What does natural selection mean?Offspring w/in a varied population, whose characteristics

best adapt them to the environment are most likely to survive and reproduce

• more fit individuals produce more offspring than less fit individuals

How and why?•Over production of offspring•Limited natural resources•Heritable variations•Differential or unequal reproductive success

Ch. 23 review

Ch. 24 -- What is a species? …and, Speciation?

• Species - Population (or group of populations) whose members can interbreed and produce fertile offspring

• Identified species are named & classified = Taxonomy– binomial scientific name:

• Homo sapiens Genus - species

• Macroevolution: origin of new species; increases diversity– How does this happen? What is

required?

• Gene flow of alleles between populations of a particular species

• What would happen if gene flow was blocked?

• Variation continues, but within isolated populations– leads to divergence

20 light10 dark

20 light20 dark

Barriers that lead to speciation• Reproductive barriers can prevent interbreeding of closely

related populations– Prezygotic = prevents fertilization

– Postzygotic = prevents development Fig. 24.3

Barriers that lead to speciation• Reproductive barriers can prevent interbreeding of closely

related populations– Prezygotic = prevents fertilization– Postzygotic = prevents development

• Temporal isolation: difference of time, (day/night, seasons, etc)e.g. western skunks in fall;

eastern skunks in late wintere.g. purple sea urchins (late fall

to early spring) vs. white sea urchins (late spring to early fall)

Stronglyocentrotus purpuratus Lytichinus pictus

Spilogale gracilis

Spilogale putorius

• Habitat isolation– Living in different places

(habitats) w/in general geographic region

e.g. herbivorous insects feeding on two different host plants

• Behavioral isolation– Different unique mating

rituals to attract mates of same species

e.g. many birds have courtship rituals before mating can commence

• Mechanical isolation– Incompatible female and

male sex organs• aka “square peg into a round

hole” probleme.g. flower parts of one species

differs from another; pollinator only passes to one

• Gametic isolation– Fertilization success depends

on molecular recognition of cell membranes (gametes)

e.g. open (broadcast) spawning of aquatic species

e.g. windblown pollen of plants

Postzygotic reproductive barriers• in the absence of pre-zygotic

isolation barriers…• Hybrid zygotes = fertilization of

two spp.• Natural blocks to continued

hybridization?– Zygotic mortality– Hybrid inviability: death in early

devpmnt– Hybrid sterility: mature

individuals, but sterile• female horse x male donkey =

sterile mule• Camel x llama = Cama• Lion x tiger = Liger• Horse x zebra = zebroid or zorse

Geographic Barriers

• Allopatric speciation (allos = other, patra = fatherland)

– Mountain range emerged– Large lake subsides and splinters into

many smaller bodies of water– Baja peninsula and Isthmus of

Panama separates marine life on each side

– Grand canyon separated by Col. River

Ch 25: History of life …as we understand it

• Conditions on early Earth made the origin of life possible– Chemical and physical processes on early Earth may have

produced very simple cells through a sequence of stages:• Abiotic synthesis of small organic molecules• Joining of these small molecules into macromolecules• Packaging of molecules into protocells

– Membraneous packets of chemicals

Synthesis of Organic Compounds…

• Earth formed about 4.6 billion years ago, along with the rest of the solar system

• Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago

• Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

Are the key building blocks of life hard to come by?

• Amino acids have been found in meteorites• RNA monomers have been produced “spontaneously” from

simple molecules• In water, lipids and other organic molecules can

“spontaneously” form vesicles with a lipid bilayer• Adding clay can increase the rate of vesicle formation• Vesicles exhibit simple reproduction and metabolism and

maintain an internal chemical environment– Resultprotocells

The fossil record documents this history of life in geologic time

• Stromatolites – mineralized organics or prokaryotic cells layered (strata) from aquatic environment

Dimetrodon

Stromatolites

Fossilizedstromatolite

Coccosteuscuspidatus

4.5 cm

0.5 m

2.5 cm

Present

Rhomaleosaurus victorTiktaalik

Hallucigenia

Dickinsonia costata

Tappania

1 cm

1 m

100 mya

175200

300

375400

5005255656001,5003,500

270

Figure 25.4

How Rocks and Fossils Are Dated

• Sedimentary strata reveal the relative ages of fossils

• The absolute ages of fossils can be determined by radiometric dating– A “parent” isotope decays to a “daughter”

isotope at a constant rate– Each isotope has a known half-life, the time

required for half the parent isotope to decay

Refer to: Keeping Time handout (see under Ch.25 ppt)

