Content Session 1

Species and Evolution

Charles DarwinTheory of Natural Selection

Natural Selection– This theory of Darwin’s basically states that in

Nature there are different levels of success in reproduction based on the ability to survive in that environment. (The differing rates of success act as a “filtering out” effect on “weak” traits.)• “weak” vs. “strong”(Strong traits would be

beneficial in surviving and reproducing; whereas, weak traits would not be beneficial to reproducing or surviving the harsh characteristics of that environment.)

You are what you inherit in terms of DNA.The egg surrounded by sperm.

– Environmental stresses affect the success rate of individuals in a population in different ways. (For example, some people work well under pressure and others fail when there is pressure.)

– POPULATIONS EVOLVE NOT INDIVIDUALS.• Somatic cells (cells that make up the body) vs.

germ cells(the cells of sperm and eggs).• Germ cells are passed on to “create” the next

generation of organisms… so the change must occur in these cells if it is going to affect the future of the species.

• Watch Video Homer Simpson Evolution Teaching Science at blinkx.mp4

Life is a struggle to exist

• Life is a struggle for existence and “nature” ultimately decides who gets to survive and reproduce and who doesn’t by excessive environmental “forces” killing them off.

Artificial Selection– This is where man selects what traits are desirable

(beneficial) in a species.• Plants (Which ones make the best or most fruit or

are the most appealing in the yard or garden.)• Domestic animals (Which ones are the most valuable

in terms of food or other characteristics.)– Man can “erase” what Nature took thousands of years

to “create” (gradualism) by controlling which organisms get to reproduce and which don’t.

– This is NOT always the best outcome for that environment.

Artificial Selection in food

Artificial Selection in Animals

Supporting evidence for Common Ancestry among organisms includes:

–Homologous (means “same’) Structures (Examples include skeletal structure, limb structure, or cephalization.)• Vestigial organs are organs that appear

to have been needed in the past, but are slowly disappearing.

– Embryological Homologies are seen as common stages of development that embryos go through.

Homologous Structures

Embryological Homologies

–Molecular Homologies refers to DNA nucleotide sequences being exact in order and function. • Analogous Structures have the SAME

function. Such as a bat wing (which has bones and muscles) and an insect wing (which doesn’t have muscles and bones in it); but they both produce flight.–DO NOT CONFUSE WITH HOMOLOGOUS

STRUCTURES.–Homologous indicates common ancestry

and analogous does not.

Molecular Homologies

Analogous Structures

Biogeography– This is the geographic distribution of species. (Where

a species is found, basically.)– Endemic –refers to a species that is only found in

ONE place on earth. (Usually refers to organisms on islands.)

– Convergent Evolution • This term is used for organisms that ONLY visually appear

to be to be closely related simply because they evolved in similar environments under similar environmental pressures. The reality is they maybe distantly related to each other.

Biogeography and Convergent Evolution

• Microevolution (Evolution/change on a small scale.)

–This term usually refers to changes in allele frequency within a population of a species.–Microevolution can eventually lead to

macroevolution. (The evolution of a new species or higher taxon in the classification system from a PRE-EXISTING species.)

Speciation• Speciation (Means “the evolution of a new

species”.)– Two types (pathways) of speciation that

have occurred in nature in the past.• Anagenesis (Basically, there is no break

within the pathway of evolution.)–The accumulation of new changes over

time within a species leads to a new species.

LE 24-2

Anagenesis Cladogenesis

• Cladogenesis (There exists a break into different groups.)–Branching off of an existing species

occurs because of moving into new environments, reproductive isolation, or other environmental stresses.

–Both pathways are supported by fossil evidence, bacterial research and/or research at Galapagos Islands.

SpeciesMale and Female Blue Footed Boobies

• The various ways of DEFINING a “species”:–Biological Species Concept (This is the main

way used in science today.)• This method is based on genetic

similarity among individuals.• The genetics are so similar that the ability

to produce viable, fertile offspring exists.• Reproductive Isolation Mechanisms to

preserve a species:(Ways to keep them pure.)

Pre-zygotic Barriers: (These prevent before a zygote, fertilized egg, can form.)

i. Habitat isolation - The organisms live in two different environments.

ii. Behavioral Isolation – The “Mating Dances” are not recognized by the other.

iii. Temporal (time) Isolation – They have different times of year they can reproduce.

iv. Mechanical Isolation – The reproductive parts just don’t fit together correctly.

v. Gametic Isolation – The sperm and egg do not recognize the other.

LE 24-4a

Prezygotic barriers impede mating or hinder fertilization if mating does occur

Postzygotic barriers prevent a hybrid zygote fromdeveloping into a viable, fertile adult

REDUCED HYBRIDVIABILITY

REDUCED HYBRIDFERTILITY

HYBRID BREAKDOWN

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION GAMETIC ISOLATION

Reducedhybrid

viability

FertilizationViable,fertile

offspring

Reducedhybridfertility

Hybridbreakdown

Matingattempt

Gameticisolation

Fertilization

Mechanicalisolation

Behavioralisolation

Temporalisolation

Habitatisolation

Individualsof

differentspecies

• Post –zygotic Barriers (These prevent after a zygote has formed from the fertilization.)

• i.Reduced Hybrid Viability – The hybrid organism can’t survive for long during development.

• ii. Reduced Hybrid Fertility – The hybrid organism survives, it just can’t reproduce.

• iii. Hybrid Breakdown – The hybrid organism lives, it just loses the ability to reproduce over successive generations.

• This concept model poses problems with bacteria which are asexual organisms.

– Ecological Species Concept (This method is used for discussing an organisms ecological niche in an area.)• Organisms defined by niche (role) within

an ecosystem. • This method uses terms like: producer,

consumer, decomposer, keystone species.

LE 54-2

Microorganismsand other

detritivores

Tertiaryconsumers

Secondaryconsumers

Detritus Primary consumers

Sun

Primary producers

Heat

Key

Chemical cycling

Energy flow

Modes (Ways to) of Speciation

–Allopatric ( Allo –means “different”; Patric - means “place”)• In this way, a geographic barrier becomes

present within the environment separating the parent population. This barrier can create two different environments which could cause each species to begin to change/evolve over time and potentially lead to two different species.

ADAPTIVE RADIATION

Species migrates into new environments. As time and successive generations go by, they

change/evolve to meet the requirements of that new environment.

Then the cycle repeats, repeats, repeats

LE 24-5

Allopatric speciation Sympatric speciation

Galapagos Islands

• i.Galapogos Islands & Darwin’s finches are great examples of this process.

• ii.If the island is close to the mainland, we see little change occur.

• iii. If the island is farthest from mainland, we see more changes occur.

Galapagos Islands close up

Darwin’s Galapagos Island finches

– Sympatric (Sym – means “same”) In this process, a new species evolves out of the parent species while both remain in the same environment.• For animals – This may occur because of

competition for resources, such as food. • The dominant individuals, having the more

favorable traits• The weaker group, having the lesser favorable

traits• This change in resource utilization may lead to

change/evolution of the weaker group over time

LE 24-5

Allopatric speciation Sympatric speciation

• For plants – This mainly occurs because of polyploidy (a condition of having abnormal chromosomal numbers) because of cross fertilization between plants that have had meiosis go awry in the formation of gametes.–Autopolyploidy (Is the result of self

fertilization.)–Allopolyploidy (Is the result of

different plants cross fertilizing.)