Processes of Evolution

Processes of Evolution

15

How do biologists use evolutionary theory to develop better flu vaccines?

Evolution Is Both Factual and the Basis of Broader Theory

In science, a theory is a well-substantiated,

unifying explanation for a set of verified,

proven hypotheses

Evolutionary theory is the understanding

and application of the processes of

evolutionary change to biological problems.

Applications:

• Study and treatment of diseases

• Development of crops and industrial

processes

• Understanding the diversification of life


Even before Darwin, biologists had suggested

that species had changed over time, but no

one had proposed a convincing mechanism

for evolution.


Charles Darwin was

interested in geology

and natural history.


In 1831, Darwin

began a 5-year

voyage around the

world on a Navy

survey vessel, the

HMS Beagle.

The Voyage of the Beagle


From the observations and insights made on

the voyage and new ideas from geologists

on the age of the Earth, Darwin developed

an explanatory theory for evolutionary

change:

• Species change over time

• Divergent species share a common

ancestor (descent with modification)

• The mechanism that produces change is

natural selection

Concept 15.2 Mutation, Selection, Gene Flow,

Genetic Drift, and Nonrandom Mating Result in Evolution

Many of Darwin’s observations of variation

and selection came from domesticated

plants and animals.

Darwin bred pigeons and recognized

similarities between selection by breeders

and selection in nature.

In both cases, selection simply increases the

frequency of the favored trait from one

generation to the next.


By 1900, the fact of evolution was established,

but the genetic basis of evolution was not yet

understood.

Then the work of Gregor Mendel was

rediscovered, and during the 20th century,

work continued on the genetic basis of

evolution.

A “modern synthesis” of genetics and

evolution took place 1936–1947.


The structure of DNA was established by

1953 by Watson and Crick.

In the 1970s, technology developed for

sequencing long stretches of DNA and

amino acid sequences in proteins.

Evolutionary biologists now study gene

structure and evolutionary change using

molecular techniques.

Evolution of Staph

Natural selection does not create new

traits, but edits or selects for traits

already present in the population

The local environment determines which

traits will be selected for or selected

against in any specific population

Evidence supporting evolution

Fossil record

• transition species

Anatomical and Molecular Homology

• anatomy

• embryology & development

• molecular (DNA & protein)

• Vestigial

Biogeography

Artificial selection

• human-caused evolution

Fossil record

Layers of sedimentary rock contain fossils

• new layers cover older ones, creating a record over time

• fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

Tiktaalik

• “missing link” from sea to land animals

What are Homologous structures?

Similar structure

Similar development

Different functions

Evidence of close evolutionary

relationship

• recent common ancestor

Anatomical record

Homologous structures

• similarities in characteristics resulting from

common ancestry

spines

tendrils

succulent leaves

colored leaves

Homologous structures in plants!

leaves

needles

Analogous structures

Separate evolution of structures

similar functions

similar external form

different internal structure &

development

different origin

no evolutionary relationship

Solving a similar problem with a similar solution

Don’t be fooledby their looks!

Analogous Structures are evidence for Convergent evolution

Flight evolved in 3 separate animal groups

• evolved similar “solution” to similar “problems”

• analogous structures

Does this mean they have a recent common ancestor?

Convergent evolution

Fish: aquatic vertebrates

Dolphins: aquatic mammals

similar adaptations to

life in the sea

not closely related

Those fins & tails & sleek bodies areanalogous structures!

Parallel Evolution

• filling similar ecological roles in similar environments, so similar adaptations were selected

• but are not closely related

marsupial

mammalsplacental

mammals

Comparative embryology

Similar embryological development in closely related

species

• all vertebrate embryos have similar structures at

different stages of development

gill pouch in fish, frog, snake, birds, human,

etc.

Which one is the salamander, human, fish, cow, pig, rabbit,

turtle, and chicken?

Molecular record

0 25 50 75 100 1250

25

50

75

100

Millions of years ago

Horse/donkey

Sheep/goat

Goat/cow

Llama/cow

Pig/cow

Rabbit/rodent

Horse/cow

Human/rodent

Dog/cow

Human/cow

Human/kangaroo

Nu

cle

oti

de s

ub

sti

tuti

on

s

Comparing DNA & protein structure

• universal genetic code!

