Homework to be submitted to biovcc@yahoo.com
Notes:
The Origins of Life
Earth is probably ~4.5 billion years old
Oldest life forms began ~3.5 bya
How did life begin???
The Origin of Life: Early Ideas
Spontaneous Generation
idea popular in the 1600-1700’s
living things come from the nonliving
evidence: beetles and other insect larvae arise from cow dung; frogs emerge from
mud
In 1688, the Italian Francisco Redi In 1668, Francesco Redi, an Italian
physician, did an experiment with flies and wide-mouth jars. He demonstrated
that meat that was covered did not produce maggots
This may have been the first true scientific experiment…
Francesco Redi experiment with flies and wide-mouth jars
Observation: There are flies around meat carcasses at the butcher shop.
Question: Where do the flies come from? Does rotting meat turn into or produce
the flies?
Hypothesis: Rotten meat does not turn into flies. Only flies can make more
flies.
Prediction: If meat cannot turn into flies, rotting meat in a sealed (fly-proof)
container should not produce flies or maggots.
Testing: Wide-mouth jars each containing a piece of meat were subjected to
several variations of “openness” while all other variables were kept the same.
Conclusion: Only flies can make more flies. In the uncovered jars, flies entered
and laid eggs on the meat. Maggots hatched from these eggs and grew into more
adult flies. In the sealed jars, no flies, maggots, nor eggs could enter, thus
none were seen in those jars. Maggots arose only where flies were able to lay
eggs. This experiment disproved the idea of spontaneous generation for larger
organisms.
Other Ideas: Life from a Biblical Creation?
Christian Creationism states that the world, including all life, was created
about 6,000 years ago in six literal days by a God.
…But how does one accurately and fairly test for this?...
What’s the observation, hypothesis, test…?
This idea does not really fit into the confines of a Science course.
Origin of Life: Another idea
Biogenic-looking features in ALH84001 Martian meteorite
In 1969, a meteorite (left-over bits from the origin of the solar system) landed
near Allende, Mexico. The Allende Meteorite (and others of its sort) have been
analyzed and found to contain amino acids, the building blocks of proteins.
This idea of panspermia hypothesized that life originated out in space and came
to earth inside a meteorite.
The amino acids recovered from meteorites are in a group known as exotics: they
do not occur in the chemical systems of living things. The ET theory is now
discounted by most scientists, although the August 1996 discovery of the Martian
meteorite and its possible fossils have revived thought of life elsewhere in the
Solar System.
Anyway….This only moves the problem to elsewhere!
The Latest on Extra-terrestrial Origins…The Raelians
Raelians believe that humanity was created from the DNA of superior alien
scientists
Follow the teachings of a former French magazine sportswriter and wannabe
race-car driver Claude Vorilhon, 56. He took the name "Rael" after he claimed a
close encounter of the third kind….
A Plausible History of Life on Earth (A Theory)
First living organism: primitive bacterium which absorbed and restructured small
organic molecules produced nonbiologically in its environment.
Explosive growth in numbers from lack of
competition led to exhaustion of ATP. Early
demise of countless billions, but also step-
by-step, from back-to-front, a fermentation
cycle to produce ATP from glucose.
When free glucose also ran out, resultant biological stress selected for
evolution of a biological mechanism to produce glucose from more abundant
natural resources: CO + (H S or H O) + sunlight. Photosynthesis, with H O, a
waste product is O .
Gradual increase in atmospheric oxygen led to selective advantage if organisms
could exploit this reactive gas in ATP production from glucose: Respiration.
Consumers (bacteria) now could survive by scavenging organic matter released
upon deaths of producers (blue-green algae).
Origin of Life: Current Theory
Chemical Evolution
.....The idea that long ago complex collections of chemicals formed the first
cells.
Life began in the oceans 4 bya from simple chemicals joining together in a
“primordial soup”
Complex chemicals evolved into living cells
Conditions on the Early Earth
A hot reducing environment
High temperatures
H2O, CO2, N2
H2S, CH4, NH3, H2
No O2
Text pg. 451
Miller Experiment
In 1950, a student, Stanley Miller, designed an experiment in which he
discharged an electric spark into a mixture thought to resemble the primordial
composition of the atmosphere.
