BIOLOGICAL EVOLUTION

WHAT IS THE ORIGIN OF TODAY'S BIODIVERSITY?

WHAT IS THE ORIGIN OF LIFE,

AND OF HUMAN BEINGS...?

RELIGIOUS/MYTHICAL EXPLANATIONS: Based on FaithA supernatural being created the world the way we see it.

PHILOSOPHICAL EXPLANATIONS: Based on Reason

SCIENTIFIC EXPLANATIONS: Based on the Scientific Method✔ Question/problem etc.✔ Observation of facts (reality) ✔ Proposing THEORIES that explain those facts, through the use of REASON.✔ Constant testing of these theories with new observations: REVISION and IMPROVEMENT of the theories.

Anaximander of Miletus: (610-546 B.C.)

Aristotle: (384-332 B.C.)

SPONTANEOUS GENERATION

- For a long time people believed that living beings -at least the simplest forms of life-

were originated from non-living matter, normally decaying matter. This is called

SPONTANEOUS GENERATION.

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 been discovered). 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”)

- Although wrong, this theory was supported by many everyday

observations: small insects seemed to emerge from rotten meat, rats

from dumps, worms from mud...

+

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

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.

Lazaro Spallanzani (1729-1799):

The End of Spontaneous Generation:

Louis Pasteur (1822-1895)

- French chemist and one of the first

microbiologists.

- 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:

PASTEURIZATION

- 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.

Pasteur proved that all living beings, no matter their size, came from other living

beings. But...

How did life start in the first place?

"Never will the doctrine

of spontaneous

generation recover from

the mortal blow struck by

this simple experiment" -

said Pasteur in his

triumphant lecture at the

Sorbonne in 1864.

Extraterrestrial origins: PANSPERMIAIn 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:

Astronomer Fred Hoyle

(1915-2001)

Chemist Svante Arrhenius (1859-1927)

But does Panspermia really answer

the question of the Origins of Life?

NO!

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

became more and more complex. - At some moment, some

of these molecules would

be able to auto-replicate.

- Some of these auto-

replicating molecules

would be isolated in tiny

structures: coacervates

- These coacervates would

later originate the first cells

INORGANIC MOLECULES:(CH

4 , NH

3 , SH

2 , H

2O) +

ENERGY SUPPLY(ULTRAVIOLET RAYS, LIGHTNING...)

SIMPLE ORGANIC MOLECULES

MORE COMPLEX ORGANIC MOLECULES

COACERVATES

FIRST CELLS

The Miller Experiment (1953)

Stanley Lloyd Miller (1930-2007:)

- He designed an experiment to test the first steps of

Oparin's Hypothesis.

- 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

chemical evolution.

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.

FIXIST THEORIES:- 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.

Aristotle's Great Chain of Being

Carl von Linnaeus

(1707-1778)

Father of Taxonomy

As time went by, evidences in favour of Evolution piled up:

- fossils

- proves of an older Earth than the one described in the Bible

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 EXTINCTION.

Ichtyosaurus

Plesyosaurus

But fossils were

still explained by

many as nature's

whims, God's

jokes, or the

remains of

animals that

hadn't survived

the Flood.

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.

The Fossil Record

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.

FIRST EVOLUTIONARY THEORIES:

- 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

ORGAN.

- 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

tail.

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

among them.

- The individuals that survive transmit their inheritable traits to

their offspring.

- The accumulation of small variations through many

generations produce the new adaptations to the environment.

- Struggle to survive: Only the

fittest, most adapted to the

environment, survive.

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.

BUT:

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

Lamarck's theory

✗

- 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!!!)

Darwin's theory

- 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)

- 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.

Let's learn a bit more about who Charles Darwin was and how he got to develop

his theory:

Darwin's birthplace

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.

University of Edinburgh

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.

Christ College, Cambridge

John Stevens Henslow, professor of Botanics at Cambridge,

RECOMENDED....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 to England.

