24 originofspecies text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The origin of new species, or speciation

– Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity

• Evolutionary theory

– Must explain how new species originate in addition to how populations evolve

• Macroevolution

– Refers to evolutionary change above the species level


• Two basic patterns of evolutionary change can be distinguished

– Anagenesis

– Cladogenesis

Figure 24.2 (b) Cladogenesis(a) Anagenesis


The Biological Species Concept

• The biological species concept

– Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations


Similarity between different species. The eastern meadowlark (Sturnella magna, left) and the western meadowlark (Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild.

(a)

Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species (Homo sapiens), defined by our capacity to interbreed.

(b)

Figure 24.3 A, B


Reproductive Isolation

• Reproductive isolation

– Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids

– Is a combination of various reproductive barriers


• Prezygotic barriers

– Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate

• Postzygotic barriers

– Often prevent the hybrid zygote from developing into a viable, fertile adult


• Prezygotic and postzygotic barriers

Figure 24.4

Prezygotic barriers impede mating or hinder fertilization if mating does occur

Individualsof differentspecies

Matingattempt

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION

(b)

(a)(c)

(d)

(e)

(f)

(g)


Viablefertile

offspring

Reducehybrid

viability

Reducehybridfertility

Hybridbreakdown

Fertilization

Gameticisolation

GAMETIC ISOLATION REDUCED HYBRID VIABILITY

REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

(h) (i)

(j)

(k)

(l)

(m)


Limitations of the Biological Species Concept

• The biological species concept cannot be applied to

– Asexual organisms

– Fossils

– Organisms about which little is known regarding their reproduction


Other Definitions of Species

• The morphological species concept

– Characterizes a species in terms of its body shape, size, and other structural features

• The paleontological species concept

– Focuses on morphologically discrete species known only from the fossil record

• The ecological species concept

– Views a species in terms of its ecological niche

• The phylogenetic species concept

– Defines a species as a set of organisms with a unique genetic history


Species Vs. Biblical Kinds • “And God said, "Let the land produce living creatures according to their kinds:

livestock, creatures that move along the ground, and wild animals, each according to its kind." And it was so. God made the wild animals according to their kinds, the livestock according to their kinds, and all the creatures that move along the ground according to their kinds. And God saw that it was good. Genesis 1:24-25

The study of the Biblical Kinds is called Baraminology (Bara=create min=kind). The Biblical Kind is most

commonly identified as the Order of Family level of modern classification. God has set

reproductive constraints on

organisms in two separate Biblical

Kinds.Read article about Baranomes


(a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population.

(b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation.

Figure 24.5 A, B

• Speciation can take place with or without geographic separation

• Speciation can occur in two ways

– Allopatric speciation

– Sympatric speciation


Allopatric (“Other Country”) Speciation

• In allopatric speciation

– Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations


Figure 24.6

A. harrisi A. leucurus

• Once geographic separation has occurred

– One or both populations may undergo evolutionary change during the period of separation


Sympatric (“Same Country”) Speciation

• In sympatric speciation

– Speciation takes place in geographically overlapping populations

• Sympatric speciation

– Can also result from the appearance of new ecological niches


Allopatric and Sympatric Speciation: A Summary

• In allopatric speciation

– A new species forms while geographically isolated from its parent population

• In sympatric speciation

– The emergence of a reproductive barrier isolates a subset of a population without geographic separation from the parent species


Polyploidy

• Polyploidy

– Is the presence of extra sets of chromosomes in cells due to accidents during cell division

– Has caused the appearance of some plant species


• An autopolyploid

– Is an individual that has more than two chromosome sets, all derived from a single species

Figure 24.8

2n = 64n = 12

2n

4n

Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.

Gametes produced by flowers on this branch will be diploid.

Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.


• An allopolyploid

– Is a species with multiple sets of chromosomes derived from different species

Figure 24.9

Meiotic error;chromosomenumber notreduced from2n to n

Unreduced gametewith 4 chromosomes

Hybrid with7 chromosomes

Unreduced gametewith 7 chromosomes Viable fertile hybrid

(allopolyploid)

Normal gameten = 3

Normal gameten = 3

Species A 2n = 4

Species B 2n = 6

2n = 10


Adaptive Radiation

• Adaptive radiation

– Is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

Figure 24.11


Studying the Genetics of Speciation

• The explosion of genomics

– Is enabling researchers to identify specific genes involved in some cases of speciation


The Tempo of Speciation

• The fossil record

– Includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear

• Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe these periods of apparent stasis punctuated by sudden change


• The punctuated equilibrium model

– Contrasts with a model of gradual change throughout a species’ existence

Figure 24.13

Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations.

Time

(a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.

(b)


• Macroevolutionary changes can accumulate through many speciation events

• Macroevolutionary change

– Is the cumulative change during thousands of small speciation episodes


• Some complex structures, such as the eye

– Have had similar functions during all stages of their evolution

Figure 24.14 A–E

Pigmented cells(photoreceptors)

Epithelium

Nerve fibers

Pigmentedcells

Nerve fibers

Patch of pigmented cells.The limpet Patella has a simplepatch of photoreceptors.

