5 - Evolution

What is evolution?

the process of change in the allele frequency of a population's gene pool over multiple generations, a cumulative change of heritable traits in a species over time.

How do fossils provide evidence for evolution?

Fossils preserve remains giving direct evidence of ancestral forms, like bones and teeth, also preserve traces which give indirect evidence of ancestral forms, like footprints and tooth marks. Fossil records show how the features of living organisms change over time.

Law of Fossil Succession

lower layers are older and newer layers form on top. Prokaryotes appear before eukaryotes, ferns before flowering plants, invertebrates before vertebrate. However, fossil records are incomplete because specific factors are needed for fossilization and only hard parts are preserved, making it difficult to determine evolutionary patterns.

Transitional Fossils

Fossils that show intermediary forms over the evolutionary pathway taken by a single genus, and as new fossils are found new patterns emerge.

Selective Breeding

artificial selection where humans breed members of a species with a desired trait to produce offspring. The trait frequency becomes more common down generations. This provides evolution evidence as target breed highly vary in a short period of time.

Selective breeding examples

Brassica genus plants have been bred and modified through artificial selection, creating broccoli, cabbage, and kale. Dogs have been bred and domesticated resulting in different breeds.

Comparative Anatomy

The similarities and differences of structural features between groups of organisms. Similar features imply common ancestry.

Homologous structures

Anatomical features that have similar structure but due to adaptive radiation are used in different ways. The more similar the more related. Adaptive radiation where multiple new species quickly diversify from ancestral sources and adapt to specific uses. For example, the pentadactyl limb: a five-digit limb in mammals that has adapted based on locomotion, birds - flying, humans - tool manipulation, dolphin finds - swimming.

What is meant by continuous variation?

A population of species holds genetic variation which is usually continuous, thus follows a normal distribution curve as the rate is gradual and cumulative. However, when populations are geographically separated they adapt to different environmental conditions and slowly diverge.

The degree of Divergence

the extent of change in genetic variation between separated populations which depends on:

proximity between separated populations if close less variation,

time since separation if short less variation. Eventually, species will diverge into separate species and will no longer be able to interbreed.

Evolution Example

Peppered moths are light in clean environments where light lichen colors trees for camouflage, and dark in polluted places with darker bark for camouflage.

After the industrial revolution, it went from clean to polluted, the advantage shifted from light to dark moths. Now, decreasing pollution is changing their frequency again.

Natural Selection

A process that increases the frequency of characteristics that make a species better adapted and decrease other characteristics, changing the species.

Natural Selection Variables

ICEAGE, Inherited variation exists within the population, Competition comes from an overproduction of offspring, Environmental pressures lead to differential reproduction,

Adaptations which benefit survival are selected, Genotype frequency changes across generations, Evolution occurs within the population

Variation in Natural Selection

Natural selection can only happen if there is variation among members of a species. Variations can be discontinuous and become distinct classes, or continuous and range in characteristics.

How does variation occur?

Genetic variation happens due to mutation where varied gamete composition leads to varied traits in offspring. This can happen in during Prophase 1, due to crossing over where non-sister chromatids exchange genetic material at chiasmata.

Further, mutations occurs during Metaphase 1 due to independent assortment where homologous chromosomes line up towards opposing poles randomly, and the orientation of bivalents is independent, thus different combos of maternal/paternal chromosomes could be inherited when bivalents separate in Anaphase 1.

Lastly, in sexual reproduction, fusion of two haploid gametes forms a diploid zygote which can then divide by mitosis and differentiate into an embryo. As meiosis results in genetically distinct gametes, random fertilization between the egg and sperm will generate different zygotes and offspring will show variation.

Natural Selection and Competition

Species produce more offspring than an environment can support, thus overproduction leads to competition for survival. Abundant resources cause populations to grow to biotic potential, more offspring makes it so less resources are available to other members causing a struggle for survival and increasing mortality. [J-curve, Environmental resistance, plateau in population growth]

Adaptations

Trait changes that allow an organism to survive and reproduce its given environment. They can be structural, behavioral, physiological, biochemical and developmental.

Adaptation types

Structural - physical differences in biological structures, like giraffe necks. Behavioral - differences in activity patterns. Physiological - detection variations, and response by vital organs. Biochemical - differences in molecular composition of cells and enzyme functions. Developmental - variable changes that occur across an organism's life span.

Biological adaptations

have a genetic basis that are encoded by genes and may be passed to offspring. Organisms with beneficial adaptations are more likely to survive and reproduce.

Natural selection and Allele frequency

Individuals that hold better alleles are better adapted, they tend to survive and produce more offspring than less adapted. Due to natural selection, the proportion of different alleles changes across generations, and if environments change what's considered beneficial changes.

adaptive radiation

A diverging evolutionary pattern in which many species evolve from a single ancestral species. It happens when a single species occupies various functions with different environmental conditions, and thus evolve different features in response to different selection pressures.

Adaptive Radiation Example

Galapagos Finches have specialized beak shapes depending on their main source of nutrition.

Antibiotics

compounds that block the growth or reproduction of bacteriostatic bacteria, used to treat bacterial infections.

Antibiotic Evolution

A small colony population of bacteria can develop antibiotic resistance via gene mutation, as resistant bacteria will survive and reproduce by binary fission and the antibiotic resistant bacteria will flourish over other bacteria strains as they die due to antibiotics. Further, they may offer resistance to other strains via plasmid transfer by bacterial conjugation. Selection pressure in the form of antibiotic introduction causes the antibiotic resistance gene to become more frequent.

