DEEPSEEK ch 18 & 19

Evolution and the Origin of Species DR BASU Texas A&M bio 112

What is the significance of Theodosius Dobzhansky's quote, "Nothing in Biology Makes Sense Except in the Light of Evolution"?

emphasizes that evolution is the foundational concept in biology, explaining the diversity and unity of life. Without understanding evolution, biological phenomena cannot be fully comprehended.

What are the main points of Darwin's Theory of Evolution? 1

Descent with modification: All present life is related through common ancestry and has changed over time.

What are the main points of Darwin's Theory of Evolution? 2

Natural selection: The mechanism by which evolution occurs. Organisms with traits that enhance survival and reproduction leave more offspring, leading to the accumulation of favorable traits over time.

What defines a scientific theory, such as the Theory of Evolution?

is a broad, well-supported explanation with rich predictive value. It is based on natural phenomena, stands up to experimental tests, and leads to accurate predictions (e.g., Theory of Gravity).

 What are some common misconceptions about evolution?

1. Evolution is goal-oriented (species do not evolve to become "better" or "higher").  

2. Evolution occurs through dramatic mutations (most changes are gradual).  

3. Organisms can evolve during their lifetime (evolution occurs over generations).  

4. Evolution is a completely random process (natural selection is not random).  

5. Organisms can influence their own evolution (traits are inherited, not acquired).

What is evolution?

is the change in organisms throughout Earth's history. Today's life is different from and descended from earlier life, a concept known as "descent with modification."

What were the views of life before Darwin?

Aristotle (384-322 B.C.): Believed in fixed, ideal species and the "scala naturae" (ladder of nature).  

- Linnaeus (1707-1778): Developed a nested classification system and binomial naming.  

- Hutton and Lyell: Proposed gradualism and uniformitarianism, suggesting the Earth is very old and changes slowly over time. Lyell was known as the father of geology

What was Lamarck's theory of evolution?  

proposed that organisms evolve through the inheritance of acquired characteristics. He believed that if an organism changes during its lifetime to adapt to its environment, those changes are passed on to its offspring (e.g., giraffes stretching their necks to reach leaves).

What were Darwin's key observations during his voyage on the HMS Beagle?

- Collected plants, wildlife, and fossils.  

- Observed species' geographic locations and adaptations.  

- Studied local geology and noted similarities and differences between species in different regions (e.g., rheas in South America, ostriches in Africa).

What are the key observations and inferences of Darwin's theory of natural selection?

1. Heritable variation exists in most species.  

2. Species produce more offspring than the environment can support.  

Inferences:  

1. Unequal reproductive success: Individuals with favorable traits leave more offspring.  

2. Accumulation of favorable traits over time leads to adaptation.

What are the main lines of evidence supporting evolution?

1. Fossil record: Shows extinct species and transitional forms (e.g., Archaeopteryx).  

2. Homology: Similar structures due to common ancestry (e.g., mammal forelimbs).  

3. Convergence: Similar adaptations in unrelated species due to similar environments (e.g., torpedo shape for swimming).  

4. Biogeography: Distribution of species corresponds to geographic history (e.g., marsupials in Australia).  

5. Molecular biology: DNA analysis shows similarities among related species.

What does the fossil record reveal about evolution?

shows that many species that once existed are now extinct (e.g., trilobites, dinosaurs). It also provides evidence of transitional forms (e.g., Tiktaalik, a fish with wrist-like fins, showing the transition from water to land).

 What is homology, and how does it support evolution?

refers to structures in different species that are derived from a common ancestor. These structures may be modified for different functions (e.g., the forelimbs of humans, bats, and whales). supports the idea of common ancestry.

What are vestigial structures, and what do they indicate?

remnants of ancestral structures that no longer serve a function (e.g., blind cave salamanders have eyes but cannot see). They indicate that the species descended from ancestors that used these structures.

What is convergent evolution, and what is an example?  

when unrelated species develop similar adaptations due to similar environmental pressures (e.g., the torpedo shape of dolphins and sharks for efficient swimming).

How does biogeography support the theory of evolution?

species distribution corresponds to geographic history. For example, marsupials are primarily found in Australia, indicating isolation and independent evolution from placental mammals.

How does molecular biology provide evidence for evolution?

particularly DNA analysis, shows that closely related organisms have similar DNA sequences. This similarity is strong evidence for common ancestry (e.g., humans and rhesus monkeys share 95% of their hemoglobin amino acid sequence).