Eyecup. The slit shellmollusc Pleurotomariahas an eyecup.

Fluid-filled cavity

Epithelium

Cellularfluid(lens)

Cornea

Optic nerve

Pigmentedlayer (retina)

Opticnerve

Pinhole camera-type eye.The Nautilus eye functionslike a pinhole camera(an early type of cameralacking a lens).

Cornea

Lens

RetinaOptic nerve

Complex camera-type eye. The squid Loligo has a complexeye whose features (cornea, lens, and retina), though similar to those of vertebrate eyes, evolved independently.

(a) (b)

(d)(c)

(e)

Eye with primitive lens. Themarine snail Murex has a primitive lens consisting of a mass of crystal-like cells. The cornea is a transparent region of epithelium (outer skin) that protects the eyeand helps focus light.

“To suppose To suppose that the eye, that the eye, (with so many (with so many parts all parts all working working together)…together)…could have could have been formed been formed by natural by natural selection, selection, seems, I seems, I freely freely confess, confess, absurd in the absurd in the highest highest degree.” degree.” Charles Charles DarwinDarwin


Evolution of the Genes That Control Development

• Genes that program development

– Control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult


• Heterochrony

– Is an evolutionary change in the rate or timing of developmental events

– Can have a significant impact on body shape

• Allometric growth

– Is the proportioning that helps give a body its specific form

Figure 24.15 ANewborn 2 5 15 Adult

(a) Differential growth rates in a human. The arms and legs lengthen more during growth than the head and trunk, as can be seen in this conceptualization of an individual at different ages all rescaled to the same height.

Age (years)


• In paedomorphosis

– The rate of reproductive development accelerates compared to somatic development

– The sexually mature species may retain body features that were juvenile structures in a supposed ancestral species

Figure 24.17


Changes in Spatial Pattern

• Substantial evolutionary change

– Can also result from alterations in genes that control the placement and organization of body parts

• Homeotic genes

– Determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a flower’s parts are arranged


Chicken leg budRegion ofHox geneexpression

Zebrafish fin bud

Figure 24.18

• The products of one class of homeotic genes called Hox genes

– Provide positional information in the development of fins in fish and limbs in tetrapods


• The supposed evolution of vertebrates from invertebrate animals

– Was associated with alterations in Hox genes

Figure 24.19

The vertebrate Hox complex contains duplicates of many ofthe same genes as the single invertebrate cluster, in virtuallythe same linear order on chromosomes, and they direct the sequential development of the same body regions. Thus, scientists infer that the four clusters of the vertebrate Hox complex are homologous to the single cluster in invertebrates.

5

First Hox duplication

Second Hox duplication

Vertebrates (with jaws)with four Hox clusters

Hypothetical earlyvertebrates (jawless)with two Hox clusters

Hypothetical vertebrateancestor (invertebrate)with a single Hox cluster

Most invertebrates have one cluster of homeotic genes (the Hox complex), shown here as coloredbands on a chromosome. Hox genes direct development of major body parts.

1

A mutation (duplication) of the single Hox complex occurred about 520 million years ago and may have provided genetic material associated with the origin of the first vertebrates.

2

In an early vertebrate, the duplicate set of genes took on entirely new roles, such as directing the development of a backbone.

3

A second duplication of the Hox complex, yielding the four clusters found in most present-day vertebrates, occurred later, about 425 million years ago. This duplication, probably the result of a polyploidy event, allowed the development of even greater structuralcomplexity, such as jaws and limbs.

4


• Biologists draw on the fossil record

– Which provides information about past organisms

Figure 25.1


Evolution Is Not Goal Oriented


– Often shows apparent trends in evolution that may arise because of adaptation to a changing environment

Figure 24.20

Recent(11,500 ya)

Pleistocene(1.8 mya)

Pliocene(5.3 mya)

Miocene(23 mya)

Oligocene(33.9 mya)

Eocene(55.8 mya)

EquusHippidion and other genera

Nannippus

Pliohippus

NeohipparionHipparion

Sinohippus MegahippusCallippus

Archaeohippus

Merychippus

Parahippus

HypohippusAnchitherium

Miohippus

Mesohippus

Epihippus

Orohippus

Paleotherium

Propalaeotherium

Pachynolophus

Grazers

Browsers

Key

Hyracotherium


• Biologists also use systematics

– As an analytical approach to understanding the diversity and relationships of organisms, both present-day and extinct

Morphological, biochemical, and molecular comparisons to infer evolutionary relationships


• Phylogenies are based on common ancestries inferred from fossil, morphological, and molecular evidence


– Is based on the sequence in which fossils have accumulated in such strata

• Fossils reveal

– Physical characteristics that may have been lost over time


*Morphology or physical structures play an important role in evolutionary relationships (i.e. Organisms that have the same types of structures must have been related in the past. This is considered Divergent Evolution)

Question: Are these skulls from organisms in the same species?


