Evolution Study Guide

A. Evolution

Evolution is the process through which species change over time through variations in traits, driven by mechanisms such as natural selection, genetic drift, and mutation. This process leads to the adaptation of organisms to their environments and can result in the emergence of new species.

Homology

Homology refers to the similarity in structure or genetic makeup between different species due to shared ancestry. For example, the forelimbs of humans, whales, and bats exhibit similar bone structures, indicating that these species share a common ancestor. Homologous traits can provide insight into evolutionary relationships and help scientists understand how species have diverged from their common ancestors.

Paleontology

Paleontology is the scientific study of the history of life on Earth through the examination of fossilized remains. Fossils provide crucial evidence of past organisms and their environments, helping to reconstruct evolutionary timelines and understand how different species have evolved over millions of years. Paleontologists analyze fossilized bones, teeth, and other remains to gather information about the morphology, behavior, and ecology of extinct species, contributing to our understanding of evolution and the history of life.

Together, the concepts of homology and paleontology illustrate the evolutionary connections among species and the historical context of life on Earth.

B. Support for evolution comes from:

1. Fossil Record: Fossils document the gradual changes in species over time, showing transitional forms that highlight evolutionary pathways.

2. Comparative Anatomy: Homologous structures across different species indicate common ancestry, while analogous structures demonstrate how different species adapt similarly to similar environments.

3. Genetics: DNA and genetic analysis reveal relationships between species, showing how genetic variation and mutations drive evolution.

4. Biogeography: The geographic distribution of species supports evolution; for example, isolated environments often lead to unique evolutionary paths.

5. Direct Observation: Instances of rapid evolution, such as antibiotic resistance in bacteria, provide real-time evidence of evolutionary processes.

6. Embryology: Similarities in the embryonic development of different organisms indicate common ancestry. For example, embryos of humans, cats, and chickens exhibit similar early developmental stages.

7. Molecular Biology: Proteins and genetic sequences show patterns of similarity and divergence that align with evolutionary theory. For example, the more closely related two species are, the more similar their proteins and genes tend to

C. Darwin and Wallace

Charles Darwin and Alfred Russel Wallace are both recognized for their foundational contributions to the theory of evolution through natural selection.

Charles Darwin

Darwin is best known for his work "On the Origin of Species," published in 1859. He proposed that species evolve over time through a process of natural selection, where individuals with advantageous traits are more likely to survive and reproduce. Darwin's observations during his voyage in the Galápagos Islands, played a crucial role in shaping his ideas about adaptation and speciation.

Alfred Russel Wallace

Wallace independently developed a similar theory of evolution by natural selection. His observations in the Amazon and later in the Malay Archipelago highlighted the role of environmental factors in species variation. In 1858, he famously sent a manuscript outlining his ideas to Darwin, prompting both to present their findings together at a meeting of the Linnean Society of London.

Both Darwin and Wallace's discoveries laid the groundwork for modern evolutionary biology, emphasizing the importance of natural selection in shaping the diversity of life.

D. More on Darwin’s theory

Darwin’s theory based on Four observations: 

 1. Reproduction increases population unless factors limit it

 2. Individuals in a species are not identical

 3. Some variation among individuals is inherited

 4. Not all offspring survive to reproduce

And one inference:

Heritable variations among individuals affect probability of surviving & reproducing 🡪 probability of passing on those characteristics

Darwin’s major contribution 🡪 Natural selection – i.e. process by which evolution occurs

E. Natural Selection is a process in evolutionary biology where organisms better adapted to their environment tend to survive and produce more offspring. This mechanism leads to the gradual evolution of species as advantageous traits become more common in a population over generations.

Types of Natural Selection

1. Directional Selection:

   • Definition: This occurs when one extreme phenotype is favored over others, causing a shift in the population's trait distribution toward that extreme.

   • Example: The peppered moth in England is a classic example. During the Industrial Revolution, darker moths were favored because they were better camouflaged against soot-darkened trees, leading to an increase in their population (example I have in class).

2. Stabilizing Selection:

   • Definition: This type of selection favors intermediate phenotypes and reduces variation in a trait, maintaining the status quo.

   • Example: Human birth weight is often cited. Babies of average weight have higher survival rates than those who are very small or very large, leading to a stabilization around the average weight (example given in the video shown in class).

3. Disruptive Selection:

   • Definition: This occurs when extreme phenotypes are favored over intermediate phenotypes, potentially leading to speciation.

   • Example: In a study of African seedcracker birds, individuals with either very large or very small beaks were favored because they could efficiently feed on either large or small seeds, while those with medium-sized beaks struggled.

F. Other types of selection

Artificial Selection

Definition: Artificial selection is the process by which humans intentionally breed plants or animals for specific traits. By selecting individuals with desirable characteristics, humans can influence the genetic makeup of future generations.

Example: Dog breeding is a common example, where breeders choose specific breeds for traits like size, temperament, or appearance, resulting in a wide variety of dog breeds.

Sexual Selection

Definition: Sexual selection is a form of natural selection where individuals with certain traits are more likely to attract mates and reproduce. This can lead to the development of characteristics that enhance mating success, even if they are not necessarily advantageous for survival.

