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.
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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