BIOLOGY NOW WITH PHYSIOLOGY - CHAPTER 11: Evidence for Evolution
Overview: Chapter 11 – Evidence for Evolution
Objectives (from the transcript):
Define evolution and list six types of evidence for evolution.
Compare and contrast artificial selection and natural selection.
Summarize how the fossil record provides evidence for evolution.
Give one example of a homologous trait and one example of a vestigial trait; explain how such traits support common descent.
Explain why even distantly related species have similar DNA.
Use knowledge of evolution and continental drift to predict geographic locations of fossils.
Relate similarities in embryonic development among species to their shared evolutionary past.
Core idea: Evolution is a change in inherited characteristics of a group over generations; populations evolve, individuals do not. The evidence for evolution is convergent across multiple, independent lines of inquiry.
Six Lines of Evidence for Evolution
1) Direct observation of evolution through artificial selection
Example: Domestic dogs (Canis lupus familiaris) are a single species, descended from gray wolves (Canis lupus). Domestication began around ext{approx. } 1.6 imes 10^4 ext{ years ago} with humans selecting for desirable traits.
Mechanism: Selective breeding; humans allow only individuals with certain inherited characteristics to mate.
Outcome: A wide variety of dog breeds with divergent traits.
2) Fossil evidence
The fossil record documents transitions from land to sea in whales, showing gradual changes in morphology over time.
Depth/age relation: Older fossils are found in deeper, older rock layers; relative dating helps reconstruct life history.
Transitional fossils: species that share features with both ancestral and descendant groups.
3) Shared characteristics among living organisms
Many traits are common to diverse groups due to descent from a common ancestor.
Examples in the whale case show how mammalian features (breathing air, mammary glands, hair, etc.) link lineages.
4) Similarities and differences in DNA
All living organisms use DNA with the same genetic code, indicating a common ancestry.
DNA sequence similarity measures relatedness: closer relatives have higher sequence similarity.
Example discussion: a sequence similarity of 95\% between humans and another species indicates a close relationship (relative to more distant relatives like some non-primate mammals).
5) Biogeographic evidence (continental drift)
The distribution of species across continents reflects historical connections and separations due to plate tectonics.
Pangaea (~2.5\times 10^8 ext{ years ago}) split over time into present continents; fossil distributions align with these movements.
6) Common patterns of embryo development
Embryos of diverse vertebrates show shared features (e.g., gill slits, tails) during early development, reflecting descent from a common ancestor.
The Whale Evolution Case Study (Thewissen and Team)
Key players and discovery trajectory:
J. G. M. “Hans” Thewissen identified ear bone features in the 50-million-year-old deerlike mammal Indohyus that resemble whale ear bones more than those of land mammals.
Fossil sequence documents a transition from land-dwelling to aquatic life.
The fossil sequence (from oldest to more derived intermediates):
Pakicetus (oldest whale ancestor; lived on land, ~5.0\times 10^7 ext{ years ago}; 50 mya)
Indohyus (land-dwelling ~4.7\times 10^7 ext{ years ago}; extinct whale cousin; shares a common ancestor with Pakicetus)
Ambulocetus (crocodile-like; ~4.8-5.0\times 10^7 ext{ years ago}; semiaquatic; strong legs)
Rodhocetus (front and back legs shaped like flippers; ~48 mya)
Dorudon (fully aquatic; blowhole and flippers; ~40 mya)
Balaena (modern baleen whale; evolved around ~3.5\times 10^7 ext{ years ago})
Percent and timing notes:
It took roughly 1.5\times 10^7 ext{ years} for whale ancestors to transition from land to water.
The sequence bridges a long gap in the fossil record and highlights progressive adaptations (tail lengthening, leg reduction, flipper-like limbs).
Notable insights:
Indohyus is an extinct whale cousin, not a direct ancestor, but shares a common ancestry with Pakicetus.
Ear bone morphology served as a crucial link in tracing whale ancestry.
The transitions included development of a streamlined body, semiaquatic to fully aquatic lifestyles, and morphological shifts in limbs.
Anatomy and Physiology of Whale Evolution (Key Features)
Shared mammalian characteristics (universal across whales):
Stable body temperature (endothermy)
Backbones (vertebral column)
Lungs for breathing air
Mammary glands to nurse young
Transitional features observed in fossils:
Longer tails and progressively shorter legs over time in whale lineages
Emergence of tail flukes and streamlined bodies for efficient aquatic movement
Evolution of a blowhole for breathing when at the surface
Early relatives contribute clues about habitat use and lifestyle shifts
Fossil Record: Definitions and Significance
Fossil: mineralized remains or impressions of formerly living organisms.
