EVOLUTION
DEFINITIONS AND EXAMPLES
Fitness: An organism’s ability to survive and reproduce in a particular environment
Gradualism: States that small evolutionary changes occur slowly and steadily over long periods of time- the process yields many transitional
forms
Punctuated Equilibrium: states that a population tends to remain relatively stable for long periods of time interrupted by periods of relatively
rapid evolutionary change- explains gaps in the fossil record
Speciation: evolving of a species
Inbreeding: crossing of genetically similar organisms to maintain the presence of certain desirable traits- tends to increase homozygous
genotypes for both desirable and undesirable traits- Ex. Purebred dogs are more likely to have joint deformities and blindness
Outbreeding (hybridization): crossing of genetically dissimilar organisms to bring together the best of both organisms- tends to increase
heterozygous genotypes and vigor (health).
Microevolution: occurs when there are relatively small-scale changes in the gene frequency of a population- may result in new phenotypes or
adaptations, but not a new species (changes within the species level)
Macroevolution: occurs when there are relatively large-scale changes in the gene frequency of a population- results in a new species (or higher
taxonomic group)
Variation: Differences that exist between members of the same species (the raw material of evolution)- Ex. Size, color, blood type
Adaptation: An inherited trait that helps an organism survive in its environment- a beneficial variation- Ex. Structural, behavioral,
physiological
Artificial Selection: selective breeding- technique that only allows those organisms with desirable traits to mate and produce the next
generation
Natural Selection: process in which organisms with favorable variations are more likely to survive and reproduce. These variations are passed
onto the next generation- Ex. Antibiotic resistance in bacteria
Population: a group of organisms of the same species that live in the same area
Radiometric dating: rock or fossil may contain elements that are radioactive. The decay (breakdown) of these radioisotopes occurs at a constant
rate and can therefore be used a geologic “time clock”. The parent isotope breaks down, through a series of steps, to form a daughter product.
Scientists use the ratio of parent isotopes to daughter product to determine how many half-lives have passed and then calculate how old the
same is. The age is given in years- A half life is the length of time it takes for exactly one-half of the parent atoms to decay to daughter atomsEx. Carbon 14 dating, Potassium 40 dating, Rubidium 87 dating, Uranium 238 and 235 dating- Axioms: the rate of decay of a radioactive
isotope is measurable and constant; the isotopes of an element appear in a mineral in precisely the same ratio as they occurred in the
environment; when an atom undergoes radioactive decay, its internal structure and chemical behavior change- Assumptions: we can determine
the amount of parent isotope present when it was formed; leaching of the parent isotope out of the rock did not occur; the daughter product was
not present when the rock formed nor was the rock contaminated by an infusion of the product- x=ln (n+)
x= number of half lives passed
____No
N+=parent isotope remaining
ln (.5)
No= parent isotope originally
ln= natural log
Stabilizing Selection: favors individuals with the intermediate phenotype (most common variation in the population) because they are more fit
than those with extreme phenotypes (less common variations in populations)- evolution is minor or absent- Ex. Weight of human infants
Directional Selection: favors individuals with an extreme phenotype because they are more fit than all the other phenotypes- evolution more in
a specific direction- Ex. Size of human brains, size of horses, color of peppered moths
Disruptive Selection: favors individuals with the extreme phenotypes that deviate in both directions from the population average. Both of the
extreme phenotypes have higher fitness than the intermediate phenotypes- evolution into 2 populations with distinct traits- Ex. Beak size in
African finches
Analogous structure: refers to the part of 2 different species that are similar in function, but not in structure- Ex. Wings of a bird and wings of a
butterfly
SCIENTISTS, etc.:
Cuvier: 1769-1832- Prominent scientist who studied fossils and was instrumental in the development of paleontology (particularly vertebrate).
He also plays a key role in proving that extinctions did occur, He believes these are a result of periodic catastrophes (revolutions). He does not
believe in evolution, he believes species are immutable (fixed and unchanging). He explains that after a catastrophe, species immigrate from
other regions to repopulate those areas. Does not go as far as to suggest new creations after each catastrophe
Bonnet: 1720-1793- (discovered parthenogenesis in aphids). Observed that fossilized organisms did not resemble modern organisms. He
supported the idea of “evolution”, however he believed that there was an “evolutionary ladder”. Bonnet believed organisms perished in
periodic, worldwide catastrophes that wiped out all life- organisms were brought back after “stepping up” a rung the “evolutionary ladder” Ex.