From the water receptacle, designed to model an ancient ocean, Miller recovered
some amino acids.
Quiz
What gases were believed to be present in the early earth’s atmosphere?
What energy source may have helped create life on earth?
What complex structures did the Miller-Urey apparatus produce?
Has life been recreated in this apparatus?
The Tree of Life An Introduction to Biological Diversity
Overview: Changing Life on a Changing Earth
Life is a continuum
Extending from the earliest organisms to the great variety of species that exist
today
Geological events that alter environments
Change the course of biological evolution
Conversely, life changes the planet that it inhabits
Geologic history and biological history have been episodic
Marked by what were in essence revolutions that opened many new ways of life
Conditions on early Earth made the origin of life possible
Most biologists now think that it is at least a credible hypothesis
That chemical and physical processes on early Earth produced very simple cells
through a sequence of stages
According to one hypothetical scenario
There were four main stages in this process
Synthesis of Organic Compounds on Early Earth
Earth formed about 4.6 billion years ago
Along with the rest of the solar system
Earth’s early atmosphere
Contained water vapor and many chemicals released by volcanic eruptions
Laboratory experiments simulating an early Earth atmosphere
Have produced organic molecules from inorganic precursors, but the existence of
such an atmosphere on early Earth is unlikely
Instead of forming in the atmosphere
The first organic compounds on Earth may have been synthesized near submerged
volcanoes and deep-sea vents
Extraterrestrial Sources of Organic Compounds
Some of the organic compounds from which the first life on Earth arose
May have come from space
Carbon compounds
Have been found in some of the meteorites that have landed on Earth
Looking Outside Earth for Clues About the Origin of Life
The possibility that life is not restricted to Earth
Is becoming more accessible to scientific testing
Abiotic Synthesis of Polymers
Small organic molecules
Polymerize when they are concentrated on hot sand, clay, or rock
Advantage for Polymerization Reactions in Protocells
Protobionts
Protobionts
Are aggregates of abiotically produced molecules surrounded by a membrane or
membrane-like structure
Laboratory experiments demonstrate that protobionts
Could have formed spontaneously from abiotically produced organic compounds
For example, small membrane-bounded droplets called liposomes
Can form when lipids or other organic molecules are added to water
Coacervates & Vesicles
The “RNA World” and the Dawn of Natural Selection
The first genetic material
Was probably RNA, not DNA
RNA molecules called ribozymes have been found to catalyze many different
reactions, including
Self-splicing
Making complementary copies of short stretches of their own sequence or other
short pieces of RNA
Early protobionts with self-replicating, catalytic RNA
Would have been more effective at using resources and would have increased in
number through natural selection
: The fossil record chronicles life on Earth
Careful study of fossils
Opens a window into the lives of organisms that existed long ago and provides
information about the evolution of life over billions of years
How Rocks and Fossils Are Dated
Sedimentary strata
Reveal the relative ages of fossils
Index fossils
Are similar fossils found in the same strata in different locations
Allow strata at one location to be correlated with strata at another location
The absolute ages of fossils
Can be determined by radiometric dating
The magnetism of rocks
Can also provide dating information
Magnetic reversals of the north and south magnetic poles
Have occurred repeatedly in the past
Leave their record on rocks throughout the world
The Geologic Record
By studying rocks and fossils at many different sites
Geologists have established a geologic record of Earth’s history
The geologic record is divided into
Three eons: the Archaean, the Proterozoic, and the Phanerozoic
Many eras and periods
Many of these time periods
Mark major changes in the composition of fossil species
The geologic record
Mass Extinctions
The fossil record chronicles a number of occasions
When global environmental changes were so rapid and disruptive that a majority
of species were swept away
Two major mass extinctions, the Permian and the Cretaceous
Have received the most attention
The Permian extinction
Claimed about 96% of marine animal species and 8 out of 27 orders of insects
Is thought to have been caused by enormous volcanic eruptions
The Cretaceous extinction
Doomed many marine and terrestrial organisms, most notably the dinosaurs
Is thought to have been caused by the impact of a large meteor
Much remains to be learned about the causes of mass extinctions
But it is clear that they provided life with unparalleled opportunities for
adaptive radiations into newly vacated ecological niches
