lab 10 Evolution and the Fossil Record Practice Flashcards

Introduction to Evolutionary Theory

• Definition and Importance: Evolution is the central theory in biology, serving to unify all branches of the field, from molecular biology to the study of ecosystems. It explains the origin of species and the processes by which organisms change over time.

• Nature of Change: Biological evolution refers specifically to changes in organisms across generations. This is contrasted with historical technological evolution, such as the development of cars and airplanes over the last century.

• Central Questions in Biology: Natural selection was the first mechanism to provide answers to two fundamental questions:

  • 1) How do species become so well adapted to their environments?

  • 2) How do new species come into existence?

• Evolution vs. Natural Selection: It is critical to distinguish between these terms:

  • Evolution: The occurrence of change over time.

  • Natural Selection: A specific mechanism that produces that change.

The Discovery of Natural Selection

• Origins of the Theory: The theory was independently developed and then jointly proposed in 1858 at a meeting of the Linnean Society by two naturalists:

  • Alfred Russell Wallace: Formulated the theory during his explorations in Indonesia.

  • Charles Darwin: Developed the theory after returning from his five-year voyage around the world on the HMS Beagle.

• Darwin’s HMS Beagle Voyage: During the journey, Darwin became convinced that species change over time. However, acknowledging the controversy of the idea, he realized he could only convince others if he provided a mechanism. He identified natural selection as that mechanism but kept his work mostly secret for years due to fear of public backlash.

• The Origin of Species: In 1859, Darwin published his seminal book, The Origin of Species, which provided extensive evidence supporting the theory. Although the theory was public a year earlier, the book facilitated its wide dissemination and became a best-seller.

Mechanisms and Principles of Natural Selection

• Mechanisms of Evolution: Natural selection is the primary mechanism because it explains adaptation, but evolution also occurs via:

  • Mutation

  • Random genetic drift

  • Migration

• Observations and Conclusion: Wallace and Darwin’s theory is based on four key observations in nature:

  • 1) Variation: Individuals within a population vary. Their insight was that this variation is significant and important for survival.

  • 2) Heritability: Characteristics are passed from parents to offspring.

  • 3) Struggle for Existence: Only a small fraction of organisms survive to adulthood.

  • 4) Correlation: There is a link between an organism’s traits and its success in survival and reproduction.

• The Logical Conclusion: Populations will change and become adapted over time as individuals with well-suited traits survive, reproduce, and pass those traits to future generations.

• Misconception Alert: Evolution via natural selection is not random. While components like mutation and genetic drift are random, natural selection is a non-random process of selection based on an organism's specific traits.

Case Study: Evolution of the Peppered Moth (Biston betularia)

• Background: A classic example of natural selection observed during the Industrial Revolution. The population consists of two color morphs:

  • Light-colored morph (Biston betularia f. typical)

  • Melanic (dark) morph (Biston betularia f. carbonaria)

• Pre-Industrial Conditions: Tree trunks were light gray. Light-colored moths were better camouflaged against predators, making them the common morph.

• Post-Industrial Change: Soot from factories blackened the trees. This shift in the environment rendered white moths visible and vulnerable, while dark moths became well-camouflaged.

• Experimental Simulation Procedure:

  • Part A (Pre-Industrial): Place 15 white and 15 dark moths on a light background. A "predator" removes moths for 5 seconds using forceps. Removed white moths are replaced with black ones (to simulate selection pressure/reproduction cycle), and removed black moths are replaced with white ones. This is repeated for 5 trials until the population shifts toward the light morph.

  • Part B (Industrial Revolution): The same procedure is followed using a dark background. Over 5 trials, the population shifts toward the black morph.

• Key Finding: Individual moths do not change color; rather, the frequency of the color traits within the population changes over generations.

Speciation and Geographic Isolation

• Endemic Species: Native species that do not exist anywhere else. Darwin observed many endemics on the Galapagos Islands (e.g., tortoises, finches, marine iguanas).

• Allopatric Speciation: The formation of new species caused by geographic isolation. Darwin hypothesized that species from South America colonized the volcanic islands and changed over time due to isolation.

• Case Study: Pupfish of Death Valley: Approximately 10,000 years ago (end of the Pleistocene), a large lake (Lake Manly) covered the region. As the lake dried up, fish were isolated in distinct natural springs differing in salinity and temperature.