Morphologies are deceiving!

YES! They are YES! They are in the same in the same

species. They species. They are both are both domestic domestic

dogsdogs..

→

→


The Fossil Record

• Sedimentary rocks

– Are the richest source of fossils

– Are deposited into layers called strata

Figure 25.3

1 Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the ocean floor.

2 Over time, new strata are

deposited, containing fossils from each time period.

3 As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion reveals strata and fossils.

Younger stratum with more recent fossils

Older stratum with older fossils


• Though sedimentary fossils are the most common

– Paleontologists study a wide variety of fossils

Figure 25.4a–g

(a) Dinosaur bones being excavated from sandstone

(g) Tusks of a 23,000-year-old mammoth, frozen whole in Siberian ice

(e) Boy standing in a 150-million-year-old dinosaur track in Colorado

(d) Casts of ammonites, about 375 million years old

(f) Insects preserved whole in amber

(b) Petrified tree in Arizona, about 190 million years old

(c) Leaf fossil, about 40 million years old


Morphological and Molecular Homologies

• In addition to fossil organisms

– Phylogenetic history can be inferred from certain morphological and molecular similarities among living organisms

• In general, organisms that share very similar morphologies or similar DNA sequences

– Are likely to be more closely related than organisms with vastly different structures or sequences


Sorting Homology from Analogy

• A potential misconception in constructing a phylogeny

– Is similarity due to convergent evolution, called analogy, rather than shared ancestry


• Convergent evolution occurs when similar environmental pressures and natural selection

– Produce similar (analogous, also called homoplasies) adaptations in organisms from different evolutionary lineages

Figure 25.5


Evaluating Molecular Homologies

• Systematists use computer programs and mathematical tools

– When analyzing comparable DNA segments from different organisms

Figure 25.6

C C A T C A G A G T C C




G T A

Deletion

Insertion

C C A T C A A G T C C

C C A T G T A C A G A G T C C

C C A T C A A G T C C

C C A T G T A C A G A G T C C

1 Ancestral homologous DNA segments are identical as species 1 and species 2 begin to diverge from their common ancestor.

2 Deletion and insertion mutations shift what had been matching sequences in the two species.

3 Homologous regions (yellow) do not all align because of these mutations.

4 Homologous regions realign after a computer program adds gaps in sequence 1.

1

2

1

2

1

2

1

2

A C G G A T A G T C C A C T A G G C A C T A

T C A C C G A C A G G T C T T T G A C T A G

Figure 25.7


• Phylogenetic systematics connects classification with evolutionary history

• Taxonomy

– Is the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences


Binomial Nomenclature

• Binomial nomenclature

– Is the two-part format of the scientific name of an organism

– Was developed by Carolus Linnaeus

• The binomial name of an organism or scientific epithet

– Is latinized

– Is the genus and species


Hierarchical Classification

• Linnaeus also introduced a system

– For grouping species in increasingly broad categories

Figure 25.8

Pantherapardus

Panthera

Felidae

Carnivora

Mammalia

Chordata

Animalia

EukaryaDomain

Kingdom

Phylum

Class

Order

Family

Genus

Species


Linking Classification and Phylogeny

• Systematists depict evolutionary relationships

– In branching phylogenetic trees

Figure 25.9

Panthera pardus

(leopard)

Mephitis mephitis

(striped skunk)

Lutra lutra (European

otter)

Canis familiaris

(domestic dog)

Canislupus (wolf)

Panthera Mephitis Lutra Canis

Felidae Mustelidae Canidae

Carnivora

Ord

er

Fa

mil

yG

enu

sS

pe

cie

s

The Biblical The Biblical Kind is found Kind is found most often at most often at the Family the Family levellevel


• Each branch point

– Represents the divergence of two species

Leopard Domestic cat

Common ancestor


• “Deeper” branch points

– Represent progressively greater amounts of divergence

Leopard Domestic cat

Common ancestor

Wolf


• Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics

• A cladogram

– Is a depiction of patterns of shared characteristics among taxa

• A clade within a cladogram

– Is defined as a group of species that includes an ancestral species and all its descendants

• Cladistics

– Is the study of resemblances among clades


• A valid clade is monophyletic

– Signifying that it consists of the ancestor species and all its descendants

Figure 25.10a

(a) Monophyletic. In this tree, grouping 1, consisting of the seven species B–H, is a monophyletic group, or clade. A mono-phyletic group is made up of an ancestral species (species B in this case) and all of its descendant species. Only monophyletic groups qualify as legitimate taxa derived from cladistics.

Grouping 1

D

C

E G

F

B

A

J

I

KH


• A paraphyletic clade

– Is a grouping that consists of an ancestral species and some, but not all, of the descendants

Figure 25.10b

(b) Paraphyletic. Grouping 2 does not meet the cladistic criterion: It is paraphyletic, which means that it consists of an ancestor (A in this case) and some, but not all, of that ancestor’s descendants. (Grouping 2 includes the descendants I, J, and K, but excludes B–H, which also descended from A.)