DNA & RNA

• compare common genes

cytochrome C (respiration)

hemoglobin (gas exchange)

Closely related species have

sequences that are more similar

than distantly related species

DNA & proteins are a molecular

record of evolutionary relationships

Why comparethese genes?

Comparative hemoglobin structure

Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans

100 20 30 40 50 60 70 80 90 100 110 120

LampreyFrogBirdDogMacaqueHuman

328 45 67 125

Why does comparingamino acid sequencemeasure evolutionaryrelationships?

Vestigial organs

Modern animals may have structures that serve little or no function

• remnants of structures that were functional in ancestral species

• deleterious mutations accumulate in genes for non-critical structures without reducing fitness

snakes & whales — remains of pelvis & leg bones of

walking ancestors

eyes on blind cave fish

human tail bone

This is notLaMarck’s loss from “disuse”!

Vestigial organs

Hind leg bones on whale fossils

Why would whaleshave pelvis & leg bonesif they were alwayssea creatures?

Biogeography

Biogeography- the geographic distribution of

species

Earth’s continents were formerly united in a single

large continent called Pangaea, but have since

separated by continental drift

An understanding of continent movement and

modern distribution of species allows us to predict

when and where different groups evolved

Artificial selection

Artificial breeding can use variations in

populations to create vastly different “breeds”

& “varieties”

“descendants” of the wolf

“descendants” of wild mustard

Speciation and the

Origin of Life

How and why do new species originate?

Species are created by a series of evolutionary processes

• populations become isolated

geographically isolated

reproductively isolated

• isolated populations evolve independently

Isolation

• allopatric

geographic separation

• sympatric

still live in same area

Obstacle to mating or to fertilization if mating occurs

PRE-reproduction barriers

behavioral isolation

geographic isolation ecological isolation temporal isolation

mechanical isolation gametic isolation

Geographic isolation

Species occur in different areas

• physical barrier

• allopatric speciation

“other country”

Harris’s antelope

squirrel inhabits

the canyon’s

south rim (L). Just

a few miles away

on the north rim

(R) lives the

closely related

white-tailed

antelope squirrel

Ammospermophilus spp

Ecological isolation

Species occur in same region, but occupy different

habitats so rarely encounter each other

• reproductively isolated

2 species of garter snake, Thamnophis,

occur in same area, but one lives in water &

other is terrestrial

lions & tigers could

hybridize, but they

live in different

habitats:

lions in grasslands

tigers in rainforest

Temporal isolation

Species that breed during different times of day, different seasons, or different years cannot mix gametes

• reproductive isolation

• sympatric speciation “same country”

Eastern spotted skunk

(L) & western spotted

skunk (R) overlap in

range but eastern mates

in late winter & western

mates in late summer

Behavioral isolation

Unique behavioral patterns & rituals isolate species

• identifies members of species

• attract mates of same species • courtship rituals, mating calls

reproductive isolation

Blue footed boobies mate

only after a courtship display

unique to their species

sympatric speciation?

Mechanical isolation

Morphological differences can prevent successful mating

• reproductive isolation

Even in closely related

species of plants, the

flowers often have distinct

appearances that attract

different pollinators.

These 2 species of monkey

flower differ greatly in

shape & color, therefore

cross-pollination does not

happen.

Plants


Mechanical isolation

For many insects, male &

female sex organs of

closely related species do

not fit together, preventing

sperm transfer• lack of “fit” between sexual organs:

hard to imagine for us… but a big issue for insects with

different shaped genitals!

Damsel fly penises

Animals

I can’t even imagine!

Gametic isolation

Sperm of one species may not be able to fertilize eggs

of another species

• mechanisms

biochemical barrier so sperm cannot penetrate egg

o receptor recognition: lock & key between egg & sperm

chemical incompatibility

o sperm cannot survive in female reproductive tract

Sea urchins release sperm

& eggs into surrounding

waters where they fuse &

form zygotes. Gametes of

different species— red &

purple —are unable to fuse.


POST-reproduction barriers

Prevent hybrid offspring from developing into a

viable, fertile adult

• reduced hybrid viability

• reduced hybrid fertility

• hybrid breakdown

Liger:Mom was

tiger

Tigon: Mom was lion

http://www.lairweb.org.nz/tiger/tigons.html

http://www.lairweb.org.nz/tiger/tigons.html

Reduced hybrid viability

Genes of different parent species may interact &

impair the hybrid’s development

Species of salamander

genus, Ensatina, may

interbreed, but most

hybrids do not complete

development & those

that do are frail.


