Darwin &Evolution
Darwin &Evolution
Topic 1 Evolution and Natural Selection Charles Darwin (1809 - 1882) Cousin of Galton 1831 - took a position as naturalist on the HMS Beagle - Was surprised by the variety of species found. e.g., Galapagos Islands Finches and Hawaiian Sicklebills Important Influences 1. Malthus [Malthusian principle] 2. Lyell’s Principles of geology. Which argued that the history of the world was the result of natural laws. 3. The domestic breeding of animals 4. His observations on the Galapagos and other Islands.
1
Law of natural selection “The differential contribution of offspring to the next generation by individuals of different genetic types but belonging to the same population.” Elements of the modern theory (David McFarland) 1. There is considerable variation within a species. 2. Much of this variation is genetically inherited. 3. More individuals are born to each generation than can survive.
2
The notion of Adaptiveness 1. A trait is adaptive if it increases the likelihood that the offspring of the individual having it will survive (reproductive fitness). 2. “Survival of the fittest”. 1. Does not always mean the strongest but means most fit for the ecological niche e.g., European Red Squirrel v. North American Grey Squirrel When the North American Grey Squirrel was introduced to Britain it gradually replaced the indigenous Red Squirrel. However there is a line across Scotland where an equilibrium is reached. Here the tree habitat becomes thinner and food more scarce so the red squirrels have an advantage.
3. Empirical evidence for the adaptiveness of a trait and natural selection. Industrial melanization of the peppered moth (Biston bitularia) Kettlewell (1955 and 1973)
3
a. Light moths like to land on light backgrounds and vice versa. b. Large numbers of light and dark moths were released in a non industrial oak forest (with light tree trunks). Birds got 194 black ones and 26 light ones.
Adaptiveness and natural selection is an economic theory Traits will be selected for which minimize energy expended or risk taken and maximize gain. In this sense gain usually mean survival of the individual and more specifically reproductive fitness. e.g., Sexual selection Darwin - Traits will evolve which appear to have no function and seem to increase the animal’s risk of predation. - These traits do help in the competition for mates.
4
Empirical support for Sexual Selection Many evolutionary explanations lack independent support and are hence circular. -One notes a trait that appears in one sex or the other. -Then notes it appears to have no function. -But it exists so it must have been selected for. -And it exists in only one sex … So let’s try to get some empirical support for at least part of the assumption. -Namely that the trait increases reproductive fitness. African Paradise Bird Experiment: 1. cut piece out of some birds’ tails. 2. Glue into other animals’ tails. 3. Let loose and measure reproductive success.
Number of Nests per Male
2 Tail Length
1.5
1
0.5
0 SHORT
NORMAL
LONG
Tail Length of Males
Result: Animals with longer tails were more successful in attracting mates to their territories.
5
This is not a complete experiment because it doesn’t measure the economic cost of the longer tail. If an even longer tail doesn’t cost why not have it? Well because it might increase predation risk …. And so on
A few terms to remember Niche or Ecological Niche. The range of each environmental variable (e.g., temperature, humidity, predation, food type and supply) in which a species can exist and reproduce. Divergent evolution. Trait with very different function have a common evolutionary ancestor. e.g., Scales and feathers Convergent evolution Traits with a common function but a different ancestor e.g., the Panda’s thumb.
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Topic 1 Evolution and Natural Selection Charles Darwin (1809 - 1882) Cousin of Galton 1831 - took a position as naturalist on the HMS Beagle - Was surprised by the variety of species found. e.g., Galapagos Islands Finches and Hawaiian Sicklebills Important Influences 1. Malthus [Malthusian principle] 2. Lyell’s Principles of geology. Which argued that the history of the world was the result of natural laws. 3. The domestic breeding of animals 4. His observations on the Galapagos and other Islands.
1
Law of natural selection “The differential contribution of offspring to the next generation by individuals of different genetic types but belonging to the same population.” Elements of the modern theory (David McFarland) 1. There is considerable variation within a species. 2. Much of this variation is genetically inherited. 3. More individuals are born to each generation than can survive.
2
The notion of Adaptiveness 1. A trait is adaptive if it increases the likelihood that the offspring of the individual having it will survive (reproductive fitness). 2. “Survival of the fittest”. 1. Does not always mean the strongest but means most fit for the ecological niche e.g., European Red Squirrel v. North American Grey Squirrel When the North American Grey Squirrel was introduced to Britain it gradually replaced the indigenous Red Squirrel. However there is a line across Scotland where an equilibrium is reached. Here the tree habitat becomes thinner and food more scarce so the red squirrels have an advantage.
3. Empirical evidence for the adaptiveness of a trait and natural selection. Industrial melanization of the peppered moth (Biston bitularia) Kettlewell (1955 and 1973)
3
a. Light moths like to land on light backgrounds and vice versa. b. Large numbers of light and dark moths were released in a non industrial oak forest (with light tree trunks). Birds got 194 black ones and 26 light ones.
Adaptiveness and natural selection is an economic theory Traits will be selected for which minimize energy expended or risk taken and maximize gain. In this sense gain usually mean survival of the individual and more specifically reproductive fitness. e.g., Sexual selection Darwin - Traits will evolve which appear to have no function and seem to increase the animal’s risk of predation. - These traits do help in the competition for mates.
4
Empirical support for Sexual Selection Many evolutionary explanations lack independent support and are hence circular. -One notes a trait that appears in one sex or the other. -Then notes it appears to have no function. -But it exists so it must have been selected for. -And it exists in only one sex … So let’s try to get some empirical support for at least part of the assumption. -Namely that the trait increases reproductive fitness. African Paradise Bird Experiment: 1. cut piece out of some birds’ tails. 2. Glue into other animals’ tails. 3. Let loose and measure reproductive success.
Number of Nests per Male
2 Tail Length
1.5
1
0.5
0 SHORT
NORMAL
LONG
Tail Length of Males
Result: Animals with longer tails were more successful in attracting mates to their territories.
5
This is not a complete experiment because it doesn’t measure the economic cost of the longer tail. If an even longer tail doesn’t cost why not have it? Well because it might increase predation risk …. And so on
A few terms to remember Niche or Ecological Niche. The range of each environmental variable (e.g., temperature, humidity, predation, food type and supply) in which a species can exist and reproduce. Divergent evolution. Trait with very different function have a common evolutionary ancestor. e.g., Scales and feathers Convergent evolution Traits with a common function but a different ancestor e.g., the Panda’s thumb.
6