D

C

E

B

G H

F

J

I

K

A

Grouping 2


• A polyphyletic grouping

– Includes numerous types of organisms that lack a common ancestor

Figure 25.10c

(c) Polyphyletic. Grouping 3 also fails the cladistic test. It is polyphyletic, which means that it lacks the common ancestor of (A) the species in the group. Further-more, a valid taxon that includes the extant species G, H, J, and K would necessarily also contain D and E, which are also descended from A.

D

C

B

E G

F

H

A

J

I

K

Grouping 3


Phylograms• In a phylogram

– The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage

Figure 25.12

Drosophila

Lancelet

Amph

ibia

n

Fish

BirdHum

an

RatM

ouse


Ultrametric Trees• In an ultrametric tree

– The branching pattern is the same as in a phylogram, but all the branches that can be traced from the common ancestor to the present are of equal length

Figure 25.13

Droso

phila

Lanc

elet

Am

phib

ian

Fish Bird Hum

an

Rat Mou

se

Cen

ozoi

cM

esoz

oic

Pal

eozo

icP

rote

rozo

ic

542

251

65.5

Mill

ions

of

year

s ag

o


Maximum Parsimony and Maximum Likelihood

• Systematists

– Can never be sure of finding the single best tree in a large data set

• Among phylogenetic hypotheses

– The most parsimonious tree is the one that requires the fewest evolutionary events to have occurred in the form of shared derived characters


APPLICATION In considering possible phylogenies for a group of species, systematists compare molecular data for the species. The most efficient way to study the various phylogenetic hypotheses is to begin by first considering the most parsimonious—that is, which hypothesis requires the fewest total evolutionary events (molecular changes) to have occurred.

TECHNIQUE Follow the numbered steps as we apply the principle of parsimony to a hypothetical phylogenetic problem involving four closely related bird species.

SpeciesI

SpeciesII

SpeciesIII

SpeciesIV

I II III IV I III II IV I IV II III

Sites in DNA sequence

Three possible phylogenetic hypothese

1 2 3 4 5 6 7

A G G G G G T

G G G A G G G

G A G G A A T

G G A G A A G

I

II

III

IV

I II III IVA G G G

GG

G

Bases at site 1 for each species

Base-changeevent

1 First, draw the possible phylogenies for the species (only 3 of the 15 possible trees relating these four species are shown here).

2 Tabulate the molecular data for the species (in this simplified example, the data represent a DNA sequence consisting of just seven nucleotide bases).

3 Now focus on site 1 in the DNA sequence. A single base-change event, marked by the crossbar in the branch leading to species I, is sufficient to account for the site 1 data.

Species

• The principle of maximum likelihood

– States that, given certain rules about how DNA changes over time, a tree can be found that reflects the most likely sequence of evolutionary events

Figure 25.15a






GG GG AA AA

GG AA

GG

GG AA GG AA

GG GG

GG

GG AA GG AA

GG GG

GG

T G T G

T T

T

T T G G

T G

T

T G G T

T T

T

10 events9 events8 events

4 Continuing the comparison of bases at sites 2, 3, and 4 reveals that each of these possible trees requires a total of four base-change events (marked again by crossbars). Thus, the first four sites in this DNA sequence do not help us identify the most parsimonious tree.

5 After analyzing sites 5 and 6, we find that the first tree requires fewer evolutionary events than the other two trees (two base changes versus four). Note that in these diagrams, we assume that the common ancestor had GG at sites 5 and 6. But even if we started with an AA ancestor, the first tree still would require only two changes, while four changes would be required to make the other hypotheses work. Keep in mind that parsimony only considers the total number of events, not the particular nature of the events (how likely the particular base changes are to occur).

6 At site 7, the three trees also differ in the number of evolutionary events required to explain the DNA data.

RESULTS To identify the most parsimonious tree, we total all the base-change events noted in steps 3–6 (don’t forget to include the changes for site 1, on the facing page). We conclude that the first tree is the most parsimonious of these three possible phylogenies. (But now we must complete our search by investigating the 12 other possible trees.)

