AP Bio chapt 19-23: Evolution

Evolution

Descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones; also defined more narrowly as the change in the genetic composition of a population from generation to generation

Strata

distinct, layered bands of sedimentary rock formed over millions of years by the accumulation and compression of sediments, such as sand, mud, and organic material. These layers function as geological time capsules, with older layers at the bottom and younger layers on top, often containing fossils that allow scientists to reconstruct Earth’s biological and environmental history

Adaptation

Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment

Natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

Artificial Selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

Members of a population often vary in their inherited traits, all species can produce more offspring than their environment can support and many of these offspring fail to survive and reproduce.

Name Darwin’s 2 observations

Homology

the similarity in anatomical structures, physiology, development, or genes between different organisms that is based on common ancestry. These features often serve different functions in modern species due to adaptive modifications but share a fundamental structural pattern inherited from a common ancestor.

Homologous structures

physical features in different organisms that share a common evolutionary ancestor, often possessing similar underlying anatomical compositions despite having different functions

Vestigial structures

A feature of an organism that is a historical remnant of a structure that served a function in the organism’s ancestors

Covergent evolution

the independent evolution of similar features in species of different lineages, typically occurring when unrelated organisms adapt to similar environments or ecological niches. It produces analogous structures—traits with similar functions but different evolutionary origins—rather than shared ancestry

Analogous structure

physical features in different species that perform similar functions but evolved independently rather than from a common ancestor. These structures arise from convergent evolution, where unrelated organisms adapt to similar environmental challenges.

Pangaea

The supercontinent that formed near the end of the Paleozoic era, when plate movements brought all the landmasses of Earth together

Endemic

Defines organisms, such as plants or animals, that are native to a specific, restricted geographic area and are found nowhere else, (ie numerous species in the Galapagos islands)

Phylogenetic tree

A branching diagram that represent a hypothesis about the evolutionary history of a group of organisms

Branch points

The representation on a phylogenetic tree of the divergence of two or more taxa from a common ancestor. This is usually shown as a dichotomy in which a branch representing the ancestral lineage splits (at the branch point) into two branches, one for each of the two descendant lineages

Sister taxa

Groups of organisms that share an immediate common ancestor and hence are each other’s closest relatives

Rooted

Term describing a phylogenetic tree that contains a branch point (often, the one farthest to the left) representing the most recent common ancestor of all taxa in the tree

Polytomy

In a phylogenetic tree, a branch point from which more than two descendant taxa emerge. A ________ indicates that the evolutionary relationships between the descendant taxa are not yet clear.

Analogy

Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait

Homoplasies

A similar (analogous) structure or molecular sequence that has evolved independently in two species

Cladistics

An approach to systematics in which organisms are placed into groups called clades based primarily on common descent

Clades

A group of species that includes an ancestral species and all of its descendants, also known as a monophyletic group

Paraphyletic

Term pertaining to a group of taxa that consists of a common ancestor and some, but not all, of its descendants

Polyphyletic

Term pertaining to a group of taxa that includes distantly related organisms but does not include their most recent common ancestor

Shared ancestral character

A character that is shared by members of a particular clade but that originated in an ancestor that is not a member of that clade

Shared derived character

a trait that evolved in the most recent common ancestor of a particular clade (lineage) and is inherited by its descendants, but not by earlier ancestors

Outgroup

A species or group of species from an evolutionary lineage that is known to have diverged before the lineage that contains the group of species being studied. A(n) ________ is selected so that its members are closely related to the group of species being studied, but not as closely related as any study-group members are to each other

Ingroup

A species or group of species whose evolutionary relationships are being examined in a given analysis

Maximum parsimony

A principle that states that when considering multiple explanations for observation, one should first investigate the simplest explanation that is consistent with the facts. (often used in the case of trees based on morphology)

Molecular clock

A scientific tool used to estimate the timing of evolutionary events, such as when species diverged from a common ancestor, by measuring the accumulation of genetic mutations over time. It operates on the principle that DNA or protein sequences evolve at a relatively constant rate.

Horizontal gene transfer

The transfer of genes from one genome to another through mechanisms such as transposable elements, plasmid exchange, viral activity, and perhaps fusions of different organisms—the occurrence of these events helps to explain why trees built using different genes can give inconsistent results.

Microevolution

the change in allele frequencies (genetic composition) within a single population or species over a short period of time. It involves small-scale changes—such as antibiotic resistance in bacteria or beak size changes in finches—that do not create new species but alter the genetic makeup of the population

Genetic variation

Differences among individuals in the composition of their genes or other DNA segments

Neutral variation

Genetic variation that does not provide a selective advantage or disadvantage. Sources of these include silent mutations and the redundancy of the genetic code.

