Evolution and the Biosphere

Evolution: Introduction

  • Course Objectives:

    • Provide a historical view of the theory of evolution.

    • Study various factors involved in the genetic change of populations over time.

  • Evolution Definitions:

    • Dictionary definition: "process of continuous change from a lower, simpler, or worse to a higher, more complex, or better state."

      • Problems with this definition:

        • Random mutations may be harmful or beneficial.

        • Pace shows extreme variation.

        • An unchanging environment may not require change.

        • Fossils document hindlimb loss as ancestors of whales transition from land to sea.

Genes of H7N9

  • Genes of H7N9 derived from four different bird strains

  • Viral reassortment allows flu strains to infect new hosts

  • Viral strains with beneficial mutations increase in frequency through natural selection, leading to a change in populations’ genetics

  • Viral strain no longer recognized by the immune system.

  • Leads to higher reproduction

  • Highest reproducer dominates population in subsequent generations (e.g., omicron)

  • Generations (time): 1, 2, 3, 4

  • P, M, G, B => M,G,B => B => B

Biological Definition of Evolution

  • Change from generation to generation in populations of organisms differing genetically in one or more traits.

    • Replace "individual" with "populations of"

Definitions of Science

  • Dictionary:

    • A possession of knowledge as opposed to ignorance.

    • Knowledge obtained through study or practice.

    • Attempt to discover nature and then predict the future.

  • Practical (use of “scientific method”):

    • observation => question (e.g., why?)

    • formulate hypothesis (speculation)

    • design experiment (predict test results) (w/ controls)

    • collect data (replicates)

    • analyze results (using statistics)

    • draw conclusion (reject null hypothesis?) (= hypothesis of no difference (btwn T & C))

    • publication by peer review (correlation ≠ causation)

    • repeated support* (including fitting new observations) => theory

      • [Note: can never prove (only disprove)], repeatable?

    • inductive (Bacon) vs. deductive (Darwin) method

Scientific Method

  • Observe and ask questions about the natural world.

  • Suggest a hypothesis to explain your observations and questions.

  • Generate predictions to test your hypothesis.

  • Design tests of the predictions of your hypothesis.

  • Test by observing or measuring.

  • Test by designing and running experiments.

  • Analyze the results.

  • Accept, reject, or modify your hypothesis, predictions, or test according to the results.

  • Communicate your results to fellow scientists for their review and input.

  • Falsifiable hypothesis

  • Correlation is insufficient

Correlation vs. Causation

  • Example: Autism prevalence vs. organic food sales

  • Sales ($ millions) vs individuals diagnosed

  • r=0.9971 (p<0.0001)

Is Evolution Science?

  • No? - events unique, not replicable

  • Yes? - "rules" are open to disproof

The Biosphere

  • Distribution of life reflects the variation of environments

    • Differential heating of the planet

      • Curved surface – near poles => diffuse light

      • Tilted axis – seasonal change in sunlight

        • Sun directly overhead between Tropic of Cancer (summer solstice) & Tropic of Capricorn (winter solstice) only (band = tropics)

      • Rotation – diurnal changes in sunlight (time zones)

      • Altitude – high = thin atmosphere, doesn’t hold heat

    • Atmospheric circulation

      • Convection cells – hot air rises, cools => ppt (drops moisture), sinks => wet equator, dry subtropics

Time Zones

  • There is a new time every 15 degrees of turn, or 24 time zones on Earth.

Convection Cell

  • Warm (less dense) air rises (and expands and cools)

  • Cool (more dense) air sinks (and is compressed and warms)

Atmospheric Circulation and Precipitation

  • Low precipitation at 30°S

  • High precipitation at the equator

  • Southeast trades and Northeast trades

Coriolis Effect

  • Equator moves faster than poles => deflection of winds

    • N. Hemisphere = winds deflect right, rise & fall w/ right-hand rule

Climatic Controls

  • Latitude –Sun angle (temp), convection cell (ppt)

  • Topography – altitude, windward vs. leeward side

    • rain shadow= moisture drops as air passes over mtn.

  • Continental vs. maritime – neighboring water => (moist air) absorbs & releases heat slowly => dampens temperature changes

  • Prevailing pressure systems – warm vs. cold ocean currents, storm paths (tornado/hurricane alley)

  • Microclimate – small scale, most important to organisms (shade, proximity to water, etc.)

Coriolis Effect Illustration

  • Deflection caused by Earth's rotation

Ocean Currents

  • Equatorial countercurrent

  • Cold and warm water currents

Biomes

  • Largest ecological unit, characteristic vegetation (and therefore soil)

    • Terrestrial (aquatic habitats covered later)

    • Plants reflect the major determinants of climate: temperature & precipitation patterns

    • Lumpers (as few as 7) & splitters (as many as 25)

      • Tropical rain forest - rainy, stratified canopy, little temperature variation, poor soils (decomposition & leaching)

      • Tropical savanna - N&S of tropical dry forests, open grass with scattered trees, wet/dry (fire) seasons, wandering grazers, human origins

      • Tropical desert (Aladdin) – evaporation > rainfall, bands ring globe at 30o N&S, drought & flood, wide daily temp. variation, little vegetation (cacti & succulents), low organic soils (islands), animals are water conservers

      • Temperate deciduous forest – deciduous trees & some conifers, moderate temperature variation, moist, richer soils

      • Temperate grasslands (steppe) – hot & cold, grasses & grazers, drought, fire, flat terrain => good agricultural land (Great Plains)

