Evolution Evidence and Speciation

Fossils

Preserved remains of living things Paleontology is the study of the fossil

record Most organisms do not leave a fossil after

death Explains the “missing links”

Sedimentation Fossils As the organism decomposes the spaces will be

filled with the minerals from the silt

Evidence for Evolution

How old is that fossil?

Relative Dating Age of fossils based according to their location

in strata

Absolute Dating Age of fossils determined by analyzing the

content of radioactive isotopes found in the fossil.Half-life: The length of time required for half of the

radioactive elements to change into another stable element.

Unaffected by temperature, light, pressure, etc.All radioactive isotopes have a dependable half life.

Ex: C14 decays into N14

Relative Dating

How radioactive “naturally occurring”

elements get inside an organism:

A.K.A – Radiometric

dating

Absolute Dating

Evidence for Evolution HOMOLOGY is a characteristic shared by

two species (or other taxa) that is similar because of common ancestry.

Types of homology

morphological homology – species placed in the same taxonomic category show anatomical similarities.

ontogenetic homology - species placed in the same taxonomic category show developmental (embryological) similarities.

molecular homology - species placed in the same taxonomic category show similarities in DNA and RNA.

MORPHOLOGICAL HOMOLOGY

Structures derived from a common ancestral structure are called:

HOMOLOGOUS STRUCTURES

Ontogenetic Homology The human embryo has gills, a post-anal tail,

webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water

Evidence for Evolution

Figure 22.15

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

MORPHOLOGICAL HOMOLOGY A structure that serves the same function in

two taxa, but is NOT derived from a common ancestral structure is said to be an

ANALOGOUS STRUCTURE

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

•Some similar mammals that have adapted to similar environments

–Have evolved independently from different ancestors

Molecular Homology

Evidence for Evolution

                                                                                      

                                                                                     

Evidence for Evolution

Evidence for Evolution

Vestigial Structures

Have marginal, if any use to the organisms in which they occur.

EXAMPLES: femurs in pythonid snakes and pelvis in

cetaceans (whales) appendix in humans coccyx in great apes

Evidence for Evolution

Vestigial organs

Why would whaleshave pelvis & leg bones

if they were alwayssea creatures?

These areremnants of

structures that were

functional inancestral species

Evolution evidence at the cellular level Domains: Archaea, Bacteria and Eukarya

Elements conserved through all: DNA, RNA and many metabolic pathways.

Eukaryotes – core features: Cytoskeleton Nucleus Membrane-bound organelles Linear chromosomes Endomembrane system

2010-2011

Mom, Dad…There’s something you need to know…

I’m a MAMMAL!

The Origin of Species

So…what is a species?

• Population whose members can interbreed & produce viable, fertile offspring

• Reproductively compatible

Western Meadowlark

Eastern Meadowlark

Distinct species:songs & behaviors are different enough to prevent interbreeding

Correlation of speciation to food sources

Adaptive radiation

Seedeaters

Flowereaters

Insecteaters

Rapid speciation:new species filling niches,

because they inheritedsuccessful adaptations.

How do new species originate?

When two populations become reproductively isolated from each other.

Speciation Modes: allopatric

geographic separation “other country”

sympatric still live in same area “same country”

Allopatric Speciation

Physical/geographical separation of two populations

Allele frequencies diverge After a length of time the

two population are so different that they are considered different species

If the barrier is removed interbreeding will still not occur due to pre/post zygotic isolation

Sympatric Speciation

Formation of a new species without geographic isolation. Causes:

Pre-zygotic barriers exist to mating Polyploidy (only organism with an even number of

chromosomes are fertile…speciation occurs quickly) Hybridization: two different forms of a species

mate in common ground (hybrid zone) and produce offspring with greater genetic diversity than the parents….eventually the hybrid diverges from both sets of parents

Gene flow has been reduced between flies that feed on different food varieties, even though they both

live in the same geographic area.

