Evolution Flashcards
what are the theories of evolution?
Lamarckian and Darwin’s Theory of Natural Selection
what is lamarckian evolution?
o New organs or changes to existing ones happened because of the needs of the organism
o The amount of change was thought to be based on the use or disuse of the organ
♣ This theory is based upon a flaw in the understanding of genetics
♣ Any useful characteristic acquired in one generation was thought to be transferred to the next
• An example of acquired characteristic was the long necks on giraffes
o Apparently early on, giraffes permanently stretched their necks to reach for high leaves
♣ The offspring were believed to inherit this valuable trait
o Modern genetics has disproved the theory of acquired characteristics
♣ Only changes in the DNA of the sex cells can be inherited
♣ Changes acquired during an individual’s life are changes in somatic cells
E.g. cutting off a mouse’s tail will not lead to tailless offspring
what is darwin’s theory of natural selection?
o Pressures in the environment select for the organism most fit to survive and reproduce
♣ Fitness is the ability to survive and reproduce
o Darwin concluded that a member of a particular species that is equipped with the beneficial traits can cope effectively in the immediate environment
♣ Therefore it can bear more offspring which will likely inherit the beneficial traits and the disadvantageous traits in other individuals will cause them to proliferate less
o Natural selection is the cause of this
Darwin outlined a number of agents that lead to evolutionary change–overpopulation, competiton, variation, natural selection, inheritance of variations, and evolution of a new species
describe overpopulation
• More offspring are produced than can survive
Therefore the food, air, light, and space are insufficient to support the entire population
describe variations
- Offspring naturally show variations in their characteristics
- Hugo de Vries attributed these differences to mutations in genes
- Some mutations cause beneficial variations, but most are harmful
describe competition
• The developing pop. Must compete for the necessities of life
• Many young must die
The number of adults in the population generally remains consistent from gen to gen
describe natural selection
• Some organisms/species have beneficial variation
o This confers an advantage in existing
• Therefore, they are “selected” to better survive in their environment
• This principal also described by “survival of the fittest”
describe inheritance of variations
• Those that survive (contain good variations) live to reproduce and transmit their favourable variations to their offspring
These favoured genes gradually dominate the gene pool
describe evolution of a new species
• Over many generations, the favourable genes are perpetuated in the species
• The accumulation of the changes results in a significant change in the gene pool
We can say a new species has evolved
what are the components of evolution?
speciation and local populations
what is speciation?
♣ The evolution of a new species
• Species=groups of individuals that can interbreed freely with each other but not with members of other species
• Gene flow is impossible between different species
♣ Each species evolves independently as different selective pressures act upon different gene pools
♣ Genetic variations, changes in the environment, migration to new environments, adaptation to new environments, natural selection, genetic drift, and isolation all lead to speciation
what are local populations?
♣ form within a species–called demes
E.g. all beavers along a specific portion of a river form a deme
♣ May be many demes in a species
♣ Members of one deme resemble each other more closely than they resemble members of other demes
♣ Closer genetically related
• Bc reproduction between members of that deme occurs more frequently
• They are also influenced by similar environmental factors
♣ If demes become isolated, speciation may occur
• When groups are isolated there’s no gene flow among them
• Any mutations that have arisen will remain in that isolated group
• Over time these mutations may make the isolate deme unable to reproduce with other demes
If gene pools within a species become unable to produce fertile offspring, two different species have developed or a new one has formed
what are the types of evolution?
divergent, convergent, parallel
what is convergent evolution
Two species that evolved from a different ancestor develop the same or similar traits due to same or similar environmental factors
what is parallel evolution?
♣ Similar to convergent evolution
♣ Occurs when more recent groups can be identified
♣ E.g. marsupial (pouched) animals and placental mammals are both in the class Mammalia but diverged due to geographic separation
• Descendants of the ancestral marsupial wolf, anteater, mouse, and mole developed parallel to the placental wolf, anteater, mouse, and mole
o Despite geographic separation, the marsupial and placental groups faced similar environments
Therefore they developed similar adaptations