The analogy of a clock
Can be used to place major events in the Earth’s history in the context of the
geological record
Stromatolites as Fossil Record of Early Unicelluar Organisms
The First Prokaryotes
Prokaryotes were Earth’s sole inhabitants
From 3.5 to about 2 billion years ago
Electron Transport Systems
Electron transport systems of a variety of types
Were essential to early life
Have: some aspects that possibly precede life itself
Photosynthesis and the Oxygen Revolution
The earliest types of photosynthesis
Did not produce oxygen
Oxygenic photosynthesis
Probably evolved about 3.5 billion years ago in cyanobacteria
When oxygen began to accumulate in the atmosphere about 2.7 billion years ago
It posed a challenge for life
It provided an opportunity to gain abundant energy from light
It provided organisms an opportunity to exploit new ecosystems
: Eukaryotic cells arose from symbioses and genetic exchanges between
prokaryotes
Among the most fundamental questions in biology
Is how complex eukaryotic cells evolved from much simpler prokaryotic cells
The First Eukaryotes
The oldest fossils of eukaryotic cells
Date back 2.1 billion years
Endosymbiotic Origin of Mitochondria and Plastids
The theory of endosymbiosis
Proposes that mitochondria and plastids were formerly small prokaryotes living
within larger host cells
The prokaryotic ancestors of mitochondria and plastids
Probably gained entry to the host cell as undigested prey or internal parasites
In the process of becoming more interdependent
The host and endosymbionts would have become a single organism
The evidence supporting an endosymbiotic origin of mitochondria and plastids
includes
Similarities in inner membrane structures and functions
Both have their own circular DNA
Eukaryotic Cells as Genetic Chimeras
Additional endosymbiotic events and horizontal gene transfers
May have contributed to the large genomes and complex cellular structures of
eukaryotic cells
Some investigators have speculated that eukaryotic flagella and cilia
Evolved from symbiotic bacteria, based on symbiotic relationships between some
bacteria and protozoans
Multicellularity evolved several times in eukaryotes
After the first eukaryotes evolved
A great range of unicellular forms evolved
Multicellular forms evolved also
The Earliest Multicellular Eukaryotes
Molecular clocks
Date the common ancestor of multicellular eukaryotes to 1.5 billion years
The oldest known fossils of eukaryotes
Are of relatively small algae that lived about 1.2 billion years ago
Larger organisms do not appear in the fossil record
Until several hundred million years later
Chinese paleontologists recently described 570-million-year-old fossils
That are probably animal embryos
The Colonial Connection
The first multicellular organisms were colonies
Collections of autonomously replicating cells
Some cells in the colonies
Became specialized for different functions
The first cellular specializations
Had already appeared in the prokaryotic world
The “Cambrian Explosion”
Most of the major phyla of animals
Appear suddenly in the fossil record that was laid down during the first 20
million years of the Cambrian period
Phyla of two animal phyla, Cnidaria and Porifera
Are somewhat older, dating from the late Proterozoic
Molecular evidence
Suggests that many animal phyla originated and began to diverge much earlier,
between 1 billion and 700 million years ago
Colonization of Land by Plants, Fungi, and Animals
Plants, fungi, and animals
Colonized land about 500 million years ago
Symbiotic relationships between plants and fungi
Are common today and date from this time
Continental Drift
Earth’s continents are not fixed
They drift across our planet’s surface on great plates of crust that float on
the hot underlying mantle
Often, these plates slide along the boundary of other plates
Pulling apart or pushing against each other
Many important geological processes
Occur at plate boundaries or at weak points in the plates themselves
The formation of the supercontinent Pangaea during the late Paleozoic era
And its breakup during the Mesozoic era explain many biogeographic puzzles
New information has revised our understanding of the tree of life
Molecular Data
Have provided new insights in recent decades regarding the deepest branches of
the tree of life
Previous Taxonomic Systems
Early classification systems had two kingdoms
Plants and animals
Robert Whittaker proposed a system with five kingdoms
Monera, Protista, Plantae, Fungi, and Animalia
Reconstructing the Tree of Life: A Work in Progress
A three domain system
Has replaced the five kingdom system
Includes the domains Archaea, Bacteria, and Eukarya
Each domain
Has been split by taxonomists into many kingdoms
Cellular Tree of Life
One current view of biological diversity
Origin of Life on Earth
Origin of Life on Earth
Modern scientific perspective of transition,
inanimate matter → animate matter,
as a physical rather than a divine process.