Apes became humans, humans became angels
Malthus- 1798 wrote an “Essay on the Principle of Populations”, Essay stated that human babies were being born faster than people were
dying. He noted that the human population could outgrow their resources, such as living space and food supply. States that factors such as war,
famine, and disease help keep population in check. Darwin will apply these principles to all organisms- not all of those born will survive, those
that survive will have to compete for limited resources
Lamarck: 1809- Believes the fossil record shows evolution has occurred and presents a theory to explain it. Theory includes Tendency Toward
Perfection, Use and Disuse, and Inheritance of Acquired Characteristics
Lyell: 1830-1833 book entitled “Principles of Geology”- Lyell studied geologic deposits and determined that geologic forces (erosion, glaciers,
etc.) showed that earth was shaped by slow, progressive changes, not catastrophic events (e.g. floods). Therefore, Earth much be millions of
years old (necessary for Darwin’s explanation of evolution)- He stressed that scientists must explain past geologic events in terms of processes
that can actually be observed today (uniformitarianism)- Although Lyell rejects the idea of evolution for most of his life, he accepts it in the
early 18h60’s and becomes a close friend and defended of Darwin
Darwin: 1809-1882- sailed on the ship HMS Beagle as its naturalist from 1831-1826. He collected numerous samples and fossils. In the
Galapagos Islands, he studied finches, tortoises, and iguanas. The diversity of these species greatly influenced his thinking on evolution. In
1859, he published the book “On the Origin of Species by Means of Natural Selection”- never uses the word ”evolution”, instead Descent With
Modification
Wallace: 1823-1913- developed a theory of evolution nearly identical to Darwin’s (“On the Tendency of Varieties to Depart Indefinitely from
the Original Type”). He sent a copy to Darwin, asked for some advice, and told him that he was going to present his theory. This motivated
Darwin to also present his research and theory to the Linnaean Society in 1858
EVIDENCE OF EVOLUTION:
Fossils: the preserved remains or traces of ancient organisms- most accurate representation of the history of life on earth, the fact that the types
of fossils present have changed over time implies that life on earth has changed over time (evolution)- many species that are alive today have
no corresponding fossils during much of earth’s history. Implies that more recent species must have evolved from older species- younger
fossils are usually more similar to modern organisms than are the older fossils. Often the fossil record shows transitional forms that reveal a
progression of evolutionary changes- the earliest fossils are all unicellular organisms and the most complex are found most recently in fossil
record- many species that were alive in the past are not alive today
Homologus Structures: compares structures found in different species that are similar in structure, but not necessarily similar in functionstructures are similar to each other because they evolved from a common ancestor for both species
Vestigial Structures: structures that have no or a reduced function in organisms- these structures evolved from an ancestor that had a greater
need for them- difficult to explain their existence without evolution
Comparative Biochemistry: compares the DNA and proteins of different species to see how similar they are- closely related species have
similar DNA because they evolved from a common ancestor- the genetic code is universal because organisms have a common ancestor- at
some point in time, chromosome number 2 combined 2 chromosomes to make the human chromosome 2. there is a remenance of telomeres.
Now humans have 23 airs, but chimps have 24
Biogeography: studies the distribution of organisms in different parts of the world- explains why regions that are separated by large physical
barriers, but that have similar environments, wound contain different species rather than the same species- this occurred because population
evolved differently in one region than they did in another
CONCEPTS:
Lamarck’s Theory of Evolution: organisms constantly strive to improve themselves and become more advanced- the effort to improve cause
the most used body structures to develop, while unused structures waste away- once a structure is modified by use or disuse, the modification is
inherited by the organism’s offspring
Darwin’s Theory of Evolution: there is variation within populations. Many variations are inherited and such traits are passed from parent to
offspring- some variations are favorable, improving the organism’s ability to function and reproduce in its environment- more young are
produced in each generation than can survive. Only a few survive long enough to reproduce (competition)- organisms that survive and
reproduce are those with favorable variations. Because the offspring of these individuals will inherit favorable variations, a larger and larger
proportion of each new generation will have these variations (natural selection)- over enormous periods of time, small changes accumulate, and
population change (gradualism).