WHAT IS THE ORIGIN OF LIFE,
AND OF HUMAN
RELIGIOUS/MYTHICAL EXPLANATIONS: Based on Faith
A supernatural being created the world the way we see it.
PHILOSOPHICAL EXPLANATIONS: Based on Reason
Miletus: (610-546 B.C.)
Aristotle: (384-332 B.C.)
SCIENTIFIC EXPLANATIONS: Based on the Scientific Method
✔ Observation of facts (reality)
✔ Proposing THEORIES that explain those facts, through the use
✔ Constant testing of these theories with new observations:
REVISION and IMPROVEMENT of the theories.
- For a long time people believed that living beings -at least the simplest forms of lifewere originated from non-living matter, normally decaying matter. This is called
- Although wrong, this theory was supported by many everyday
observations: small insects seemed to emerge from rotten meat, rats
from dumps, worms from mud...
Jan Baptist van Helmont (1579-1644):
He experimented with plants, growing them and comparing their
increase in size with the insignificant loss in the soil: he deduced it was
the water that formed the new living mass (photosynthesis had not
He also had a peculiar recipe for mice (“place a dirty shirt or some
rags in an open pot or barrel containing a few grains of wheat or some
wheat bran, and in 21 days, mice will appear”) and scorpions ( “basil,
placed between two bricks and left in sunlight”)
Francesco Redi (1626-1697):
- First to try to falsify Spontaneous Generation.
- He designed an experiment to prove that flies don't arise from
rotten meat by spontaneous generation, but from maggots:
he placed pieces of meat in open and closed jars (some sealed,
some covered with a cloth to allow air into them), and observed
that flies only appeared in the open ones.
In spite of Redi's results, the discovery of microorganisms gave fresh air to Spontaneous Generation
Lazaro Spallanzani (1729-1799):
He boiled broth in an open flask and observed that
microorganisms appeared, while if the boiled broth was
kept in closed flasks this didn't happen.
He was criticised by saying that he had only proved that
life could not survive without air.
The End of Spontaneous Generation:
Louis Pasteur (1822-1895)
- French chemist and one of the first
- He supported the Germ Theory of Disease.
Pasteur was a great scientist and among his
contributions to science are:
- The first VACCINES (anthrax, rabies): one of
the founders of Immunology.
- The invention of a method to prevent milk and wine from causing sickness:
- The experiment that put a definitive end to the theory of spontaneous generation:
In 1859 Pasteur boiled a meat broth in a flask that had a long neck which curved
downward, like a goose (“col de cygne” = swan neck). The bend in the neck prevented
any particles from reaching the broth, while still allowing the free flow of air. Nothing
grew inside the flask unless when it was broken.
This experiment put a definitive end to the theory of spontaneous generation,
and also supported the Germ Theory.
"Never will the doctrine
generation recover from
the mortal blow struck by
this simple experiment" said Pasteur in his
triumphant lecture at the
Sorbonne in 1864.
Pasteur proved that all living beings, no matter their size, came from other living
How did life start in the first place?
Extraterrestrial origins: PANSPERMIA
In the 19th and 20th centuries some scientists supported the
theory that life might have arrived to the Earth in the form
of bacteria carried by meteorites, or even sown by other
intelligent extraterrestrial beings.
Cons: the conditions these bacteria must have endured in their
journey through space are really extreme (ultraviolet radiation,
extremely cold temperatures, etc)
Among the supporters of this theory were:
Chemist Svante Arrhenius (1859-1927)
Astronomer Fred Hoyle
But does Panspermia really answer
the question of the Origins of Life?
IT ONLY DIVERTS IT TO OTHER
PLACES IN THE UNIVERSE
Biochemical explanations: Oparin's Hypothesis
Alexander Oparin (1894-1980):
1º) The first organic molecules originated through the reactions of the gases
of the primitive atmosphere, using the energy of the electrical storms
(lightning) and ultraviolet radiation from the sun.
