Evolutionary Thought & Theory Quizlet
Section 1: Foundations of Evolutionary Thought
The fundamental biological concept defining a change in a species over time, ultimately driven by genetic variations and environmental pressures.
An early evolutionary theorist who correctly concluded that complex organisms descended from less complex ones, but incorrectly proposed the mechanism of evolution before Darwin.
Lamarck’s flawed hypothesis stating that if an organism does not use a body part, it loses it, and the parts used the most grow stronger over its lifespan.
Lamarck’s disproven idea that physical characteristics an organism develops or acquires during its lifetime (e.g., stretched neck, amputated arm) are passed directly to its offspring.
Lamarck’s classic (but incorrect) analogy that a giraffe’s neck grows longer during its lifetime specifically to reach higher leaves, and this longer neck is then passed to babies.
The scientist who officially disproved Lamarck’s theory of acquired traits in the late 1800s through physical experimentation across multiple generations.
Weismann repeatedly cut off the tails of mice and mated them. Because the offspring were always born with normal-length tails, it proved acquired traits are not inherited.
Organisms are BORN with genetic characteristics; they do not “acquire” or grow new heritable characteristics during their lifespan based on need or use.
Proposed the widely accepted Theory of Natural Selection in 1859, noting how pre-existing variation among members of a species provided unique adaptations to their environment.
Darwin’s term for evolution, indicating that over vast amounts of time, species diverge from common ancestors while accumulating specific modifications (adaptations).
A core tenet of Darwinian evolution: a trait must exist first in the genetic variation of a population for the environment to select it; organisms cannot simply summon a trait when needed.
The concept that the environment limits the growth of all populations by causing deaths or limiting births, creating the selective pressure necessary for natural selection.
Section 2: Mechanisms of Evolution & Natural Selection
The primary mechanism of evolution consisting of four main parts: Overproduction, Genetic Variation, Competition, and Differential Reproduction.
Organisms naturally produce more offspring than can possibly survive in a given environment, creating a struggle for limited resources.
An economist whose writings on human population growth outstripping food supply directly inspired Darwin’s concept of overproduction in nature.
The natural, underlying differences found among individuals of a species. Darwin knew it was essential for adaptation, though he lacked the knowledge of DNA to explain its true source.
The direct consequence of overproduction; individuals must struggle against each other to secure resources, mates, and territory for survival.
The ultimate selective step: Organisms with the best adaptations are the most likely to survive, mate, and pass their advantageous traits to the next generation.
A phrase summarizing differential reproduction, where “fitness” refers exclusively to an organism’s ability to survive and reproduce in a specific environment.
Specific, inherited genetic traits that inherently increase an organism’s chance of survival and reproductive success in a given environment.
Mistakes in DNA replication or exposure to radiation/chemicals. This is the ultimate, original source of all genetic variation in both asexual and sexual populations.
The process of creating sex cells that introduces massive genetic variation into a population through crossing-over of homologous chromosomes.
An event specific to sexual reproduction during meiosis where chromosomes align randomly, creating unique genetic combinations in gametes.
The biological mechanism where any one specific sperm can fuse with any one specific egg, further amplifying genetic diversity within a population.
Section 3: Types of Adaptations & Selection Forces
Physical features of an organism that improve survival, such as a bird’s beak shape, large ears for cooling, or thorns on a plant.
Actions and habits that control how an organism acts to survive. Examples include nocturnal activity, hibernation, or specific blooming times for plants.
Internal biological traits based on body chemistry and metabolism that are not usually visible from the outside, such as plant toxins or highly efficient kidneys in desert animals.
Innate, genetically programmed behavioral adaptations that do not require teaching, such as migration, defensive mechanisms, and courtship rituals.
Behaviors acquired through experience and interaction, such as how to find specific food sources, build shelters, or communicate effectively.
Cooperative behavioral adaptations that increase the survival of the collective, including flocking (birds), schooling (fish), herding, and team hunting.
Highly specific inherited behavioral adaptations designed to attract mates of the same species, preventing cross-breeding and ensuring reproductive success.
Driven by the environment (“Mother Nature”), this process selects traits that improve organism fitness over long, generally slow periods of time.
Fast-paced evolutionary change driven entirely by humans choosing which organisms breed, based solely on traits desirable to humans (e.g., dog breeds, farm crops).
Natural selection directly improves overall fitness for specific circumstances. If conditions change, the previously selected trait may suddenly become disadvantageous.
Because traits are chosen for human utility or aesthetics rather than survival, artificial selection often causes a decrease in the overall natural fitness of an organism.
Environmental forces—like predators, climate, or food scarcity—that dictate which alleles are advantageous or deleterious in a specific habitat.