Important steps in creation of life:
Nonbiological synthesis of organic compounds in nonoxidizing atmosphere.
Polymerization by removal of water from chemical joints of monomers.
Survival advantage of protocells that can make polymers.
Evolution of metabolic chains from back-to-front.
Natural selection for objects that have genetic apparatus (nucleic acids) for
remembering metabolic recipes that can pass down that apparatus (DNA) to
daughter cells.
Importance of sex, eukaryotic cells, and cell differentiation.
Viruses Lie at the Borderline of Life
Historical Context of Ideas
Before advent of modern science, people’s perception of living and nonliving
things were blurred: “ frogs from slime,” “maggots from decaying meat.”
Careful observation demonstrated that complex organisms always originated from
parents (e.g., maggots from flies alighting on meat).
Discovery of single-celled organisms (e.g., bacteria) and Louis Pasteur’s
(1822-1895) theories of fermentation and disease.
Pasteur’s saving of French wine industry, vaccination against anthrax, cure for
rabies.
Pasteur’s Experiment on Spontaneous Generation
Importance of Long Timescale and No Competition
Charles Darwin in 1871:
“It is often said that all the conditions for the first production of a living
organism are now present, which could ever be present. But if (and oh! What a
big if!) we could conceive in some warm little pond, with all sorts of ammonia
and phosphoric salts, light, heat, electricity, etc., present, that a protein
compound was chemically formed ready to undergo still more complex changes, at
the present day such matter would be instantly devoured or absorbed, which would
not have been the case before living creatures formed.”
A. I. Oparin (1894-1980) in Russia and J. B. S. Haldane (1892-1964) in Great
Britain stressed the important role of a non-oxidizing atmosphere.
Molecular Clues to the Origin of Life
Important Steps in Creation of Life from Inanimate Matter
Creation of small organic molecules in a nonoxidizing atmosphere via lightening
strokes, UV light, etc. (Miller-Urey experiments).
Dissolving of small organic molecules in primitive oceans to form Haldane’s warm
and dilute primordial soup. Contribution of phosphates, etc., from rocks.
Synthesis of ATP, GTP, CTP, UTP, and their deoxy counterparts dATP, dGTP, dCTP,
dTTP, as the precursors to nucleic acids. Mostly ATP.
Polymerization by nonbiological means of amino acids into proteins and of
nucleoside triphosphates into nucleic acids (RNA and DNA). Primary difficulty is
to remove water in the joints:
monomer: H-M-OH
polymer: H-M1-M2…-Mn-OH
H-M1-…-Mn1-OH + H-Mn-OH → H-M1-…-Mn-OH + H-O-H
Miller-Urey (1953) Experiments
Chicken or Egg?
Extremophiles and Archaea
A major surprise of the past three decades is the discovery of the existence of
life under extreme environments – near cracks on the ocean floor, in boiling hot
sulfur springs, and at a few km depths in the interior of the solid Earth. These
organisms derive their ultimate source of energy and nutrients from below, the
deep earth, rather than from above, sunlight.
“Extremophiles,” the generic name given such organisms, give rise to the hope
that life may exist under extraterrestrial conditions much more harsh than
believed possible previously.
Many of the single-celled organisms that belong to the category of
“extremophile” form a branch of life, archaea, distinct from the
bacteria/blue-green algae and eukarya. The relationship between these three
branches is complex, with recent research indicating considerable mixing of
genetic material among the different groups.
