OPTION D: EVOLUTION. Origins of Life Abiogenesis – the spontaneous formation of life 19 th...
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Spontaneous Origin of Life In order for life to have begun spontaneously, there must be four conditions met first: 1. Chemical reactions would need to produce simple organic molecules (like amino acids) from inorganic molecules (like water, carbon dioxide and ammonia) 2. The simple organic compounds must be monomers that can assemble into polymers like amino acids chained into proteins. 3. Also the polymers must be able to self replicate allowing for the inheritance of characteristics 4. Development of membranes to create an internal chemistry different from its surroundings
Transcript of OPTION D: EVOLUTION. Origins of Life Abiogenesis – the spontaneous formation of life 19 th...
OPTION D: EVOLUTION
Origins of Life Abiogenesis – the
spontaneous formation of life 19th Century – Louis Pasteur
performed experiments Oldest undisputed bacterial
fossils are 1.9 billions years old in the Gunflint cherts of Ontario
Unanswered question: where did “life” come from and when exactly did it become “alive”
Spontaneous Origin of LifeIn order for life to have begun spontaneously, there
must be four conditions met first:1. Chemical reactions would need to produce simple
organic molecules (like amino acids) from inorganic molecules (like water, carbon dioxide and ammonia)
2. The simple organic compounds must be monomers that can assemble into polymers like amino acids chained into proteins.
3. Also the polymers must be able to self replicate allowing for the inheritance of characteristics
4. Development of membranes to create an internal chemistry different from its surroundings
Miller and Urey Performed experiments
on the possibility of spontaneous origins of life
Experiment recreated the conditions that probably existed on earth before life
Miller and Urey Experiment
Inside the apparatus they mixed ammonia, methane and hydrogen gases to represent the atmosphere
Electrical charges represented lightning Water was boiled and then cooled repeatedly to
represent the rain cycle After one week, the water turned into a murky
brown 15 different amino acids were found in the water
as well as other organic compounds Supported the conclusion that life could
spontaneously form
Problems with Miller and Urey
No functional proteins in any amount at all No polysaccharides in any amount No nucleic acids in any amount No lipids in any amount None of the building blocks of lipids (in any
significant amount) None of a dozen sugars used by life (in
any significant amount). . . (and what tiny amount does form, degrades in a very short amount of time)
Origins of Organic Compounds
Miller and Urey – like ideas› Suggest that organic compounds could have been
synthesized by chemical reactions in the atmosphere and water
Hydrothermal vents› There are hydrothermal vents deep in the oceans with
chemicals welling up from deep below. Some of the conditions are very odd and unique.
› Problem: these vents are usually much more destructive to organic compounds than they are likely to form them
The aliens did it› NASA scientists have some data that suggests that
organic compounds and proto-cells could have been made in space and delivered via meteorites
The Life Problem All of these theories share one major
problem – life is complicated! Modern prokaryotic cells are only as
good as the sum of its parts› Genes can’t replicate without the help of
enzymes› Proteins can’t form without RNA
Because life is so complicated, it simply couldn’t have evolved all at once› Intermediate forms must have existed in
some way
RNA – Our Solution? RNA has two significant properties that may
have allowed it to play a significant role in the origins of life: catalysis and self-replication1. RNA catalyses many chemical reactions so it’s
plausible that it functioned as an early enzyme2. RNA is capable of self-replication – one
molecule forming a template for many using complimentary base pairing
RNA was superseded by DNA billions of years ago as the genetic material and by proteins as the catalysts of life
DNA > RNA The maximum length of an RNA
molecule is about 1500 nucleotides long Causes a severe restriction on the
amount of genetic information that can be held
Origin of Prokaryotes and Eukaryotes
Membranes – super important barriers that create a separation between the internal and external environments› Had to be hydrophobic to keep water out
Early forms of life› Microsphere – similar in appearance to a
vesicle found in cells today, microspheres are simple water containing spheres
› Coacervate – the viscous, cloudy water found in the microsphere
› Protobionts – primitive cell-like structures that may have preceded living cells
Prokaryotes and the early atmosphere
Prokaryotes were the first organisms on Earth to use photosynthesis for converting organic molecules into usable energy
In photosynthesis carbon is converted into sugar with oxygen as a waste product
Oxygen concentration built up over the next 100 million years until other types of prokaryotic cells were able to begin aerobic respiration
Atmospheric Evidence Banded iron formation in
Greenland from 3.7 – 3.8 million years ago gives us evidence of oxygen in the atmosphere
This proves that prokaryotes had evolved and were producing oxygen at this point
Endosymbiotic Theory Both mitochondria and chloroplasts were
once independent prokaryotic cells that were engulfed by a larger heterotrophic cell
Instead of being digested, however, the cells were kept alive and continued to function as usual
Eventually this evolved into the eukaryotic cell
