Darwin, Evolution, and Speciation: Key Concepts and Evidence

most important concept in biology?

Evolution

plato

Each species has an 'essential' form.

Aristotle

The 'Great Chain of Being', organizing life in increasing complexity.

Zhuang Zhou

The idea of 'constant transformation' and species adapting to environments.

dominant belief during the Middle Ages regarding species

Fixity of Species, meaning species were created independently and unchanging.

Georges-Louis Leclerc (Comte de Buffon)

He found evidence for evolution and the 'struggle for existence' but was inconsistent in his beliefs.

Carolus Linnaeus

Father of Taxonomy

Jean-Baptiste Lamarck's

'Inheritance of Acquired Characteristics' and 'Transformism' (descent with modification).

Georges Cuvier introduce

Catastrophism, which suggests global catastrophes followed by new creations. tried to explain fossil changes

James Hutton

Uniformitarianism, stating changes occur at slow, uniform rates due to natural processes.

Charles Lyell

He popularized Uniformitarianism and provided research on geology and climate change.

Thomas Malthus

predicted human population growth would be limited by resources, leading to competition

What was a key observation made by Darwin during his voyage on the HMS Beagle?

The geology of South America indicated an old Earth.

What is biogeography in the context of Darwin's observations?

Species in nearby locations are more similar due to common ancestry and adapt to new areas.

Who independently developed the idea of natural selection alongside Darwin?

Alfred Russell Wallace

What are the four observations that form the basis of natural selection?

1. Heritable variation exists. 2. Organisms compete for resources. 3. Individuals differ in survival and reproduction. 4. Species adapt to changing conditions.

fitness

An individual's ability to survive and reproduce relative to others in the population.

What is a key principle of natural selection?

It operates on existing variation; it does not create new variation.

artificial selection

The process of humans modifying plants and animals through selective breeding.

fossils provide evidence for

Past life and evolutionary changes.

transitional fossils

Fossils that show intermediate evolutionary forms, such as Archaeopteryx and Tiktaalik roseae.

What does biogeography reveal about evolutionary history?

The geographic distribution of related organisms reflects their evolutionary history.

homologous traits

Similar structures in different species due to common ancestry.

vestigial structures

Remnants of features that served important functions in ancestors but are reduced in modern species.

microevolution

Change in allele frequencies in a population over time.

gene pool

The total collection of gametes produced by breeding individuals in a population.

allele frequency

The proportion of a specific allele type relative to the total number of alleles for that gene in a population.

Hardy-Weinberg Principle

It describes the expected genotypic and allelic frequencies in a population if no evolution is occurring.

Hardy-Weinberg Equation for allele frequencies

p + q = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

Hardy-Weinberg Equation for genotypic frequencies

p² + 2pq + q² = 1

p²

the frequency of homozygous dominant (AA)

2pq

the frequency of heterozygous (Aa),

q²

frequency of homozygous recessive (aa).

assumptions of Hardy-Weinberg Equilibrium

1. Large population size, 2. No gene flow, 3. No mutation, 4. No natural selection, 5. Random mating.

mutation in the context of evolution

The ultimate source of all new genetic variation in a population, typically resulting from base substitutions in DNA.

gene flow

The movement of alleles between populations, which homogenizes allele frequencies and increases genetic variation within populations.

genetic drift

Random fluctuations of allele frequencies due to chance events

where is genetic drift more impactful?

small populations

genetic bottleneck

A severe reduction in population size that impacts allele frequencies through drift and can lead to a loss of rare alleles.

founder effect

A type of genetic drift where a small group breaks off from a larger population

what does the founder effect lead to?

loss of genetic variation

natural selection

The only evolutionary force that leads to adaptation, operating when individuals with certain heritable traits have an advantage in survival and reproduction.

what is the only evolutionary force that leads to adaptation?

natural selection

inbreeding depression

Increased homozygosity and expression of deleterious recessive alleles due to non-random mating in small populations.

macroevolution

Broad-scale and long-term changes encompassing the origination, diversification, and extinction of species.

speciation

The process by which new species arise, typically involving the splitting of one species into multiple.