Example: The peacock's extravagant tail is a classic example. Male peacocks display their colorful feathers to attract females, even though a large tail may make them more vulnerable to predators.

G. Convergence

Convergence in the context of evolution, often referred to as convergent evolution, is the process where unrelated or distantly related organisms develop similar traits or adaptations in response to similar environmental pressures or challenges. This phenomenon occurs despite these organisms not sharing a recent common ancestor.

Key Points:

• Analogous Structures: The traits that arise from convergent evolution are called analogous structures, which serve similar functions but have different evolutionary origins.

• Environmental Pressures: Convergent evolution typically happens in similar habitats or ecological niches where different species face comparable challenges, leading to adaptations that enhance survival and reproduction.

Example:

A classic example of convergent evolution is the development of wings in bats (mammals) and birds (avian species). Both have evolved wings for flight, but their wing structures are different due to their distinct evolutionary paths. Another example can be seen with the body shape of dolphins (mammals) and sharks (fish), both of which have streamlined bodies that facilitate swimming in aquatic environments.

H. What are the mechanisms through which traits are inherited?

he mechanism by which organisms inherit traits from their parents is primarily through genetics, specifically the transmission of genes. Here’s how it works:

Key Concepts:

1. Genes: Genes are segments of DNA that encode instructions for building proteins and determining traits. Each gene can exist in different forms called alleles.

2. Chromosomes: Genes are located on chromosomes, which are structures made of DNA and proteins. Humans, for example, have 23 pairs of chromosomes, inheriting one chromosome of each pair from each parent.

3. Meiosis: During sexual reproduction, gametes (sperm and egg cells) are produced through a process called meiosis. This process reduces the chromosome number by half and involves the mixing of genetic material, leading to genetic diversity.

4. Fertilization: When a sperm fertilizes an egg, the resulting zygote has a complete set of chromosomes (half from the mother and half from the father). This zygote develops into a new organism, inheriting traits from both parents.

5. Expression of Traits: The combination of alleles inherited from the parents influences the organism's phenotype (observable traits). Dominant alleles can mask the effects of recessive alleles, determining which traits are expressed.

H. Genetic variation occur through mutations, gene flow and genetic drift

Mutation

Definition: A mutation is a change in the DNA sequence of an organism's genome. Mutations can occur naturally due to errors during DNA replication or as a result of environmental factors, such as radiation or chemicals.

Mutations can lead to new traits, which can be beneficial, neutral, or harmful.

Gene Flow

Definition: Gene flow, also known as gene migration, is the transfer of genetic material between populations through the movement of individuals or their gametes (e.g., pollen). This process can introduce new alleles into a population and increase genetic diversity.

Significance: Gene flow can counteract the effects of natural selection and genetic drift by maintaining genetic variation, and it can also lead to the homogenization of populations, making them more genetically similar.

Genetic Drift

Definition: Genetic drift is the random change in the frequency of alleles (gene variants) in a population over time, particularly in small populations. It occurs due to chance events that affect which individuals survive and reproduce.

Key Points:

• Bottleneck effect: A significant reduction in population size due to an event (e.g., natural disaster) that results in a loss of genetic diversity.

• Founder effect: When a small group of individuals establishes a new population, the genetic makeup of that group can significantly influence the future gene pool.

Genetic drift can lead to the fixation or loss of alleles in a population, independent of natural selection. 

Summary

Collectively, mutations introduce genetic variation, gene flow facilitates the movement of genes between populations, and genetic drift contributes to random changes in allele frequencies, all of which play important roles in the evolutionary process.

I. Linnaeus 

Carl Linnaeus was a Swedish botanist, physician, and zoologist who is best known for developing the system of binomial nomenclature, the formal system of naming species. His work laid the foundation for modern taxonomy, classifying and naming organisms in a systematic way.

Key Contributions:

1. Binomial Nomenclature: Linnaeus introduced the two-part naming system where each species is given a genus name followed by a specific epithet (e.g., Homo sapiens for humans). This system standardizes names and helps avoid confusion.

2. Taxonomic Hierarchy: He established a hierarchical classification system that includes ranks such as kingdom, class, order, genus, and species, which is still in use today.

The classification of species, known as taxonomy, involves organizing living organisms into hierarchical categories based on shared characteristics and evolutionary relationships. The primary levels of classification are:

1. Domain

• The highest taxonomic rank. There are three domains:

  • Bacteria: Prokaryotic, unicellular organisms.

  • Archaea: Prokaryotic, unicellular organisms often found in extreme environments.

  • Eukarya: Eukaryotic organisms, which include plants, animals, fungi, and protists.