Mules are vigorous,

but sterile

Reduced hybrid fertility

Even if hybrids are vigorous they may be sterile

• chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes

Donkeys have 62

chromosomes

(31 pairs)

Horses have 64

chromosomes

(32 pairs) Mules have 63 chromosomes!

Hybrid breakdown

Hybrids may be fertile & viable in first generation,

but when they mate offspring are feeble or sterile

In strains of cultivated rice,

hybrids are vigorous but

plants in next generation are

small & sterile.

On path to separate species.


Gradualism

Gradual divergence over

long spans of time

• assume that big

changes occur as the

accumulation of

many small ones

Punctuated Equilibrium

Rate of speciation is not

constant

• rapid bursts of change

• long periods of little or

no change

• species undergo rapid

change when they 1st

bud from parent

population

Time

Bacteria Archae-bacteria

AnimaliaFungiProtista Plantae

4500

4000

3500

3000

2500

2000

500

1500

0

1000

Formation of earth

Molten-hot surface ofearth becomes cooler

Oldest definite fossilsof prokaryotes

Appearance of oxygenin atmosphere

Oldest definite fossilsof eukaryotes

First multicellularorganisms

Appearance of animalsand land plants

Colonization of landby animalsPaleozoic

Mesozoic

Cenozoic

Millio

ns

of

ye

ars

ag

o

AR

CH

EA

N PR

EC

AM

BR

IAN

PR

OT

ER

OZ

OIC

The evolutionary tree of life can be documented with evidence.

The Origin of Life on Earth is another story…

What is Life?

First we have to define LIFE…

• organized as cells

• respond to stimuli

• regulate internal processes homeostasis

• use energy to grow metabolism

• develop change & mature

within lifetime

• reproduce heredity

o DNA / RNA

adaptation & evolution

Conditions on early Earth

Reducing atmosphere

• water vapor (H2O), CO2, N2, NOx, H2, NH3,

CH4, H2S

• lots of available H & its electron

• no free oxygen

Energy source

• lightning, UV radiation,

volcanic

low O2 =

organic molecules

do not breakdown

as quickly

What’s missingfrom thatatmosphere?

Water vapor

Condensed liquid with complex, organicmolecules

Condenser

Mixture of gases("primitiveatmosphere")

Heated water("ocean")

Electrodes discharge sparks(lightning simulation)

Water

Origin of Organic Molecules: Organic Soup Model

Abiotic synthesis

• 1920Oparin & Haldanepropose reducing atmosphere hypothesis

• 1953Miller & Ureytest hypothesis

formed organic compounds

o amino acids

o adenine

CH4

NH3

H2

Origin of Genetics

RNA is likely first genetic material

• multi-functional

• codes information

self-replicating molecule

makes inheritance possible

natural selection & evolution

• enzyme functions

ribozymes

replication

• regulatory molecule

• transport molecule

tRNA & mRNA

Dawn of natural selection

Prokaryotes

Prokaryotes dominated life

on Earth from 3.5–2.0 bya

3.5 billion year old

fossil of bacteria modern bacteria

chains of one-celledcyanobacteria

Stromatolites

Fossilized mats of prokaryotes resemble modern microbial colonies

Lynn Margulis

Oxygen atmosphere

Oxygen begins to accumulate 2.7 bya

• reducing oxidizing atmosphere

evidence in banded iron in rocks = rusting

makes aerobic respiration possible

• photosynthetic bacteria (blue-green algae)

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

Endosymbiosis

Ancestral eukaryotic cell

Eukaryotic cellwith mitochondrion

internal membrane

systemaerobic bacterium mitochondrion

Endosymbiosis

Evolution of eukaryotes• origin of mitochondria

• engulfed aerobic bacteria, but did not digest them

• mutually beneficial relationship

natural selection!

mitochondrion

chloroplast

Eukaryotic cell with

chloroplast & mitochondrion

Endosymbiosis

photosynthetic

bacterium

Endosymbiosis

Evolution of eukaryotes• origin of chloroplasts

• engulfed photosynthetic bacteria, but did not digest them

• mutually beneficial relationship natural selection!

Eukaryoticcell with mitochondrion

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

Theory of Endosymbiosis

Lynn Margulis

Processes of Evolution

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