Population

A group of individuals of the same species that live in the same area and interbeed, producing fertile offspring

Hardy Weinberg Equilibrium

The state of a population in which frequencies of alleles and genotypes remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.

No mutations, random mating, no natural selection, large population size, no gene flow

What are the 5 conditions a population must follow to be considered in Hardy Weinberg Equilibrium?

Founder effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population. This might occur, for example, when a few members of a population are blown by a storm to a new island.

Bottleneck effect

Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically the surviving population is no longer genetically representative of the original population. By chance alone, certain alleles may be overrepresented among the survivors, others may be underrepresented, and some may be absent altogether.

Genetic drift

A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of ________ are most pronounced in small populations. This process can lead to a loss of genetic variation within populations, as it can gradually eliminate alleles from a population; it can also cause harmful alleles to become fixed

Gene flow

The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes (e.g. pollen drifting to new areas). It increases genetic diversity within a population while reducing differences between populations (via hybridization), acting as a crucial force in evolution and maintaining species consistency.

Adaptive evolution

A process in which traits that enhance survival or reproduction tend to increase in frequency in a population over time

Relative fitness

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population. This does not indicate strength or size, and is measured only by reproductive success.

Directional selection

A type of natural selection that shifts the overall makeup of the population by favoring phenotype variants that are at one extreme of the distribution.

Disruptive selection

Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes

Stabilizing selection

Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes

Balancing selection

a type of natural selection that maintains multiple alleles (genetic variations) in a population, preventing any single allele from becoming fixed or lost. Unlike directional selection which favors one phenotype, this mechanism preserves genetic diversity, typically through heterozygote advantage, frequency-dependent selection, or spatial heterogeneity

Heterozygote advantage

a phenomenon in population genetics where individuals with two different alleles (heterozygotes) for a specific gene have higher fitness—better survival or reproductive success—than individuals with two identical alleles (homozygotes); maintains genetic diversity by preventing deleterious alleles from being eliminated from the population

Frequency dependent selection

Selection in which the fitness of a phenotype depends on how common the phenotype is in a population. It can be negative (rare types have an advantage, maintaining diversity) or positive (common types are favored, reducing diversity).

Sexual selection

A process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates. Can result in sexual dimorphism.

Sexual dimorphism

Differences between the secondary sex characteristics of males and females of the same species. These distinctions include differences in size, color, ornamentation, and behavior.

Intersexual selection

Sexual selection within the same sex; individuals of one sex compete directly for mates of the opposite sex. In many species, this occurs among males.

Instrasexual selection

Type of sexual selection in which individuals of one sex (usually the females) are choosy in selecting their mates from the other sex. In many cases, the female’s choice depends on the showiness of the male’s appearance or behavior

Speciation

the evolutionary process by which new, genetically distinct species arise from existing ones. It occurs when populations become reproductively isolated, preventing gene flow and allowing them to evolve independently through natural selection or genetic drift.

Macroevolution

Evolutionary change above the species level. Examples of __________ change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinctions on the diversity of life and its subsequent recovery.

Prezygotic barriers

A type of reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted. Key types include habitat, temporal, behavior, mechanical, and gametic isolation

Postzygotic barriers

A reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults. Key types include hybrid inviability, hybrid sterility, and hybrid breakdown (future generations are weak and sterile)

Morphological species concept

Species concept that defines species based on distinct physical, structural, or anatomical features. It is a foundational, practical approach in taxonomy where individuals that look alike are grouped together. This method is essential for classifying fossils and asexual organisms, though it faces challenges from subjective interpretation and phenotypic variation.

Ecological species concept

Definition of a species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment

Phylogenetic species concept

Definition of a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life

Allopatric speciation

The formation of a new species in populations that are geographically isolated from one another, which prevents gene flow and leads to independent evolution

Sympatric speciation

The process by which new species evolve from a single ancestral population while inhabiting the same geographic location. Unlike allopatric speciation, it occurs without physical barriers, driven instead by reproductive isolation, disruptive selection, or polyploidy.

Polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division.

autopolyploidy

An individual that has more than two chromosome sets that are all derived from a single species. . It often results from meiotic errors producing unreduced (2n) gametes or mitotic failures, leading to increased cell size and often, increased, though sometimes less fertile, phenotypes

Allopolyploid

A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes/hybridization of these species followed by chromosome doubling.

Hybrid zone

A geographic area where two distinct, closely related populations or species meet, interbreed, and produce offspring of mixed ancestry. These zones exhibit characteristic allele frequency patterns that reveal the balance between dispersal (gene flow) and selection. The most common pattern is a sigmoidal (S-shaped) curve, where allele frequencies change slowly at the ends (parental populations) and rapidly in the center (______ ____)

Reinforcement

In evolutionary biology, a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing the chances of hybrid formation. Such a process is likely to occur only if hybrid offspring are less fit than members of the parent species.

