Unit 10 science: evolution

What is evolution?

The change in a population's genetic composition over generations — specifically, changes in allele frequencies in a gene pool.

Do individuals evolve during their lifetime?

No. Evolution occurs over many generations through population-level changes in allele frequencies, not within a single organism's life.

Why is evolution a theory, not just an opinion?

Because it is an explanation backed by a vast body of evidence — a scientific theory is not a guess; it is a well-supported explanatory framework.

Lamarck's principle of Use and Disuse

Body parts used extensively become larger and stronger; body parts not used deteriorate over time.

Lamarck's principle of Acquired Inheritance

Traits modified during an organism's lifetime are passed on to its offspring.

How did Lamarck explain the giraffe's long neck?

A giraffe stretching its neck to reach high leaves would physically lengthen it during its lifetime, then pass that longer neck to its offspring.

Why was Lamarck wrong?

Physical changes to the phenotype do not alter the DNA in gametes, so traits gained during life cannot be inherited by offspring.

Where did Darwin travel that most influenced his ideas?

The Galápagos Islands.

What book did Darwin publish in 1859?

On the Origin of Species.

What is Natural Selection?

The process by which individuals with favorable traits survive and reproduce more, passing those traits to offspring, causing favorable traits to increase in frequency over time.

What is Fitness (evolutionary)?

Reproductive success — measured by an organism's ability to survive AND reproduce. Not necessarily the strongest or fastest.

What is an Adaptation?

An inherited trait that increases an organism's survival or reproduction. Adaptations arise from existing variation, not from need.

Give three examples of adaptations.

Camouflage, mimicry, and specialized structures (beaks, claws, etc.).

What are the Four Pillars of Natural Selection?

Variation, Overproduction, Competition, and Survival of the Fittest.

Pillar 1: Variation

Within a population, individuals differ in their traits — size, color, speed, etc.

Pillar 2: Overproduction

Organisms produce more offspring than the environment can support.

Pillar 3: Competition

Because resources are limited, not all offspring survive.

Pillar 4: Survival of the Fittest

Individuals with traits best suited to their environment survive and reproduce, passing favorable traits to the next generation.

Lamarck vs. Darwin — Mechanism

Lamarck: driven by need or use. Darwin: driven by natural selection.

Lamarck vs. Darwin — Timeline

Lamarck: changes occur within a single lifetime. Darwin: changes occur over many generations.

Lamarck vs. Darwin — Variation

Lamarck: variation is created after the environment changes. Darwin: variation is present before the environment changes.

Lamarck vs. Darwin — Inheritance

Lamarck: acquired traits are passed on. Darwin: only genetic traits encoded in DNA are passed on.

How did Darwin explain the giraffe's long neck?

Giraffes born with naturally longer necks had easier access to food, so they survived and reproduced more. Short-necked giraffes died off. Over generations, long necks became more common in the population.

What is Stabilizing Selection?

A selection pattern where individuals with the average form of a trait have the greatest fitness; it reduces variation and stabilizes the population over time. The most common type of natural selection.

Example of Stabilizing Selection

Human birth weight — babies born too small face health risks, very large babies risk birth complications; most births fall in a narrow middle-ground weight range.

What is Directional Selection?

A selection pattern where individuals with one extreme form of a trait have the greatest fitness; the average phenotype shifts toward that extreme over time.

Example of Directional Selection

Peppered Moths — industrial soot darkened trees, giving dark moths a survival advantage over light ones, shifting the population toward darker coloration.

What is Disruptive Selection?

A selection pattern where individuals at both extremes of a trait have the greatest fitness; average individuals are selected against; can lead to speciation over time.

Example of Disruptive Selection

Darwin's Finches — large-beaked birds cracked big seeds, small-beaked birds handled small seeds, medium-beaked birds struggled, so both extremes were favored.

How does the Fossil Record support evolution?

Fossils provide a chronological record of life on Earth; older fossils appear in deeper rock layers; transitional fossils show in-between evolutionary stages.

What are Transitional Fossils?

Fossils that show intermediate states between ancestral and descendant groups — evidence of evolution in progress.

Archaeopteryx — what makes it a transitional fossil?

It has feathers like a modern bird, but also has teeth and a bony tail like a dinosaur, bridging the gap between dinosaurs and birds.

