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
what is divergent evolution?
♣ Occurs when the species with a shared ancestor develop differing traits due dissimilar environments
• Polar bears have white coats to blend in with the snow, black bears have dark coats to blend in with the wet forest environments
Over time additional changes accumulated in these bears, resulting in the inability to cross-bread and eventual speciation
what is adaptive radiation?
♣ The emergence of a number of lineages from a single ancestral species
• A single species can diverge into many distinct ones
• The differences between them are those adaptive to a distinct lifestyle, or a niche
o E.g. darwin’s finches
♣ A single species of finch underwent adaptive radiation
• Resulted in 13 separate species, some on the same island
♣ This reduced competitive pressure between species
• Helped each species to become situated in its environmental niche
