Exam 1: ORIGINS OF LIFE AND EVOLUTION Flashcards
Charles Darwin’s Theories
Darwin’s theory was based on VARIATION and NATURAL SELECTION. it ecmpased the following ideas:
OVERPRODUCTION - within a pop;uation more offspring are born than possibly survive
COMPETITION - since the # of individuals in a population tends to remain constant from generation to generation, a struggle of survival suggested.
SURVIVAL OF THE FITTEST: the individuals who survive are the ones best adapted to exist in their environment due to the possession of variations that maximize their fitness
ex. industrial melanism in peppered moths (one mostly white, now 90% dark)
- H.B. Kettlwell experimanted with moths to prove the Theory of Natural Selection
REPRODUCTION - individuals that survive and then reproduce transmit these variations to their offspring
SPECIATION** - As time and generations continue adaption and perpetuated in individuals and new species evolve from cmoon ancestral species.
- factors that affect reproductive success: longevity, fertility, attractiveness, disease resistance, ability to raise offspring, and vigor. (if any of these fail, successful reproduction cannot occur)
He wrote “Orgin of Species” but his theory of natural selection DID NOT explain the GENETIC BASES FOR VARIATION.
Darwin proposed that life’s diversity arose from ancestral species through natural selection, a departure from prevailing views
The age of Earth was important for Darwin’s ideas about evolution because he thought that descent with modification occurred as a gradual, steplike process
If Earth was only a few thousand years old (as conventional wisdom suggested), there wouldn’t have been sufficient time for a major evolutionary change
descent with modification by natural selection explains the adaptions of organisms
darwin’s experiences during the voyage of the Beagle gave rise to his idea that new species originate from ancestral forms through the accumulation of ADAPTATIONS.
wallace came to the same idea.
in The Origin of Species, Darwin proposed that over long periods of time, descent with modification produced the rich diversity of life through the mechanism of NATURAL SELECTION
Darwin observed: individuals in a population vary in their heritable characteristics, organisms produce more offspring than the environment can support
Darwin inferred: individuals who are well-suited to their environment tend to leave more offspring than other individuals. Overtime, favorable traits accumulate in the population
Lamarck’s Theories
hypothesized that species evolve, but the underlying mechanisms he proposed are not supported by evidence
composed of two main ideas:
USE AND DISUSE- new organs arise according to the needs of an organism and the SIZE OF ORGANS is DETERMINED BY THE DEGREE TO WHICH THEY ARE USED
TRANSMISSION OF ACQUIRED CHARACTERISTICS-
- USEFUL CHARACTERISTICS acquired by and INDIVIDUAL during its lifetime can be TRANSMITTED TO ITS OFFSPRING. these acqureied characteristics result in species better adapted to their environment (this is obviously a theory proven wrong)
Wiesmann’s Theories
his experuemtns involded removal of tails of mice over several generations to help DISPORVE LAmarck’s Theory of the inheritance of acquired characteristics.
Hardy and Weinberg’s Theories
POPULATION - a localized group of organisms belonging to one species, is united by its GENE POOL, the aggregate of all the alleles in the population
for a population in HARDY-WEINBERG EQUILIBRIUM, the allele and genotype frequencies will remain constant if the population is large, mating is random, mutation is negligible, there is no gene flow, and there is no natural selection
Miller’s Theories
Experiments by Stanley Miller (UChicago) have stimulated that primitive Earth in the lab and resulted in the production of organic compounds
- in time, these organic molecules interacted and formed more complex organic molecules.
he’s basically saying that he did an experiment of putting inorganic substances in a container and waiting. he found that organic substances were made over a period of time
history of life on earth
3.5bya first prokaryotes (single celled)
1.8bya first eukaryotes (single-celled)
1.2bya first multicellular eukaryotes
535-525mya CAMBRIAN EXPLOSION (great increase in diversity of animal forms)
500mya colonization of land by fungi, plants, and animals
MODERN THEORY OF EVOLUTION
supports darwin’s concepts of varaition and natural selection and incorporated the genetic basis of variation in nidivudal organisms and populations.