2º) These organic molecules would gather in the ocean for millions of
years, becoming a primordial soup in which molecules reacted and
- At some moment, some
became more and more complex.
of these molecules would
be able to auto-replicate.
- Some of these autoreplicating molecules
would be isolated in tiny
- These coacervates would
later originate the first cells
(CH4 , NH3 , SH2 , H2O)
The Miller Experiment (1953)
Stanley Lloyd Miller (1930-2007:)
- He designed an experiment to test the first steps of
- He reproduced the conditions of the primitive atmosphere
in his lab, and found that after some time small organic
molecules such as amino acids were formed.
Miller DID NOT create life in his lab, but he proved that life may have begun from a
What is Biological Evolution?
- Evolution is the change in the inherited traits in one population over time.
This change produces a gradual transformation of simple living things into more
complex species across the generations.
- For a long time, until the 19th century, most people believed that all the species on
Earth were invariable and stable, and had been created the way we see them today.
- This was supported by the literal interpretation of the Bible, which many people,
scientists included, took for a scientific book.
Carl von Linnaeus
Father of Taxonomy
As time went by, evidences in favour of Evolution piled up:
- proves of an older Earth than the one described in the Bible
But fossils were
still explained by
many as nature's
Mary Anning (1799-1847) a
famous British fossil collector who
made many great discoveries of
fossils in the cliffs of Lyme, such as
the first specimen of Ichtyosaurus
and the first Plesyosaurus. Her
findings helped to scientifically prove
jokes, or the
Georges Cuvier (1769-1832):
- French naturalist who established EXTINCTION as a fact.
- He explained the existence of fossils with his theory of
CATASTROPHISM: the fossils were the remains of animals that
had died during past geological catastrophes.
- Still, Cuvier was a fixist: according to him fossils were the result of “successive
creations” to replace the extinct species after each catastrophe. He counted up to
27 different creations.
- Presumably, the last catastrophe had been the Universal Flood.
FIRST EVOLUTIONARY THEORIES:
Erasmus Darwin: (1731 – 1802):
- He belonged to the British Enlightment movement: he was a natural
philosopher, doctor (he refused to be king's George III's personal
physician), abolitionist and poet.
- In his work Zoönomia he expressed some views that foreshadowed a
theory of evolution, which were read and commented on by his
grandson Charles Darwin.
- In addition to being an abolitionist, Erasmus Darwin advocated
a proper education for girls: they should be educated in
schools and learn proper subjects like physical exercise, botany,
chemistry, mineralogy, etc.
- Although Erasmus's evolutionary ideas were primitive and more poetical
than scientifically grounded (his poem The Botanic Garden offered a
glimpse of evolution), his free-thinking had undoubtedley an important
influence on his grandson Charles.
Jean-Baptiste Pierre Antoine de Monet, Chevalier
de la Marck, known as Lamarck: (1744-1829)
- French soldier and naturalist, first to formulate a theory of evolution, that included
a mechanism, however wrong, for it.
He was also one of the first in using the term “Biology” in its modern sense.
Lamarck's theory was based in the following principles:
- The ENVIRONMENT is able to induce changes in animals.
- In all the organisms there is a drive to PERFECTION, a force that makes them change from more
simple to more complex and to be better adapted to their environment.
- If an organism needs a new organ for a new function, it will develop it: the FUNCTION creates the
- ADAPTATION: when there is a change in the environment, the organisms also change to be better
adapted to it. These changes are always beneficial, never damaging.
- USE AND DISUSE: the more an animal uses an organ, the more developed it becomes. Organs that
are seldom used weaken and finally disappear.
- INHERITANCE OF ACQUIRED CHARACTERISTICS: once an individual has developed a feature,
this is transmitted to the offspring. Although wrong, this was shared by many scientists, Darwin
included, as they didn't know how characters are transmitted from parents to offspring (GENETICS).