Limitations of Carbon dating

• Radiocarbon dating can be used to date fossils up to 75,000 years old

• For older fossils, other isotopes can be used to date sedimentary rock layers above and below the fossil

Geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons

The Phanerozoic encompasses multicellular eukaryotic life and is divided into three eras: Paleozoic, Mesozoic, and Cenozoic

The Cambrian explosion refers to the sudden appearance of a multitude of modern body designs (530 million years ago)first evidence of predator-prey interactions

Appearance of selected animal groups in the fossil recordAnd, the colonization of land…

Fungi, plants, and animals began to colonize land about 500 million years ago

Vascular tissue in plants transports materials internally and appeared by about 420 million years ago

Plants and fungi today form mutually beneficial associations and likely colonized land together

Arthropods and tetrapods are the most widespread and diverse land animals

Tetrapods evolved from lobe-finned fishes around 365 million years ago

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran CambrianPROTEROZOIC PALEOZOIC

Time (millions of years ago)635 605 575 545 515 485 0

Figure 25.10

The fossil record shows that most species that have ever lived are now extinct…

Further reading: the last parts of Ch 25 that includes Mass extinctions

Ch 26: Phylogeny and Systematics

• What is meant by phylogeny?

• Evolutionary history of a species…– Based on common ancestry– Supported by shared

characteristics and genetics– Documented by fossils and

genetics

Eon > Era > Periods > Epochs

Systematics?

= study of the organismal diversity of life

How do we make sense of all this diversity?

Organize it… using fossil, molecular, and genetic data to infer evolutionary relationships

Taxonomy & classification

* visually clear diagram, yet oversimplified

Phylogenies show evolutionary relationships --Diversity of Life

Taxonomy is the ordered division and naming of organisms

Domain Kingdom Phylum Class Order

Family Genus

Species

Each group is nested within the level above

Broad or less specific

More specific

Closely related species belong to the same genus, similar genera are included in a family, etc…Species that share the same structures, behaviors, etc, can interbreed and produce fertile offspring.

• Grouped by shared characters (Evolutionary relationships)– Embryology– Reproduction strategies– Symmetry (body plan)– Morphology– Feeding mode– Interspecific interactions

(e.g. symbiosis)– Etc…

Systematists depict evolutionary relationships in branching phylogenetic trees

• A phylogenetic tree represents a hypothesis about evolutionary relationships• Each branch point represents the divergence of two species• Sister taxa are groups that share an immediate common ancestor

Branch point:where lineages diverge

ANCESTRALLINEAGE

This branch pointrepresents thecommon ancestor oftaxa A–G.

This branch point forms apolytomy: an unresolvedpattern of divergence.

Sistertaxa

Basaltaxon

Taxon A

Taxon B

Taxon C

Taxon D

Taxon E

Taxon F

Taxon G

• Cladistics groups organisms by common descent• A clade is a group of species that includes an

ancestral species and all its descendants– Terminal taxon share the most recent common

ancestor at the branch node

Which node occurs earliest in time?

Of the cladograms shown below, which one shows a different evolutionary history from the others?

B and C are sharing the most recent common ancestor, whereas in the others, C shares its most recent common ancestor with D

Figure 26.11

TAXA Lancelet(outgroup)

Lamprey

Bass

Frog

Turtle

Leopard

Vertebralcolumn

(backbone)

Four walkinglegs

Hinged jaws

Amnion

Hair

Vertebralcolumn

Hinged jaws

Four walking legs

Amnion

Hair

(a) Character table (b) Phylogenetic tree

CHAR

ACT

ERS

Lanc

elet

(out

grou

p)

Lam

prey

Bass

Frog

Turt

le

Leop

ard

0

0

0

0

0

1

0

0

0

0

1

1

0

0

0

1

1

1

0

0

1

1

1

1

0

1

1

1

1

1

Try to create a cladogram from the given character table?

Lancelet Lamprey Bass Frog Turtle Leopard

Backbone

Hinged Jaws

Tetropod

Amnion

Hair

Phylum Chordata

How has taxonomy evolved?

• It depends on the types and amount of data

• Historical 5 Kingdom system… until about 1970

3 domains, many kingdoms