What are the two main ideas in Darwin's book On the Origin of Species?

1. Descent with modification: All life is related through common ancestry and has changed over time.  

2. Natural selection: The mechanism by which evolution occurs, favoring traits that enhance survival and reproduction.

!!1859!!

What is an example of natural selection in action?  

Antibiotic resistance in bacteria is an example. Bacteria that survive antibiotic treatment give rise to resistant strains (e.g., MRSA, methicillin-resistant Staphylococcus aureus).

What are some things not explained by Darwin's theory?

1. Origin of life.  

2. How variation arises.  

3. How inheritance works.  

4. Why variation still exists.  

5. Sudden changes in the fossil record.  

6. Source of totally new characters.  

(Note: Many of these are now explained by modern genetics and molecular biology.)

How is a species defined according to the biological species concept?

a group of organisms that can interbreed and produce viable, fertile offspring. It is not based on similarity of appearance, though appearance can help identify species.

What is speciation?

the formation of two or more species from one original species. It occurs when genetic differences between populations prevent gene flow, leading to reproductive isolation.

What is gene flow, and how does it relate to speciation?

the movement of alleles (different forms of a gene) across a species' range. Speciation occurs when gene flow between populations is prevented due to genetic differences.

What is the biological species concept?

defines species as groups of organisms that are reproductively isolated from other groups. Members of the same species share the same gene pool and can interbreed.

Prezygotic barriers

Prevent fertilization from occurring (e.g., temporal, habitat, behavioral, mechanical, and gametic isolation).

Postzygotic barriers

Prevent hybrid offspring from being viable or fertile (e.g., hybrid inviability, hybrid sterility, hybrid breakdown).

Hybrid inviability

a condition where hybrid embryos do not develop properly and fail to reach maturity.

Hybrid sterility

A condition in which hybrid offspring are unable to reproduce, leading to infertility.

Hybrid breakdown

A condition where hybrid offspring are viable and fertile, but their descendants are inviable or sterile.

What are some limitations of the biological species concept?

• It cannot be applied to fossil species.

• It does not work for asexual organisms.

• Hybrids can sometimes occur between species.

What is allopatric speciation, and how does it occur?

occurs when populations are geographically separated, leading to genetic divergence and the formation of new species. This can happen through dispersal (movement to a new area) or vicariance (physical division of a population).

What is adaptive radiation, and what is an example?

the rapid diversification of an ancestral species into multiple new forms, often due to environmental changes that create new resources or niches. Examples include Darwin's finches in the Galapagos Islands and honeycreeper birds in Hawaii.

What is sympatric speciation, and how does it differ from allopatric speciation?

occurs when new species arise in the same geographic area without physical separation. It is rare in animals but can occur through mechanisms like polyploidy (chromosomal errors) or behavioral changes.

What is polyploidy, and how does it contribute to sympatric speciation?

a condition where an organism has more than two sets of chromosomes. It can lead to sympatric speciation because polyploid individuals are often reproductively isolated from their diploid ancestors. This is common in plants but rare in animals.

What are hybrid zones, and what are the possible outcomes for hybrid populations?

Hybrid zones are areas where two closely related species interact and interbreed. Possible outcomes include:

• Reinforcement: Hybrids are less fit, and species continue to diverge.

• Fusion: Species merge back into one.

• Stability: Hybrids continue to be produced.

Gradual speciation

is the process by which species evolve slowly over time through small, incremental changes, rather than through sudden shifts or events.

Punctuated equilibrium

is a theory in evolutionary biology that proposes species experience long periods of stability interrupted by brief episodes of rapid change and speciation.

What is a vestigial structure, and what does it indicate?

remnant of an ancestral structure that no longer serves a function (e.g., the human appendix). It indicates that the species descended from ancestors that used these structures.

Homologous structures

• Structures derived from a common ancestor (e.g., human arm, bat wing, whale flipper).

Analogous structures

Structures that serve similar functions but evolved independently (e.g., butterfly wing and bat wing).

Can speciation occur without geographic separation?

in a process called sympatric speciation. This is rare in animals but can happen through mechanisms like polyploidy or behavioral changes.

How can chromosomal errors lead to speciation?

nondisjunction during meiosis, can result in offspring with extra or missing chromosomes (aneuploidy). This can lead to reproductive isolation and the formation of new species, especially in plants.

What is reinforcement in the context of hybrid zones?

occurs when hybrids are less fit than purebred species, leading to stronger reproductive barriers and further divergence between the species.