Section 4: Speciation and Reproductive Isolation
Defines a species as a population whose members can interbreed and produce viable, fertile offspring, but cannot do so with members of other populations.
The ultimate test of a species classification: offspring must not only survive (viable) but also be able to have their own offspring (fertile) to be considered the same species.
The evolutionary formation of an entirely new species, typically resulting from prolonged reproductive isolation over multiple generations.
When groups of individuals from the same original population become separated and can no longer successfully interbreed and produce fertile offspring.
The initial barrier in many speciation events, where populations are separated by physical obstacles like rivers, mountains, canyons, or stretches of water.
A classic example of geographic isolation where the Northern Spotted Owl and Mexican Spotted Owl evolved separately after being divided by geographic barriers.
Populations live in the same general geographic region but occupy entirely different habitats or micro-environments, preventing them from interacting to mate.
Populations are capable of interbreeding physically but do not because their reproductive strategies, courtship rituals, or mating songs are too different.
The Eastern and Western Meadowlarks look identical and overlap in territory, but experience behavioral isolation because they use completely different songs to attract mates.
A pre-zygotic barrier where the physical sex organs of different populations evolve to become structurally incompatible, physically preventing mating.
A post-zygotic barrier where mating occurs, but hybrid offspring are either never fully formed, born sterile, or have significantly lower survival fitness.
Reproductive isolation caused by populations breeding at different times of day, different seasons, or different years. Example: Eastern spotted skunk breeds in winter; Western breeds in fall.
Section 5: Macroevolution & Evolutionary Patterns
Major biological changes that occur over long spans of time, leading to speciation and large-scale patterns that are highly visible in the fossil record.
A pattern of macroevolution characterized by the rapid and widespread disappearance of species globally due to extreme ecological stress, human activity, or natural disasters.
Following a mass extinction, the disappearance of dominant species leaves open ecological niches, allowing surviving species to experience rapid speciation to fill them.
An evolutionary pattern where two species evolve in direct response to changes in each other’s adaptations due to their close ecological interactions.
Commonly seen in mutualistic relationships (flowers evolving specific shapes for particular pollinators) or evolutionary “arms races” (predator improving hunting vs. prey improving camouflage).
A process where a single ancestral species rapidly diverges into a vast variety of distinct species, each equipped with unique adaptations for specific environments.
The classic textbook example of adaptive radiation; one ancestral finch species from South America radiated into multiple species across the Galapagos, primarily differing in beak size for specific diets.
Adaptive radiation is driven by the sudden availability of multiple uninhabited ecological niches, often seen when species colonize isolated islands.
The underlying mechanism of adaptive radiation, where species with common ancestry accumulate differences as nature selects traits optimized for their separate environments.
Evolution on the absolute smallest scale: defined specifically as a generation-to-generation change in the actual frequencies of alleles within a single population.
Microevolution looks at shifting DNA/allele percentages in one localized population over a few years, whereas macroevolution looks at the emergence/death of entire species over millions of years.
Extinctions occur rapidly during times of extreme ecological stress, which can be natural (asteroids, volcanism, disease) or anthropogenic (pollution, habitat destruction).
Section 6: Genetics and Natural Selection Types
The combined, total genetic information (all alleles) present among all members of an interbreeding population at any given time.
The percentage or ratio of times a specific allele occurs in a gene pool compared to the total number of times other alleles for that gene occur.
From a purely genetic standpoint, evolution is occurring anytime there is a measurable change in the relative frequency of alleles within a population’s gene pool.
A primary source of genetic variation in sexually reproducing organisms, resulting from the independent assortment and crossing-over of chromosomes during meiosis.
A trait controlled by exactly one gene that has only two alleles, leading to only two distinct possible physical phenotypes (e.g., widow’s peak or no widow’s peak).
A famous historical example of natural selection on a single-gene trait. During the Industrial Revolution, soot darkened trees, shifting the allele frequency to favor the dark phenotype moth.
Complex traits controlled by the interaction of two or more genes (like human skin color, controlled by at least 6 genes), where gene products are additive.
The hallmark graphical expression of a polygenic trait’s phenotype in a population; it shows a continuous distribution where the intermediate trait is most common.
The three primary ways natural selection alters the bell curve of polygenic traits: Directional, Disruptive, and Stabilizing selection.
Natural selection favors individuals at one extreme end of the phenotypic range, causing the entire bell curve to physically shift in that direction.
Natural selection strongly favors individuals at both extremes of the phenotypic range while acting against the intermediate trait, creating a graph with two distinct peaks.
Natural selection favors the intermediate variant and acts against extreme phenotypes, causing the bell curve to become narrower and taller (e.g., human birth weight).
Section 7: Causes of Microevolution
Changes in allele frequencies occur primarily due to three mechanisms: Random Mutations, Nonrandom Mating, and Genetic Drift.