Sympatric Speciation

Pre-zygotic IsolationSperm never gets a chance to meet eggGeographic isolation: barriers prevent matingEcological isolation: different habitats in same regionTemporal isolation: different populations are fertile at different timesBehavior Isolation: they don’t recognize each other or the mating ritualsMechanical isolation: morphological differencesGamete Isolation: Sperm and egg do not recognize each other

PRE-Zygotic barriers

Obstacle to mating or to fertilization if mating occurs

behavioral isolation

geographic isolation ecological isolation temporal isolation

mechanical isolation gametic isolation

Post Zygotic Isolation

Hybrid Inviability – the embryo cannot develop inside the mothers womb

Hybrid Sterility – Adult individuals can be produced BUT they are not fertile

Hybrid Breakdown – each successive generation has less fertility than the parental generation

Patterns of Evolution• Divergent Evolution (adaptive radiation)• Convergent Evolution

– Two or more species that share a common environment but not a common ancestor evolve to be similar

Is it a shark or a dolphin??

Coevolution

Two or more species reciprocally affect each other’s evolution predator-prey

disease & host competitive species mutualism

pollinators & flowers

Evolutionary Time Scale

Microevolution – changing of allele frequencies in a population over time.

Macroevolution – patterns of change over geologic time. Determines phylogeny Gradualism – species

are always slowly evolving

Punctuated equilibrium – periods of massive evolution followed by periods with little to no evolution

RATE OF EVOLUTION Gradual evolution Punctuated

evolution

Mass Extinctions

• At least 5 mass extinctions have occurred throughout history.

• Possible causes: dramatic climate changes occurring after meteorite collisions and/or continents drift into new and different configurations.

Origin of the Earth

What must Earth have been like before living things took over?

The Primitive Earth

Atmosphere: All chemicals/compounds necessary are thought

to have originated on earth Inorganic precursors:

Water vapor Nitrogen Carbon dioxide Small amounts of hydrogen and carbon monoxide

These were the monomers for forming more complex molecules.

Experiments have shown that it is possible to form organic from inorganic.

Water vapor

Condensed liquid with complex, organicmolecules

CondenserMixture of gases("primitiveatmosphere")

Heated water("ocean")

Electrodes discharge

sparks(lightning

simulation)

Water

Origin of Organic Molecules Abiotic synthesis

1920 - Oparin first molecules

formed by strong energy sources

1953 - Miller & Urey test hypothesis formed organic compounds

amino acids adenine

CH4

NH3

H2

Key Events in Origin of Life

Origin of Cells (Protobionts) lipid bubbles separate inside from outside

metabolism & reproduction Origin of Genetics

RNA is likely first genetic material multiple functions: encodes information (self-

replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA) makes inheritance possible makes natural selection & evolution possible

Origin of Eukaryotes endosymbiosis

Timeline

Key events in evolutionary history of life on Earth 3.5–4.0 bya:

life originated 2.7 bya:

free O2 = photosynthetic bacteria

2 bya:first eukaryotes

First Eukaryotes

Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency

natural selection!

infolding of theplasma membrane

DNA

cell wall

plasmamembrane

Prokaryoticcell

Prokaryotic ancestor

of eukaryotic

cells

Eukaryoticcell

endoplasmicreticulum (ER)

nuclear envelope

nucleus

plasma membrane

~2 bya

1st Endosymbiosis

Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but

did not digest them mutually beneficial relationship

natural selection!

Ancestral eukaryotic cell

Eukaryotic cellwith mitochondrion

internal membrane system

aerobic bacterium mitochondrion

Endosymbiosis

mitochondrion

chloroplast

Eukaryotic cell withchloroplast & mitochondrion

Endosymbiosis

photosyntheticbacterium

2nd Endosymbiosis

Evolution of eukaryotes origin of chloroplasts engulfed photosynthetic bacteria,

but did not digest them mutually beneficial relationship

natural selection!

Eukaryoticcell with

mitochondrion

Theory of Endosymbiosis

Evidence structural

mitochondria & chloroplasts resemble bacterial structure

genetic mitochondria & chloroplasts

have their own circular DNA, like bacteria functional

mitochondria & chloroplasts move freely within the cell

mitochondria & chloroplasts reproduce independently from the cell

Lynn Margulis

Cambrian explosion

Diversification of Animals within 10–20 million years most of the major

phyla of animals appear in fossil record

543 mya