BUT inherited traits acquired during lifetime are not transmitted
to the offspring, as German biologist August Weismann proved:
Weismann cut the tails off mice, then crossed them, and checked the offspring. If a mouse
without a tail produced offspring without tails it would be the ultimate example of Lamarck's
definition of disuse. If Lamarck was correct, the disuse of a tail due to removal would be
passed on to successive generations. Weismann cut the tails off 901 mice over 5
generations. His results? Every mouse, in every generation, was born with a normal
Charles Robert Darwin
(Shrewsbury, 12th February, 1809 -Downe, 19th April, 1882):
Evolution by NATURAL SELECTION:
- Living beings produce larger offsprings that can survive
with the limited resources of the environment:
- Individuals in the populations are not identical: there are small inheritable differences
- Struggle to survive: Only the
fittest, most adapted to the
- The individuals that survive transmit their inheritable traits to
- The accumulation of small variations through many
generations produce the new adaptations to the environment.
Charles Darwin: Evolution through Natural Selection
- there is a natural variability of inheritable traits in a population.
- some of these traits give an advantage to the individuals to survive and leave more
offspring in a certain environment, so they are transmitted to the next generation in a
higher frequency: they are favoured by Natural Selection.
- changes add over time through the generations and produce the adaptations
Not all offspring survive to become adults. Those with favourable variations, such as
long, thick fur in a cold environment, are more likely to survive and leave offspring
than those without. This effect of different characteristics on survival is what Charles
Darwin called NATURAL SELECTION.
What would happen if the beetles lived on the grass or on the leaves of
the trees instead of on the bark?
THERE ARE NOT “GOOD” OR “BAD” TRAITS:
NATURAL SELECTION DEPENDS ON THE ENVIRONMENT
- The environment induces the organisms to change.
- These changes are always positive (perfection drive)
- Use and disuse.
- Inheritance of acquired characters (ALSO SHARED BY DARWIN!!!)
- Pre-existing variation
- Not all the variations are equally adaptative in a given environment.
-S truggle to survive: The best adapted survive and leave more offspring:
the next generation will be better adapted (survival of the fittest)
Let's learn a bit more about who Charles Darwin was and how he got to develop
- Son of a doctor, Robert Darwin (very strict with his children), and grandson of the
proto-evolutionist Erasmus; his mother died when he was a child. He showed a deep
interest in nature since his childhood.
The 7- year- old Darwin
The young Darwin was not a good student, and after
attending the Shrewsbury school he moved at the age
of 16 to study in the University of Edinburgh Medical
School to become a doctor, like his father. After
witnessing the bloody surgeries that were performed in
the operating theatres of the time (no anaesthesia!) he
convinced himself that he could never be a doctor, and
left Edinburgh in only two years. However, it was there
that he heard for the first time about Lamarck's
evolutionary ideas, which made no impression on him,
as his own grandfather's hadn't either.
After leaving Edinburgh, Darwin went to
Cambridge's Christ College, where he
was to study Theology to become an
Anglican parson. There he met the botany
professor John Stevens Henslow. He
was the one who proposed the young
Darwin (only 21!) for the position of
companion -rather than naturalist- to
captain Robert Fitzroy, who was to start
an almost 5-years voyage around the
world in the H.M.S. Beagle.
University of Edinburgh
Christ College, Cambridge
Henslow, professor of
Botanics at Cambridge,
the young Darwin (21) to Captain Robert Fitzroy (26)
(who accepted him in spite of his nose!)
for one of the most exciting voyages, that was about
to change the history of Science
The HMS Beagle, in her second voyage left Plymouth on
27th December, 1831 and returned to Falmouth, Cornwall,
on 2nd October, 1836
27,5 m long, 7,46 width... and 75 people
to live in it!!!
and Darwin, who shared Fitzroy's cabin, was sea-sicked
most of the time...!
But the Darwin that had left England in the Beagle was an unknown young naturalist
that shared the fixist views of his times...
and the one that returned almost 5 years later was a famous scientist because of the
amazing discoveries of new species that he had made, and, most important: HE HAD A
SECRET, a revolutionary theory that he still did not dare to share with his fellow
scientists... a theory of EVOLUTION, with the right mechanism: NATURAL SELECTION
What had happened in this voyage...?