Endosymbiotic Evidence1. Mitochondria and chloroplasts grow and
divide like cells2. They each have a loop of naked DNA like
prokaryotes3. They synthesize their own individual
proteins using 70s ribosomes like a prokaryote
4. They have double membranes – something you would only expect a self sufficient cell membrane to have, and not an organelle
Eukaryotic Development Some evidence that cilia and flagella
could possibly have endosymbiotic origins, but not clear
Eukaryotic chromosomes, meiosis and sexual reproduction had to evolve in eukaryotic cells as well
Once this occurred, evolution could occur at a much more rapid pace than before› Described as “an explosion of life” on Earth
once sex finally evolved
Evolution of Species Every new individual produced by sexual
reproduction is a genetic recombination of two parents
If the mating is random, any two individuals could interbreed so technically a new individual could inherit any of the available genes in a population
The sum total of all the available genes in a population is known as the gene pool.
How many times an individual allele appears is presented in a percentage between 1.00 and 0.00. The amount of times an allele appears is known as the allele frequency
What is a species? A group of actually or potentially
interbreeding populations with a common gene pool which are reproductively isolated from other such groups
In other words – you gotta be able to make babies together or you’re kicked out of the gene pool
Problems with the definition of species
Sibling species are such that cannot interbreed but show no significant differences in appearance. This makes it very difficult for biologists to identify which species the animals really belong to.
Some species look clearly different morphologically but will still be able to interbreed
Some species always reproduce asexually so the definition of species can’t really apply
Fossils cannot be classified as species either because they can’t exactly breed for us when they’re fossils.
Ruddy duck White-headed duck Two species of ducks with obvious
morphological differences yet can interbreed
Speciation Formation of a new species
› Can be allopatric or sympatric Allopatric speciation – when members of a
species migrate to a new area forming a population that is geographically isolated
Example: Galapagos Islands tortoises, lizards or finches
Sympatric Speciation Occurs when two varieties
of a species live in the same geographic area but do not interbreed. Two forms:
1. Barriers occur that prevent reproduction from occurring altogether.
a. Behavioral isolationb. Temporal isolation
2. Barriers occur based on hybrid infertility, often due to polyploidy
Evolutionary Trends Divergent evolution – each species evolves in
different ways by becoming adapted to different ecological roles
Adaptive radiation – if species in a group diverge rapidly, one species forming many
Convergent Evolution
Organisms who find similar solutions to the same problem but are not closely related to each other
Rates of Evolution Gradualism – the idea that evolution occurs
very slowly over time Punctuated equilibrium – evolution occurs
at a slow pace but is occasionally interrupted by some sort of event that causes brief periods of major changes Supported more by the fossil record
Polymorphism When a population has two alleles of the same
gene in the gene pool it is said to be polymorphic
If one allele is gradually replacing the other, the population shows transient polymorphism› Peppered moths of England
Sometime both alleles can persist indefinitely in the gene pool. This is known as balanced polymorphism› Sickle cell anemia
HbAHbA = normal genotype, susceptible to malaria HbSHbS = resistant to malaria, has sickle cell anemia HbAHbS = best adapted in area, resistant to malaria and
free of sickle cell anemia
HUMAN ORIGINS AND EVOLUTIONBio HLMrs. Ragsdale
Full Classification of Humans Kingdom - Animalia Phylum - Chordata Class - Mammalia Order - Primata Family - Hominidae Genus - Homo Species - Homo sapiens subspecies - H. s. sapiens
Humans are primates?? Primates are an order of mammals including monkeys,
tarsiers and lemurs We share this classification because we have similar
anatomical features that are characteristic of that order Grasping limbs with long fingers with a separated opposable
thumbs Sensitive fingers with nails Mobile arms with shoulder joints that allow movement in
three planes Our arms have a shoulder girdle that allow weight to be
transferred via the arms Stereoscopic vision with forward facing eyes on a flattened
face giving overlapping fields of view Excellent hand-eye coordination Skull modified for upright posture
Anatomical and Biochemical Evidences 98% of Human and Chimpanzee DNA is
the same Fossils of human intermediate species
have been found Similarities with how we raise our youth
for a relatively long time before being considered an adult
Hominid Fossil Trends Hominids are members of the family
Hominidae Includes humans Primary feature – bipedalism Humans are currently the only species in this
family but others have existed in the past Fossils show two major trends:
Increased adaptation to bipedalism Increased brain size to body size ratio
Other Fossil Changes and Trends Enlargement of brain and taller and more
erect structure. The spike connection to the skull becomes
more central to balance centre of gravity. Pelvis changes to support organs in walking. Pelvis shorter and broader to attach walking
muscles. Legs become stronger and longer while arms
become shorter and weaker. Knee can now be fully straightened. Foot forms more of a platform and rigid
shape without opposable toe.