2. Kingdom

• The second highest rank, dividing organisms into major groups. For example:

  • Animalia (animals)

  • Plantae (plants)

  • Fungi (fungi)

  • Protista (mostly unicellular eukaryotes)

3. Phylum

• Groups organisms based on major body plans or organizational features. For example:

  • Chordata (animals with a notochord, including vertebrates)

  • Arthropoda (invertebrates with exoskeletons, including insects and crustaceans)

4. Class

• A further division of phyla. For example:

  • Mammalia (mammals)

  • Aves (birds)

  • Reptilia (reptiles)

5. Order

• Groups within classes. For example:

  • Carnivora (carnivorous mammals, like cats and dogs)

  • Primates (primates, including humans, apes, and monkeys)

6. Family

• A group of related genera (plural of genus). For example:

  • Felidae (the cat family, including lions and tigers)

  • Hominidae (the great ape family, including humans and their ancestors)

7. Genus

• A group that includes one or more species that are closely related. For example:

  • Panthera (the genus that includes big cats like lions and tigers)

  • Homo (the genus that includes modern humans and their close relatives)

8. Species

• The most specific level of classification, representing individuals that can interbreed and produce fertile offspring. For example:

  • Panthera leo (lion)

  • Homo sapiens (modern humans)

J. Evolution of the brain

Comparative Anatomy

• Description: Scientists compare the brain structures of different species to identify similarities and differences.

• Example: Analyzing the size, shape, and complexity of brains across vertebrates, such as comparing the brains of mammals, birds, reptiles, and amphibians.

• Brain structure and behavior: Generally speaking, amount of brain devoted to a particular structure 🡪 importance of that particular function. For example,  Warblers – have larger HVC and produce more songs, Birds that store food have larger hippocampi. In rat, whiskers – very imp. in exploring world – therefore, large amount of cortex devoted to whisker representation

K. Brain structures in vertebrates

• Some region’s functions have changed/been altered, e.g. midbrain optic tectum responsible for visual processing in lower vertebrates – has become visual reflex center in mammals

•  Mammals – all have neocortex with 6 layers – more recent mammals have >50% of brain devoted to neocortex

• Reptiles have 3-layered cortex – may be homologous to mammalian hippocampus (also has 3 layers)

L. Human Brain Evolution

• Increase in Brain Size: Over the course of human evolution, there has been a significant increase in brain size, particularly in the neocortex, which is associated with higher cognitive functions such as reasoning, planning, and language.

• Cultural Evolution: The development of language, culture, and technology has further influenced brain evolution, as these factors require complex social interactions and problem-solving abilities.

However, size is NOT a direct predictor of intelligence

The Encephalization Factor (EF), often referred to as the Encephalization Quotient (EQ), is a measure used to estimate the relative brain size of an animal compared to what would be expected for an animal of a given body size. It helps researchers assess cognitive abilities and potential intelligence across different species.

The relationship between body weight and brain size is a generally observed trend in biology. This principle states that, in many animal species, larger body size tends to correlate with larger brain size. However, this relationship is not straightforward. For example, elephants have larger brains than humans but they also weight much more. Plotting body weight vs. brain size shows a perfect relationship for elephants. Critically, humans have a much larger brain than expected from their body weight, which can be calculated taking into account the Encephalization Factor (EF).

M. Differences between primate and human brain

The differences between primate and human brains can be attributed to several factors, including evolutionary adaptations, brain structure, and developmental processes. One key aspect of human brain evolution is protracted development, which refers to the extended period of growth and maturation that human brains undergo compared to other primates.

Key Differences Between Primate and Human Brains

1. Size and Complexity:

   • Humans have larger brains relative to body size than most primates, particularly in the neocortex, which is associated with higher cognitive functions such as reasoning, problem-solving, and social behavior.

   • The human brain has more intricate folding (gyrification) and greater surface area, allowing for more neurons and synaptic connections.

2. Functional Specialization:

   • Certain areas of the human brain, such as the prefrontal cortex, are more developed than in other primates. This region is crucial for executive functions, decision-making, planning, and social interactions.

3. Neural Connectivity:

   • Humans exhibit more extensive neural connections within and between brain regions, facilitating complex information processing and integration.

Protracted Development

Protracted development refers to the extended period of brain maturation that occurs in humans, which has several implications:

1. Extended Childhood:

   • Human children take longer to reach maturity compared to other primates. This prolonged childhood allows for more extensive learning and socialization, which are crucial for developing complex cognitive skills and cultural knowledge.

2. Increased Plasticity:

   • The extended developmental period enhances neural plasticity, allowing the brain to adapt and reorganize in response to experiences. This flexibility is vital for learning languages, social norms, and problem-solving skills.

3. Social Learning:

   • Protracted development facilitates social learning, where children learn from their parents and peers over time. This is essential for the transmission of culture, tools, and social behaviors, contributing to the advancement of human societies.

4. Cognitive Development:

   • The extended maturation period allows for the development of sophisticated cognitive abilities. As the brain develops, children acquire advanced skills such as language, critical thinking, and emotional regulation.

Final discussion
what made human brains so big?

Social brain hypothesis

Larger cortex necessary to handle complex social relationships

Others have suggested: Behavioral innovations, tool use, and social learning (by observing others)

Sexual selection hypothesis

Creativity was regarded as sexually desirable

Metabolic Hypothesis 

Larger brains require more energy, humans have adapted through diet and social structures to support the metabolic costs associated with brain growth

Most likely:

Multiple sources of pressures favored bigger brains