- During the voyage on the Beagle, Darwin collected and discovered plentiful of new
species that he sent to England in every stop of the ship, and studied the geology of the
South American lands.
His observations were influenced by his previous knowledge and his new readings:
Charles Lyell, geologist, and his Principles
of Geology, in which he pointed out that the
earth was shaped by slow-moving forces
still operating today
(UNIFORMITANIARISM): slow forces could
make big changes if given the time. Captain
Fitzroy had given the book to Darwin as a
gift when they started their voyage..
Thomas Malthus, demographer and economist,
who in his An Essay on the Principle of
Population (published 1798) stated that “the
population grows faster than the resources”
Darwin read Malthus work soon after he returned
And then, he arrived to the Galapago Islands...
Each island had a slightly different finch species, each perfectly adapted to its diet.
Why had God bothered to create a slightly different species for each island?
Darwin had the genius to see the importance of what all the other scientists of his time
had dismissed as unimportant: VARIATION among the individuals:
If in one island the main nourishment was seeds then the
finches with a hard peak, able to open them would have an
advantage from the others, and would leave more offspring with
the same features
If in other island they need to peck on wood, or suck nectar
from the flowers, other shapes of peaks were favoured, .
So after many generations (TIME) the population of each island
had different peaks.
Darwin called NATURAL SELECTION this mechanism that chooses (selects) from the different
VARIETIES present in a population the best adapted for a certain environment. As these leave more
offspring than the others, after enough TIME had passed, the characteristics of the population are
changed. If many changes accumulate over time, a new species would be originated.
ADAPTED TO DIFFERENT
One population of
slightly different finches:
VARIATION in the population
Back in England, Darwin was famous and introduced to the most important
scientists of the time. Although he had already shaped his theory of Evolution
through Natural Selection in his mind, instead of staying in London, he decided to
marry his cousin Emma and retire to Downe House, in Down (Kent), from where he
kept in touch with the scientific world through the post mail.
Emma Darwin was very religious
and liked to play the piano (she
had studied with Chopin).
In his greenhouse Darwin experimented with different
plants (carnivorous plants, orchids...) and published books
on his findings. He was also a world expert on barnacles!
Darwin was a loving father, not at all strict, and loved to play with his children
George Darwin, mathematician
Charles with his son William
Annie. Her death at
the age of 10
Francis Darwin, scientist
Although Darwin continued studying
different fields of science, and
corresponding with hundreds of
scientists all around the world on
different matters, he seemed in no
hurry to publish the theory which
he knew, would make him pass
Darwin used to walk along his sandwalk in Downe
House, thinking about his scientific theories.
- He knew his Theory of Evolution would bring him problems with the Church, and
maybe he didn't want to hurt his wife, Emma.
- He knew his theory might also be polemical among the scientists, and wanted to
have it well grounded with enough proves and examples.
- He knew the WEAK POINTS of his theory: he didn't know
HOW VARIATION WAS ORIGINATED, and HOW FEATURES
WERE TRANSMITTED TO THE OFFSPRING (in fact, he
believed in the inheritance of acquired features, like
Lamarck). HE HAD NO CHOICE: GENETICS WAS BEING
DISCOVERED AT THAT TIME by an obscure Czech monk,
So, only after receiving a letter from another naturalist,
ALFRED RUSSELL WALLACE, who had reached
very similar conclusions as his, did he decide to
publish his book, On the Origins of Species by Means
of Natural Selection, on 22nd November, 1859, more
than 20 years after the end of his voyage in the
Beagle! The book was an immediate success in sales,
and a controversy began among the population
(actually, the scientific communitiy accepted it quite
Alfred Russell Wallace (1823-1913). He independently reached a
theory of evolution due to natural selection that prompted Charles
Darwin to publish his own theory. Unlike Darwin, the financial problems
were a constant concern during his life, and Darwin was very aware of
Wallace's financial problems and lobbied long and hard to get him a
government pension for his lifetime contributions to science. A £200
annual pension was awarded in 1881 which helped to stabilise
Wallace's financial position, in addition to the income from his writings.
