Clues From Nature

Main Points

  1. 1 Paleontological – fossils trace gradual change through sediment layers.
  2. 2 Embryological – early vertebrate embryos share common structures.
  3. 3 Comparative anatomy – homologous limbs reveal shared blueprints.
  4. 4 Molecular biology – DNA and proteins map genetic relatedness.
  5. 5 Observed selection – rapid changes like antibiotic resistance show evolution now.

Key Highlights

  • Five independent “witnesses” align like testimony for evolution.
  • Fossils in sediment layers provide the geological timeline.
  • Shared embryos and homologous parts expose hidden ancestry.
  • DNA sequences act as molecular clocks confirming the tree of life.
  • Modern selection events prove evolution is active today.

Fossils Across Time

Fossil Counts per Geological Era Bar graph showing relative number of fossil finds from Cambrian to Quaternary layers. Cambrian Devonian Jurassic Cretaceous Quaternary Rise of Dinosaurs

Key Insights

Sedimentary layers pile up oldest first, creating a vertical timeline.

Age-specific fossils occur only in the layer that matches their era.

Such ordered remains form core paleontological evidence for gradual evolution and extinction.

Think: Why don’t dinosaur fossils appear in modern beach sand?

Legend

Cambrian
Devonian
Jurassic
Cretaceous
Quaternary

Data Source

Illustrative fossil counts adapted from CBSE Biology Grade 12 materials.

Embryonic Echoes

Embryological Evidence

Early vertebrate embryos display pharyngeal gill slits and a post-anal tail, signalling shared ancestry; later development diverges, setting lineage-specific paths.

Key Characteristics:

  • Transient pharyngeal gill slits appear in every vertebrate embryo.
  • A post-anal tail extends beyond the anus before being modified or lost.
  • von Baer’s law: embryos do not pass adult stages of other species, limiting evidence.

Example:

Human embryo (4 weeks) shows both structures before differentiating into lungs and coccyx.

Structures Tell Tales

Homologous Organs

Common ancestry ↔ same basic skeletal plan.
Divergent evolution: functions vary with habitat.
Example: human arm, whale flipper, bat wing.

Analogous Organs

Different ancestry ↔ internal design unlike.
Convergent evolution: similar function evolves independently.
Example: bird wing & insect wing; penguin flipper & fish fin.

Key Similarities

Both compare structure & function across species.
Each provides evidence for evolutionary change.
Used with fossils to map relationships.

Molecular Mirrors

Amino-acid differences in Cytochrome c versus Humans Bars show number of amino-acid substitutions; lower bars mean closer evolutionary relationship. Chimp Horse Pigeon Dogfish Yeast Closest to Humans

Key Insights

Protein sequence homology is powerful biochemical evidence for evolution.

Cytochrome c shows 0 amino-acid changes in chimps, but 67 in yeast.

Fewer differences mean a more recent common ancestor—genetic similarity mirrors relatedness.

Legend

Chimpanzee
Horse
Pigeon
Dogfish
Yeast

Data Source

Cytochrome c amino-acid differences from human sequence (NCBI Protein Database).

Industrial Melanism Lab

Peppered Moth Selection

In soot-darkened Victorian forests, dark morphs out-hid predators while light morphs vanished on clean bark—classic proof that camouflage drives predation and natural selection. Vary bark darkness in the simulator to feel the survival advantage flip in real time.

Drag “Bark Darkness”, press “Predator Sweep” thrice. Goal: both colours survive within two moths—can you balance the selection pressure?

Key Takeaways

Fossils: Rock layers reveal a time-ordered sequence from ancient microbes to modern mammals.

Embryology: Early embryos share gill slits and tails, pointing to a common starting plan.

Anatomy: Homologous limbs—bat wing, whale flipper, human arm—show one flexible blueprint.

Molecules: DNA and protein sequences map a branching genetic tree matching fossil evidence.

Real-time selection: Peppered moths and drug-resistant bacteria evolve within decades before our eyes.

Which line of evidence convinces you most, and how would you justify it?

Thank You!

We hope you found this lesson informative and engaging.