Biol 214 - Topic 2 Definition of Terms

Topic 2, tested on the 9/18/2025 exam for topics 1-6. Development of Evolutionary Thinking.

Biological Evolution

The process by which a population of organisms changes its genetic makeup and heritable characteristics over successive generations.

Adaptation

A heritable, physical, physiological, or behavioral trait that evolves through natural selection to increase an organism's chances of survival and reproduction in its specific environment.

Natural Theology

A way of understanding God or a higher power through human reason and the observation of the natural world. This belief did not allow the process of evolution or extinction, since each organism was presumed to be perfect and unchanging.

Comparative Morphology

The study of how homologous (shared) structures vary across different organisms to understand evolutionary relationships and the process of evolution.

Biogeography

The branch of biology that deals with the geographical distribution of plants and animals.

Natural Selection

A biological process where organisms with advantageous traits for their environment are more likely to survive and reproduce, passing those traits to their offspring.

Comparative Embryology

The study of similarities and differences in the developmental processes of embryos across different species, used to understand evolutionary relationships and a shared common ancestor.

Paleontology

The branch of science concerned with fossilized animals and plants.

Micro vs Macroevolution

Microevolution involves small genetic changes within a population over short periods. Macroevolution refers to large-scale changes over long periods, resulting in new species and higher taxonomic groups.

Macrobiology

The study of large, macroscopic living organisms that can be seen with the naked eye.

Paleobiology

A sub-discipline withing paleontology that applies modern biological principles/methods to understand the biological aspects of extinct organisms.

Strata

A layer or series of layers of rock in the ground. Singular noun: stratum.

Radiometric Dating

A scientific method of calculating the age of rocks, fossils, and Earth materials by measuring the decay of radioactive isotopes as they turn from unstable parent isotopes into stable daughter isotopes. Measured via half-lives, which are constant and predictable. Works best on igneous rocks.

Continuous Distribution

A mathematical concept used to model biological phenomena where a variable can take an infinite, uncountable number of values within a given range. Describes phenomena that changes gradually over a range of values.

Disjunct Distribution

A pattern where a species or taxon has populations that are separated by a significant geographic distance or a barrier, preventing continuous interaction.

Dispersal

The active (requiring effort) or passive (requiring no effort) movement of organisms, or their propagules (like seeds or spores), from their place of origin to new locations where they can establish new populations.

Vicariance

The geological or environmental process of fragmentation that creates a dispersal barrier, separating a once continuously distributed species into two or more isolated populations.

Endemic Species

A plant or animal that is found exclusively in a particular geographic area and not found anywhere else in the world.

Continental Drift

The movement of continents with relation to time. Currents in the mantle break apart plates of Earth’s crust, creating new environments and selection pressures. This is especially notable in latitudinal changes.

Convergent Evolution

The evolution of similar adaptations in distantly related organisms that occupy similar environments.

Adaptive Radiation

Rapid speciation that produces closely related species. These species occupy different niches in their habitat.

Background Extinction

The slow, constant, and gradual rate of species disappearance due to organisms being poorly adapted as environments change. The “natural” rate for extinction.

Mass Extinction

A large number of species and lineages that die out over relatively short periods of geological time. At least 6 have happened. Hinges on Cuvier’s theory of catastrophism.

Late Ordovician Mass Extinction

~445 million years ago, the first of the "Big Five" mass extinctions wiped out about 85% of marine species in two pulses. Caused primarily by global cooling and glaciation.

The Permian Mass Extinction

~252 million years ago, known as the “Great Dying” and marked the most severe extinction event in Earth’s history. Resulted in the loss of approximately 90-96% of marine species and about 70% of land species due to massive volcanic eruptions, which led to extreme global warming, ocean acidification, and anoxia (lack of oxygen).

Cretaceous–Paleogene (K-T) Mass Extinction

~ 666 million years ago. Marked the mass extinction of 75% of all plant and animal species on Earth, as well as the extinction of all non-avian dinosaurs from a massive asteroid impact.

Phyletic Gradualism

The idea that evolution is a slow, continuous change over time.

Ex; the development of trilobite tail ribs steadily increased over a 3-million year period, so much so that there was no clear break between the ancestral species and its descendants.

Punctuated Equilibrium

Long periods of no morphological change (stasis) punctuated by brief periods of speciation.

