Evolutionary Biology Concepts

Overview of Evolution

• The theory of evolution, proposed by Darwin, suggests all living organisms descended from a common ancestor.
• Evolution involves changes in a species over time.
• Genes can be transferred from one cell to another within the same generation through horizontal gene transfer. Bacteria exchanging plasmids is an example.
• Many species become extinct before they are even classified or studied.
• Variations in individuals within a population occur through mutation, allowing desirable traits to be passed to the next generation through sexual reproduction, recombination, and random assortment of tetrads.
• Individuals with more adaptive characteristics are more likely to survive and reproduce, passing those traits to the next generation with increased frequency

Continued Overview

• Unfavorable traits may become favorable, and vice versa, when environments change.
• Organisms evolve through an accumulation of favorable traits in succeeding generations.
• Natural selection explains the unity and diversity of life.
• Divergent evolution occurs when two species evolve in different directions from a common point.
• Convergent evolution occurs when similar traits with the same function evolve in multiple species exposed to similar selection pressure.
• Evolution continues to occur, but might be slow for some species.

Introduction to Evolutionary Thought

• Linnaeus’ classification system attempted to organize all living things into schemes that showed an increasing complexity of life.
• Cuvier found fossilized remains of organisms changed as he dug deeper into rock layers, indicating organisms present in the area had changed over time.
• Darwin observed finches in the Galapagos Islands that were similar, but had distinct differences.
• The finches closely resembled one present on the mainland, leading Darwin to initially think they were modified.
• Varied beaks helped the birds acquire specific types of food.

Levels of Biological Classification

• Taxonomy is the science of classifying organisms to construct inclusive groupings.
• A hierarchical system organizes life from largest to smallest categories.
• The levels of classification for Canis lupus (domestic dog) are:
  • Domain: Eukarya
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Order: Carnivora
  • Family: Canidae
  • Genus: Canis
  • Species: Canis lupus
• LUCA refers to the Last Universal Common Ancestor of all life.

Binomial Nomenclature

• Each name is capitalized except for species
• Genus and species names are italicized
• Binomial nomenclature is a two-name system comprised of genus and species to make an organism's scientific name.
• Taxon is the name at each classification level.
• Subspecies are members of the same species that are capable of mating and reproducing viable offspring, but considered separate subspecies due to geographic or behavioral isolation.
• Organisms become more similar at each sublevel because they are more closely related.
• Scientists use DNA for classification to build more precise phylogenies, rather than physical characteristics (morphology).

Phylogeny Trees

• A phylogeny tree is a tool used to show evolutionary pathways and connections between organisms. It's hypothetical and not a taxonomic classification diagram.
• Rooted trees contain a single lineage at the base, representing a common ancestor.

Natural Selection

• Natural selection or "survival of the fittest" is the greater reproductive of individuals with favorable traits to survive environmental change, leading to evolutionary change.
• Most characteristics of organisms are inherited and passed down from parent to offspring.
• More offspring are produced than are able to survive, since resources for survival and reproduction are limited, leading to competition.
• Offspring vary in characteristics, and these variations are inherited.
• The most successful variants outcompete others for limited resources, and these traits are then better represented in the next generation, changing populations over generations through descent with modification.
• Adaptive evolution is ultimately the greater adaptation of a population to its local environment.
• In 1858, Darwin & Wallace separately presented the idea of natural selection, before Mendel.
• "Origin of Species" outlined arguments for evolution by natural selection in detail.
• Demonstrations of evolution by natural selection are time-consuming and difficult to obtain.

Variation

• Variation is the genetic differences among individuals in a population.
• Development involves changes that happen during a lifetime and are not heritable.
• Natural selection can only take place if there is variation.
• Mutation, a change in DNA, is the ultimate source of new alleles.
• A change in phenotype may result in decreased or increased fitness, leading to a lower likelihood of survival or fewer offspring, or vice versa.
• Sexual reproduction also leads to genetic diversity, producing unique combinations of alleles (Hybrids), specifically through recombination/crossover and random arrangement of tetrads.

Mutation

• Mutation is changes to an organism's DNA.
• Mutations drive diversity in populations.
• Species evolve because of accumulations of mutations that occur over time.
• Introducing new genotype and phenotype variety arises most often by mutation.
• Harmful mutations are quickly removed by natural selection.
• Whether a mutation is beneficial is defined by whether it helps an organism survive and/or reproduce.
• Natural selection does not affect some mutations (neutral).