Two basechanges

Figure 25.15b


• Sometimes there is compelling evidence

– That the best hypothesis is not the most parsimonious

Lizard

Four-chamberedheart

Bird Mammal

Lizard

Four-chamberedheart

Bird Mammal

Four-chamberedheart

(a) Mammal-bird clade

(b) Lizard-bird clade

Assuming the four-Assuming the four-chambered hear chambered hear

evolved onceevolved once

Assuming the four-Assuming the four-chambered hear chambered hear

evolved twiceevolved twice


• Much of an organism’s supposed evolutionary history is documented in its genome

• Comparing nucleic acids or other molecules to infer relatedness

– Is a valuable tool for tracing organisms’ evolutionary history


Molecular Clocks

• The molecular clock

– Is a yardstick for measuring the time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates


Neutral Theory

• Neutral theory states that

– Much evolutionary change in genes and proteins has no effect on fitness (neutral) and therefore is not influenced by Darwinian selection

– And that the rate of molecular change in these genes and proteins should be regular like a clock


Difficulties with Molecular Clocks

• The molecular clock

– Does not run as smoothly as neutral theory predicts


The Universal Tree of Life • The tree of life

– Is divided into three great clades called domains: Bacteria, Archaea, and Eukarya

• The early history of these domains is not yet clear

Figure 25.18

Bacteria Eukarya Archaea4 Symbiosis of

chloroplast ancestor with ancestor of green plants

3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes

2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells

1 Last common ancestor of all living things

4

3

2

1

1

2

3

4

0B

illio

n ye

ars

ago

Origin of life


• Conditions on early Earth are supposed to have made the origin of life possible

• Most biologists now think that it is at least a credible hypothesis

– That chemical and physical processes on early Earth produced very simple cells through a sequence of stages

• According to one hypothetical scenario

– There were four main stages in this process


Synthesis of Organic Compounds on Early Earth

• Earth formed about 4.6 billion years ago

– Along with the rest of the solar system

• Earth’s early atmosphere

– Contained water vapor and many chemicals released by volcanic eruptions


As material circulated through the apparatus, Miller and Urey periodically collected samples for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms. They also found many other amino acids and complex,oily hydrocarbons.

RESULTS

Figure 26.2

Miller and Urey set up a closed system in their laboratory to simulate conditions thought to have existed on early Earth. A warmed flask of water simulated the primeval sea. The strongly reducing “atmosphere” in the system consisted of H2, methane (CH4), ammonia (NH3), and water vapor. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds into the miniature sea.

EXPERIMENT Electrode

Condenser

Cooled watercontainingorganic molecules

H2O

Sample forchemical analysis

Coldwater

Water vaporCH4

H 2NH

3

CONCLUSION Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere.

• Laboratory experiments simulating an early Earth atmosphere

– Have produced organic molecules from inorganic precursors, but the existence of such an atmosphere on early Earth is unlikely


Problems with the Miller and Urey ExperimentProblems with the Miller and Urey Experiment

*Miller and Urey didn't add *Miller and Urey didn't add oxygen to the apparatus oxygen to the apparatus

(science shows that oxygen (science shows that oxygen has always been present on has always been present on

Earth) because it would Earth) because it would explode when the spark was explode when the spark was

produced.produced.*The experiment *The experiment

produced left and right produced left and right handed amino acids, handed amino acids,

however, living however, living organisms are only organisms are only

composed of left handed composed of left handed amino acids.amino acids.

Chemical Evolution Video Clip


• Instead of forming in the atmosphere

– The first organic compounds on Earth may have been synthesized near submerged volcanoes and deep-sea vents

Figure 26.3


Protobionts

• Protobionts

– Are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure


• Laboratory experiments demonstrate that protobionts

– Could have formed spontaneously from abiotically produced organic compounds

• For example, small membrane-bounded droplets called liposomes

– Can form when lipids or other organic molecules are added to water


• The first genetic material

– Was probably RNA, not DNA

• RNA molecules called ribozymes have been found to catalyze many different reactions, including

– Self-splicing

– Making complementary copies of short stretches of their own sequence or other short pieces of RNA

Ribozyme(RNA molecule)

Template

Nucleotides

Complementary RNA copy

3

5 5


• Early protobionts with self-replicating, catalytic RNA

– Would have been more effective at using resources and would have increased in number through natural selection


• Index fossils

– Are similar fossils found in the same strata in different locations

– Allow strata at one location to be correlated with strata at another location

Figure 26.6


• The absolute ages of fossils

– Can be determined by radiometric dating

Figure 26.7

1 2 3 4

Accumulating “daughter”

isotope

Ra

tio o

f p

are

nt

iso

top

e

to d

au

gh

ter

iso

top

e

Remaining “parent” isotope

1

1

11

Time (half-lives)

2

4

816


• The magnetism of rocks

– Can also provide dating information

• Magnetic reversals of the north and south magnetic poles

– Have occurred repeatedly in the past

– Leave their record on rocks throughout the world


• The geologic record is divided into

– Three eons: the Archaean, the Proterozoic, and the Phanerozoic

– Many eras and periods

• Many of these time periods

– Mark major changes in the composition of fossil species


• The geologic record according to evolutionist

Table 26.1

According to Creationist


Creationist Model


Mass Extinctions

• The fossil record chronicles a number of occasions

– When global environmental changes were so rapid and disruptive that a majority of species were swept away

Figure 26.8

Ca

mbr

ian

Pro

tero

zoic

eo

n

Ord

ovic

ian

Silu

rian

De

von

ian

Ca

rbo

nife

rou

s

Per

mia

n

Tri

assi

c

Jura

ssic

Cre

tace

ous

Pal

eoge

ne

Ne

oge

ne

Nu

mbe

r of fa

milie

s ( )

