Charles Darwin and Natural Selection
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500 years ago, most people thought that their natural surroundings changed very little and life forms were thought to be ________.
What does 'immutable' mean?
Unchanged and unchanging
Strong evidence of a changing Earth began with careful examination of ________.
Who was the dude that pondered the nymerous seashell remains he found high in the Tuscany mountains, far away from any nearby sea? When did this happen?
Leonardo da Vinci, end of the 15th century
What did the seashell remains in the Tuscany mountains convince Leonardo da Vinci of?
That the old shell deposits had been formed in an ancient ocean and that the Earth's surface had changed dramatically over time.
What is the systematic study of fossils called? When did it start? Who started it?
Paleontology, began in the 18th century, started by Baron Georges Cuvier
What is Cuvier's theory of catastrophism?
Numerous global catastrophes in the past had repeatedly caused the extinction of species that were then replaced by newly created forms.
Cuvier's theory of catastrophism was flawed because, although it could account fo rthe fossils of new species being found above fossils of extinct species in the same location, (....).
...it could not account for the trend towards increasing complexity of species.
Who was James Hutton? When did he propose his theory?
Scottish geologist, proposed his theory of actualism in 1795
What theory contrasted Cuvier's catastrophism?
James Hutton's theory of actualism
What does James Hutton's theory of actualism state?
The same geological processes occuring in the present also occurred in the past.
Who was the one to build on Hutton's ideas? When was this? What was the theory called?
Sir Charles Lyell built on Hutton's ideas, developed his theory of uniformitarianism in 1830.
What does Sir Charles Lyell's theory of uniformitarianism state?
The theory that earth's surface has always changed and continues to change through similar, uniform, and very gradual processes.
The work of Hutton and Lyell led to two significant conclusions:
- 1. Earth must be imaginably old
- 2. Dramatic change could result from small gradual changes occurring over very long periods of time.
Who was a leading naturalist in the second half of the 18th century?
What did Georges Buffon propose?
The idea that species can change over time and these changes could lead to new organisms.
Who was Carl Linnaeus?
The founder of biological nomenclature.
What did Carl Linnaeus propose?
The theory that relatively few species formed new species through hybridization and interbreeding.
Who was Erasmus Darwin?
Grandfather of Charles Darwin
What did Erasmus Darwin propose?
The idea that all life on earth originated from a single source; believed that humans and primates were closely related.
Who was Jean de Lamark?
The first prominent biologist to recognize the key role played by the environment in evolution.
What did Jean de Lamark reason?
For species to survive over long periods of time, they must adapt to a changing environment.
What theory did Lamark develop?
Lamark developed the theory of inheritance of acquired traits.
What does the theory of inheritance of acquired traits state?
Changes acquired by an organism, as a result of adaptation to changing environmental conditions, could be inherited by future generations.
What is an example of the theory of inheritance of acquired traits?
One generation of giraffes might have had to strive to obtian food higher in trees, so that, over their lifetime, continual stretching might have led to a slightly longer neck. It was a beneficial phenotype that became an acquired trait that was passed onto future generations.
Name the 7 historical evolutionary theories (those which are available) and their creators in order.
- Baron Georges Cuver - Catastrophism
- James Hutton - Actualism
- Sir Charles Lyell - Uniformitarianism
- Georges Buffon
- Carl Linnaeus
- Erasmus Darwin
- Jean de Lamark - Inheritance of Acquired Traits
What is natural selection?
The process by which heritable traits that make it more likely for an organism to survive and reproduce become more common over successive generations.
Natural selection acts on the ________ of organisms, but any ______ which gives an organism a reproductive advantage will ________ in frequency over the following generations. Over time, this process could result in _________ that specialize organisms for particular ecological niches and may eventually result in the emergence of a new _______.
phenotypes, allele, increase, adaptations, species
In evolution by natural selection, how is the fitness of an individual measured?
By how reproductively successful its offspring are in the next generation
Evolution by natural selection requires (4):
- a) Variation - members of a population must differ from one another
- b) Inheritance - these differences must be heritable
- c) Differential adaptedness - the organisms that are best adapted get to reproduce more often
What concept is central to natural selection?
Explain survival of the fittest.
Individuals who are more fit have a better potential for survival, fit being, how successful the organism is at reproducing.
What are the 3 types of natural selection?
- Stabilizing selection
- Direction selection
- Disruptive selection
What is stabilizing selection?
A type of natural selection that favours the intermediate phenotype.