Mutations change nucleotide sequences and act as the ultimate source of all new alleles, serving as the essential raw material that makes microevolution possible.
A change as tiny as a single nucleotide in a protein-coding gene can cause severe phenotypic changes and evolutionary pressures, as seen in sickle-cell disease.
Occurs when individuals actively choose partners based on specific traits rather than mating blindly. This gives certain genes more opportunity to be passed on.
Because certain individuals get more opportunities to mate, their specific genetic alleles rapidly increase in frequency in the subsequent generations’ gene pool.
Random, unpredictable changes in allele frequencies that occur completely by chance. This phenomenon heavily impacts small populations rather than large ones.
A type of genetic drift where a small group of individuals breaks off to start a new population; their gene pool does not accurately reflect the diversity of the original larger population.
A type of genetic drift where a sudden, catastrophic environmental change drastically reduces population size. The few random survivors dictate the narrow gene pool of future generations.
Scientists prove a population is evolving by measuring and comparing the exact genotype/allele frequencies of the current generation against the frequencies of the next generation.
If the math shows the percentage of an allele (like ‘B’ or ‘b’) has shifted up or down from one generation to the next, microevolution has definitively occurred.
External environmental mutagens that trigger the random mistakes in DNA replication, artificially or naturally inducing mutations that feed microevolution.
Small populations lack a buffering effect; the random death of a few individuals carrying a rare allele can completely wipe that allele out of the gene pool by genetic drift.
Section 8: Biological Evidence for Evolution
The study of similarities and differences in the physical body structures of various species to determine their evolutionary relationships.
Anatomically similar body structures inherited from a common ancestor, though they may function entirely differently in the modern species (e.g., human arm, whale flipper, bat wing).
A specific, classic example of a homologous structure where vertebrates share a similar five-digit bone layout inherited from a distant common ancestor.
Structures that serve the exact same biological function (like flying or swimming) but are constructed completely differently and are NOT inherited from a common ancestor.
The fins of sharks (fish), flippers of penguins (birds), and flippers of dolphins (mammals) are analogous structures; they all evolved to swim but possess completely different internal anatomies.
The evolutionary process that produces analogous structures. Unrelated, genetically distinct species develop similar adaptations because they are subjected to the same environmental pressures.
The evolutionary process that produces homologous structures. Closely related species with common ancestry become more structurally different over time as they adapt to different environments.
Evidence of evolution found at the cellular level. Because all living things are made of cells with similar organelles (membrane, cytoplasm, ribosomes), it suggests universal common ancestry.
A core concept of cytology: the fewer differences there are in the cell structures of two organisms, the closer their evolutionary relationship appears to be.
The study of structural and developmental similarities in the embryos of different vertebrate species. Early stage similarities (directed by DNA) provide evidence of common ancestry.
Analyzing nucleic acids (DNA/RNA) and amino acid sequences. Highly similar proteins and enzymes across different species confirm close evolutionary relationships on a molecular level.
Physical remnants of organs or structures that functioned fully in an ancestral species but no longer serve any useful function today (e.g., the femur and pelvis bones hidden inside whales and snakes).
Section 9: Geological Evidence and Phylogeny
The preserved remains or traces of organisms that lived in the past, providing a sequential record of biological history and visible changes in biotic factors over time.
Cosmic rays collide with atmospheric atoms to produce neutrons. These neutrons collide with Nitrogen-14 to produce unstable Carbon-14, which enters the food chain via photosynthesis.
When plants and animals die, they stop taking in new Carbon-14. The remaining unstable Carbon-14 in their bones undergoes radioactive beta decay to turn back into Nitrogen-14.
Carbon-14 decays at a predictable rate with a half-life of 5,730 years. By measuring the ratio of C-14 to N-14, scientists can determine the exact (“absolute”) age of the sample.
Relative dating estimates age based on the fossil’s depth in rock layers (older is deeper). Absolute dating (like Carbon dating) uses chemical decay to give a precise numerical age.
The formal study of the evolutionary history and relationships of a species or group of related species, mapped out using structural and molecular evidence.
Classical phylogenetic data collected from observable physical similarities in living or fossil species (e.g., number of legs, petal colors, vein organization).
Modern phylogenetic data collected from exact DNA/RNA nucleotide sequences or amino acid sequences in proteins. This is considered the BEST and most definitive evidence for relatedness.
Laboratory procedures used to obtain molecular data. Electrophoresis separates DNA segments by size, while chromatography separates pigments.
A branching diagram that depicts patterns of shared characteristics among groups. The closer two branches come together in the past, the more closely related the species are.
Specific evolutionary adaptations or novelties (e.g., hair, opposable thumbs) that are unique to a particular clade and are used to construct the branching points on a cladogram.