- PRODUCING VARIATION: the genetic bases for variation within a species are provided by MUTATIONS and SEXUAL REPRODUCTION
- mutations re spontaneous and provide the raw material for evolution
- sexual reproudction involves the sorting out and recombination of genes, this producing and painting variation
- NATURAL SELECTION: involves the struggle of organisms to survive and reproduce in a given environment
- traits which are BENEFICIAL to the survival of an organism in a particular environment tend to be RETAINED AND PASSED ON to organisms, tend to DIMINISH IN FREQUENCY from gerentation to generation.
- if environmental conditions change, traits that were formerly associatedwith a low survival value may, in a new environment, have greater survival value and may increase accordingly
ex.
- roaches, mosquitoes and houseflies resitant to insecticides (resistance is not in response to the insecticide, the insecticide acts as a selecting agent) (the bugs survived bc the insecticide did not kill them)
- penicillin resistance strains of microorganisms
heterotroph hypothesis
by A.I. Oparin
is an explanation for how early life forms may have developed on the primitive Earth
according to this hypothesis, the first life forms were NOT ABLE to synthesize their own organic nutrients from inorganic compounds
all the evidence for evolution
organisms share characteristics b/c of common descent (HOMOLOGY) or b/c natural selection affects independently evolving species in similar environments in similar ways (CONVERGENT EVOLUTION)
fossils show that past organisms differed from living organisms, that many species have become extinct, and that species have evolved over long periods of time; fossils also document the evolutionary origin of new groups of organisms
evolutionary theory can explain some biogeographic patterns
EVOLUTION (biological evolution)
1. EVOLUTION is a process of change over time
EVOLUTION THEORY
1. EVOLUTION THEROY is a unifying principle for the biological sciences. It provides an explanation for the differences in structure, function, and behavior among life forms.
2. Evolution includes the change in characteristics of populations through generations. Thus, existing life forms have evolved from earlier life forms
3. observations supporting the theory of evolution can be made through the study of the GEOLOGIC RECORD AND COMPARATIVE STUDIES in the field of cytology, biochemistry, anatomy, and embryology.
geographic isolation
GEOGRAPHIC ISOLATION favors speciation by segregating a small group from the main population. chanfges in gene frequencies are more likely in small populations than in large populations.
in time, this isolated population may evolve into separate species due to the following factors:
- it may have possessed different initial gene frequencies than the main population
- different mutations occur within the main population and the isolated population
- different environmental factors, and this, different selection pressures, may be acting on each population
ex. include Darwin’s Finches in the Galapagos Islands (tree finches and ground finches bc of beak size) and Marsupials in Australia (kangaroos)
reproductive isolation
REPRODUCTIVE ISOLATION LEADS TO SPECIATION
Two types:
- Prezygotic mechanisms (before fertilization of egg)
- postsygotic mechanisms (after fertilization of egg)
speciation
when a species inbreeds and cannot breed with a different species anymore, it can only breed fertile offspring amongst itself
3 TYPES OF SPECIATION:
allopatric speciation - involves two separated populations of the same species. over long periods of time, with differing environmental factors, geographically or spatially separated from one another, these demes (a subdivision of a population consisting of closely related plants or animals typically breeding mainly within the group) could evolve into different races or subspecies, and eventually species. They will differ slightly in the frequency of inheritable traits. These divergent populations could be reproductively isolated and not breed together.
sympatric speciation - involves instantaneous occurrence of reproduction isolation of two ports of the same population living the same area
ex. polyploidy (many chromosomes) plants (extra sets of chromosomes) new plants could cross with each other but not parent species. Therefore a new species is formed.
parapatric speciation - involves two related populations living in separate but adjacent geographical regions not separated by geographic barrier. Populations remain in contact at their borders but selection for divergence is strong and gene flow between the populations is weak. This can result in divergence of traits and reproductive isolation while the populations remain in contact.
natural selection and all it encompasses
in natural selection, individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits
Why Natural Selection Cannot Fashion Perfect Organisms:
1. Selection can act only on existing variations
2. Evolution is limited by historical constraints
3. Adaptations are often compromises
4. Chance, natural selection, and the environment interact
One organism had greater RELATIVE FITNESS than another organism if it leaves more fertile descendants.