Examples in the chapter: trilobites, seed fern leaves, amber-preserved termites, petrified wood, and multiple dinosaur fossils found together.
The fossil record enables reconstruction of life's history and provides powerful evidence for evolution over time.
Transitional fossils: evidence of species with similarities to both ancestral and descendant groups.
The Thewissen-led work bridges a ~1.0\times 10^7 ext{ to } 1.5\times 10^7 ext{ years} gap in the whale fossil record, clarifying the land-to-sea transition timeline.
Anatomy: Homologous and Vestigial Traits
Homologous traits: similar structures in different species due to a common ancestor; may diverge in form and function over time.
Vestigial traits: reduced or degenerated structures inherited from a common ancestor that have little or no current function (e.g., remnants of hind limbs in some cetaceans, human appendix in many contexts).
Examples from the chapter:
Forelimbs of mammals (humans, whales, bats, dogs) show divergent forms yet common ancestry.
Vestigial examples include internal limb remnants in some species and reduced structures that no longer serve their original function.
Why these support common descent:
The presence of similar skeletal frameworks across diverse lineages implies inheritance from a shared ancestor, with modifications over time.
Clues in the Code: DNA Evidence
All life uses DNA with a universal genetic code; this commonality supports a single or interconnected set of ancestors.
DNA sequence similarity quantifies relatedness; more similar DNA sequences indicate closer evolutionary relationships.
Conceptual example from the text: a gene with 95\% sequence similarity between humans and another species suggests a closer relationship than with more distant relatives.
Implication: DNA similarities, together with structural and fossil data, build a coherent picture of evolutionary history.
Biogeography and Continental Drift
Plate tectonics moves continents; ~2.50\times 10^8 ext{ years ago}, all landmasses formed Pangaea.
By ~2.00\times 10^8 ext{ years ago}, Pangaea started breaking apart, shaping current continental configurations.
Biogeography: the geographic distribution of fossils and living species reflects historical connections and separations.
Example: Neoceratodus fosteri (lungfish) currently found in NE Australia, but its ancestors lived during the time of Pangaea; fossils found globally as predicted by its ancient distribution.
Qs to consider (from the lecture):
Why would N. fosteri fossils be found worldwide if it first evolved in Pangaea? (Because of global distribution before continental breakup.)
Can biogeography be used to support evolution without fossil evidence? (Yes, in combination with other evidence.)
How might biogeography and DNA similarities together strengthen evolutionary inferences? (Convergent lines of evidence.)
Embryology and Development
Embryo development reveals shared patterns among species due to descent from a common ancestor.
Figure 11.16 illustrates that fish, reptiles, birds, and humans share features like gill slits and tails during certain embryonic stages.
Questions posed for understanding:
Why are similarities in embryonic development evidence for evolution?
Are embryonic homologous structures? (Yes, in the sense of shared developmental programs.)
Why do embryonic structures persist if not used later? (Retained vestiges or developmental constraints; may reflect shared ancestry.)
Real-time Evolution: Watching Evolution Happen (Escherichia coli Study)
Experimental design (UC Irvine, 2012):
115 separate, genetically identical E. coli populations grown at a control temperature of 37^ ext{°} ext{C} or subjected to a hotter environment at 42.2^ ext{°} ext{C} (107.96°F).
Populations reproduced for 2{,}000 generations.
One sample per population was sequenced after the experiment.
Outcomes:
$1{,}258$ molecular changes detected across the populations (average 11 genetic mutations per clone).
Two key mutations enabling heat survival: in the RNA polymerase complex and in the rho gene (which regulates transcription termination).
Significance: Demonstrates rapid, real-time evolution under selective pressure and clarifies the genetic basis for adaptation.
Human Practice: Questions, Answers, and Applications (Selected from the Transcript)
Natural vs artificial selection: comparison prompts include Q1–Q3 on pages 11–16; major themes include how artificial selection (man-made) parallels natural selection (environment-driven) and how both lead to trait changes in populations over time.
Examples used in exams: selective breeding across dog breeds, finch beak size under varied rainfall, and peppered moth coloration during the Industrial Revolution.
DNA and common descent questions: similarities in DNA sequences; how to interpret percent similarities; the idea that DNA informs evolutionary relationships.
Fossil and embryology questions: definitions of fossil, transitional fossil, and the significance of embryonic patterns as evidence for common descent.
