Darwinism and Evolution

Vocabulary:

• Descent with modification: Darwin’s term for evolution, the accumulation of changes coming from a single ancestor

• Fitness: A measurement of how many offspring an organism leaves

• Unity of life: Different species on Earth all share similar life features

• Population: All of the organisms in a given environment that are capable of reproducing with one another

• Lamarckian Evolution: The various traits an organism develops over its life span will be passed to its offspring (example giraffes got longer necks because in the parent’s life they stretched to reach trees)

• Darwinian Evolution: Mutations in DNA lead to differences in phenotype, some of which can make a certain organism better at surviving and reproducing, increasing the likelihood that they will have offspring who also possess this trait

• Lamarck: An early evolutionary thinker back in the 1800s, had the right concept but the wrong specifics, highly ridiculed in the scientific community

• Cuvier: Studied evolution through fossils, if the Earth is changing and species adapt to live on Earth, the species must also be changing

• Common ancestor: A shared ancestor among various species, from which they have evolved past but share a similar lineage, being the common ancestor

• Phylogeny: The study of evolution through the use of diagrams that look like trees called cladograms, with branches emerging from various traits or genetic changes, each branch being a new species

• Extinct: A species that is no longer living

• Extant: A species that is sill living

• Genetic drift: A cause of non-adaptive evolution, describes the change in population because of a random event, common with small populations

• Gene flow: A cause of non-adaptive evolution, describes a change in allele frequency due to the entrance or department of various individuals from the gene pool

• Artificial selection: Selective breeding, done with dogs

• Reproductive success: A measure of fitness, how many offspring an individual leaves

• Epigenetics: The turning on/off of specific genes within a genome, can be passed from parent to offspring. Certain genes are turned on due to factors like stress, and passed on activated until it is turned off. This somewhat follows Lamarckian evolution

• Evolutionary adaptation: An inherited trait that enhances an organism’s ability to survive and reproduce on a particular environment

• Comparative anatomy: The process of comparing two organisms based on their number of shared characteristics, provides information about how related the two species are

• Homologous structures: Derived from a common ancestor, same/similar feature in two branched species

• Analogous structures: Similar structures, though evolved seperatley, independent of each other. These creatures do not share a recent common ancestor, results from convergent evolution

• Convergent evolution: Occurs when there are similar environmental pressures resulting in analogous structures

• Macroevolution: Change that occurs above the species level, results in speciation (branching of species)

• Microevolution: Adaptations that evolve within a population as a result of allelic frequency change, confined within a single gene pool, only applies to one species

• “Modern Synthesis”: Defines evolution as the change of genetic make-up of a population over time, provides a way for natural selection to be tested

• Gene pool: All of the alleles for every single loci for all individuals in a population that reproduces

• Bottle neck effect: When a large disaster occurs, leaving a population significantly smaller. This can cause dramatic genetic drift

• Founder effect: When a small group of a population splits off and created a new population, the allelic frequencies of the new population will more match that of the founders/original migrators rather than the original population

• Directional selection: When natural selection changes the average allele frequency to something else

• Disruptive selection: When natural selection shifts the mean to two separate opposite ends

• Stabilizing selection: When natural selection shifts more towards the mean allelic frequency

• Sexual selection: When a particular trait are only adaptive in terms of attracting mates. This commonly occurs in the males, examples being putting on a show with fancy colors or dancing. This commonly occurs in the males, impressing the females

• Neutral variation: Describes genetic variation that is preserved, things aren’t selected for or against anything

• Diploidy: There are two genes for a trait with one being recessive. This helps maintain variation, heterozygous individuals allow variation to continue even when not displayed

• Heterozygote advantage: When an organism has an advantage due to being heterozygous, for example sickle-cell in areas high with malaria

• Frequency dependent selection: When a particular allele not being common is a good thing, balancing selection

• Balancing selection: Natural selection maintaining two or more phenotypic forms, including frequency-dependent selection and heterozygotes

