BILD3 Midterm

What is a “lineage” in evolutionary biology?

A lineage is a sequence of species that form a line of descent, each one evolved from its predecessor.

What is a “trait” in the context of evolution?

A trait is a specific characteristic or feature of an organism, which can be inherited, acquired, or environmentally influenced.

How do you draw the lineage of a species on an evolutionary tree?

Trace a path from the species back through its ancestors to the base (root) of the tree.

What is convergent evolution?

The independent evolution of similar traits in species that are not closely related, due to similar environmental pressures.

ex: streamlined bodies of sharks and dolphins, despite their different evolutionary paths

What is homology?

A similarity in traits due to shared ancestry.

How can you identify homologies and convergent traits on an evolutionary tree?

Homologies occur in species sharing a common ancestor with that trait; convergent traits appear in unrelated species without a shared recent ancestor for that trait.

What does "descent with modification and divergence" mean?

Species descend from common ancestors, accumulating changes (modifications) over time, leading to divergence into different species.

How do descent, modification, and divergence explain evolutionary patterns?

They explain how species arise, change, and diversify over time through branching lineages on an evolutionary tree.

What are three evolutionary processes, and which are random?

Mutation (random), genetic drift (random), and natural selection (non-random).

What happens to a population with infinite resources?

It will grow exponentially, without constraints from competition, disease, or food limitations.

What mechanisms can limit population growth?

Predation, disease, competition, limited resources, and environmental changes.

What is a histogram used for?

To visualize the distribution of numerical data, showing the frequency of data within certain ranges (bins).

Do individuals or populations evolve?

Populations evolve, not individuals.

What are the 3 properties a trait must have to evolve by natural selection?

Variation, heritability, and differential reproductive success.

Why must a trait vary for natural selection to occur?

Without variation, there’s nothing for selection to act on.

Why must a trait be heritable for natural selection to cause evolution?

Only heritable traits can be passed to offspring and increase in frequency in a population.

Why is differential reproductive success essential for natural selection?

It ensures individuals with advantageous traits leave more offspring.

differential reproduction is refers to certain individuals reproducing more than others, usually due to certain environmental factors they’re better adapted to

Can there be natural selection without evolution? Example?

yes, if the selected trait isn’t heritable.

ex: muscle gain from gym workouts.

Can there be evolution without natural selection? Example?

Yes

ex: genetic drift ; 5 green beetles 5 brown beetles —> natural disaster —> all brown beetles die off —> doesn’t mean green is better, just so happened to be the brown ones killed off.

frequency in allies increases

What was the prevailing view of evolution and species in Europe during the 1800s?

Most people believed species were fixed, unchanging, and created independently; the idea of evolution was not widely accepted.

What is the hypothesis of gradual and consistent geologic change, who proposed it, what does it predict about Earth’s age, and what evidence did Darwin find to support it?

Proposed by Charles Lyell, the hypothesis (uniformitarianism) states that geological changes occur slowly and continuously. It predicts Earth is very old. This introduced Darwin to the idea that biological changes also occur gradually. Darwin supported this with evidence like marine fossils in the Andes and uplifted land from earthquakes.

What biogeographical patterns did Darwin observe on his voyage, and how do they support evolution?

Darwin saw that species on islands resembled nearby mainland species and that different islands had slightly different species. This supports evolution by suggesting species spread, then adapted to local conditions.

What is the principle of succession, and how does it support descent with modification?

The principle states that extinct species resemble living species in the same region. This supports descent with modification, suggesting modern species evolved from those extinct forms.

What is artificial selection, how does it compare to natural selection, and how did it influence Darwin’s thinking?

Artificial selection is human-directed breeding for specific traits. Like natural selection, it causes changes over generations, but is intentional. Darwin saw it as a model for how natural selection could drive evolution.

How do organisms establish populations in new habitats through dispersal?

Organisms can reach new areas by wind, water, or animals, survive, reproduce, and form new populations—e.g., birds or plants colonizing islands.