Why is sympatric speciation more common in plants than in animals?

more common in plants because they can undergo polyploidy (having multiple sets of chromosomes), which can lead to reproductive isolation. In animals, polyploidy is rare and often lethal.

Morphological Species Concept

A classification method that defines species based on structural features and physical characteristics, often used in paleontology and botanical studies.

What is a population in biological terms?

a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring.

What is the smallest unit of evolution?

The population, Individuals do not evolve; evolution occurs at the population level through changes in allele frequencies over generations.

What is genetic variation, and why is it important for evolution?

refers to differences in the genetic makeup of individuals within a population. It is important for evolution because it provides the raw material for natural selection and other evolutionary mechanisms to act upon.

Mutation

New genes and alleles can arise by mutation or gene duplication.

Sexual Reproduction

Recombination of existing alleles through crossovers, independent assortment, and random fertilization.

What is a gene pool?

The collection of all the alleles of all the genes in a population. It represents the total genetic diversity available in that population.

Genotypic Frequency

The proportion of each genotype (e.g., AA, Aa, aa) in a population.

Allelic frequency

• The proportion of each allele (e.g., A or a) in a population.

What is microevolution?

a change in allele frequencies in a population over generations. It is driven by mechanisms such as natural selection, genetic drift, and gene flow.

What are the five conditions required for Hardy-Weinberg equilibrium?

1. No mutations.

2. Random mating.

3. No natural selection.

4. Very large population size.

5. No gene flow (no migration in or out of the population).

What is the Hardy-Weinberg equation, and what does it represent?

The Hardy-Weinberg equation is p²+2pq+q²=1, where:

• p = frequency of the dominant allele.

• q = frequency of the recessive allele.

• p² = frequency of homozygous dominant genotype.

• 2pq = frequency of heterozygous genotype.

• q² = frequency of homozygous recessive genotype.

What are the three mechanisms that cause allele frequency changes in populations?

1. Natural selection: Non-random selection of phenotypes that leads to adaptation.

2. Genetic drift: Random changes in allele frequencies, especially in small populations.

3. Gene flow: Movement of alleles between populations through migration.

What is genetic drift, and what are its two main effects?

1. Reduction in genetic diversity.

2. Possible fixation of one allele (loss of other alleles).

Genetic drift is the random change in allele frequencies due to chance events. Its two main effects are:

What is the founder effect?

occurs when a few individuals from a larger population establish a new, isolated population. The new population's gene pool may differ from the original due to the small number of founders and increased genetic drift.

What is the bottleneck effect?

occurs when a population's size is drastically reduced due to a random event (e.g., natural disaster). The surviving population has a gene pool that may not represent the original population, leading to reduced genetic diversity.

What is gene flow, and what are its effects on populations?

the movement of alleles between populations through migration. Its effects include:

1. Increasing genetic diversity within a population.

2. Reducing genetic differences between populations.

What are the three forms of natural selection?

1. Directional selection: Favors phenotypes at one extreme of the trait distribution.

2. Stabilizing selection: Favors intermediate phenotypes and reduces variation.

3. Disruptive selection: Favors extreme phenotypes at both ends of the trait distribution.

What is sexual selection, and how does it differ from natural selection?

form of natural selection where individuals with certain traits are more successful in obtaining mates. It often leads to sexual dimorphism (differences in appearance between males and females) and is not directly related to environmental adaptation.

What are the limitations of natural selection?

1. Natural selection can only act on existing variation; it cannot create new traits.

2. Adaptations are often compromises between different selective pressures.

3. Chance events (e.g., genetic drift) can influence evolutionary outcomes.

What is frequency-dependent selection?

occurs when the fitness of a phenotype depends on how common it is in the population. Rare phenotypes may have higher fitness, leading to their increase in frequency.

What is relative fitness?

the contribution an individual makes to the gene pool of the next generation relative to other individuals in the population. It measures reproductive success.

What is an example of stabilizing selection?

in human birth weight, where infants of intermediate weight have the highest survival rates, while very low or very high birth weights are selected against.

Intrasexual selection

is a type of natural selection where individuals of the same sex compete for mates, often leading to the evolution of traits that improve competition.

Intersexual selection

is a type of natural selection where individuals of one sex choose mates based on specific traits, leading to the evolution of those traits in the other sex.