Nevertheless, because many of the classic arguments given earlier for a single
origin of life still holds, consensus holds that a “last universal common
ancestor” (LUCA) existed which gave rise to all these lifeforms. But it is an
open question whether LUCA originated near the surface or the deep bowels of the
Earth (or more fancifully, from extraterrestrial material brought here via
meteorites).
Martian Meteorite: LUCA?
Amoeba Engulfing a Ciliate
Conjugation: Bacterial Sex
Paramecia Dividing and Conjugating
The Emergence of Multicellular Organisms Among Eukarya
When there are predatory cells about, it pays to be as large as possible so that
you cannot be engulfed. But there exists limits on how large a single cell can
grow and still function efficiently. Solution: band together in colonies
(filamentous green algae, sponges, etc.). Not directed!
Advanced multicelluar organisms show more cell differentiation. Hallmark of
higher organisms is ability of its cells to specialize to form tissues,
different tissues to act collectively as organs, and different organs to
coordinate activities to give the entire specimen.
Traditional Tree of Life
Intelligence and Civilization
Most remarkable among the specialized cells is the nerve cell, the neuron; and
most remarkable among all organs is the brain, a hierarchical arrangement of
neurons.
The ascent of man is due in large measure to humanity’s ability to pass down,
not only inherited traits, but the accumulated knowledge and skills of society
as a whole: civilization.
How long has human culture been in existence? Only since the waning of the last
ice age, 13,000 years ago.
Power of Hierarchical Structures for Producing Complex structures
Literary world: letters of alphabet, words, sentences, paragraphs, chapters,
books.
Physical world: elementary particles, nuclei, atoms, and molecules; minerals and
rocks; continents, oceans, and atmosphere; Earth.
Biological world: elementary particles, nuclei, atoms, small molecules,
macromolecules, cells, tissues, organ systems, organisms, societies,
civilization.
Business world: organizational hierarchy, efficiency of modules for mass
production.
Number of Different Offsprings Possible in Human Reproduction
Even without crossover events in meiotic division and fertilization, the number
of different fertilized eggs and sperms potentially available to single pair of
parents is
With six billion people on Earth, the number of different possible pairings of
father and mother are
Number of Different Offsprings Possible in Human Reproduction
Thus, the number of potentially different descendants from the current pool of
human beings on Earth without mutations or crossover events is
enough to colonize every solar system in the observable universe with a
population of humans comparable to the Earth!
Whether this is desirable even if feasible is debatable. Nevertheless,
reproductive success and diversity are the power behind life and a perhaps
frightening hallmark of aggressive civilizations.
People are the product of alien-controlled cloning experiments
On Dec. 13, 1973, Vorilhon said he was walking in the Clermont-Ferrand volcanic
mountain range in France when a UFO touched down. Humanoid creatures with pale
greenish skin and almond-shaped eyes took him aboard, saying they wanted him to
be their messenger to humankind.
The aliens explained they cloned the first people 25,000 years ago. The little
green people said Vorilhon was himself a clone and that they impregnated his
mother in 1946 after the use of the first atomic bombs awakened them to
mankind's advanced scientific knowledge.
"When I told my mother and grandmother the true story, my grandmother was
relieved because she said that she had seen UFOs lingering around the house over
the years and had never told anyone," Vorilhon told the Village Voice last year
(2002).
Vorilhon, who frequently dons flowing white garments, said his mission is to
spread the word that there is no God, and that science and our alien forefathers
would set people free -- physically and sexually -- and help them live forever.
Two years after the aliens' first visit, they reappeared and took Vorilhon to
another planet where he said he met Jesus, Mohammed and Buddha. All became
immortal through cloning, he said.
Ever since, he's been preaching the message of protecting the rights of the
"unreborn" --
Jan. 2003: Raelians claim to clone first human baby
The Raelian religious cult claim that a company founded by its adherents has
cloned the first human baby.
Consider, for one moment, the objective circumstances: a crackpot cult, whose
French founder says he got his marching orders from a space alien, calls a press
conference in Miami to announce that a cloned child has been born to an
unidentified woman in an unspecified place the day after Christmas. Proof,
according to the company's CEO -- a chemist named Brigitte Boisselier -- will be
forthcoming in nine days --not 10, not eight, but nine.