DE Bio -- Evolution

What is evolution in the context of biology?

The greatest unifying theme of biology — it explains the adaptations of organisms and accounts for both the unity and diversity of life.

What does "descent with modification" mean?

It means that living species have arisen from earlier life forms (descent) and that species change over time (modification), accumulating diverse adaptations as descendants spread into various habitats over millions of years.

What are adaptations?

Inherited traits that enhance an organism's ability to survive and reproduce in a particular environment.

What questions arose before Darwin that set the stage for evolutionary theory?

Whether the Earth could be older than 6,000 years, why fossils resemble living organisms, and whether organisms can pass on acquired characteristics (Lamarck's idea).

What was Lamarck's Theory of Inheritance of Acquired Characteristics?

The idea that organisms could pass on traits they developed during their lifetime to their offspring — this was ultimately shown to be incorrect.

Who was Charles Darwin, and what was the HMS Beagle?

Darwin was born in 1809 and in 1831, at age 22, became the ship's naturalist on the HMS Beagle, traveling around the world for 5 years collecting and documenting species.

What book did Darwin publish, and when?

In 1859, Darwin published "On the Origin of Species by Means of Natural Selection."

What were Darwin's two general conclusions from his voyage?

First, that living species have arisen from earlier life forms (descent). Second, that species change over time (modification).

Summarize Darwin's full concept of descent with modification.

All organisms are related through descent from a common ancestor that lived in the remote past. Descendants spread into various habitats over millions of years and accumulated diverse modifications, or adaptations.

What are the four components of Darwin's Theory of Evolution by Natural Selection?

1) Overreproduction — more offspring are produced than can survive. 2) Variety in every population. 3) Survival of the fittest. 4) Accumulation of beneficial traits over time.

What is natural selection?

The mechanism of descent with modification — it equals differential reproductive success, meaning individuals with favorable traits are more likely to survive and reproduce.

What are paleontologists?

Scientists who study fossils.

What are the different ways fossils can form?

Hard parts (bones, teeth, shells) can remain; petrification occurs when minerals replace organic matter; molds and casts form when organisms decay in sediment and minerals fill the space; trace fossils include footprints and burrows; some fossils retain organic material like leaves; entire organisms can be preserved in resin, ice, or acid bogs.

What is petrification?

A fossilization process in which minerals dissolved in groundwater seep into the tissues of dead organisms and replace the organic matter with mineral material.

What are trace fossils?

Fossilized evidence of an organism's activity rather than its body — examples include footprints, burrows, and trails.

What is the fossil record, and why is it evidence for evolution?

An ordered array of fossils appearing within layers of sedimentary rock, with the oldest at the bottom and the youngest at the top, showing a progression of life forms over time.

What is biogeography, and how does it support evolution?

The geographic distribution of species — for example, the unique finches on the Galapagos Islands and the presence of marsupials in both North America and Australia point to descent with modification from common ancestors in different locations.

What is comparative anatomy, and what does it reveal about evolution?

The study of structural similarities and differences among organisms. It reveals homologous structures (shared ancestry) and vestigial structures (evolutionary leftovers).

What are homologous structures?

Structures found in different types of organisms that are similar in underlying structure but do not necessarily have the same function, because the organisms share a common ancestor.

What are vestigial structures?

Structures that are no longer used by an organism — they are "left-overs" from evolutionary history and can indicate common ancestry.

What are analogous structures?

Structures found in different organisms that may or may not look similar structurally, share no common ancestor, but have the same function — for example, bat wings, insect wings, and bird wings.

What is convergent evolution?

When species from different evolutionary branches come to resemble one another because they live in very similar environments — this leads to analogous structures.

How does comparative embryology support evolution?

Many organisms that look very different as adults share similar embryonic features, such as pharyngeal pouches, suggesting they evolved from a common ancestor.

How does molecular biology provide evidence for evolution?

Organisms with closer DNA, RNA, and amino acid sequences share a more recent common ancestor. All life forms are related because they all use the same DNA, RNA, and amino acids.