Antibiotic resistance example

Staphylococcus aureus, or golden staph bacteria show antibiotic resistance. Cause skin infections and treated with antibiotic methicilin which caused the strain to become resistant to it. The strains procreated while past strains died. Methicilin resistant golden staph infections are now present in places where methicilin was most used. Thus, various antibiotics are used for treatment.

Taxonomy

The binomial system of names for species, proposed by a Swedish botanist, Carolus Linnaeus. It identifies and compares organisms based on traits.

Taxonomy Hierarchy

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species, Mnemonic "Do Kinky Professors Cause Older Females Genital Spasms?"

Taxonomy Example Animal

Eukarya, Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, Sapiens.

Taxonomy Example Plant

Eukarya, Plantae, Angiospermophyta, Eudicotidae, Ranunculales, Ranunculacae, Ranunculus, acris, Buttercup.

Domain

The biggest taxonomic category; three domains are Archaea - prokaryotes lacking a nucleus that consist of extremophiles, Eubacteria - prokaryotes lacking a nucleus that consist of common pathogens , and Eukarya - eukaryotes that contain a membrane-bound nucleus, plants and animals.

Artificial classification

a classification based on traits first. Advantages: schemes are easy to develop and are unlikely to change. Disadvantage: do not show evolutionary relationships and thus are not commonly used.

Natural Classification

a classification based on similarities first and then shared traits. A given group share a common ancestor, allowing to predict shared traits. However, the system changes as new info is found.

Phylogenetic classification

A classification based on evolutionary history that allows to differentiate organisms based on genetics. Organisms who share a greater level of homology in their DNA or Amino acid sequences are more related.

Plant Phyla

Bryophyta - no vascularity, no leaves or stems but root-like structure, moss. Filicinophyta - vascularity, triangular leaves divided into leaflets, reproduce by spores, ferns. Coniferophyta - vascularity, waxy leaves and needle-shaped stems, pines. Angiospermophyta - flowering plants, vascularity, leaves and roots, reproduce by seeds.

Animal Phyla

Animalia is divided into invertebrates and vertebrates. Porifera - no symmetry, no mouth or anus, pores to circulate material, silica or CaCO3 spicules for structure, sea sponges. Cnidaria - radial symmetry, mouth no anus, may have stinging cells for capturing and disabling prey, jellyfish. Platyhelmintha - flat body to increase SA:Vol ratio, possibly parasitic, bilateral symmetry, mouth no anus, tapeworms. Annelida - bilateral symmetry, separate mouth and anus, ringed specialized body segments, worms and leeches. Mollusca - bilateral symmetry, separate mouth and anus, visceral mass body, muscular foot, mantle with possible shell. Arthropoda - bilateral symmetry, separate mouth and anus, jointed body sections with exoskeleton, insects. Chordata - bilateral symmetry, separate mouth and anus, notochord and hollow, dorsal nerve tube, mammals, birds, reptiles...

Chordata and vertebrates

Chordates that posses a notochord, hollow dorsal neural tube, pharyngeal slits, and a post-anal tail. The neural tube develops into a spine and notochord forms a backbone.

Fish

bony plate scales, reproduction through external fertilization where the egg and sperm are released into the environment, breathe via gills, no constant internal body temp, ectothermic

Amphibian

Moist skin, permeable to gases and water, Reproduce via external fertilization, spend larval state in water, adult state on land, breathe through skin and have simple lungs, no constant internal body temperature, ectothermic

Reptiles

keratin scales, reproduce via internal fertilization where females lay soft shell eggs, breathe through lungs with folding to increase SA:Vol ratio, no internal body temperature, ectothermic.

Birds

keratin feathers, internal fertilization where female lay hard shell eggs, breathe through lungs with parabronchial tubes, constant internal body temperature, endothermic.

Mammals

Skin has follicles which make keratin hair,

internal fertilization where females feed offspring milk from mammary glands,

breathe through lungs with alveoli,

constant internal body temperature, endothermic.

Dichotomous key

a method of identification where organisms are repeatedly divided into wo categories. With each division, more information is revealed, and when no more traits are shared then it has been identified. it is good to identify features that do not change.

Clades

a group of organisms which evolved from a common ancestor. A clade consists of ancestral organisms and all evolutionary descendants and share common traits.

Cladistics

classification based on common ancestry

Cladograms

branching diagrams that show the most probable sequence of divergence in clades. Node - each branch point represents a speciation event where species diverged. Closely related species will be separated by fewer nodes. Root - initial ancestor common to others in the cladogram. Outgroup - distantly related species.

Molecular evidence

Evidence for which species are part of a clade, from gene base sequences of a protein amino acid sequence. Molecular heritage is compared to find levels of relatedness and divergence. The more differences between comparable base sequences the more time has passed since diversion. Non-coding DNA provides the best comparisons as less mutations occur, and gene sequences mutate slower.

Molecular clock

Model that uses DNA comparisons to estimate for how long divergent species have been evolving independently. Different genes or proteins change at different rates, but the rate of change for a given gene differs between different groups of organisms.

Cladistics limitations

Classification was based on structural differences and closely related species showed more similarities indicating common ancestry. However, closely related organisms can have drastic structural differences due to adaptive radiation, and distantly related organisms can be very similar due to convergent evolution.

Convergent evolution

The independent evolution of similar features in different lineages. It happens when different species live in the same habitat and adapt to the same selection pressures. Shared conditions cause similar adaptations and increase similarity.

Analogous traits

similar traits due to from convergent evolution, thus no common ancestor but common selection pressures.

Homologous traits

different traits due to divergent evolution, thus a common ancestor and different selection pressures.

Reclassification of figworts

cladistics evidence shows figworts who were the 8th largest Angiospermophyta family were not all part of the figwort family. As many figworts were too different in structure and was split into 5 different clades.