Darwin and him presented their theory together to the Linnean
Society in London, on the 1st July, 1858
Young Wallace in Singapore.
First evolutionary tree
Darwin avoided in this book the controversial term “evolution”, but he did insist on the common
ancestor that all living beings shared. About the origins of life, the only alusion he made was
“light will be thrown on the origin of man and his history". Only in a later book would he adress the
origins of man: Descent of Man, 1871.
The Origins of Species's final paragraph: “There is grandeur in this
view of life, with its several powers, having been originally
breathed into a few forms or into one; and that, whilst this planet
has gone cycling on according to the fixed law of gravity, from so
simple a beginning endless forms most beautiful and most
wonderful have been, and are being, evolved”
- NEODARWINISM or SYNTHETIC THEORY
- PUNCTUATED EQULIBRIUM OR SALTATIONISM
NEODARWINISM or SYNTHETIC THEORY:
It fuses the theory of Natural Selection with the knowledge in Genetics that
we have acquired all through the 20th and 21st centuries:
- We now know that the inherited traits are in the GENES, made of DNA.
- Any mistake in the copying of DNA (MUTATION) results in a different
protein===> different trait: Now we have the source of VARIABILITY among
the population: MUTATION
- Evolution occurs GRADUALLY: small changes that accumulate over time
The NEO-DARWINISM or MODERN EVOLUTIONARY SYNTHESIS is the
modern version of Evolution:
Mechanism: NATURAL SELECTION
Source of Variation: MUTATION, RECOMBINATION, GENETIC DRIFT
Transmission of features: DNA (Genes)
Theodosius Dobzhansky (1900-1975)
“Nothing in Biology Makes Sense Unless in
the Light of Evolution”
Prominent geneticist and evolutionary biologist, and
a central figure in the field of evolutionary biology for
his work in shaping the unifying modern
evolutionary synthesis. One of his most famous
essays has as a title:
His Spanish student
Ayala (1934- ) continued his work.
Richard Dawkins (1941- ), one of the most
popular neo-darwinians due to his many books
popularising science, such as The Selfish
Gene, and his bold defence of science and
reason against pseudosciences.
“Living beings have been on Earth for
more than 3000 million years without
knowing why before the truth was at
last known by one of them: By a man
named Charles Darwin”
"We are survival machines - robot vehicles
blindly programmed to preserve the selfish
molecules known as genes”
PUNCTUATED EQUILIBRIUM or SALTATIONISM:
- it opposes gradualism: species go through long periods of
stability followed by abrupt short periods of change:
evolutionary change occurs relatively quickly, while most
of the time species are stable.
- this is consistent with the discontinuities that the fossil record
shows (Neodarwinians explain these discontinuities by
claiming the fossil record is incomplete)
Stephen Jay Gould (1941-2002)
The deep impression that the huge T.rex
in the hall of the American Museum of
Natural History in New York were his
father took him when he was only 5
decided him to become a paleontologist.
Niles Eldredge (1943-)
studying Latin at
University, but soon
which he graduated
and completed his
Very popular paleontologist
and evolutionary biologist,
most of all because of his
many books popularizing
Evolution. He worked in
different universities and in
✔ He has been working in
the American Museum of
the American Museum of
Natural History in New York
He was also active in the defense of the
civil rights, fighting against racism, sexism,
cultural oppression and pseudosciences,
especially creationism and others used in
the service of racism and sexism.
of Natural History,
Both Gradualism and Punctuated Equilibrium accept Natural Selection as
the mechanism for evolution. They disagree in the rythm of evolutionary
How would Lamarck explain the following examples of evolution? And
fixists? And Darwin? And Neodarwinians?
moths (Biston betularia)
Bacteria's resistance to
Our place among the species.
We often make the mistake of thinking humans are at the
center of the biosphere or even the universe. This is not
the case. We are only one of over a million known species
living on this planet, and it’s estimated that we’ve only
discovered a fraction of the total number in existence.
What Makes Us Humans?