How does pesticide resistance demonstrate evolution?

When pesticides are applied, organisms that are resistant survive and reproduce while those that are not resistant die. Over time, the entire surviving population is resistant — this is natural selection in action.

How does antibiotic resistance in bacteria demonstrate evolution?

When antibiotics are used, resistant bacteria survive and reproduce while non-resistant bacteria die. The resistant bacteria can also pass resistance genes to other bacteria through plasmids, rapidly spreading resistance.

What is artificial selection, and how does it relate to evolution?

Humans selectively breed organisms for desired traits — examples include the many varieties of wild mustard and dog breeds. It demonstrates that selection pressures can drive significant changes in organisms over time.

Why is natural selection described as more of an editing process than a creative mechanism?

Because natural selection can only act on variations that already exist in a population — it does not create new traits, but rather selects among existing heritable variations.

Why is natural selection said to be contingent on time and place?

Because what counts as a favorable trait depends on the specific environment and conditions at that moment — a trait that is advantageous in one context may be neutral or harmful in another.

Can individuals evolve?

No. Individuals do not evolve — populations evolve. Evolution is a change in the genetic makeup of a population over generations.

What is phylogeny?

The evolutionary history of a group of organisms.

What is systematics?

An analytical approach to studying the diversity of life and the evolutionary relationships between organisms.

What is taxonomy?

The branch of biology concerned with naming and classifying the diverse forms of life.

What is binomial nomenclature?

A naming system in which every organism has a scientific name with two parts: Genus and species (e.g., Homo sapiens).

What is the hierarchy of biological classification, from broadest to most specific?

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (remembered by "Did King Philip Come Over For Good Spaghetti" or similar mnemonics).

What are phylogenetic trees?

Diagrams that represent the evolutionary history of life, resembling a tree with many branchings from a common trunk. At each fork is an ancestor common to all lines of descent branching from that point.

What is cladistics?

A method of classification that involves identifying clades — evolutionary branches consisting of an ancestral species and all its descendants.

What are shared primitive (ancestral) characters?

Original traits that were present in the ancestral group and are shared broadly among descendants — they do not help distinguish between closely related groups.

What are shared derived characters?

New, heritable traits that developed in an organism and were passed on to descendants. Sharing these traits means organisms are more closely related to each other than to groups that only have the original ancestral set of traits.

What is a cladogram?

A diagram depicting the pattern of shared derived characters used to determine evolutionary relationships among organisms.

What is molecular systematics?

A method of inferring evolutionary relatedness by comparing nucleic acids (DNA, RNA) or other molecules such as proteins.

What is the principle of maximum parsimony in phylogenetics?

The idea that the simplest explanation consistent with the facts should be investigated first. For trees based on morphology, the most parsimonious tree requires the fewest evolutionary events. For DNA-based trees, it requires the fewest base changes.

What is a molecular clock?

An approach for measuring the absolute time of evolutionary change, based on the observation that some genes and genomic regions evolve at roughly constant rates. The number of nucleotide substitutions is assumed to be proportional to the time elapsed since divergence.

How is a molecular clock calibrated?

By graphing the number of genetic differences against dates of evolutionary branch points known from the fossil record, establishing a rate of change that can then be applied to estimate unknown divergence times.

What is horizontal gene transfer, and why is it important?

The transfer of genetic material between organisms by mechanisms other than vertical inheritance (parent to offspring). It plays an important role in evolution, especially in prokaryotes, and complicates the construction of simple phylogenetic trees.

What is a transposon?

A segment of DNA that can move from one position to another within a genome, sometimes called a "jumping gene." Transposon activity can contribute to gene duplication and genetic variation.

What are the three domains of life?

Bacteria, Archaea, and Eukarya.

What is a population in evolutionary biology?

A group of interbreeding organisms, all of the same species, that live in the same place at the same time and compete for the same resources.

What is microevolution?

A change in allele frequencies in a population over generations.

What is genetic variation?