With stabilizing selection, (...) + example
the intermediate phenotype is favoured (higher in numbers) and the extremes are selected against. ie. birth weight in humans
What is directional selection? +Example
Type of natural selection that favours one extreme (the curve shifts in that direction.) ie. eohippus to equus
The phenotypic shift in directional selection usually occurs when...
a population is adapting to a changing environment.
What is disruptive selection? +example
Type of natural selection that favours both extremes and selects against the intermediate phenotype. ie. African finches
What are the two case studies that provide evidence of natural selection explaining microevolution?
- Sickle-Cell Anemia
- Industrial Melanism
Sickle Cell Anemia
- Hereditary disease affecting hemoglobin molecules in the blood
- Disease soon found to be common among American blacks
- The allele is present in 8% of the American black population, and less than 1% in the American white population
- The allele in Central Africa can reach 46%
- People who are heterozygous for sickle cell are much less susceptible to malaria, one of the leading causes of illness and death in the areas where the allele is common
- As Darwin's theory predicts, it is the environment that acts to maintain the sickle-cell allele at high frequency
- Basically: the allele is an advantage in Central Africa
What is industrial melanism?
A phrase used to describe the evolutionary process in which initially light-colored organisms become dark due to natural selection.
Describe the peppered moths situation
- Until the mid-nineteenth century, almost every individual of this species that was captured had the light-colored wings. From that time on, the individuals with dark-colored wings increased in frequency in the moth populations near industrialized centers
- It was soon noticed that in industrialized regions where the dark moths were common, the tree trunks were darkened almost black by the soot of poppultion, and the dark moths were much less conspicuous resting on them than were the light moths
All cases of microevolution share the same main characteristic:
Changes in allele frequencies occur because certain alleles are favoured in a changing environment and other alleles (the deleterious alleles) will decrease in numbers.
In every case, it is the __________ that dictates the direction and extent of the change.
members of groups or populations that do not interbreed with other populations under natural conditions
How can species be differentiated on a biological basis?
By identifying their reproductive isolating mechanisms.
What are reproductive isolating mechanisms?
Any behavioural, physical, or biochemical factors that prevents different species from reproducing.
What are the two main types of reproductive isolating mechanisms?
- Prezygotic mechanisms
- Postzygotic mechanisms
Define prezygotic mechanisms
Reproductive isolating mechanisms that prevent interspecies from mating and fertilizating, thereby maintaining species isolation.
Name the six types of prezygotic mechanisms.
- Geographic Isolation
- Ecological Isolation
- Temporal Isolation
- Behavioral Isolation
- Mechanical Isolation
- Gametic Isolation
Define geographic isolation + example
Occurs when species do not exist together in the same place. ie. moose and zebra live on different continents and will never mate
Define ecological isolation + example
Even if two species live in the same place, they may reside in different habitats within that environment. ie. frogs do not mate with toads because although they live in the same forest, frogs live near water while toads live inland.
Define temporal isolation + example
Occurs when member sof different species breed at different times or different seasons. ie. several species of frogs live together in the same pond, however, they will not breed together because their mating seasons do not coincide.
Define behavioral isolation + example
Different species do not mate with members of other species because they are not attracted to the elaborate courtship displays. ie. male bearded dragons attract females by head bobbing and push ups. This will not attract females of different species.
Define mechanical isolation + example
Occurs when structural differences exist that prevent mating from occuring (like structures of male and female reproductive organs may be incompatible) ie. flowers of a different species cannot be pollinated by another species due to structural differences
Define gametic isolation + example
Occurs when there is a prevention of fusion between gametes. ie. on coral reefs, where external fertilization often occurs, sperm and egg of the same species are attracted to each other by specific biochemical markers.
Define postzygotic mechanisms
Reproductive isolating mechanisms that prevent hybrids from reproducing
What are the three types of postzygotic mechanisms?
- Zygotic mortality
- Hybrid Inviability
- Hybrid Inferitlity
Define zygotic mortality + example
No fertilized zygotes or embryos develop to maturity. "Baby" is never born. ie. hybridization between sheep and goats usually produce embryos that die in early stages of development.
Define hybrid inviability
Hybrids are born but are unlikely to live long
Define hybrid infertility + example
Offspring of different species are likely to be born and live, but they will be sterile. ie. hybrid of a horse and donkey, a mule, is sterile.
What are the two types of speciation?
- Georgraphic isolation
- Reproductive isolation
What is speciation
Occurs when one species gives rise to two species
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