Biological Species Concept (BSC)

Defined by Ernst Mayr, it states that a species is a group of actually or potentially interbreeding populations that are reproductively isolated from other such groups.

Morphological Species Concept

Defines species based on morphological similarity, useful for fossils but can fail for cryptic species.

Phylogenetic Species Concept

Defines a species as the smallest monophyletic group, requiring a good phylogeny to identify diagnostic traits.

prezygotic barriers

Barriers that prevent the formation of a zygote, including temporal, habitat, behavioral, structural isolation, and gametic incompatibility.

postzygotic barriers

Barriers that prevent hybrid offspring from developing or reproducing, including hybrid inviability, hybrid sterility, and hybrid breakdown.

temporal isolation

A prezygotic barrier where species breed at different times, preventing interbreeding.

hybrid inviability

A postzygotic barrier where hybrid offspring do not survive or are frail.

hybrid sterility

A postzygotic barrier where hybrid offspring are healthy but infertile, such as mules.

hybrid breakdown

A postzygotic barrier where first-generation hybrids are fertile, but subsequent generations are sterile or inviable.

reinforcement in speciation

when two allopatric populations produce hybrids with lower fitness, leading to natural selection favoring traits that increase reproductive isolation.

allopatric speciation

when populations are geographically isolated, preventing gene flow and leading to genetic divergence and reproductive isolation.

sympatric speciation

when populations diverge into new species without geographic isolation, often due to strong selection or mate choice.

Give an example of sympatric speciation.

Apple maggot flies diverging based on their preferred fruit (hawthorns vs. apples), creating temporal isolation.

adaptive radiation

when a single ancestral species rapidly gives rise to many new species that adapt to fill available ecological niches.

What triggers adaptive radiation?

Factors like ecological release, environmental changes, or colonization of a new area

convergent evolution

the independent evolution of similar traits in unrelated species due to similar environmental pressures.

evolution

Evolution is driven by random mutations and natural selection acting on existing variations based on fitness differences.

What is the age of the universe?

The known universe is approximately 13.8 billion years old.

When did the solar system and Earth form?

The solar system and Earth formed approximately 4.6 billion years ago.

What is LUCA and what did it mark?

stands for Last Universal Common Ancestor, marking the beginning of biological evolution.

What are the four overlapping stages of life's origin?

1. Abiotic synthesis of small organic molecules.

2. Formation of polymers.

3. Formation of protocells.

4. Emergence of living cells with self-replicating molecules.

Oparin-Haldane Hypothesis

proposes that organic molecules spontaneously formed on early Earth.

reducing atmosphere hypothesis

It suggests that early Earth's atmosphere was reducing, composed of gases like H2O, N2, CH4, and NH3, with low oxygen concentrations.

Miller-Urey experiment

an experiment that simulated early Earth conditions and produced amino acids, supporting the reducing atmosphere hypothesis.

extraterrestrial origins hypothesis

(panspermia) suggests that organic molecules or life originated in space and were brought to Earth.

protocells

aggregates of prebiotically produced molecules and macromolecules packaged within a membrane, exhibiting key characteristics like self-replication.

RNA world hypothesis

says that RNA was the primary genetic material and catalyst in early life due to its ability to store information and self-replicate.

significance of the fossil record

provides evidence of past life and is limited by factors such as time, place, and the type of organism.

relative dating

places fossils in a geologic context, estimating age based on the strata in which they are found.

absolute dating

uses the constant rate of decay of radioactive isotopes to determine the age of fossils.

four eons of Earth's history

The four eons are Hadean, Archean, Proterozoic, and Phanerozoic.

What significant event occurred during the Archean Eon?

Prokaryotic cells arose, with the first known fossils dating back to 3.8-3.5 billion years ago.

What role did cyanobacteria play in Earth's history?

early autotrophs that produced oxygen, significantly influencing subsequent evolution.

When did single-celled eukaryotes appear?

Proterozoic Eon, with the first fossils around 2.1 billion years ago.

What is endosymbiotic theory?

explains the origin of eukaryotes through symbiotic relationships with prokaryotes, leading to mitochondria and chloroplasts.