Differences among individuals in the composition of their genes or DNA sequences. It can be measured as the average percentage of loci that are heterozygous and provides the raw material for evolutionary change.

What are the main sources of genetic variation?

Mutations, gene duplication, and other processes that produce new alleles and new genes.

How do new alleles form?

New alleles arise by mutation — a change in the nucleotide sequence of an organism's DNA. Some mutations are harmful, some are neutral, and a few are beneficial.

How can changes in gene number or position contribute to variation?

Chromosomal changes that delete, disrupt, or rearrange loci are usually harmful, but gene duplications (from errors in meiosis, DNA replication slippage, or transposon activity) can persist and accumulate mutations over generations, leading to an expanded genome with new genes that may have new functions.

Why can prokaryotes generate genetic variation quickly despite low mutation rates?

Because prokaryotes reproduce rapidly and have many more generations per unit of time than plants and animals, so even low mutation rates can quickly generate significant genetic variation. Viruses do this as well.

How does sexual reproduction contribute to genetic variation?

By shuffling existing alleles through crossing over, independent assortment, and random fertilization, producing unique individual genotypes each generation.

What is the Hardy-Weinberg equation?

p² + 2pq + q² = 1, where p² represents the frequency of homozygous dominants (AA), 2pq represents heterozygotes (Aa), and q² represents homozygous recessives (aa). Also, p + q = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

What does the Hardy-Weinberg equation allow us to determine?

Whether a population is evolving — if allele frequencies change from what the equation predicts, evolution is occurring.

What is a gene pool?

The sum total of all the alleles in a population.

What is allelic frequency?

The proportion of a particular allele (dominant or recessive) for a given trait within a population. The frequency of one allele plus the frequency of the other must equal 100% (or 1).

What is the Hardy-Weinberg Equilibrium Principle?

It states that allelic frequencies in a population will remain constant from generation to generation unless one or more factors cause those frequencies to change.

What are the five conditions required for Hardy-Weinberg Equilibrium (i.e., no evolution)?

1) All mating is random. 2) The population is very large. 3) There is no movement into or out of the population. 4) There are no mutations. 5) There is no natural selection.

What is genetic drift?

Evolution resulting from random chance events rather than natural selection — it has a larger effect in small populations.

What is the founder effect?

A type of genetic drift in which a small subset of a population breaks off to form its own colony, and the genetic diversity of the new group may be very different from the original population.

What is the bottleneck effect?

A type of genetic drift in which a population's size is drastically reduced by a catastrophic event, leading to inbreeding and drastically reduced genetic diversity. If a new environmental pressure arrives, the entire remaining population may be wiped out.

What is gene flow?

The movement of alleles into or out of a population when fertile individuals immigrate or emigrate, or when gametes like pollen are transferred between populations.

What is adaptive evolution?

The process by which natural selection increases the proportion of individuals with favorable traits, improving how well a species is suited for life in its environment.

What is sexual selection?

A form of natural selection in which the most "attractive" mate is chosen and gets to reproduce, driving the evolution of traits that improve mating success.

What is sexual dimorphism?

A difference in secondary sexual characteristics between males and females of the same species — for example, differences in size, coloration, or ornamentation.

What is 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.

What is directional selection?

A type of natural selection in which one extreme phenotype is favored, shifting the population's trait distribution in one direction.

What is stabilizing selection?

A type of natural selection in which an intermediate phenotype is favored, reducing variation and keeping the population clustered around the average.

What is disruptive selection?

A type of natural selection in which both extreme phenotypes are favored over the intermediate, potentially splitting the population into two distinct groups.

What is balancing selection?

Selection that maintains two or more phenotypic forms in a population. In diploid organisms, many unfavorable recessive alleles persist because they are hidden from selection in heterozygous individuals.

What is heterozygote advantage, and what is the classic example?

When heterozygotes at a particular locus have greater fitness than either type of homozygote. The classic example is sickle cell: ss causes sickle cell anemia, SS gives high susceptibility to malaria, but Ss provides protection against malaria with only a few sickled cells — not enough to cause anemia symptoms.