What is adaptive radiation, and how did it lead to the diversity of Galápagos finches? How does local adaptation increase differences between populations?

Adaptive radiation occurs when one species rapidly evolves into many species adapted to different environments. A single finch species from the mainland colonized the Galápagos and evolved into multiple species with different beak shapes to exploit different food sources. Local adaptation to specific island conditions increased differences between populations, eventually leading to speciation.

What are the two main ideas in Darwin’s Origin of Species?

(1) All species share common ancestry and descend with modification from earlier forms. (2) Natural selection is the primary mechanism driving evolution, as individuals with advantageous traits reproduce more successfully.

What is the difference between microevolution and macroevolution?

Microevolution refers to small-scale changes within populations (e.g., allele frequency shifts), while macroevolution involves large-scale changes that result in the formation of new species or groups over long time periods.

What is the principle of stratigraphy, and how does it relate to fossil and sedimentary rock formation?

Stratigraphy is the study of rock layers (strata). As sediments build up over time, they form layers with the oldest at the bottom and the youngest at the top. Fossils in these layers provide a timeline of life on Earth.

How do extinction and transitional forms in the fossil record support evolution?

Extinction shows that species change and disappear over time. Transitional fossils show intermediate traits between older and newer species, illustrating gradual evolutionary change.

What hypothesis were Tiktaalik’s discoverers testing?

They hypothesized that a transitional form between fish and tetrapods would be found in 375-million-year-old rocks, marking the move from water to land.

How does Tiktaalik resemble modern tetrapods, and how does it resemble fish?

Like tetrapods: flat head, neck, ribs, limb-like fins.
Like fish: fins with fin rays, scales, and gills.

What evidence supports Archaeopteryx as a transitional form between reptiles and birds?

It has bird traits (feathers, wings) and reptile traits (teeth, clawed fingers, long bony tail), showing a blend of both groups.

What are some vestigial structures in humans and what were their functions in ancestors?

Examples include the appendix (digesting cellulose in plant-eating ancestors), tailbone (a remnant of tails), and goosebumps (raising body hair for insulation or intimidation).

Why are vestigial structures evidence for evolution?

They show that species have inherited traits from ancestors that no longer serve a purpose, indicating evolutionary change over time.

How do molecular, structural, and developmental homologies reveal common ancestry? Give an example.

These homologies show similarities due to shared ancestry. For example, the forelimb structure in humans and bats has the same bone pattern, revealing a common origin despite different functions.

What is an example of evolution in a multicellular species in the past 50 years?

Pesticide resistance in mosquitoes or antibiotic resistance in bacteria affecting humans. Another example: beak size changes in Galápagos finches due to drought.

Why does the NIH fund research on non-human organisms?

Many genes and biological processes are conserved due to shared ancestry, so studying other species helps us understand human biology and disease.

Gene

a small region of a chromosome that codes for a molecule (usually a protein) which performs a function

Allele

alternative forms of a game (D1 or D2, B or b, etc.)

Diploid

Having 2 copies of each gene

Genotype

The alleles an individual has for a gene (e.g. Bb)

Heterozygote

An individual with two different alleles for the gene (e.g. Bb)

Homozygote

An individual with two identical alleles for a gene (e.g. BB or bb)

Phenotype

The physical trait determined by the genotype

Population

Group of interbreeding individuals

How is evolution defined in genetic terms?

Evolution is a change in allele frequencies in a population over time.

Allele frequency

the proportion of a specific allele among all alleles at.a gene locus

Genotype frequency

The proportion of individuals with a specific genotype in a population

Genotype count

The number of individuals with a specific genotype in a population.

Gene pool

The total set of alleles in a population

Why do we test for Hardy-Weinberg Equilibrium, and what do we learn from it?

esting for HWE helps us determine if a population is evolving. If observed genotype frequencies differ from expected, it suggests one or more evolutionary forces are acting

What are the five evolutionary processes that disrupt Hardy-Weinberg Equilibrium?