Fusion

In evolutionary biology, a process in which gene flow between two species that can form hybrid offspring weakens barriers to reproduction between the species. This process causes their gene pools to become increasingly alike and can cause the two species to fuse into a single species.

Stability

In evolutionary biology, a term referring to a hybrid zone in which hybrids continue to be produced/one of the possible fates for a hybrid zone. In some cases, this occurs because the hybrids survive or reproduce better than members of either parent species, at least in certain habitats or years; this causes the hybrid zone to be “stable” in the sense of persisting over time.

Punctuated equilibria

In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change.

Radiometric dating

A method for determining the absolute age of rocks and fossils, based on the half-life/decay of radioactive isotopes. In this process, a radioactive “aprent” isotope decays to a “daughter” isotope at a characteristic rate.

Half-life

The amount of time it takes for 50% of a sample of a radioactive isotope to decay.

Geologic record

A standard time scale dividing Earth’s history into time periods grouped into four eons—Hadean, Archaean, Proterozoic, and Phanerozoic—and further subdivided into eras, periods, and epochs.

Stromatolites

Layered rock that results from the activities of prokaryotes that bind thin films of sediment together. The earliest direct evidence of life comes from the Archaean eon, based on 3.5 billion-year-old fossils of ________

Plate tectonics

The theory that the continents are part of great plates of Earth’s crust that float on the hot, underlying portion of the mantle. Movements in the mantle cause the continents to move slowly over time in a process called continental drift.

Mass extinction

The elimination of a large number of species throughout Earth, the result of global environmental changes

Adaptive radiation

Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities. Common drivers are colonizing new habitats, mass extinctions, or development of new adaptations. Different from normal adaptation in that it occurs at a rapid pace + involves high-speed diversification and the emergence of multiple, distinct species from a common ancestor to fill vacant ecological niches

Heterochrony

an evolutionary mechanism defined as a change in the timing or rate of developmental events (ontogeny) in a descendant species compared to its ancestor. This alteration in development leads to significant shifts in the size, shape, and structure of adult organisms, playing a crucial role in evolution

Paedomorphosis

A biological phenomenon where an organism retains juvenile or larval traits into its adult stage. This evolutionary developmental process results in adults that look similar to the young of their ancestors. Examples include the Mexican axolotl

Binomial

A common term for the two-part, latinized format for naming species, consisting of the genus and specific epithet

Basal taxon

In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group

Gene pool

The aggregate of all copies of every type of allele at all loci at every individual in a population.

Natural selection favors only the fittest phenotypes among those currently in the population (existing variation) which may not be ideal traits, evolution is limited by historical constraints/operates on traits an organism already has, adaptations are often compromises, and chance, natural selection, and the environment interact.

Why can’t natural selection create perfect organisms? (4)

Biological species concept

Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups

Reproductive isolation

The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring

Hybrid

Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species

Homeotic gene

Any of the mater regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells (e.g. Hox genes)

Temporal isolation

a prezygotic reproductive barrier where two or more species are prevented from interbreeding because they reproduce at different times. This isolation can occur based on different breeding seasons, times of day, or mating years, even if the populations inhabit the same geographic location, reducing gene flow and promoting speciation

Mechanical isolation

a prezygotic reproductive barrier where physically incompatible reproductive structures or differences in size and shape prevent two different species from mating—mating is attempted, but morphological differences prevent successful completion

Gamete isolation

a prezygotic reproductive barrier where sperm and egg from different species are incompatible, preventing fertilization and zygote formation

ex: in sea urchins, species like the giant red urchin and purple urchin may release sperm and eggs into the same water, but biochemical mismatches in egg-recognition proteins prevent cross-fertilization

Habitat isolation

A prezygotic reproductive barrier where two closely related species, inhabiting the same geographic area, live in different environments or ecological niches. As they rarely encounter each other, they do not interbreed, allowing them to remain genetically distinct even while sharing a general location.

Behavioral isolation

A prezygotic reproductive barrier in biology where distinct courtship rituals, mating calls, or pheromones prevent closely related species from interbreeding.

RNA world hypothesis

Idea which proposes that early life forms relied solely on self-replicating RNA for both genetic information storage and catalytic functions, preceding modern DNA and protein-based life

Endosymbiotic hypothesis

Theory that posits that eukaryotic cells evolved when large prokaryotic cells engulfed smaller, aerobic, or photosynthetic bacteria, which then lived inside the host and evolved into organelles (mitochondria and chloroplasts). This theory explains how organelles possess their own circular DNA, double membranes, and 70S ribosomes, similar to bacteria