      • Temperate desert – evaporation > rainfall, cooler at night, & moister (more vegetation & flowers during moist season) than tropical desert

      • Northern coniferous (Brother Bear) (boreal) forest (taiga) – evergreen forest, some birches/aspens, cold winters, bogs (permafrost), large mammals

      • Tundra (Zootopia) – polar grassland, permafrost, low vegetation (or above treeline), very cold, little solar E

      • Cool/cold desert – high altitude* or latitude, cold at night (huge temp. extremes), evaporation > precipitation, *(warm during day = scrub/sagebrush)

        • the effects of altitude mimic the effects of latitude

Factors Affecting Biomes

*Temperature and precipitation

  • 3 X 3 matrix of temperature (x) & precipitation (y):

    • hot = tropical, warm/cool = temperate, cold = polar

    • ppt.: high = forest, mod. = grassland, low = desert

  • human activity “stresses” the biosphere – pollution, acid rain, deforestation, landuse, warming

Biome Distribution

  • Effects of latitude and altitude on climate and biomes.

  • increasing altitude mimics increasing latitude

Earth’s Convection Cells

  • Relationship between latitude, ppt, press, air, temp, and biomes

  • precipitation is related to rise/fall

  • biomes are determined by temperature & precipitation

Climate and Biome Limiting Factors

  • Average precipitation and temperature are limiting factors that determine the type of biome.

  • 3 x 3 matrix of biomes

Historical Framework

  • Plato (427-347 B.C.) & Aristotle (384-322 B.C.) – "idealism" => everything, including animals, represented by an ideal (archetype)

    • The “Ladder of Nature” or “Great Chain of Being” (ensured the stability of an ordered society)

  • Linnaeus (1707-1778) –

    • binomial nomenclature (Genus species) (particularization vs. generalization/stereotype) => species, genera, families, orders, classes, phyla, kingdoms (=> nested hierarchical structure)

  • spontaneous generation – living organisms from non-living material (e.g., flies from rotten meat, mice from dirty laundry) => belief that creation not a “done deal”

Aristotle's Ladder of Nature

  • Arrangement of organisms from inanimate matter to perfection

Taxonomy and Binomial Nomenclature

  • Carolus Linnaeus (1707-78)

  • Use proper format! Homo sapiens or Homo sapiens (capitalize Genus, lowercase species, underline or italicize)

  • Domain (Archaea, Bacteria, Eukarya)

  • Plantae, Fungi, Protista, Monera

Darwin’s Observations

  • Darwin’s (1809-1882) observations (conflicted with 4,000 B.C. origin of Earth):

    • fossil evidence – extinct mammals => living species have ancestors (modification with time, not all survive) (Lyell’s “Principles of Geology” => the antiquity of the Earth, uniformitarianism)

    • geographic distributions – one species replaced by another (e.g., N. to S.), change w/ distance from equator, etc.

    • island organisms – mainland ancestor => several varieties on isolated islands

    • selective breeding – change in domestic breeds

Scientific Precursors to Darwin’s Understanding

  • Nicolas Steno (1638-86): change in fossils => reconstruct the past

  • Jean-Baptiste Lamarck (1744-1829): evolution through acquired traits, spontaneous generation

  • Georges Buffon (1707-88): Earth followed laws of physics & chemistry, old Earth

Natural Selection

  • organisms display descent with modification

    • Lamarck (1809) – “evolution” in Darwin’s time, neck stretching => longer necks (Not!!)

      • acquired traits are not inherited! (although Darwin also believed this (gemmules))

    • Malthus (1766-1834) – in 1788 published “An Essay on the Principle of Population”

      • human population will increase exponentially, faster than food supply

      • population limited by its subsistence

Population Growth

  • Malthus pointed out that human populations can, but don’t (back then) grow exponentially due to resource limitation.

  • (N)(t)(N) (t)

  • (# indiv) (yr)

Darwin & Alfred Russel Wallace

  • Darwin & Alfred Russel Wallace (1850s) – recognized organisms’ “struggle for existence”

    • real populations don’t expand at exponential rate (nature limits)

    • natural dangers => not all survive/reproduce

    • individuals vary (have different traits)

    • some heritable traits assist survival and reproduction (adaptations) => “survival of the fittest”

    • differential reproduction = bottom line “reproduction of the suited” (better represents natural selection)

Selection for MRSA

  • natural selection can lead to antibiotic resistance

  • any bacteria that are randomly resistant to the antibiotic (selection pressure) can better survive and reproduce

  • frequency (proportion) of resistant bacteria increases in the surviving population = evolution

Evolution by Natural Selection

  • interaction between individuals & environment (living (biotic) & non-living (abiotic)) determines number of descendants

  • better adapted locally => more reproduction

  • with time, population (not individual) => more closely matched to its environment

  • change & “improvement” ( = match) => organizing principle of biology

  • selection acts not just to preserve, but to create new types

Peppered Moths

  • light and dark versions (phenotypes) of the species

Industrial Melanism

  • Proportion of the dark vs. light phenotypes changed rapidly when the color of the tree bark changed (with pollution & when cleaned up).

Natural Selection and Environmental Change

  • Dark bark vs light bark

  • Selection pressure for dark bark or light bark

Darwin Quote

  • "Can we doubt . . . that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable variation, I call natural selection.” Charles Darwin, 1859

Why No Perfection?

  • changing environment (living & non-living)

  • selection can only act on existing traits (arise by chance mutation)

  • speed of change depends on magnitude of selection pressure