1. natural selection

2. mutation

3. gene flow (migration)

4. genetic drift

5. non-random mating

How does gene flow affect allele frequencies, population similarity, and natural selection? Give an example.

Gene flow is the movement of alleles between populations, which can change allele frequencies, make populations more genetically similar, and counteract local natural selection. Example: Pollen carried between plant populations by wind or insects.

What is mutation and why is it essential to evolution?

Mutation is a random change in DNA that creates new alleles. It's the ultimate source of genetic variation, which evolution depends on.

What are assortative and disassortative mating, and how do they affect genotype frequencies?

• assortative mating: individuals mate with similar genotypes —> increases homozygosity

• disassortative mating: individuals mate with dissimilar genotypes → increases heterozygosity

How does genetic drift arise and what determines its impact?

Genetic drift is random change n allele frequencies due to sampling effects in small populations. Its impact is stronger in smaller populations because each random event has a bigger effect

Why does genetic drift reduce genetic diversity and how can it reduce population?

Drift can randomly eliminate alleles, reducing variation. It may also fix harmful alleles or lose beneficial ones, lowering overall fitness.

What are the bottleneck and founder effects, and how do they impact allele frequencies and genetic drift?

• Bottleneck: A sudden reduction in population size (e.g., disaster) leads to random allele loss.

• Founder effect: A new population started by a few individuals carries only a small part of the original gene pool.
  Both increase genetic drift by reducing population size.

What is nested hierarchical categorization of organisms, and is it still used today?

It’s a system where organisms are grouped into increasingly inclusive categories (like species within genera, genera within families, etc.). Yes, it’s still used today in taxonomy and reflects evolutionary relationships.

Why are phylogenetic trees considered hypotheses?

Because they are scientific models of evolutionary relationships based on available evidence, and they can change with new data.

What are the key parts of a phylogenetic tree and how are they identified?

• Branchpoints (nodes): Indicate common ancestors.

• Branches: Represent evolutionary lineages.

• Most recent common ancestor: The node where two taxa share ancestry.

• Species: Tips of the tree.

• Sister taxa: Two species or groups that share an immediate common ancestor.

• Root: The common ancestor of all taxa in the tree.

• Time axis: Often moves from root (past) to tips (present).

Define and correctly use: taxon, lineage, character/trait, character transition.

• Taxon (plural: taxa): A group of organisms (e.g., species, genus).

• Lineage: A continuous line of descent.

• Character/trait: An observable feature (e.g., fur, wings).

• Character transition: A change in a trait along a branch (e.g., gaining feathers).

How do you determine relative relatedness of taxa using a phylogenetic tree?

Taxa that share a more recent common ancestor are more closely related. For example, if A and B share a node more recently than A and C, A is more closely related to B.

What is the role of topology and branch length in phylogenetic trees? How can topology be represented?

• Topology shows branching order (relationships); it’s key to interpreting relatedness.

• Branch length may show evolutionary time or amount of change, depending on the tree.

• Parenthetical notation: (A,(B,C)) means B and C are more closely related to each other than to A. Different-looking trees can share this same topology.

Describe the geographical range of H. neanderthalensis

H. neanderthalensis lived across Europe and west to Central Asia

What are some of the technological advancements of H. sapiens

• use of fire

• tools / weapons

• created art

• shelters

When did land plants first evolve, and what era did this occur in?

Land plants first evolved during the Paleozoic Era.

Plants were small and non-vascular and they began colonizing in moist environments.

How and when did vascular plants evolve to survive on land ?

When: During Paleozoic Era

They were able to survive due to adaptations like vascular tissue, stomata, waxy cuticles and true roots, which enabled them grow upright on land (and retain water)

What were the first land animals? How and when did they evolve?

• Paleozoic Era

  The first land animals were arthropods that from aquatic ancestors. They developed exoskeletons and jointed legs, which allowed them to move and survive in terrestrial environments.

