History of Life on Earth

History of Life on Earth

• Biological and geological changes are key to understanding the history of life.
• The formation of organic compounds, the emergence of first and later organisms, and the oxygen revolution were significant events.

The First Organisms

• Likely evolved in the ocean.
• Performed anaerobic respiration because there was no free oxygen in the atmosphere.
• Were heterotrophs.

Later Organisms

• Autotrophs emerged later.
• Cyanobacteria utilized photosynthesis.
• Chemosynthesis uses energy from chemical reactions to produce food.

Oxygen Revolution

• Cyanobacteria produced oxygen before land plants evolved.
• Aerobic respiration became possible, providing more energy (more ATP in aerobic vs. anaerobic respiration)
• Different types of organisms evolved as a result.

Geologic Time Scale

• Major explosions or extinctions that create space/resources mark time.
• Rapid adaptive radiation occurs to fill niche space.

Four Major Eras

• Precambrian: 4.6 BYA – 570 MYA and consisted of primitive marine life.
• Paleozoic: 570-225 MYA: marine life, first land plants, and first land animals.
• Mesozoic: 225-65 MYA is the age of dinosaurs.
• Cenozoic: 65 MYA-Present and is the age of mammals, including humans (Tertiary).

Mass Extinctions

• Mass extinctions occur when 40% or more of life dies.
• Climate change, volcanic eruptions/plate tectonics, asteroid impacts, sea-level changes, and atmospheric changes can cause extinctions.

Notable Mass Extinctions

• End Ordovician: 444 MYA, 86% of species lost due to ice age lowering sea levels.
• Late Devonian: 375 MYA, 75% species lost, newly evolved land plants caused algal blooms, suffocating bottom dwellers.
• End Permian: 251 MYA, 96% species lost in "the great dying," likely a perfect storm of natural catastrophes.
• End Triassic: 200 MYA, 80% species lost; cause unknown.
• End Cretaceous: 66 MYA, 76% species lost; asteroid impact delivered the final blow to the dinosaurs after precedent volcanic activity and climate change killed off ocean species.

Origin of Life

• Where and how life originated is currently unknown.
• The early Earth's atmosphere likely contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
• UV radiation, lightning, and asteroids/meteors bombarded early Earth.
• Hydrothermal vents were active.

Hypotheses on the origin of life

• Abiogenesis: Life arose naturally from non-living matter, like simple organic compounds.
• Panspermia: Life exists throughout the Universe and can be distributed by celestial bodies.
• Tidal Pools: Gases from volcanoes energized by UV light/electrical discharge hit tidal pools, creating conducive environments for life.

Support for Origin Theories

• Miller-Urey Experiment (1952) demonstrates organic molecules can be made from inorganic molecules to an amino acid.
• Murchison meteorite hit Australia in 1969 and contained 90 amino acids, 19 of which were already found on Earth.

Early Cell Structure Hypotheses

• Iron-Sulfide Bubbles: Hydrothermal vents produce sulfur that mixes with ocean water, creating compartments for early life forms.
• Lipid Membrane: Lipid molecules spontaneously form membrane-enclosed spheres "liposomes,” leading to early cells.

RNA World Hypothesis

• Early genetic material was RNA rather than DNA.
• RNA can replicate itself without enzymes.
• Ribozymes are RNA molecules that catalyze chemical reactions to make organic molecules.

Evolution

• Evolution is a change in allele frequency in a population over time.
• Evolution explains natural world phenomena.

Historical Context of Evolutionary Theory

• Linnaeus (1735): Natural Theology to discover a Creator's plan through species classification.
• Hutton (1785): Uniformitarianism suggests profound change via cumulative slow, continuous processes.
• Malthus (1798): Population Trends stating unchecked population growth will deplete resources.
• Lamarck (1809): Inheritance of Acquired Characteristics to explain evolution.
• G. Cuvier (1810): Catastrophism suggests Earth's history is marked by floods/droughts causing extinctions.
• Lyell (1830): Uniformitarianism describes slow, constant rates of geologic processes through time.