Practice multiple-choice themes (as presented in the transcript):
Assessing evidence for evolution (e.g., distinguishing natural selection from mere adaptation or other processes).
Interpreting vestigial and homologous traits; understanding their evolutionary implications.
Evaluating how biogeography and plate tectonics support evolutionary history.
Key Terms and Concepts to Remember
Evolution: change in inherited characteristics of a group over generations; population-level process.
Direct observation of evolution: examples include artificial selection (breeding) and lab/field experiments showing adaptive changes.
Fossil record: chronological layering of fossils; helps infer ancestry and transitions; includes transitional fossils.
Homologous traits: similar features due to shared ancestry; may diverge in form and function.
Vestigial traits: remnants of ancestral features with reduced or lost function.
Common descent: all organisms descended from a single common ancestor.
Common ancestor: a single organism from which multiple species evolved.
DNA as evidence: universal genetic code; sequence similarities gauge relatedness.
Biogeography: geographic distribution of species; informed by plate tectonics and historical connections.
Embryology: shared embryonic development patterns reflect deep ancestry.
Adaptive trait: a trait that provides a functional advantage in a given environment.
Adaptive vs. vestigial: context-dependent; some traits shift roles across lineages.
Contingent numbers and dates in evolution: e.g.,
Pangaea formation: 2.50\times 10^8 ext{ years ago}
Breakup into current continents: roughly 2.00\times 10^8 ext{ years ago} and onward
Whale transition timeline: roughly 1.5\times 10^7 ext{ years} from land to sea
Whale lineage-branch dates: Pakicetus (~50 mya), Ambulocetus (~48–50 mya), Dorudon (~40 mya), Balaena (~35 mya)
Quantitative examples (for quick recall):
Temperature shifts in E. coli evolution experiment: 37^ ext{°} ext{C}
ightarrow 42.2^ ext{°} ext{C}Population samples: 115 parallel cultures
Generations: 2{,}000 generations
Mutations observed: 1{,}258 total changes; average 11 mutations per clone
DNA similarity example: 95\% sequence similarity to a given human gene
Connections to Foundational Principles and Real-World Relevance
Evolutionary theory integrates multiple lines of evidence to build a coherent understanding of life's history, consistency across genetics, morphology, and geography.
The whale case study demonstrates the predictive power of phylogenetics and paleontology: if a lineage shows stepwise functional changes (lungs, blowhole, flippers), then fossil evidence should reveal intermediate forms with those features.
Biogeography complements genetics and paleontology by explaining distribution patterns through plate tectonics and historical continental arrangements.
Embryology highlights deep, shared developmental programs that persist across diverse groups, underscoring common ancestry rather than independent design.
Real-time experiments (e.g., E. coli heat adaptation) reveal that natural selection acts on existing variation and can yield measurable genetic changes in a relatively short time span, reinforcing the mechanism by which evolution operates.
Practice-style Quick Questions (Sample Answers)
What is natural selection? A population-level process where individuals with advantageous inherited traits survive and reproduce more effectively, causing these traits to become more common over generations; the environment “chooses” winners.
Differentiate artificial vs natural selection:
Artificial selection: humans intentionally select for desired traits; rapid trait divergence within species (e.g., dog breeds).
Natural selection: environmental pressures select for traits that confer fitness; no conscious agent.
How does the fossil record support evolution? It shows progressive changes over time, transitional forms, and a chronological sequence of life forms consistent with descent from common ancestors.
What is a homologous trait? A trait shared by species due to common ancestry; may be modified for different functions (e.g., forelimbs in humans, whales, bats).
What is a vestigial trait? A reduced or degenerated trait that was functional in a common ancestor but is now of little or no use in the present organism.
Why do distantly related species have similar DNA? They share a common ancestor; conserved genes and genetic codes reflect deep evolutionary relationships within the tree of life.
What does continental drift imply for fossil distributions? Fossil distributions align with historical land connections and separations; similar fossils found on now-distant continents support past connections (and subsequent isolation).
How can embryology support evolution? Similar embryonic stages across diverse taxa indicate a shared developmental heritage from a common ancestor.
In the E. coli experiment, what were the two key mutations enabling heat survival? In the RNA polymerase complex and in the rho gene.
Quantitative recap: the whale transition involved roughly 1.5\times 10^7 ext{ years}; major intermediates include Pakicetus, Ambulocetus, Rodhocetus, Dorudon, and Balaena; Indohyus is a close relative that helps illuminate water-dwelling adaptations.
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