• Specific Pupfish Species tracked:

  • Cyprinodon salinus

  • Cyprinodon milleri (Cottonball Marsh pupfish)

  • Cyprinodon diabolis

  • Cyprinodon nevadensis

  • Cyprinodon radiosus

• Divergence Factors: Populations adapted to specific environments (some 6 times saltier than the sea). The degree of divergence is correlated with the length of time the population has been isolated.

• Legal Context: The Cyprinodon diabolis was saved by a 1976 U.S. Supreme Court decision.

Reconstructing Evolutionary History: Skull Morphology

• Methodology: Reconstructing relationships involves comparing anatomical features (morphology) and DNA. Closely related species share more characteristics derived from a common ancestor.

• Skull Measurement Indices:

  • Cranial Index: Measures the cranium (brain case) relative to the face.         $Cranial\,Index = \frac{Cranial\,width}{Facial\,width} \times 100$

  • Facial Extension Index: Measures how far the jaw projects forward.         $Facial\,extension\,Index = \frac{Facial\,extension\,length}{Skull\,length} \times 100$

  • Dental Formula: The count of incisors, canines, premolars, and molars on one side of the jaw. (e.g., $2 \times 1 \times 3 \times 3$).

  • Brow Ridge (Supraorbital ridge): A mass of bone above the eye orbits.

  • Sagittal Crest: A bone ridge for chewing muscle attachment. (0 = present, 1 = absent).

  • Frontal Bone: Slope of the forehead (flat, sloping, or vertical).

  • Canine-Incisor Index:         $Canine\,incisor\,index = \frac{\text{2nd incisor length}}{\text{Canine length}} \times 100$

  • Foramen Magnum Index: Position of the spinal cord opening, indicating posture and locomotion (e.g., bipedalism vs. quadrupedalism).         $Foramen\,magnum\,index = \frac{\text{Foramen magnum distance}}{\text{Ventral cranium length}} \times 100$

  • Relative Brain Size: Cranial capacity divided by average animal height multiplied by 100.

Comparative Morphological Data

Phylogenetics and the Fossil Record

• Phylogenetic Trees: Graphs depicting evolutionary relationships. Tips represent species; nodes represent speciation events.

• Ancestral vs. Derived Characters: Ancestral (0) is the same as the ancestor; Derived (1) is a changed trait.

• The Fossil Record: Study of fossils (remains of past life) by paleontologists. It reveals anatomy of extinct organisms including bones, shells, and plants.

• Trace Fossils: Indirect evidence of life, such as footprints or burrows.

• Geological Eras:

  • Paleozoic: Oldest era.

  • Mesozoic: The "Age of Reptiles," including dinosaurs. Divided into the Triassic, Jurassic, and Cretaceous periods.

  • Cenozoic: Recent era.

• Mass Extinctions: Events where >50% of species disappear.

  • Permian-Triassic Extinction: The largest mass extinction in Earth's history.

  • K-T (Cretaceous-Tertiary) Extinction: Marked by the disappearance of dinosaurs.

Representative Fossils and Transitional Forms

• Paleozoic: Trilobites: Members of the phylum Arthropoda. They existed for hundreds of millions of years; thousands of species are known.

• Mesozoic: Tyrannosaurus rex: A carnivore (determined by teeth/jaw structure) from the Cretaceous period with unusually small arms.

• Cenozoic: Sabre-tooth Cat: Preserved in locations such as asphalt/tar pits; characterized by long canine teeth used for hunting.

• Transitional Fossils ("Missing Links"): Fossils that fill gaps in the record by showing characteristics of two distinct types of organisms.

• Example: Archaeopteryx: A transitional form between reptiles and birds.

  • Reptilian traits: Teeth, long bony tail, claws on wings.

  • Avian traits: Feathers, wishbone (furcula).

Questions & Discussion

• Which morph was common at the end of the 5th trial (Industrial Revolution)? The black (melanic) morph.

• What was Lake Manly? A lake formed in Death Valley at the end of the Pleistocene epoch.

• What are the three rivers feeding Death Valley? The Amargosa, Mojave, and Owens Rivers.

• What happens to individual moths during the industrial revolution? Individuals do not change; the common color within the population changes (the accurate statement is "The common color of moths in the population changed").

• What determines the position of the foramen magnum? Posture and locomotion; it moves toward the center of the skull base as an animal becomes more upright (bipedal).