Darwin's Voyage

• Darwin sailed on the H.M.S. Beagle as a naturalist in 1831.
• He collected plant, animal, and fossil specimens; some resembled existing organisms, others were completely unknown.
• The Galapagos Islands (west of South America) are where he found giant land tortoises, marine iguanas, and finches with differently shaped beaks
• Darwin returned to England in 1836
• Darwin discovered that the organisms found on the Galapagos were found nowhere else
• Each species looked like similar species found on the mainland
• Darwin published The Origin of Species in 1859
• Darwin proposed the idea of natural selection: struggle for existence, survival of the fittest focused on resources and reproduction.

Key Figures in Evolution

• Wallace (1858): Natural Selection and the Father of Biogeography where he independently of Darwin came up with the theory of evolution via natural selection.

Darwin's 8 Observations

• Natural Variation
• Overproduction
• Struggle for Existence
• Unique Organisms
• Survival of the Fittest
• Change Over Time
• Descent with Modification
• Common Descent

Evidence for Evolution

• Fossils
• Biogeography
• Anatomy
• Embryology & Biochemistry/Genetics

Fossils

• Fossils provide evidence of organisms that lived long ago.
• Parts or whole organisms are preserved or petrified.
• They can be frozen in ice or enclosed in amber, sand, or clay that turns to rock.

Fossil Record

• Layering in sedimentary rock gives clues as to when organisms lived.
• Lower layers are older than upper layers.
• Absolute Dating uses Radiometric Dating and Half-Life
• Relative Dating uses the Law of Superposition

Dating Rocks

• Relative Dating estimates the time during which an organism lived based on the placement of other fossils.
• Radiometric Dating measures the natural decay of unstable isotopes.
• Isotopes are the same element with different # of neutrons
• Half-Life is the time it takes for half of the isotope to decay into a different element; carbon is often used to date organic substances.

Fossil Types

• Transitional Fossils (Intermediate Fossils) show an intermediate state between an ancestral trait and that of its later descendants.
• Archaeopterix is an example of Transitional Fossils.
• Therapsids and Tiktaalik are also examples of Transitional Fossils.
• Therapsids are a link to the first mammal-like skulls
• Tiktaalik connect aquatic and terrestrial animals

Radiometric Dating

• Determines the age of rocks/fossils based on the decay of radioactive isotopes, using the half-life to date certain fossils

Biogeography

• Study of geographic distribution, similar fossils found on east coast of South America and west coast of Africa
• Biogeography was one of Darwin's first clues/evidence for evolution suggesting relationships between organisms and ecological equivalents.

Anatomy

• Vestigial organs are structures with no function in living organisms (appendix, wisdom teeth, coccyx).
• Analogous structures have a similar function but no common ancestry (wings).
• Homologous structures are body parts arising from the same embryonic tissues.

Embryology and Biochemistry

• Comparative Embryology studies developing organisms, and embryos start out very similar but become distinct.
• Comparative Biochemistry studies organisms on a biochemical level using proteins and DNA.

Genetics

• Production of new alleles and genetic recombination.
• Mutations
• Sexual selection
• Selective breeding
• Human DNA is 99% similar to chimpanzees, 65% similar to chickens, and 50% to fruit flies.

Mechanisms for Evolution

• Natural Selection
• Gene Flow via Immigration/Emigration
• Genetic Drift: Bottleneck Effect and Founder Effect
• Mutations: +/0/-

Change in Allele Frequency

• Genetic drift involves rapid change in the numbers/kinds of genes in a small, isolated population by chance events.
• The Founder effect occurs when isolated individuals set up a new population with a different gene frequency from the parent population.
• The Bottleneck effect is the reduction in population size which affects gene frequencies in surviving members.
• Gene flow involves movement of genes from one population to another causing a gain or loss of alleles in the gene pool.

Hardy-Weinberg Equilibrium

• Used to assess if evolution is occurring using a formula.
• Genetic variation in a population remain constant from one generation to the next in the absence of disturbing factors.
• With random mating in a large population and in the abscence of disruptive circumstances.
• Genotype and allele frequencies remain constant because they are in equilibrium.

Conditions for Hardy Weinberg Equilibrium

• No mutations
• Random mating
• No natural selection
• Large population
• No gene flow

HWE Equation

• p + q = 1
• p = frequency of dominant allele (A)
• q = frequency of the recessive allele (a)
• p² + 2pq + q² = 1
• p² = AA
• 2pq = Aa
• q² = aa

Sources of Variation

• Mutations
• Gene Flow
• Sexual Reproduction which leads to crossing over and recombination.