How did the first land vertebrates evolve, and when did this occur?

the first land vertebrates evolved in the Paleozoic era

transitional species: tiktaalik

• shows features of both fish and tetrapod

• limb-like fins, lungs, flexible neck

  Marks shirt from water to land-dwelling vertebrates.

What was the adaptive radiation of amphibians and bony fish in the Paleozoic Era?

Some fish adapted to shallow, oxygen-poor waters by developing lungs and stronger limb-like fins. —> this led to the rise of amphibians, which began exploring land environments.

How did the amniotic egg evolve, and what did it lead to?

- evolved in the Carboniferous period (Paleozoic era)

- allowed reproduction away from water, leading to the evolution of reptiles

Vascular plants

• have vascular tissues: xylem (for water) and phloem (for nutrients)

• can grow taller and larger

• include ferns, conifers, and flowering plants

• have true roots, stems, and leaves

Non-Vascular Plants

• lack vascular tissues

• stay small and close to the ground

• rely on diffusion for water and nutrient transport

• includes mosses

• typically found in moist environments

How would a phylogenetic tree showing the relationship between H. heidelbergensis, H. neanderthalensis look like?

Homo heidelbergensis

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Homo neanderthalensis Homo sapiens

Adaptive Radiation of mammals

• When: Cenozoic Era

• triggered by K-Pg extinction event

  • large predators and herbivores gone, ecological niches left open

• mammals (who were mostly small, began to expand and diversify)

Evolution of humans

When: Cenozoic Era

• Evolved in Africa from earlier hominid species

• These earlier species showed some bipedal traits , freeing of hands and tool use

• brains grew and skulls rounded

• migrated out of Africa in waves and we replaced/interbred with other hominins

Pleistocene megafauna

• animals that were typically much larger than modern relatives

• most were mammals , but included birds and reptiles

• they were adapted to cold climates

  • thick fur, fat layers

  • climate change altered habitats and food availability

• human activity could’ve also killed them off

Background extinction

the ongoing natural process of species going extinct over time at a relatively steady rate

causes: normal factors like:

• competition

• predation

• disease

Estimated 1-5 species per year

Mass extinction

Sudden and widespread loss of many species across multiple groups.habitats in a relatively short time

Causes: driven by catastrophic events like:

• asteroid impacts

• volcanic eruptions

• rapid climate change

Over 50% of species may go extinct in a short time

Give evidence that a 6th mass extinction is happening

• extinction rates are estimated to be around 100-1000 times higher than natural background rates

• rapid loss of biodiversity, especially in birds

• climate changing , oceans getting warm

• corals dying

How have migration and gene flow influenced human genetic and phenotypic variation over time?

Migration: As humans migrated out of Africa, they encountered new environments which led to natural selection for traits like skin color, nose/eye shapes, and body shapes

Gene flow: Homo sapiens interbed with other populations like Neanderthals, introducing new genetic traits.

What phenotypic evidence shows that human racial groups are not biological categories?

Human phenotypic traits vary gradually and continuously, not in discrete racial categories

examples:

• skin color forms a gradient based on UV

  • darker skin helps with UV exposure

• nose shoes are correlated with climate

  • narrow noses in colder climates, broader noses in humid, tropical regions

• hair texture

  • tightly coiled hair helps dissipate heat

  • straight/wavy hair retains warmth better

What genetic evidence shows that racial groups are not biologically meaningful?

• humans are 99.9% genetically identical

• most human genetic variation exists within a population, not between them

  Example:

• two people from the same country could have just as many genetic differences between each other , compared to someone from another country

what is evidence that suggests racial groups are socially/culturally defined

we , as a society have put certain traits under an umbrella and labeled them as belonging to a race. but there are so many other traits like ear wax type , (that you wouldn’t be able to tell someone has from just looking at them) that we don’t consider as being “under the umbrella”

explain how essentialist thinking can be misleading when thinking about race and biological variation in humans.