UNIT 8: THE ORIGIN AND EVOLUTION

OF LIFE

INDEX1. The beginning of life2. Evolutionary theories before the 20th century3. Evidence of evolution4. Present-day theories of evolution5. The beginning of new species6. The appearance of human beings

Stanley Miller

1. The beginning of life

Spontaneous generation = life can appear from inanimate objects

WRONGIt was accepted In ancient Egypt and in the Middle Ages

Francesco Redi was the first one to prove that spontaneous generationwas FALSE. (17th century) .

He proved that larvae found in rotting meat came from fly eggs.

http://www.phschool.com/atschool/phsciexp/active_art/redi_pasteur_experiment/

In the 19th century Louis Pasteur demonstrated that microorganismsdid not com from spontaneous generation either.

Spontaneouschemical

reactions amongmethane, ammonia,

hydrogen and water vapor occurred.

The reactionswere started byelectric chargesfrom storms,

volcaniceruptions…

Organicmoleculesappeared

Water vapourcondensed primitive seas were formed. (primordial

soup)

Coacervatesappeared

Life arose from processes which ocurred in the atmosphere of the primitive Earth.

Coacervate:

• stable sphericalstructure madeup of organicmolecules.

Coacervates isolated organic moleculesinside themselves.

They also could divide and multiply, thanks to a nucleic acid.

http://www.wiley.com/college/trefil/0470118547/vdl/lab_miller_experiment/

They proved that organic molecules could be synthetised from inorganic molecules.

Inorganic compounds

Organic compounds

Electrical currents

Current additions to Oparin’s theory:

• The process probably happened in areas with clay or muddysoil, not in water.

• The first nucleic acid to appear probably would have beenRNA.

Other theories: Theory of panspermiaLife comes from the spores of other microorganisms that were inside meteorites.

Activities 5, 6 and 7 page 145

Previously there were only non-evolutionary theories:

Linnaeus stated that species hadbeen created separately and

independently by God. They wouldbe static or unchanging.

Cuvier explained the existence of fossils from species that had

disappeared as a result of catastrophesthat killed these organisms.

Animals developed structures and organs that they needed to adapt to

their environment.

These new characteristics weretransmitted to their descendants

First hypothesis of evolution were developed:

A. Lamarckism

(Evolutionary theory)

Theory of inheritance of acquired characteristics

No longer accepted

B. Darwinism

• Individuals in a population have differences among them.

• Struggle for existence: There is competition betweennew-born individuals for space and food.

• Survival of the fittest: individuals whose variations helptheir survival in a certain environment are favoured.

• The surviving individuals produce the next generation, so that the more favourable variations are transmitted to theoffspring.

Basic principles of Darwinism

When Charles Darwin was only 22, he set out on a voyage around the world, to discover new species and help in the age of exploration. What was to be a 2 year voyage stretched into 5. The young explorer gathered a lot of data and based on them he wrote “The origin of Species”.

He discovered 14 different species of finches in Galapagos Islands, whichwere adapted to different types of food.

Natural selection

The individuals that have the mostadvantageous characteristics

survive and their frequency in thepopulation increases progressively.

There is a gradual disappearanceof these less favoured traits.

After many generations, significantchanges are produced.

Explain the evolution of giraffesaccording toDarwin’s theory of evolution

3. Evidence of evolution

Homologous organs same structural patternbut different functions. Proof of divergentevolution.

Analogous organs same function althoughthey have a different evolutionary origin.

Vestigial organs remains of organs which tendto disappear because they no longer have a function

Some human vestigial organs

Homologous organs

Analogous organs

Fossils show that organisms in the past were different from the organisms today.

•Slow but clear changes can be observed in these fossils.

•An increase in diversity and complexity can be seen.

•There are fossils with intermediate characteristics which later evolved in different groups.

Archaeopteryx

Fossil evidence for evolution

Some embryos from different species are similar, which shows that there is a clearevolutionary relationship between them.

Similarities between embryos are greater within more closely related groups

Groups of organisms which were isolated geographically evolved differently to form new species.

Biogeographical evidence for evolution

All living beings are made up of the same type of molecules

(proteins, nucleic acids…)

By comparing the molecular sequences in different species, the evolutionary relationship

between them can be established

Page 151 activities 9, 13, 14, 16 and 17

4. Present-day theories of evolution

New discoveries have been included in Darwin’s theory:

Mendel’s laws

Sexual reproduction,

which produces

variation in the offspring

Genetic recombination, which happens during meiosis

mutations

Theory of the selfish gene

(Richard Dawkins)

The unit of evolution is the gene, not the population and

competition is between genes themselves

rather than between individuals

Theory of the

punctuated equilibrium

The process of evolution has not

always been slow and gradual

Endosymbiotic theory

(Lynn Margulis)

Eukaryotic cells originated from the

fusion of two types of bacteria.

They had the capacity to phagocytose other

cells whic became cellular organelles,

such as mitochondria and chloroplasts.

https://www.youtube.com/watch?v=3ESXvLHceDc Endosymbiotic theoryhttps://www.youtube.com/watch?v=-FQmAnmLZtE

Lynn Margulis

5. The origin of new species

Species = set of individuals that can reproduce with each otherand create fertile offspring.

1. Natural selection favours some individuals and prejudices other

new populations of the same species2. Genetic isolation of the new population: the members of 2 different populations in the same species cannot reproduce with the other population.

Possible reasons of genetic isolation

Geographical barriers: mountains, a river…

Physiological barriers: incompatibilities in the functioning of gametes

Ethological barriers: new types of behaviour

…

3. Gradual differentiation: after isolation, populations become more and more different.

23 4

1

4. Speciation: over time genetic changes producessuch significant differences that it is no longer

possible for the two populations to produce fertile offspring.

Microevolution

The process of evolution that causes the appearance of new species.

Species belonging to the same genus werecaused bymicroevolution.

Macroevolution

The type of evolutionthat resulted in largegroups of differentspecies because of drastic changes.

Example: Birds and mammals evolvingfrom reptiles.

6. The appearance of human beings

Characteristics of Hominids

Bipedal

Changes in the cranium, pelvis, spine and limbs

Upright position

It improved their sight and freed

their hands

Craniums of1. Gorilla2. Australopithecus3. Homo erectus4. Neanderthal5. Steinheim Skull6. Homo sapiens

Characteristics of the Homo genus

• Capacity to use tools

• Opposable thumb

• Developed brain

Opposable thumb

Chronological appearance of

Homo

Homo habilis

Homo erectus

Homo sapiens

Glossary Spontaneous generation

Coacervate

Natural selection

Phlylogenetics

Speciation