Adaptations

• Adaptations can be structural, physiological, or behavioral.

What is an Adaptation

• Adaptations are traits that aid survival and reproduction.
• Variations are raw materials for natural selection (good or bad), while adaptations are products of natural selection (always good).

Complex Adaptations

• Complex adaptations do not arise overnight.
• These modifications occur over many generations.
• Complex adaptations modify what already exists (ancient photoreceptor cell) like eyes.

Types of Adaptations

• Structural adaptations involve anatomy (woodpecker's beak, anteater's snout).
• Physiological adaptations have a chemical basis (spider's web, snake venom).
• Behavioral adaptations result from an organism's response to environment (bird's migrating).

Primate Adaptations

• Humans are primates including monkeys and apes
• Problem-solving ability.
• Flexible shoulders with forelimbs that can be rotated.
• Opposable thumb.

Coevolution

• Cases where two or more species reciprocally affect each other's evolution, e.g., pollinator and plant, predator and prey, parasite and host.

Natural Selection

• Process by which organisms better adapted to their environment tend to survive and produce more offspring can take many forms
• Distribution of traits across a population will form a Bell Curve

Natural Selection Types

• Stabilizing Selection favors an average trait, narrowing the curve like human babies who are 6-8 lbs increasing their chances of survival.
• Directional Selection shifts the bell curve in one direction creating a more extreme trait. Example: thicker shelled oysters resist breakage and have less crabs prey on them.
• Diversifying/Disruptive Selection favors both extremes over the average and creates two peaks and a trough. An example of this is lobsters.

Sexual Selection

• Contest is competition within the same sex for access to the opposite sex, like rams butting heads and kangaroo boxing.
• Choice is competition for attention of the opposite sex, like bird calls, dances, and roaring

Artificial Selection

• Humans choose traits perceived as advantageous during domestication of animals and plants

Side Effects of Artificial Selection

• Farmers and breeders allowed only the plants and animals with desirable characteristics to reproduce, causing the evolution of farm stock where there are unintentional consequences
• An example of this are narcolepsy in dogs and fainting goats

Speciation

• Speciation is the formation of a new species.

What is a Species?

• A group of organisms that can interbreed and produce fertile offspring in nature.
• Hybrids like mules, ligers, and tiglons are not considered species.

Evolution of a Species

• Reproductive isolation and is the inability to exchange genes among species

Pre-Zygotic Barriers

• Barriers that prevent mating or hinder fertilization if mating does occur, including:
• Habitat isolation
• Temporal isolation
• Behavioral isolation
• Mating attempt
• Mechanical isolation
• Gametic isolation

Post-Zygotic Barriers

• Barriers that prevent a hybrid from passing on genes, including:
• Reduced viability
• Reduced fertility
• Hybrid breakdown

Types of Speciation

• Allopatric Speciation happens when gene flow is prevented by geographic isolation due to the environment changing, or a subset of the population migrating to a new area = Slow.
• Sympatric Speciation happens when new species evolve while still in the same area and results from sexual selection and polyploidy = Fast.

Evolution Types

• Divergent Evolution emerges when one species evolves into two or more species with different characteristics to see homologous structures in the species
• Adaptive Radiation is the divergent evolution and adaptation of species to different roles in new habitats.
• Convergent evolution is when species that are not closely related evolve similar traits (dolphin and shark) to see analogous structures.

Tempo of Speciation

• Gradualism consists of a slow steady change in species.
• Punctuated Equilibrium consists of slow evolution punctuated by short events of rapid evolution.

Macro vs. Micro Evolution

• Macroevolution is a major evolutionary change that applies mainly to the evolution of whole taxonomic groups over long periods. An example is different groups evolving from a single common ancestor over millions of years
• Microevolution is a minor evolutionary change within a species or small group of organisms, especially over a short period. An example is lighter fur becoming more common in a population of rabbits in the arctic

Cultural Evolution

• Culture consists of the transmission of accumulated knowledge over generations: language (spoken and written).
• Enlargement of brain, by a prolonged growth period that helps acquire culture that's unique to Homo sapiens
• Extended period of development lengthens the time parents care for their offspring, resulting in the Basis of culture.