The modes of natural selection differ in their effect on phenotype:
Directional selection (as the population goes down the evolved population goes up); Disruptive selection (as the population goes up then back down, the new population goes down then back up); Stabilizing selection (the population goes up and then back down, the evolved population goes higher than back down)
unlike genetic drift and gene flow, natural selection consistently increases frequencies of alleles that enhance survival and reproduction, thus improving the degree to which organisms are well-suited for life in their environments
SEXUAL SELECTION can result in secondary sex characteristics that can give individuals advantages in mating
BALANCING SELECTION occurs when natural selection maintains two or more forms in a population
there are constraints to evolution: natural selection can act only on available variation; structures result from modified ancestral anatomy; adaptations are often compromises; and chance, natural selection, and the environment interact.
atmospheric conditions in the primitive Earth
raw materials: it is assumed that the primitive earth was an EXCEPTIONALLY HOT body consisting of inorganic substances in solid, liquid, and gaseous states, which a rich supply of energy in the environment
matter: water condensing and falling as rain, carried dissolved atmospheric gases (AMMONIA, METHANE, and HYDROGEN) (NH3+, CH4, H) and minerals into the seas, forming a “HOT THIN SOUP”
energy sources: in addition to heat, energy in the form of LIGHTNING, SOLAR RADIATION (including x-rays and UV rays), and RADIOACTIVE MATERIALS in the rocks, provided an energy rich environment
synthesis: energy from the environment contributed to the formation of chemical bonds among the dissolved proteins in the “HOT THIN SOUP OF THE SEAS”
- this type of synthesis led to the formation of ORGANIC MOLECULES SUCH AS SIMPLE SUGARS AND AMINO ACIDS
- Experiments by American biologist, SIDNEY FOX, have demonstrated interactions among these organic molecules. using supplies of amino acids she formed proteins through non-biological processes
interpreting graphs, diagrams, and family trees plus charts
genetics
GENETIC DRIFT, chance fluctuations in allele frequencies over generations tend to reduce genetic variation
GENE FLOW, the transfer of alleles between populations, tends to reduce genetic differences between populations over time
Describe how over-reproduction and heritable variation relate to evolution by natural selection
all species have the potential to over-reproduce– that is, to produce more offspring than can be supported by the environment. this ensures that there will be what Darwin called a “struggle for existence” in which many of the offspring are eaten, starved, diseased, or unable to reproduce for a variety of other reasons. members of a population exhibit a range of heritable variations, some of which make it likely that their bearers will leave more offspring than other individuals (for ex. the bearer may escape predators more effectively or be more tolerant of the physical conditions of the environment). Overtime, natural selection resulting from factors such as predators, lack or food, or the physical conditions of the environment can increase the proportion of individuals with favorable traits in a population (EVOLUTIONARY ADAPTATION).
summarize the different lines of evidence supporting the hypothesis that cetaceans descended from land mammals and are closely related to even-toed ungulates
the hypothesis that cetaceans originated from terrestrial mammals and are closely related to even-toed ungulates is supported by several lines of evidence. for ex. fossils document that early cetacean had hind limbs, as expected for organisms that descended from a land mammal; these fossils also show that cetacean hand limbs became reduced overtime. Other fossils show that early cetaceans had a type of ankle bone that is otherwise found only in even-toed ungulates, providing strong evidence that even-toed ungulates are the land mammals to which cetaceans are most closely related. DNA sequence data also indicate that even-toed ungulates are the land mammals to which cetaceans are, most closely related.
ungulates
mammals with hooves
primitive life forms
nutrition: some of the large, complex molecules formed aggregates. these aggregates probably incorporated molecules from the seas as “food”, thus carrying on HETEROTROPHIC NUTRITION
reproduction: in time, as these aggregates become INCREASINGLY COMPLEX and HIGHLY ORGANIZED, the ability to reproduce evolved. these aggregates are considered to have been alive when they developed the ability to reproduce.
spontaneous generation or ABIOGENESIS
is the early belief that organisms could arise spontaneously out of “thin air”
TF ancient Egyptians thought that life formed from “mud” along the Nile
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Greek Philosopher Aristotle thought that an “Active Principle” was
responsible for life and this was in the mud.