Tiktaalik — what makes it a transitional fossil?

It serves as a bridge between fish and tetrapods (four-limbed animals), showing features of both groups.

Law of Superposition

Older fossils are generally found in deeper rock layers; allows scientists to track the appearance of new traits over time.

How does Comparative Anatomy support evolution?

By comparing body structures of different species, scientists find shared structural blueprints suggesting descent from a common ancestor.

What are Homologous Structures?

Body parts with the same basic structure but different functions — evidence of divergent evolution from a common ancestor.

Example of Homologous Structures

The pentadactyl (5-digit) limb in tetrapods — humans, whales, bats, and horses all share the same basic limb bone structure despite different functions.

What are Analogous Structures?

Body parts that share a function but not an evolutionary origin — evidence of convergent evolution.

Example of Analogous Structures

Wings of butterflies, bats, and birds — all used for flight but each has a completely different internal anatomy and evolutionary origin.

What are Vestigial Structures?

Leftover organs or bones that no longer serve a function but were useful to the organism's ancestors.

Examples of Vestigial Structures

The human tailbone (coccyx) and pelvic bones found in whales.

How does Embryology support evolution?

Many vertebrate species go through remarkably similar developmental stages as embryos, suggesting they share a common evolutionary history and the same basic genetic script.

Embryology example

Human embryos develop gill slits and tails at certain stages, just like fish and chicken embryos do.

How does Molecular Biology (DNA) support evolution?

DNA sequence comparisons show exactly how closely related two species are — more similar sequences mean a more recently shared ancestor. It is the most modern and definitive line of evidence.

What is Cytochrome C and why does it matter for evolution?

A protein used in cellular respiration; the fewer differences in its amino acid sequence between two species, the more recently they shared a common ancestor.

What is Divergent Evolution?

Two or more species evolve from a common ancestor and become increasingly different over time.

What is Adaptive Radiation?

The process by which one species rapidly diversifies to fill many ecological niches; the key driver of divergent evolution.

Example of Divergent Evolution

Darwin's Finches — one original species reached the Galápagos Islands and evolved into many different species, each with unique beaks suited for different food sources.

What is Convergent Evolution?

Different, unrelated species with no common ancestor independently evolve similar traits due to similar selective pressures and environments.

Example of Convergent Evolution

Sharks and dolphins — sharks are fish, dolphins are mammals, but both independently evolved streamlined body shapes and fins for fast movement through water.

What is Parallel Evolution?

Two species that share a common ancestor independently evolve similar traits while living in similar environments in different parts of the world.

How does Parallel Evolution differ from Convergent Evolution?

In parallel evolution, the two species share a common ancestor. In convergent evolution, the species are completely unrelated with no common ancestor.

Example of Parallel Evolution

Marsupial vs. placental mammals — Australian marsupials evolved separately but independently evolved into animals that fill very similar ecological roles as placental mammals elsewhere.

What is Coevolution?

Two or more species influencing each other's evolution; a change in one species acts as a selective pressure on the other, creating an ongoing feedback loop.

Coevolution example — mutualism

Flowers and pollinators: flowers evolve to attract more pollinators; other flowers adapt in response, creating an evolutionary arms race.

Coevolution example — mimicry

The viceroy butterfly evolved to resemble the toxic monarch butterfly, deterring predators that mistake it for the poisonous species.

Coevolution example — predator/prey

Bats hunt hawkmoths via echolocation; hawkmoths evolved ultrasonic noise to disrupt bat sonar; bats then shifted to frequencies moths cannot detect.

What is Artificial Selection?

Humans choosing desired characteristics in parent organisms to produce offspring with those traits; driven by human choice, not natural selection.

Example of Artificial Selection

Domestication of dogs — all modern breeds descend from wolves but were selectively bred by humans for temperament, size, coat type, and other traits.

What does a node (branching point) on a phylogenetic tree represent?

A divergence event — the point at which one ancestral group split into two distinct descendant groups.

How do you find the most recent common ancestor on a phylogenetic tree?

Look for the shared node closest (most recent) to the species in question. Species sharing a closer node are more closely related than those whose shared node is further back on the tree.

How does DNA similarity relate to position on a phylogenetic tree?

Species with highly similar DNA sequences share a more recent common ancestor and are positioned closer together on the tree.