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.

DIFFERENT SPECIES, ADAPTED TO DIFFERENT ENVIRONMENTS

One population of slightly different finches:VARIATION in the population

+Different environments ( NATURAL SELECTION)

TIME+

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).

Downe House

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

Francis Darwin, scientist

George Darwin, mathematician

Annie. Her death at the age of 10 deeply affected Darwin.

Emma Darwin

Charles with his son William

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 into history...

WHY...???

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,

GREGOR MENDEL.

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 quickly)...

Old Wallace

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.

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.

First evolutionary tree

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”

EVOLUTION NOWADAYS:- NEODARWINISM or SYNTHETIC THEORY

- PUNCTUATED EQULIBRIUM OR SALTATIONISM

- 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

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:

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)

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:

“Nothing in Biology Makes Sense Unless in the Light of Evolution”

His Spanish student Francisco José 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)

- CATASTROPHES

- MACROMUTATIONS

Stephen Jay Gould (1941-2002)

✔ Very popular paleontologist and evolutionary biologist, most of all because of his many books popularizing Evolution. He worked in different universities and in the American Museum of Natural History

✔ 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.

Niles Eldredge (1943-)

✔ He started studying Latin at Columbia University, but soon switched to Anthropology, in which he graduated and completed his PhD.

✔ He has been working in the American Museum of Natural History in New York since 1969.

✔ 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.

American Museum of Natural History, New York

✔Both Gradualism and Punctuated Equilibrium accept Natural Selection as the mechanism for evolution. They disagree in the rythm of evolutionary change.

GRADUALISMPUNCTUATED EQUILIBRIUM

Manchester's peppered moths (Biston betularia)

Bacteria's resistance to antibiotics

How would Lamarck explain the following examples of evolution? And fixists? And Darwin? And Neodarwinians?

EVIDENCE OF

EVOLUTION

1.- COMPARATIVE ANATOMY

HOMOLOGOUS ORGANS: share a common structure because they have a common

origin, though they may have evolved to perform different functions

VESTIGIAL ORGANS: organs that have lost their function.

ANALOGOUS ORGANS: organs that have similar functions but have a different

structure (they have different origins)

2.- EMBRYOLOGY

The first stages of

development of different

organisms show many

similarities.

3.- PALEONTOLOGY: fossils

Archaeopteryx shows

intermediate features

between reptiles and

birds.

4.- BIOGEOGRAPHY:

5.- MOLECULAR BIOLOGY:

MUTATION creates VARIATION

MUTATION happens RANDOMLY (preadaptative)

MECHANISMS FOR EVOLUTION

NATURAL SELECTION (NS) preserves

favourable variation and removes unfavourable

NS depends on the ENVIRONMENT

NS needs TIME to produce changes

NS acts GRADUALLY

NS HAS NO GOAL: IT ACTS BLINDLY

Other sources of variability:

- Genetic RECOMBINATION

- Random FERTILIZATION

Peppered moth in Manchester

WHAT IS A SPECIES?

A group of individuals with similar features that can interbreed (exchange

genes) and produce a fertile offspring.

How are new species formed?: SPECIATION

Gradual

accumulation of

small changes

Genetic isolationTIMEA BARRIER splits

a population

Two mechanisms of speciation:

Isolation:

- geographical

- ecological

- behavioural

- genetic isolation

- reproductive isolation

HUMAN EVOLUTION

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.

Australopithecus, Homo habilis, Homo erectus, Homo heidelbergensis, Homo neanderthalensis Homo sapiens

BIPEDALISM

ENCEPHALIZATION

LANGUAGE

CULTURE

TECHNOLOGY (TOOLS)

OPPOSABLE THUMB

What Makes Us Humans?

BIPEDALISM

ENCEPHALIZATION

OPPOSABLE THUMB

TECHNOLOGY (TOOLS)

LANGUAGE

CULTURE