other ideas from this time were that fleas and live came from sweat, mice from garbage, and flies from decaying meat
Jan Baptista van Helmont
performed an experiment putting wheat grains in a sweaty shirt, after 21 days the wheat was gone and mice were present
poorly controlled experiment gained acceptance from the scientific community at this time
Francesco Redi
did an experiment that DISPROVED the idea of spontaneous generation
it was “known” that meat lying out on the table often “formed maggots”. his experiments placed meats in different open containers. as the flies came and went, maggots appeared. these maggots formed pupas, which of course, turned into flies.
he had one open jar of meat, one closed, and one open with a see-through fabric thing over it. he saw that the closed jar did not have maggots or flies in it, but the others did.
Anton van Leeuwoenhoek
invented his microscope in the mid-1600s, he started observing microorganisms in drops of pond water
1745, John Needham
performed experiments to reinforce the belief in spontaneous generation in microorganisms.
he boiled “for a SHORT time” broth of corn, chicken, and lamb, to kill any organisms and than sealed the containers. after several days, he observed them full of microorganisms
Lorenzo Spallanzani
repeated the experiments of John Needham correctly by boiling the broth for a LONGER PERIOD OF TIME. this killed ALL the organisms and disproved Needham’s work
the two argued fiercely and the debate continued
Louis Pasteur
set out to disapprove the theory of spontaneous generation
he stated that microorganisms and their spores were present in the air and became active, and reproduced when they entered a nutrient-rich broth
”s” shaped flask prevented contamination by the air and the broth remained sterile and void of life until the flask was tipped and the broth came in contact with the air in the flask’s contaminated neck
- this contaminated broth grew microorganisms, finally putting an end to the greater debate on spontaneous generation
Curier
studied fossils but denied that evolution occurs; he proposed that sudden catastrophic events in the past caused species to disappear from an area
Hutton and Lyell
thought that geologic change could restart from gradual mechanisms that operated in the past in the same manner as they do today
Heterotroph to Autotroph (primitive life)
- it is thought that these heterotrophs evolved a PATTERN OF RESPIRATION similar to the ANAEROBIC PROCESS of FERMENTATION
- extended periods of fermentation activity by these organisms added quantities of CARBON DIOXIDE in the Earth’s environment
- some HETEROTROPHS evolved a means of using the CARBON DIOXIDE to SYNTHESIZE ORGANIC COMPOUNDS; these were the first PIONEER AUTOTROPHS
genetic variation
refers to genetic differences among individuals within a population
TF nucleotide differences that provide the basis of genetic variation originate when mutation and gene duplication produce new alleles and new genes.
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Mendel’s Laws
Dominance; Segregation; Independent Assortment
TF new genetic variants are produced rapidly in organisms with short generation times.
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TF in sexually reproducing organisms, most of the genetic differences among individuals result from CROSSING OVER, the INDEPENDENT ASSORTMENT OF CHROMOSOMES, and FERTILIZATION.
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typically, most of the nucleotide variability that occurs within a genetic locus does not affect the phenotype, explain why.
much nucleotide variability at a genetic locus occurs within introns.
nucleotide variation at these sites typically doesn’t affect the phenotype b/c introns do not code for the protein product of the gene.
there are also many variable nucleotide sites within exons.
however, most of the variable sites within exons reflect changes to the DNA sequence that do not change the sequence of amino acids encoded by the gene (and hence may not affect the phenotype).
effects of genetic drift
- genetic drift is significant in small populations
- genetic drift can cause allele frequencies to change at random
- genetic drift can lead to a loss of genetic variation within populations
- genetic drift can cause harmful alleles to become fixed
would two small, geographically isolated populations in very different environments be likely to evolve in similar ways?
it is unlikely that the two such populations would evolve in similar ways since their environments are very different, the alleles favored by natural selection would probably differ between the two populations.
although genetic drift may have important effects in each of these small populations, drift causes unpredictable changes in allele frequencies, so it is unlikely that drift would cause the populations to evolve in similar ways.
both populations are geographically isolated, suggesting that little gene flow would occur between them (again making it less likely that they would evolve in similar ways)
