Why Evolution Is True
Chapter 1: What Is Evolution
Life on earth evolved gradually beginning with one primitive species that then branched out
over time, throwing off many new and diverse species. The mechanism for most but not all
of evolutionary change is natural selection.
6 parts to this:
1)Evolution – species undergoes genetic change over time. Differences based on change
2)Gradualism – takes many generations to make a substantial change
3)Common Ancestry – recent ancestor—similar trait, which creates “natural”
classification this is strong proof for evolution. If we were created = no “natural”
agreed upon classification
4)Speciation (splitting) ---starts with 2 populations of the same species that cannot
interbreed—exponential rise on the number of possible future species
5)Natural Selection –requires individuals of species to vary genetically in ability to
survive and reproduce causes species to look specifically “designed” for
environment – not perfect
a.Mutations MOSTLY change in pre-existing trait. Rarely creates new ones.
Descendants entirely dependent on ancestor’s pre-existing design.
b.Natural selection produces the “fitter” species--- not the fittest
6)Non-selective mechanisms of evolutionary change – simple random change in
proportion of genetics caused by the fact that families have different numbers of
offspring (not adaptive)
Theory of Evolution ---documented set of principles that explains how and why evolution
happens. Testable and can make verifiable predictions. Tests: fossil evidence of lineage;
species show genetic variation, which accounts for speciation. Also, retrodictions: fact and
data not necessarily predicted by evolution, but only make sense in the light of evolution.
Chapter 2: Written In the Rocks
Making the Record
Process: reach bottom of water; get covered by sediments (thus, rare fossils of dead plants
and land animals); soft parts aren`t preserved causing a bias (explains lack of worms and
jellyfish fossils); many are too buried in the earth’s surface to reach and many lost to
natural forces like weather. Thus, fossil records severely incomplete.
Relative age Layers dictate age, but not all layers laid down in one place. Must therefore
cross-reference. (Same type of rock with same type of fossil= same age)
Actual ageradioactivity. Different isotopes decay at different rates. (Radiometric dating)
The Facts: Evidence of Evolution in Fossils
1)Early life simpler than complex modern life
2)Visible connected changes in lineage; most modern fossils have similar traits to
3)Transitional species in fossils (Darwin did not have this) transition ancestor differs
in some respect to all descendants (not an intermediate mix of the two)i.e. birds
and reptiles—reptiles older so ancestor must have looked like a reptile- wings and
other bird traits evolve so much later on in the lineage fossils need not be one
single species but rather fossils that show linking traits (dating most important)
4)BacteriaSimple eukaryotes multicellular organisms (worms, jellyfish,
sponges)terrestrial plants and tetrapodsamphibiansreptilesmammals and
5) Mosses and algaefernsconifersdeciduous treesflowering plants
6)Pace of evolution need not be evendue to fluctuating environment (strength of
natural selection varies)
7)Not all species must evolve
8)On to Land: Fish to Amphibians—Shubin—Canadian Artic: Ellesmere Island:
TIKTAALIKdirect link to lobe-finned fish and amphibians: had gills, scales, fins,
flat head like salamander, eyes and nostrils on top of head and not on the sides,
robust fins, had neck (fishes have no necks), STURDY RIBS THAT ALLOWED IT
TO BREATH BOTH WAYS, STURDY LIMB BONES
9)Origin of Birds – “half a wing argument” probably started with gliding::
ARCHAEOPTERYXmore reptile than bird, jaw with teeth, long bony tail,
separated fingers, neck attached from skull from behind and not below. BIRDLIKE
TRAITS: large assymetrical feathers, opposable big toe. Could possible fly. China
then discovered more transitions. MICRORAPTORfeathered arms AND LEGS.
Theropod dinosaurs behaved like birds (nesting and sleeping like birds). Feathers
first evolved not for flying.
a.Evolution of flights:
i.Trees down scenario
ii.Ground up theorydue to runs and leaps of feathered dinosaurs
10)Whales Hippos: mammals that mostly live in waters, closest relative to whales.
Adapting to life at sea from land did not require new features, only modifications of
old ones. Extinction of dinosaurs probably opened a niche.
What Fossils Say
Other transitional forms:
a. INSECTS—combination of ant and wasp.
b.SNAKES are from reptiles and amphibians
a) proof that evolution is true –confirmed predictions based on evolutionary theory (gradual
change, speciation, common ancestry, transitional forms)
b) transitional forms show up in era we expect it to be in
c) evolutionary change remodels old into new (i.e. wings from legs, legs from fins)
Chapter 3: Remnants: Vestiges, Embryos, and Bad Design
There are features (vestigial) and genes that were once useful.
Vestiges – feature of species that was an adaptation in its ancestors but has lost
its usefulness or has been adapted for other uses. VESTIGIAL BECAUSE NO
LONGER PERFORMS FUNCTION FOR WHICH IT EVOLVED (not necessarily
that it has no function).
Example: ostrich wings not for flight but for balance, weaponry and mating. Flightless
birds descend from flying ancestors. Bones of wings same in both flying and flightless birds.
Life on earth evolved gradually beginning with one primitive species that then branched out over time, throwing off many new and diverse species. The mechanism for most but not all of evolutionary change is natural selection. 6 parts to this: evolution species undergoes genetic change over time. Differences based on change in dna: gradualism takes many generations to make a substantial change, common ancestry recent ancestor similar trait, which creates natural classification this is strong proof for evolution. Theory of evolution ---documented set of principles that explains how and why evolution happens. Tests: fossil evidence of lineage; species show genetic variation, which accounts for speciation. Also, retrodictions: fact and data not necessarily predicted by evolution, but only make sense in the light of evolution. Relative age layers dictate age, but not all layers laid down in one place. Must therefore cross-reference. (same type of rock with same type of fossil= same age)