, vestigial structures, and the fossil record).
  • Understand the similarities and differences between artificial and natural selection.
  • Understand homologous and analogous traits, convergent and divergent evolution, and the differences between them.
  • Be aware of vestigial structures and what this refers to.