• Mutagens: Things that cause mutation in DNA

Darwinism

• Descent with modification: The term Darwin used rather than evolution, provides a definition and specification to evolution

  • Descent: shared ancestry, resulting in shared characteristics

  • Modification: accumulation of differences

• Life changes, life is not immutable, things survive due to their fitness quality

• Certain animals have distinguishing qualities, similar to others (moths and butterflies) but many differing features as well. This leads to the idea of a common ancestor

• Within a population variation naturally occurs, nature selects them with various factors from the environment (fitness factors)

• Observations of life:

  • Fit between organism and environment, life adapts to biotic and abiotic factors

  • Share characteristics between different animals (unity of life)

  • Diversity of life, despite differences

• Darwin was NOT the first with these theories

  • Lamarck was an early thinker, but had the incorrect idea/concept of evolution

    • Early 1800s

    • Proposed organisms adapt to the environment

    • Though acquired characteristics were passed on to offspring (example if you got a tattoo your kid would have the same tattoo)

    • Often made fun of, people thought species did not change over time back then

  • Cuvier studied fossils to study change over time, if the planet changes and species adapt to them, creatures must be changing

• An earthquake occurred in the Andean Mountains that Darwin witnessed, which revealed rock that had ocean fossils in it. From this he concluded that the land had once been oceanic there

• Galapagos Island/Finches

  • Many of the difference species had beaks, adapted for different food sources

    • Cacti eaters are long to avoid spikes

    • Insect eaters are narrow

    • Seed eaters are stubby but strong to crack

  • The species more resembled those of the South American climate, hinting towards migration

• 2 big ideas in Origins of Species

  • Current species descended from ancestral species (common ancestor)

  • Natural selection is the mechanism for species modification

• More offspring are left than can be supported, so those with better traits will likely live longer and have higher chances to reproduce

• Early criticisms included how it only applied over a long period of time, how it cannot be tested experimentally, how it only describes selection on pre-existing variation without a source, and how it could not explain how traits were inherited

Evolution

• A phylogenetic tree can be called a cladogram

  • A fork is there a common ancestor had been before splitting off

  • More recently related species are closer related, they share more common ancestors

  • The bottom access can be either time or genetic changes that cause particular traits

  • Large gaps between related species are either branching or extinction events (example extinction of older species explains why elephants are unlike their most related species, manatees, as they all died off, there is a missing link). Transitional fossils can be left by these creatures, displaying the evolutionary line

• Artificial selection (selective breeding) is when specific organisms are bred, or made to reproduce based on genetic factors. Doing this process over many generations can exemplify a specific trait (dogs, for example with breeds). People do this, but so does nature

• Sometimes advantages come with trade offs

• An example includes antibiotics and bacteria, if a population is given an antibiotic all the bad ones will die, and then the population will be comprised of individuals with a high resistance who will also pass on this high resistance, the allele frequency rises

• Natural selection works on an individual, but a population evolves

• Mutation is the source of variation

• Natural selection can impact the allelic frequencies, and change the average

  • Directional selection changes the average

  • Disruptive selection shifts the mean to two separate opposite ends

  • Stabilizing selection shift more towards the mean

• It does not work to make a single ‘perfect’ organism, but rather an organism that fits within a given environment

• Only acts on mutations already present

Sickle Cell/Malaria

• Sickle cell is caused by a point mutation, changing glutamate to valine, from A to U in the mRNA strand

• The disease causes red blood cells to be shaped differently, causing them to not carry oxygen as efficiently

• Sickle shaped cells end up trapping the parasite for malaria, causing those who have a sickle-cell allele to have partial immunity

• Even those who are heterozygous for sickle-cell have some qualities of the disorder

Mutations

• Everything is in fluxuation, including the enzymes that check DNA for accuracy, some base pairs will be wrongly replicated

• Chemicals and radiation can damage DNA and mutate it, changeing the genotype affects the phenotype

• Evolution acts on the mutations already present

• Happens by random chance