Adaptation

• Adaptation involves heritable traits that promote survival and reproduction in an organism's present environment, unlike changes during a lifetime; those traits are present at birth.
• Adaptation increases an organism’s chances of survival through:
  • Increased chances of Mating
  • Increased chances of producing offspring
  • Increased chances of passing on genetic information
• A population is considered adapted when a change affects the range of genetic variation over time, increasing its fitness.
• A "fit" organism is equipped to have higher chances of surviving in its current environment.
• Environmental conditions at the time define whether a trait is favorable. Same trait is not always selected because environment can change.

Fitness in Evolution

• Natural selection only affects heritable traits in a population, as these are the only traits passed to the next generation.
• Adaptive evolution is an increase in the frequency of beneficial alleles and a decrease in deleterious alleles due to selection.
• Natural selection acts at the level of the individual.
• Evolutionary fitness is an individual's ability to survive and reproduce (Darwinian).
• Relative fitness is an individual's ability to survive and reproduce compared to the rest of the population.
• This relates directly to which individuals contribute more offspring for the following generation and how the population evolves.
• Natural selection influences the allele frequencies in a population.

Time

• Physical changes occur over large spans of time.
• Natural selection acts on individual organisms, which in turn can shape entire species.
• Natural selection starts in a single generation, in one individual, but it can take thousands or millions of years for the genotype of an entire species to evolve.
• Fossils provide solid evidence that organisms from the past are not the same as today.

Divergent Evolution

• A species is a group of similar organisms which can:
  • Mate with each other
  • Produce offspring
  • The offspring can mate
  • The offspring can reproduce
• Divergent evolution: when 2 species evolve in diverse directions from common point
• Natural selection results in the eventual split of one species into two because they have been physically separated and exposed to different environments, which have led to different adaptations and the inability to reproduce or make fertile offspring.
• A classification system was led to by this theory of natural selection based on morphology (physical characteristics) where organisms that were more physically alike meant were more closely related to each other

Convergent Evolution

• Morphological similarities are due to selective environmental pressures.
• A trait may be favorable in a given environment, meaning adaptable individuals with increased fitness proportionally pass these characteristics to future generations if environmental circumstances remain unchanged.
• Similar phenotypes can evolve independently in distantly related species because they increase fitness in a given environment.
• Convergent evolution describes analogous traits evolving independently in separate species that don't share common ancestry.
• In other words, mutations can arise independently in populations/species, and then can be passed onto their offspring.

Adaptive Convergence

• Adaptive Convergence is a type of convergent evolution
• Analogous structures are features of different species that
• are similar in function, but not necessarily in structure
• are not derived from a common ancestor
• arise in response to a similar environment.

Homologous Structures

• The presence of structures in organisms that share the same basic form are a common type of evidence for.
• Homologous structures are similar physical features in organisms that share a common ancestor.
• Examples include the appendages of humans, dogs, birds, and whales.

Vestigial Structures

• Vestigial structures are structures without functions but appear to be residual parts or a common ancestor.
• Examples include wings on flightless birds, hind leg bones of whales, or the human tail bone.

Shared Characteristics

• Shared ancestral characters are found an ancestor of group
• Shared derived characters do not include all ancestors in the tree.
• Both terms are relative to the starting point of how the relationship is read.
• Distinguishing between clades in a phylogeny tree is useful.
• Organizing evolutionary relationships of all life on Earth requires use of the geological time scale, along with organisms that have gone extinct. Distinguishing homologies from analogies along with genetic sequence analysis is also necessary.
• Taxonomy can be a subjective discipline: when organisms have connections with more than one other, personal decision is required to decide how to classify them.
• Parsimony is the assumption that events occur with the fewest steps.

Phylogeny Tree Terminology

• Branch point: place where an evolutionary split occurs.
• Represents when a single lineage evolved into a distinct, new one.
• Basal Taxon: a lineage that evolved early from root and remains un
• Sister Taxa: 2 Lineages stemming from the same branch point.
• Polytomy: Branch with > 2 lineages, and is served to illustrate what is definitive
• Organisms in 2 taxa may have split apart at specific branch point but neither taxa gave rise to other.

Cladogram

• A cladogram is a diagram shows the relationships between different organisms based on their similar characteristics

Embryology

• Embryology focuses on development of the anatomy of an organism until adulthood
• Embryology provides evidence of relatedness between divergent groups of organisms
• Humans have a tail structure during embryonic development, but it is usually lost by the time they are born.
• Embryology shows the relationship between primates
• Mutations in embryos can have magnified consequences in an adult.

Biogeography

• Biogeography is the geographic distribution of organisms.
• Biogeography patterns are explained best in conjunction with movement of tectonic plates over geological time.
• Broad groups which evolved the breakup of Pangea, 200 million years ago, are distributed globally.
• Groups that evolved after breakup appear unique in regions around planet.
• Endemic: a species that is found nowhere else.
  • Typical islands or isolated regions species are found nowhere else because they cannot migrate.