Number oftaxonomic

familiesExtinction rate

Cretaceous mass extinction

Permian mass extinction

Millions of years ago

Ext

inct

ion

rat

e (

)

Paleozoic Mesozoic

0

20

60

40

80

100600 500 400 300 200 100 0

2,500

1,500

1,000

500

0

2,000

Ceno-zoic


• Two major mass extinctions, the Permian and the Cretaceous

– Have received the most attention

• The Permian extinction

– Claimed about 96% of marine animal species and 8 out of 27 orders of insects

– Is thought to have been caused by enormous volcanic eruptions


• The Cretaceous extinction

– Doomed many marine and terrestrial organisms, most notably the dinosaurs

– Is thought to have been caused by the impact of a large meteor

Figure 26.9

NORTHAMERICA

Chicxulubcrater

YucatánPeninsula


• Much remains to be learned about the causes of mass extinctions

– But it is clear that they provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches


• The analogy of a clock

– Can be used to place major events in the Earth’s history in the context of the geological record

Figure 26.10

Land plants

Animals

Multicellulareukaryotes

Single-celledeukaryotes

Atmosphericoxygen

Prokaryotes

Origin of solarsystem andEarth

Humans

Ceno-zoicMeso-

zoic

Paleozoic

ArchaeanEon

Billions of years ago

ProterozoicEon

1

2 3

4


• As prokaryotes evolved, they exploited and changed young Earth

• The oldest known fossils are stromatolites

– Rocklike structures composed of many layers of bacteria and sediment

– Which date back 3.5 billion years ago


Lynn Margulis (top right), of the University of Massachussetts, and Kenneth Nealson, of the University of Southern California, are shown collecting bacterial mats in a Baja California lagoon. Themats are produced by colonies of bacteria that live in environments inhospitable to most other life. A section through a mat (inset) shows layers of sediment that adhere to the sticky bacteria asthe bacteria migrate upward.

Some bacterial mats form rocklike structures called stromatolites,such as these in Shark Bay, Western Australia. The Shark Baystromatolites began forming about 3,000 years ago. The insetshows a section through a fossilized stromatolite that is about3.5 billion years old.

(a)

(b)

Figure 26.11a, b


The First Prokaryotes

• Prokaryotes were Earth’s sole inhabitants

– From 3.5 to about 2 billion years ago


• Oxygenic photosynthesis

– Probably evolved about 3.5 billion years ago in cyanobacteria

Figure 26.12


• When oxygen began to accumulate in the atmosphere about 2.7 billion years ago

– It posed a challenge for life

– It provided an opportunity to gain abundant energy from light

– It provided organisms an opportunity to exploit new ecosystems


• Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes

• Among the most fundamental questions in biology

– Is how complex eukaryotic cells evolved from much simpler prokaryotic cells

• The oldest fossils of eukaryotic cells

– Date back 2.1 billion years


Endosymbiotic Origin of Mitochondria and Plastids

• The theory of endosymbiosis

– Proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells


• The prokaryotic ancestors of mitochondria and plastids

– Probably gained entry to the host cell as undigested prey or internal parasites

Figure 26.13

CytoplasmDNA

Plasmamembrane

Ancestralprokaryote

Infolding ofplasma membrane

Endoplasmicreticulum

Nuclear envelope

Nucleus

Engulfingof aerobic

heterotrophicprokaryote Cell with nucleus

and endomembranesystem

Mitochondrion

Ancestralheterotrophiceukaryote Plastid

Mitochondrion

Engulfing ofphotosyntheticprokaryote insome cells

Ancestral Photosyntheticeukaryote


• The evidence supporting an endosymbiotic origin of mitochondria and plastids includes

– Similarities in inner membrane structures and functions

– Both have their own circular DNA


• Some investigators have speculated that eukaryotic flagella and cilia

– Evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans

Figure 26.14

50 m


• Multicellularity evolved several times in eukaryotes

• After the first eukaryotes evolved

– A great range of unicellular forms evolved

– Multicellular forms evolved also


The Earliest Multicellular Eukaryotes

• Molecular clocks

– Date the common ancestor of multicellular eukaryotes to 1.5 billion years

• The oldest known fossils of eukaryotes

– Are of relatively small algae that lived about 1.2 billion years ago


• Larger organisms do not appear in the fossil record

– Until several hundred million years later

• Chinese paleontologists recently described 570-million-year-old fossils

– That are probably animal embryos

Figure 26.15a, b

150 m 200 m(a) Two-cell stage (b) Later stage


The Colonial Connection

• The first multicellular organisms were colonies

– Collections of autonomously replicating cells

Figure 26.1610 m


The “Cambrian Explosion”

• Most of the major phyla of animals

– Appear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian period

Cambrian Explosion?