What is frequency-dependent selection?

A type of selection in which the fitness of a phenotype depends on how common it is in the population — rare phenotypes may have an advantage.

Why can't natural selection produce perfect organisms? (List all four reasons.)

1) Selection can only act on existing variations. 2) Evolution is limited by historical constraints — each species carries a legacy of descent with modification. 3) Adaptations are often compromises. 4) Chance, natural selection, and the environment interact in unpredictable ways.

What is speciation?

The emergence of a new species, which increases biological diversity.

What is the difference between microevolution and macroevolution?

Microevolution deals with changes in the gene pool of a single population. Macroevolution includes the origin of new species and higher taxonomic groupings.

What is the Biological Species Concept?

It defines a species as organisms that can mate with each other and produce fertile offspring.

What are the problems with the Biological Species Concept?

Plants freely hybridize across species boundaries; it doesn't apply to asexually reproducing organisms; hybrids like mules are sterile but their parents are considered separate species; and it cannot be applied to fossils.

What are prezygotic barriers?

Reproductive barriers that prevent mating or fertilization from occurring in the first place.

What is temporal isolation?

A prezygotic barrier in which mating or flowering occurs at different seasons or different times of day, preventing interbreeding.

What is habitat isolation?

A prezygotic barrier in which populations live in different habitats within the same area and therefore do not encounter each other to mate.

What is behavioral isolation?

A prezygotic barrier in which there is little or no sexual attraction between members of different species, often due to differences in courtship rituals or signals.

What is mechanical isolation?

A prezygotic barrier in which structural differences in genitals or flowers prevent copulation or pollen transfer between species.

What is gamete isolation?

A prezygotic barrier in which male and female gametes from different species die before uniting or simply fail to fuse.

What are postzygotic barriers?

Reproductive barriers that act after fertilization, preventing the development of fertile adult hybrids.

What is hybrid inviability?

A postzygotic barrier in which hybrids fail to develop properly or fail to reach sexual maturity.

What is hybrid sterility?

A postzygotic barrier in which hybrid offspring of two different species grow to maturity and are vigorous but are sterile — the mule (horse × donkey) is a classic example.

What is hybrid breakdown?

A postzygotic barrier in which first-generation hybrids are viable and fertile, but when they mate with one another or with either parent species, the resulting offspring are feeble or sterile.

What is the Morphological Species Concept?

A species concept based on observable and measurable phenotypic traits — it is somewhat subjective.

What is the Ecological Species Concept?

A species concept that identifies species in terms of their ecological niches, focusing on unique adaptations to particular roles in a biological community.

What is the Phylogenetic Species Concept?

A species concept that defines a species as a set of organisms with a unique genetic history — essentially one tip on the branching tree of life.

What is geographic isolation, and how does it lead to speciation?

When a population of a species is separated from other populations for long enough to evolve differently, to the point where they can no longer interbreed — a reproductive barrier develops.

What is allopatric speciation?

Speciation that occurs when a geographic barrier (such as a mountain range, lake, or land bridge) physically isolates a population from the rest of the species. The isolated population evolves independently until reproductive isolation develops.

Does the size of the geographic barrier needed for allopatric speciation vary?

Yes — the size of the barrier required depends on the ability of the organisms to move about. A small stream might isolate a mouse population but not a bird population.

What is sympatric speciation?

Speciation in which reproductive isolation develops and new species arise without any geographic separation — the new species emerges within the range of the parent population.

In what group of organisms does sympatric speciation occur most commonly?

It occurs mainly in plants.

What is polyploidy?

A condition in which an organism has extra sets of chromosomes beyond the normal diploid number. It can lead to instant speciation.

What is a tetraploid, and why does it represent instant speciation?

A tetraploid has four complete sets of chromosomes (4n). Because it cannot successfully mate with diploid (2n) members of the parent species, it is reproductively isolated — instant speciation.