Evolution & Natural Selection Study Notes

Comprehensive question-and-answer flashcards covering evolutionary theory, natural selection, early scientific concepts, lines of evidence, and selection patterns from sections 14.1, 14.2, and 15.1.

What core agreement did both Charles Darwin and Jean-Baptiste Lamarck share regarding living organisms?

Both agreed that living things change over time to become better suited to their environment, resulting from a long, slow process called evolution.

What was Jean-Baptiste Lamarck's proposed mechanism for evolution?

The Theory of Inheritance of Acquired Characteristics, which stated that organisms changed parts of their bodies over a lifetime through use or disuse and passed those acquired traits to offspring.

According to Charles Darwin, what two factors drive the survival and reproduction of organisms?

Variation (small, random differences in traits within individuals in every population) and Competition (limited environmental resources leading to a struggle for existence, where organisms with better-suited traits survive and pass them to offspring).

What concept did Georges Cuvier propose regarding Earth's history and species extinction?

Catastrophism, which stated that local catastrophes caused mass extinctions, followed by repopulation by new species.

What principle did Charles Lyell propose in 'Principles of Geology', and what did it prove about Earth?

Uniformitarianism, which proposed that slow cycles of erosion and uplift occur at a uniform rate, proving that Earth is extremely old and allowing time for gradual evolutionary changes.

How are fossils defined in the notes, and what do they reveal?

Remains of once-living species preserved in rock layers (strata) formed from sedimentary material, revealing age and past environments.

What is the central thesis of evolutionary theory presented in the notes?

Species are not fixed; they change over time and are related through common descent with modifications adapted to specific environments.

How did the beak shapes and sizes of Galápagos finches adapt to different diets?

Ground finches developed beaks suited for seed sizes, tree finches developed beaks for catching insects, cactus finches evolved pointed beaks for cactus flowers, and woodpecker finches developed sharp beaks.

How did physical variations among Galápagos tortoises reflect local island vegetation?

Long-necked tortoises were found where food was scarce or tall, allowing them to reach tall growing cacti, whereas short-necked tortoises adapted to areas with plentiful ground vegetation.

How did isolation on different islands lead to speciation and adaptive radiation in bird populations?

Geographic isolation allowed bird populations to evolve independently over time, accumulating unique changes to fit their local environments and forming new species.

How do genetic variations arise in a population, and what functional effects can they have?

They arise randomly via meiosis, fertilization, and mutations in DNA, and can be beneficial, harmful, or neutral (e.g., camouflage).

How is evolutionary fitness defined?

Reproductive success in surviving, finding food, avoiding predators, and passing genes.

What is artificial selection?

The process by which humans choose which organisms reproduce based on desired traits.

What are the four sequential components of the natural selection process?

1. Variation (inherited random trait differences), 2. Overproduction / Problem (populations produce more offspring than resources can support), 3. Differential Survival & Reproduction (favorable traits reach resources and survive), and 4. Adaptation (favorable traits represent a higher ratio over generations).

What are the four primary lines of empirical evidence supporting evolutionary change?

Fossil evidence, biogeographical evidence, anatomical evidence, and molecular evidence.

Which anatomical traits establish Archaeopteryx as a transitional fossil between reptiles and birds?

It possessed reptile characteristics (jaws with teeth, long jointed tail) combined with bird characteristics (feathers, wings).

What transitional features are present in the Tiktaalik fossil dated to approximately $375\text{ Mya}$?

It shows an intermediate form between fish (gills, fins) and four-legged tetrapods (wrist bones, flexible neck, flat head, ribs).

What evolutionary relationship is revealed by snake fossils dated to approximately $90\text{ Mya}$?

They possess hip bones and hind limbs found in lizards, showing descent from lizard ancestors.

What ancestral lineage demonstrates the transitional evolution of modern whales?

Terrestrial hoofed ancestors (Mesonychid) evolved into semi-aquatic forms (Ambulocetus), swimming forms (Rodhocetus), and finally modern whales.

What universal molecular features are shared by all living organisms?

All life shares DNA, ATP, identical nucleotide bases, and the same $20$ amino acids.

What is the evolutionary function of Hox genes across animal species?

They are shared developmental genes that determine the body axis across animals ranging from worms to humans.

What level of DNA sequence homology is shared between humans and chimpanzees?

Humans and chimpanzees share approximately $98.8\%$ DNA similarity.

How is the respiratory protein cytochrome c used to determine evolutionary relationships?

Fewer amino acid differences in cytochrome c reflect closer evolutionary relationships between species.

How do cacti and spurges exemplify convergent evolution?

Although not closely related, cacti (Americas) and spurges (Africa) independently evolved similar adaptations—such as spines, water-storing succulent stems, and reduced leaves—due to inhabiting similar hot, dry climates.

What biogeographical event drove the adaptive radiation of Galápagos finches and Hawaiian honeycreepers?

An ancestral species migrated to an island chain, where geographic isolation in varied island environments drove adaptive radiation into distinct species.

Why did marsupials diversify extensively in Australia compared to placental mammals?

Marsupials and placentals coexisted when South America, Antarctica, and Australia were connected; after continental drift, Australia became geographically isolated, allowing marsupials to diversify without placental competition.

How do reproductive strategies differ between marsupials and placental mammals?

Marsupials have a short gestation period inside the womb, after which tiny, underdeveloped young finish developing in an external pouch; placental mammals retain embryos longer in the uterus supported by a placenta, giving birth to fully developed offspring.

What are vestigial structures, and what are common examples in humans, birds, and marine mammals?

Body parts fully developed and functional in an ancestral group that are reduced and have little to no function in modern descendants. Examples include reduced wings in flightless birds (ostriches, penguins), unused hind limb/hip bone remnants in whales and snakes, and goosebump follicle muscles, wisdom teeth, and tailbone remnants in humans.

What are homologous structures, and how are vertebrate forelimbs an example?

Structures with similar basic anatomy due to common ancestry modified for different environments ('same structure, different function'). Examples include vertebrate forelimbs modified in whales (swimming), cats (walking), horses (running), humans (grasping), and bats/birds (flying).

What are analogous structures, and how are bird wings and insect wings an example?

Structures that perform similar duties but are constructed differently ('same function, different structure'), indicating no recent common ancestry. For example, bird wings have bony/feathered structures, whereas insect wings consist of chitinous membranes.

What early developmental traits are shared by all vertebrate embryos?

Eyes, pharyngeal pouches, and a postanal tail.

How do pharyngeal pouches diverge in development between fish and humans?

They develop into gills in fish, but in humans they turn into parts of the middle ear, tonsils, thymus, and parathyroid glands.

What is the distinction between an organism's genotype and its phenotype?

Genotype is the genetic makeup or specific combination of alleles inherited from parents, whereas phenotype is the physical expression or outward appearance of an organism's traits.

What is directional selection?

A pattern of natural selection where an extreme phenotype is favored, shifting the distribution curve toward that extreme direction (e.g., adaptation to changing environments).

What is stabilizing selection?

A pattern of natural selection where an intermediate (moderate) phenotype is favored over extreme phenotypes; it is the most common form of selection.

What is disruptive (diversifying) selection?

A pattern of natural selection where two or more extreme phenotypes are favored over intermediate values, maintaining polymorphism (distinct forms) in a population.