Similar to a cladogram, but incorporates fossil and molecular data to show the actual amount of evolutionary change over time. Branches ending before the “present day” line indicate extinction events.
Section 10: Earth’s Origins & Contemporary Evolution
Forming ~4.6 billion years ago, primitive Earth was highly volcanic. Gases included carbon dioxide, water vapor, methane, and ammonia, but notably lacked free atmospheric oxygen (O2).
The ocean-based mixture of simple inorganic compounds and energy (lightning, heat) that spontaneously combined to synthesize the very first organic building blocks (amino acids/nucleotides).
A famous lab experiment that recreated early Earth conditions (gases, sparks for lightning, water). It successfully formed simple amino acids in a week, proving organic molecules could form without life.
Tiny, semi-permeable bubbles formed by large organic molecules. While not alive, they can store and release energy, hypothesizing how simple chemical structures gained cell-like traits.
The scientific theory that the earliest genetic material was RNA, not DNA. RNA is capable of both storing genetic information and acting as a self-replicating enzyme.
About 2.2 billion years ago, early photosynthetic bacteria began pumping oxygen into the oceans and atmosphere. This drove many anaerobic organisms to extinction but paved the way for complex aerobic life.
The theory that complex eukaryotic cells arose when an ancestral prokaryotic cell engulfed aerobic and photosynthetic bacteria, forming a permanent mutualistic relationship.
Mitochondria and chloroplasts have their own circular DNA matching living prokaryotes, reproduce by binary fission, and have prokaryote-like ribosomes, proving they were once independent bacteria.
Unlike asexual reproduction (which restricts variation to mutations), sexual reproduction constantly shuffles genes, dramatically increasing genetic variation and evolutionary adaptability.
Evolution occurring today: A bacterial population naturally has a few individuals with random mutations granting antibiotic resistance. Drugs kill off all the weak bacteria, leaving only the resistant ones.
Once antibiotics remove the competition (the non-resistant bacteria), the resistant bacteria face optimal conditions. They grow, take over, and can even horizontally transfer their resistance genes to other bacteria.
The observable, rapid microevolution of viruses and bacteria leading to emergent global diseases. For example, the continuous genomic mutations and adaptation of the 2019 Coronavirus (nCoV).
Section 11: Miscellaneous & Specific Examples
Asexual reproduction yields exact copies, restricting variation solely to random DNA mutations[cite: 669, 670, 671]. Sexual reproduction continuously shuffles genes, increasing the probability of favorable combinations for natural selection[cite: 672, 674, 675].
Random mutations—the ultimate source of new alleles—are caused by mistakes in DNA replication or exposure to environmental factors like radiation, chemicals, and pesticides[cite: 64, 65, 308].
To determine evolutionary relatedness, scientists look specifically at the structure and function of nucleic acids (DNA/RNA) and the exact amino acid sequences of specific proteins and enzymes[cite: 399, 400, 477, 478, 479].
Earth formed ~4.6 billion years ago (bya) and remained too hostile for life until 3.9 bya[cite: 544]. The absolute earliest fossil evidence for single-celled life dates back to 3.5 bya[cite: 545].
The first life evolved without oxygen[cite: 634]. Around 2.2 billion years ago, early photosynthetic bacteria began pumping oxygen into the oceans [cite: 634], though it wasn’t abundant in the atmosphere until 600-800 million years ago[cite: 635].
A key piece of evidence for the Endosymbiotic Theory is that mitochondria and chloroplasts reproduce independently within the eukaryotic cell through binary fission, just like free-living prokaryotes[cite: 664].
Chloroplasts have their own distinct DNA that matches living prokaryotes[cite: 665]. Specifically, chloroplast genes closely match the genes of cyanobacteria, proving their evolutionary origin[cite: 665].
Microscopic fossils of unicellular, prokaryotic organisms that resemble modern bacteria, found in rocks dating back over 3.5 billion years, representing the earliest known life forms[cite: 633].
A major piece of evidence supporting the RNA World Hypothesis is that RNA is found in the catalytic site of modern ribosomes and actively plays a role in forming peptide bonds[cite: 626].
Geographic: The Northern Spotted Owl and Mexican Spotted Owl were separated by mountains[cite: 132, 134, 145]. Temporal: The Eastern spotted skunk breeds in late winter, while the Western spotted skunk breeds in the fall[cite: 150, 151].
The Eastern and Western Meadowlarks look identical and overlap in territory, but do not interbreed because they use completely different songs to attract mates[cite: 142, 143].
Directional: Peppered moths shifting to dark colors[cite: 300]. Disruptive: Rock pocket mice favoring distinct light or dark coats[cite: 300]. Stabilizing: Human birth weight favoring average sizes over dangerous extremes[cite: 300].