Molecular Biology Evidence

• Evidence of a common ancestor for all life is reflected in the universality of DNA as genetic material and genetic code, and as is also reflected in similarities in replication and expression machinery.
• The relatedness of groups of organisms is reflected in similarity between DNA sequences, which can be obtained from DNA Sequencing
• All organisms are made up of cells and come from cells (Cell Theory)
• All organisms have a plasma membrane, ribosomes, and cytoplasm.

Overview of Speciation

• Speciation explains the diversity of organisms that inhabit the Earth.
• All life shares genetic similarities, but only certain organisms combine genetic info by sexual reproduction and produce viable offspring referred to as species.
• Microevolution is changes in allele frequencies within a population over generations.
• Macroevolution: leads to evolution of new species when populations diverge from common ancestor and become reproductively isolated from original population.

Overview of Speciation Part 2

• Allopatric Speciation is a form of geographic Separation
• With geographically isolated populations, the flow of alleles is prevented:
• Populations diverge and become genetically independent species over time and under selective pressures.
• Sympatric Speciation: occur Within A Shared Habitat,
• Explains why diff Species can inhabit Same Area, and can occur when there is a serious chromosomal (extra) error during cell division of gametes.

Overview of Speciation Part 3

• Adaptive radiation, an important factor of allopatric radiation, occurs when a single ancestral species gives rise to many new species, and the phenomenon can happen when new habitats become available over time.
• Prezygotic barriers block reproduction before the formation of a zygote:
  • Can be due to different mating seasons or unique courtship behaviors
• Postzygotic barriers block reproduction after fertilization occurs:
  • Hybrid individuals: are produced from the cross of two different species and are infertile, meaning they cannot reproduce with either species.
  • Example: horse plus donkey makes a mule.

Ability to Exchange Genetic Material

• Members of genetic same species share share both external an internal characteristics
• Develop from DNA, the closer 2 organ shares more dna they have in common
• Appearance can be misleading in suggesting an ability or inability to breed
• Hybrid: offspring between two parents, which can be unfertile
• Gene pool: Collection of all variations of genes in all population of species
• Changes must be gentic to pass on the traits. Only heritable traits can evolve, so must change in the gametes.

Mechanisms of Speciation

• Presence of genetic nature of Hybrids between similar species that that descended from signle interbreeding
• Speciation: Formation of 2 from 1 originla species.
• Alloatric Speciation: Geographic: Other homeland involving speartion of new species
• Symptratric Speciation: parent remaints in one location.

Gene Flow in Speciation

• A geographically continuous population has has one gene pool: relativaly homogeneous
• Geneflow: range of Species relatively Individuals can mate with
• A Similar allele similar Distribution similar across geographic
• Aiscontiuntous flow, prevemtiong
• • When separtaion last for long populations different.
• Climate and resources Differ Divergent

Gene Flow in Populations

• In populations, the flow of the population is important to consdier
• Gene flow allows for and causes a new genrtic variatiion
• In geological isloation/hataitar

Allopatric Speciation

• Geographic Separation River Eroison, to isloation
• Dispersal: few species
• Vicariance: naturally selecitng that. Distnace same

Adaptive Radiation

• Radiation origin caused species new.
• In reponse

Sympatric Speciation

– A divergence occurring lacking a physical barrier Aneuploidy: Polyploidy Autopolyploidy: if have means otherwise Allopatric: 2 diff species reproducer, Plants more orror to surve.

Sympatric Speciation through Competition

• When Population groiws, competetion for food also grows
• To find food on another resourtce

Reproductive Isolation

• Reproductive Isolation: to intereeding
• Zyogote: Fertliazed egg (repros
• PostZYGOTIC barriers:
• Canot form womb +
• Could

Prezygotic Barriers

• A mechanish blocking reproduction places.
• Temporal Isolcation schedue
• Habilat Isoation no longer
• Betabioal ISlation
• Gametic Barriers Structures

Varying Rates of Speciation

• Gradual Speciation: overitme Punctuated equilibrim:
• Influence

Ring of Species

• When new species Transition inctinues interact
• Species, tricky

Genetic Drift

• Mechna of Inheritence before Mendels
• Allel Frw
• Genetic Drift: Chanve that some havving offspring

Test your knowledge of evolutionary fitness, natural selection, and speciation. Explore the processes driving adaptation, such as divergent and convergent evolution. Understand the criteria for defining a species and the dynamics of phenotype inheritance.