Ex; transitional fossils showcase occasional "jumps" in morphology. These transitional forms were unlikely to be preserved because they existed in small, isolated populations, making them "rare" in the fossil record and explaining why the "missing links" are not abundant, as gradualism might predict.

Allometric Growth

A biological principle describing how different body parts of an organism grow at different relative rates, leading to changes in shape as the organism matures. This usually suggests that a body part's size doesn't scale uniformly with the entire body; it either grows faster (positive allometry) or slower (negative allometry) than the organism as a whole.

Allows scientists to see similarities in species.

Heterochrony

An evolutionary mechanism involving changes in the timing of development, leading to variations in the final adult form of an organism compared to its ancestor.

Allows scientists to see differences in species.

Paedomorphosis

An evolutionary process where a sexually mature adult organism retains juvenile features (in opposition to a transformation, such as growth spurts that change an organism’s physiological state).

Exaptation

When an original version of a trait shifts in function through modification.

Ex; dinosaurs with feathers for mating eventually changed into birds with feathers for flight.

Homeobox Genes

Also collectively known as a genetic toolkit that is applied in different ways. The idea that most multicellular organisms bind DNA similarly, but gene regulation causes differences among them.

Governs the basic design of the body plan by controlling the activity of thousands of other genes.

Taxonomic Hierarchy

Organisms become more similar & share more characteristics the further down you go on the hierarchy.

Phylogenetic Trees

A diagram showing hypothesized evolutionary history.

Clades

An area of a phylogenetic tree that includes a common ancestor and ALL of its descendants.

Synapomorphy

A trait that is similar among species because the common ancestor of those species had that trait.

Monophyletic Taxon

Considered a clade. A taxon (grouping on the phylogenetic tree) that includes a recent common ancestor and ALL of its descendants.

Polyphyletic Taxon

NOT considered a clade. A taxon (grouping on the phylogenetic tree) that includes descendants from different evolutionary lineages and NO common ancestor.

Paraphyletic Taxon

NOT considered a clade. A taxon (grouping on the phylogenetic tree) that includes SOME descendants and their most recent common ancestor.

Phylogenetic Analyses

Phenotypic similarities (observable physical and functional traits) between organisms reflect their underlying genetic similarities.

Homology

A principle used within phenotypic analysis. The study of likeness due to genetic similarities, used to determine shared ancestry.

Homoplasy/Non-Homologus/Analogous Similarities

Phenotypic similarities between organisms that have little genetic relation and evolved independently, such as through convergent evolution.

Comparative Morphology vs Homology

Morphology is the scientific study of form and structure, while homology is the concept that two structures in different species are similar because they were inherited from a common ancestor. Therefore, morphology is a field of study, and homology is a type of evidence used within that field to understand evolutionary relationships.

Prezygotic Barrier

A reproductive isolating mechanism that prevents members of different species from mating and forming a zygote, or a fertilized egg.

Postzygotic Barrier

A reproductive isolating mechanism that acts after fertilization, preventing a hybrid offspring from developing into a viable, fertile adult.

Molecular Sequencing

The examination of RNA and DNA nucleotide base sequences (A, G, C, T, U).

Advantages include its abundant data, its ability to compare distant and closely related organisms, and the fact that genes aren’t damaged by external factors such as environment or morphological features.

Disadvantages include the fact that there are only 4 bases and 20 amino acids. Because of this, it’s hard to judge whether organisms are homologous or homoplastic without further lab experiments.

Polymerase Chain Reaction (PCR)

A scientific technique used to make copies of specific DNA fragments during molecular sequencing.

Cladistics

Classification based on evolutionary relationships. Morphology provides the data (the structural features), whereas this practice is the analytical method used to construct cladograms (evolutionary trees) from that data.

Ancestral Character

A term used in cladistics describing a specific heritable attribute or property passed down from a distant ancestor.

Derived Character

A term used in cladistics that describes a new specific heritable attribute or property that evolved in a common ancestor and is then passed down to its descendants, setting them apart from other lineages.

Synamorphy

A term used in cladistics that describes a TYPE of derived character that is shared by two or more species or groups.

Outgroup Comparison

Using an outgroup (a group of organisms not belonging to the clade whose evolutionary relationships are being investigated) to identify ancestral & derived characteristics.

Ancestral vs Derived Characteristics

Look at the phylogenetic tree. Ancestral traits should be persisting characteristics that organisms usually share, while derived characteristics should be new characteristics that create a recent branch that differentiates the organism(s).