Diversifying Selection

is a type of natural selection that favors extreme traits over intermediate ones, leading to increased variation within a population.

scala naturae

is a hierarchical classification system that arranges living organisms in a linear order from simplest to most complex, reflecting a belief in the progression of life forms. Aristotle

allopolyploidy

is a form of polyploidy that occurs when two different species hybridize, resulting in an organism with multiple sets of chromosomes from both parent species.

autopolyploidy

is a form of polyploidy that arises from the duplication of chromosome sets within a single species, leading to an organism with multiple identical sets of chromosomes.

What is phylogeny?

study of the evolutionary history and relationships among species or groups of organisms, often represented in a tree-like diagram called a phylogenetic tree.

What are the two types of phylogenetic trees?

1. Rooted trees: Have a single lineage at the base representing a common ancestor.

2. Unrooted trees: Show relationships but do not indicate a common ancestor.

What are the three domains of life, and what distinguishes them?

Archaea, Bacteria, and Eukarya. They are distinguished by differences in cellular structure, genetic material, and metabolic pathways.

Bacteria

Cells lack a nucleus and have cell walls with peptidoglycan.

Archaea

Cells lack a nucleus but have different cell walls from bacteria.

Eukarya

Cells have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

Root (Phylogenetic tree )

Indicates the ancestral lineage that gave rise to all organisms on the tree.

Branch point ( Phylogenetic Tree )

Where two lineages diverge.

Basal taxon ( Phylogenetic Tree )

A lineage that evolved early and remains unbranched.

Sister taxa ( Phylogenetic Tree )***

Two lineages that stem from the same branch point.

Polytomy ( Phylogenetic tree )

A branch with more than two lineages.

What is a Clade?***

grouping that includes a common ancestor and all of its descendants (living and extinct). It is also known as a monophyletic group.

What is cladistic analysis?

method of grouping organisms based on their evolutionary relationships. It focuses on shared derived characteristics to construct phylogenetic trees.

Monophyletic***

Includes a common ancestor and all of its descendants (e.g., a clade)

Paraphyletic***

Includes a common ancestor and some, but not all, of its descendants.

Polyphyletic***

Includes distantly related species but not their most recent common ancestor.

What is the difference between shared ancestral and shared derived characteristics?

• Shared ancestral characteristics: Traits present in the ancestor of a group (e.g., vertebral column in vertebrates).

• Shared derived characteristics: Traits that evolved in some members of a group but not all (e.g., amniotic egg in amniotes).

What is the principle of maximum parsimony in phylogenetics?

the best phylogenetic tree is the one that requires the fewest evolutionary changes (simplest explanation).

What is taxonomy, and how does it differ from phylogeny?

the science of classifying organisms based on similarities and differences, often using a hierarchical system (e.g., Linnaean classification). Phylogeny, on the other hand, focuses on evolutionary relationships.

What is binomial nomenclature, and who developed it?

the system of naming species using two parts: the genus name and the specific epithet (e.g., Homo sapiens). It was developed by Carl Linnaeus.

What are the levels of the Linnaean classification system?

The levels, from broadest to most specific, are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

What is horizontal gene transfer (HGT), and how does it occur in prokaryotes?

the transfer of genetic material between different species. it occurs through:

Transformation: Uptake of naked DNA from the environment.

Transduction: Transfer of genes by viruses.

Conjugation: Transfer of genes between bacteria via a pilus.

How does horizontal gene transfer occur in eukaryotes?

rare but can occur through mechanisms like transposons (jumping genes) or gene transfer between species that cannot cross-pollinate. Examples include gene transfer between fungi and aphids.

What is the endosymbiotic theory, and what evidence supports it?

proposes that eukaryotic cells evolved from prokaryotic cells that were engulfed by other cells and formed a symbiotic relationship. Evidence includes mitochondria and chloroplasts having their own DNA, similar to prokaryotic DNA.

What is genome fusion, and how does it relate to eukaryotic evolution?

the idea that the eukaryotic nucleus resulted from the fusion of archaeal and bacterial genomes. This may explain why eukaryotic cells have both archaeal and bacterial genes.

What are shared ancestral and shared derived characteristics?

• Shared ancestral characteristics: Traits inherited from a common ancestor (e.g., vertebral column in vertebrates).

• Shared derived characteristics: Traits that evolved in some members of a group but not all (e.g., feathers in birds).

How do you interpret a phylogenetic tree?

In a phylogenetic tree:

• Branch points (nodes): Represent common ancestors.

• Sister taxa: Share an immediate common ancestor.

• Basal taxon: The earliest diverging lineage.

• Polytomy: A branch with more than two lineages, indicating unresolved relationships.