Hominids1. Australopithicus afarensis: 3 - 3.9 million years –
ape-like face2. A. africanus: 2.3 - 3 million years – flatter face, larger
molars for plant based diet3. A. robustus: 1.4 - 2.2 million years – very large
molars, bones and skull4. Homo habilis: 1.6 - 2.4 million years – smaller teeth
and jaw for meatier diet, first with tools, size like humans
5. H. erectus: .4 - 1.8 million years – more complex tools so meat significant part of diet and changed teeth.
6. H. neanderthensis .5 million years – larger brains and bones, larger teeth and jaw, shorter limbs for the cold
7. H. sapiens
Dating Fossils Radioisotopes – radioactive isotopes (have
different numbers of neutrons) of a chemical element As an atom of a radioactive isotope decays, it
changes into another isotope and gives off radiation
Most common radioisotope used are 14C and 40K The rate of decay varies between different
isotopes Half-life = the time taken for the radioactivity
to fall to half of its original level
Decay Curves Radiocarbon dating – the percentage of
surviving 14C atoms in the sample is measured In potassium-argon dating, the proportions of
parent 40K atoms and daughter 40Ar atoms are measured.
The age in half-lives can be deduced from the decay-curve
Half-life of 14C is 5730 years (useful for 1,ooo to 100,000 years old)
Half-life of 40K is 1250 million years old (useful for samples older than 100,000)
Decay Curve Examples
Fossil Record – as a whole Missing major portions of all species that
have ever existed – very incomplete Only a tiny portion of animals became fossils
REGARDLESS – shows how intermediate species have developed Humans => Hominid trends Horses => transition from 4 toes to only one
Horse Toes!!
Hominid Fossil Record Consists of only bones and teeth Hominid fossil record is FAR from complete –
“missing links” are still missing Small findings can lead to major changes in
theory because we don’t completely understand how we transitioned from species to species Australopithecus species shares similar
characteristics to Ardipithecus ramidus and Australopithicus afarensis
Dating of fossils of the three species suggest that they did not co-exist but form an evolutionary lineage
What spurred the evolution of man? Climate changes in Africa – transition
from a woodland to a drier, more sparse environment
Switch from tree-dwellers to land-dwellers came with the depletion of the forests
Later, Africa became cooler – advantage to groups of hominids working together to hunt, use of tools, etc
Hominid Diet Earliest hominids (Australopithecus) were
only slightly larger in body/brain size than apes. They had powerful teeth and jaws indicating a primarily vegetarian diet.
Later hominids (once Africa cooled) Homo hominids began developing tools. With this came the ability to eat meats. Transition from vegetarian to omnivorous diet.
Advantages of Eating Meat More meat = more protein = more energy Meat = more fat = more energy More meat + more fat = larger brain
capability and size
Natural selection will begin to work and favor individuals with the biggest brains and intelligence
Will also favor individuals who are able to work together
Advantages of Culture Learn to hunt and work together
Language Learn to make better tools – better
survival Learn to limit environment’s influence :
make clothing, build shelters
Cost = mature individuals take longer time to develop, bigger investment
Genetic and Cultural Evolution Cultural evolution – able to slow and even
hamper the effects of genetic evolution Language Tool making and other skills Religion and art Medicine
Genetic evolution Involves inherited differences and allele
frequencies