Principle of Parsimony

The simplest explanation of any phenomenon is often the best. This train of thought is less effective for molecular data, as some animals who don’t share many external characteristics may still be genetically related.

Genetic Distance Method

Considers genetic differences to build evolutionary relationships. Used to build evolutionary tree and estimate divergence times. Less accurate than the maximum likelihood method since it relies on pairwise genetic distances (rather than taking in the whole account of a phylogenetic tree).

Maximum Likelihood Method

A statistical technique for estimating unknown probability by finding the phylogenetic tree that maximizes the probability of observing the given data.

Molecular Clock

A technique for dating the time of divergence of 2 species based on the number of molecular sequence differences. Large differences = more time since the species diverged.

Vertical Gene Transfer

Gene transfer from parent to offspring.

Horizontal Gene Transfer

Genes move between organisms and species via conjugation (through touch), transformation (through environment), and transduction (through a virus).

Oparin-Haldane Hypothesis

Proposed that a reducing atmosphere (lacking free oxygen) exposed to energy sources like lightning and UV radiation facilitated the formation of accumulating simple organic molecules.

Miller-Urey Experiment

An experiment that simulated a reducing atmosphere and produced organic molecules, showing that abiotic synthesis of these molecules are possible. Now outdated, as we know now that early Earth had a neutral environment.

RNA World Model

The proposition that RNA is most likely the first genes and enzymes/replicators and that DNA evolved later.

Pros to early RNA development: central in replication and biology today

Cons: Unstable and difficult to form long strands.

Membrane Development

These structures held useful molecules, genetic info, and the intracellular environment. Formed the lipid bilayer spontaneously. Permeable to amino acids/nucleotides. An early replication method involved splitting after the accumulation of too many lipids.

LUCA

Stands for the Last Universal Common Ancestor. Evolved DNA-based genome replication & transcription machinery, ribosomes and RNA for protein synthesis, oxidative metabolism, membranes, and cell division mechanisms.

Evidence: isotope ratios, stromatolites and microfossils.

Domains: Archaea, Eukarya, and Bacteria.

Archaea, Eukarya, and Bacteria

The three domains of cellular life. Archaea is more closely related to eukarya than bacteria due to the presence of histones, RNA, and introns. However, archaea and bacteria share circular chromosomes and operons.

“Ring of Life”

The belief that eukarya is a fusion of archaeal and bacterial domains.

Deuterostomes

Bilaterally symmetrical animals whose anus forms before their mouth.

Echinodermata

Simple oceanic herbivores & predators with no excretory or respiratory systems.

Ex; starfish, sea cucumbers, sea urchins.

Chordata

A deuterostome that possesses a notochord (the pre-cursor to a spinal chord), segmental body wall muscles, a dorsal hollow nerve chord, and a perforated pharynx.

Cephalochordata

A deuterostome that retains chordate traits in adults.

Urochordata

A deuterostome that possesses chordate traits in larvae, but not in adulthood.

Verbrata

Any living organism that possesses a cranium, vertebrae, neural crest cells, or bone cells.

HOX Gene

Genes that regulate early locational development in the fetus. Vertebrates have 4 copies. Proteins activate or repress genes.

Jaws (Gnathostoma) & Fins (Fish)

Developed from pharyngeal arches in invertebrate chordates. Bones in gills came closer and closer, providing structural support for jaws. Increased frequency of moveable spines in fins, alongside jaws. Swim to eat, eat to swim dynamic.

Chondrichthyes

Fish with cartilaginous endoskeletons.

Osteichthyes

Fish with bony endoskeletons. Separated into Actinopterygii (ray-finned) and Sarcopterygii (flesh-finned).

Tetrapoda

Evolved from Sarcopterygii, with homologous structures in the hands. Contains amphibians.

Amniota

Characterized by rough, dry, skin, amniote legs, and uric acid present in urine to prevent the dehydration brought on by terrestrial living. Laid eggs and contained Reptilia (precursor of reptiles) and Synapsida (precursor to mammals, with glandular skin and fur).

Birds

Similar structures to dinosaurs, emerging from the Reptilia line of evolution. Practices flight, possesses scales and feathers. Evolved hollow bones.

Mammals

Possesses a high metabolic rate & body temp, requiring lots of oxygen. Specialized teeth & jaws for food, practices parental care, and possesses complex brains.