• Phyla of two animal phyla, Cnidaria and Porifera

– Are somewhat older, dating from the late Proterozoic

Figure 26.17

EarlyPaleozoicera(Cambrianperiod)

Mill

ion

s o

f ye

ars

ag

o

500

542

LateProterozoiceon

Spo

ng

es

Cni

da

ria

ns

Ech

ino

de

rms

Cho

rda

tes

Bra

chio

pod

s

Ann

elid

s

Mo

llusc

s

Art

hro

pod

s


• Molecular evidence

– Suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

• Plants, fungi, and animals

– Colonized land about 500 million years ago

• Symbiotic relationships between plants and fungi

– Are common today and date from this time


Continental Drift• Earth’s continents are not fixed

– They drift across our planet’s surface on great plates of crust that float on the hot underlying mantle

Figure 26.18

NorthAmericanPlate

CaribbeanPlate

Juan de FucaPlate

Cocos Plate

PacificPlate

NazcaPlate

SouthAmericanPlate

AfricanPlate

Scotia Plate AntarcticPlate

ArabianPlate

Eurasian Plate

PhilippinePlate

IndianPlate

AustralianPlate


• Many important geological processes

– Occur at plate boundaries or at weak points in the plates themselves

Volcanoes andvolcanic islands

TrenchOceanic ridge

Oceanic crust

Seafloor spreading

Subduction zone

Figure 26.19


• The formation of the supercontinent Pangaea during the late Paleozoic era

– And its breakup during the Mesozoic era explain many biogeographic puzzles

Figure 26.20

India collided with Eurasia just 10 millionyears ago, forming theHimalayas, the tallestand youngest of Earth’smajor mountainranges. The continentscontinue to drift.

By the end of theMesozoic, Laurasiaand Gondwanaseparated into thepresent-day continents.

By the mid-Mesozoic,Pangaea split intonorthern (Laurasia)and southern(Gondwana)landmasses.

Ce

no

zoic

North AmericaEurasia

AfricaSouth

America

IndiaMadagascar

AntarcticaAustra

lia

Laurasia

Mes

ozo

ic Gondwana

At the end of thePaleozoic, all ofEarth’s landmasseswere joined in thesupercontinentPangaea.

Pangaea

Pal

eozo

ic

251

135

65.5

0

Mill

ions

of y

ear

s a

go


Previous Taxonomic Systems

• Early classification systems had two kingdoms

– Plants and animals

• Robert Whittaker proposed a system with five kingdoms

– Monera, Protista, Plantae, Fungi, and Animalia

Figure 26.21

Plantae Fungi Animalia

Protista

Monera

Eukaryo

tes

Prokaryotes


Reconstructing the Tree of Life: A Work in Progress

• A three domain system

– Has replaced the five kingdom system

– Includes the domains Archaea, Bacteria, and Eukarya

• Each domain

– Has been split by taxonomists into many kingdoms


• One current view of biological diversity

Figure 26.22

Pro

teob

acte

ria

Chl

amyd

ias

Spi

roch

etes

Cya

noba

cter

ia

Gra

m-p

ositi

ve b

acte

ria

Kor

arch

aeot

es

Eur

yarc

haeo

tes,

cre

narc

haeo

tes,

nan

oarc

haeo

tes

Dip

lom

onad

s, p

arab

asal

ids

Eug

leno

zoan

s

Alv

eola

tes

(din

ofla

gella

tes,

api

com

plex

ans,

cili

ates

)

Str

amen

opile

s (w

ater

mol

ds,

diat

oms,

gol

den

alga

e, b

row

n al

gae)

Cer

cozo

ans,

rad

iola

rians

Red

alg

ae

Chl

orop

hyte

s

Cha

roph

ycea

ns

Domain Archaea Domain Eukarya

Universal ancestor

Domain Bacteria

Chapter 27 Chapter 28


Bry

ophy

tes

(mos

ses,

live

rwor

ts,

horn

wor

ts)

Plants

Fungi

Animals

See

dles

s va

scul

ar p

lant

s (f

erns

)

Gym

nosp

erm

s

Ang

iosp

erm

s

Am

oebo

zoan

s (a

moe

bas,

slim

e m

olds

)

Chy

trid

s

Zyg

ote

fung

i

Arb

uscu

lar

myc

orrh

izal

fun

gi

Sac

fun

gi

Clu

b fu

ngi

Cho

anof

lage

llate

s

Spo

nges

Cni

daria

ns (

jelli

es,

cora

l)

Bila

tera

lly s

ymm

etric

al a

nim

als

(ann

elid

s,ar

thro

pods

, m

ollu

scs,

ech

inod

erm

s, v

erte

brat

es)

Chapter 29 Chapter 30 Chapter 28 Chapter 31 Chapter 32 Chapters 33, 34

Figure 26.21


Creation and Evolution: Major Beliefs

Topic Evolutionists believe….. Creationists believe….

Date of the Earth

The Earth is at least 4.6 billion years old. Evolutionists must have vast amounts of time in order for mutations to accumulate; otherwise the variations we see today would not have had enough time to accumulate.

Creationists are divided on the age of the Earth; however, a straight forward reading of the book of Genesis indicates a young Earth. Using the generations from Adam to Jesus we deduce approximately 4,000 years have passed and from Jesus to the present another 4,000 years. Approximate age of the Earth taken from scripture is between 6,000-7,000 years old.

Mutation Mutations have always existed since the first organism evolved. Mutations are believed to be the major element and contributing factor causing the enormous quantity of variations we see in organisms today.

Mutations originated at the fall of man (Genesis) and have accumulated from this point, however, mutations are not considered to be the major cause of variations within organisms, rather, variations were created by God and then selected to best fit an environment. Mutations are most often negative and therefore could not have produced the organisms and variations we see today.


Creation and Evolution: Major Beliefs Topic Evolutionists believe….. Creationists believe….

Natural Selection A process that selects from existing traits and variations and fits organisms to their environment. Evolutionists extrapolate this observable process and belief that natural selection had the ability to guide evolving organisms through innumerable changes and alterations and to produce the organisms we see in the present. Natural selection (being a process) must act on living organisms and couldn’t have in itself functioned before organisms evolved.

A process that selects from existing traits and variations and fits organisms to their environment. Creationists see natural selection as a process that was instituted by God after the fall in order to preserve variations and to fit organisms to their changing environment. Creationists view natural selection as a method of preservation rather than a method of selection. Creationists insist that natural selection explains the “survival of the fittest” but not the “arrival of the fittest”.

Tree of Life

All organisms are related to an ancestral organism. The tips of the branches are modern day species and the trunk represents the first organism that evolved. New evidence is continually altering major branches.

All organisms are not related. Instead of a tree, Creationists envision a lawn or orchard, where the tips represent modern day species and the base represents God’s Created Kinds (barmins, Genesis). Creationists would agree that the connections of the branches in the evolutionary tree of life are not real relationships rather are only hypothesized and undocumented relationships.



Species

Species are finely tuned organisms to their environments that have the capabilities of reproducing with those in their same species. Evolutionists believe that new species are constantly forming due to geographic isolation, etc.

Species are viewed as finely tuned to their environment through natural selection, however, not all Creationists agree with the modern view of fixed species. Creationists instead view all modern day species as descendants of a Biblical Kind, sometimes still being able to breed with others of the same Biblical Kind.

Information (DNA and RNA)

DNA had to accumulate over the vast eons (4.6 bya). The first organism had little information compared to modern day species with vast quantities of information. Evolutionists believe that the quantity of DNA has increased through mutational events.

DNA was created by God as the instructions for each Biblical Kind. Written into the DNA are variations. Creationists do not believe that new and novel DNA can be produced through mutations and have challenged evolutionists with the problem of DNA complexity.



Variation Variations are a result of mutational events.

Variations were written into the DNA code by God. New variations are possible through mutational events but they are almost always harmful or not beneficial. Creationists would argue that mutations are incapable of producing all of the variations we see in the Biblical Kinds.

Missing-links

They are fossilized organisms that exhibit a transitional form between (usually) a more ancient species and a more modern species. Archaeopteryx is an example of a supposed missing-link between reptiles and birds.

Would suggest that missing-links do not exist and are still missing. Creationists would view missing-links as an evolutionary forced relationship between two organisms that are in fact distinct species.



Microevolution Small incremental changes in the frequency of alleles within a species.

Creationists would agree that microevolution occurs but would credit the frequency of alleles within a species as being selected from variation that was created by God rather than solely produced by mutation. Creationists would also emphasize that microevolution fluctuates within a population.

Macroevolution

Evolutionists would extrapolate the small changes found in microevolution as accumulating to produce a much larger event, incorporating all of life into a large continuum.

Creationists would suggest that microevolution is not possible nor has been observed and that any extrapolation by evolutionists to prove macroevolution is hypothetical rather than actual. Creationists believe that macroevolution is not possible because God set natural limitations between the Biblical Kinds.



Darwin The first scientist that united various preconceived ideas to make a whole realm of thought, which later came to be known as evolution. Some scientist credit Darwin with allowing them to become “intellectually fulfilled atheists”, but not all evolutionists agrees with this view.

Creationists do not generally vilify Darwin but disagree with his final conclusion; that all life evolved in a continuum without the need of an intelligent designer. Creationists view Darwin as a scientist who was a product of his time, making misguided extrapolations based on somewhat good reasoning but spoiling that good reasoning with unsubstantiated hypothetical reasoning. Creationists often claim that Darwin made conclusions based on faith rather than true science.

Human Evolution Evolutionists include humans in the overarching evolutionary scenario, claiming that humans descended from ape-like organisms.

Creationists reject human evolution entirely, based on the belief that humans were created in the image of God (Genesis). Creationists believe that humans were created (Adam and Eve) fully formed with the ability to communicate with each other and with God from the beginning and reject any step-by-step process of human evolution.

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