[qwiz]

[h]Interactive reading: natural selection

[i]

[q] Natural selection begins with the idea of inherited variation. In any population of any species, individuals are not identical. Just go for a walk in the community that you live in, and look at your fellow human beings. On any dimension you can imagine, individuals have differences.

[q]In the case of a leaf insect, the ancestor may have been a much more generalized type of insect. And within that ancestral population, some were perhaps darker in color, while others were greener. Some were flatter, and others longer. Some had fatter legs, and others had skinnier legs.

[q]The second idea is overproduction of offspring: All species produce offspring at a rate that far exceeds the actual growth rate of that species. Here are some examples:

• Bacterial cells might reproduce themselves every 20 minutes.
• A pair of nesting robins can reproduce three times each year, and lay 3 – 5 eggs each time.
• A dandelion flower produces hundreds of winged seeds.
• A nesting female sea turtle can lay up to 100 eggs every breeding season.

Even slow breeders like elephants or grizzly bears, will, over the course of their long lives, produce more offspring than will survive to become adults.

[q multiple_choice=”true”] Overproduction applies to leaf insects, too. Guess how many eggs a typical female leaf insect lays?

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[q] And to double check the first two ideas

1. All populations have [hangman]. The type that matters in terms of natural selection is caused by [hangman] (or genes) and not by the [hangman]
2. In any population, the number of offspring born is much [hangman] than the number of adults who will survive to adulthood and successfully [hangman].

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[q]The third idea is that competition for limited resources leads to differential survival. If many are born, but few survive, what determines who survives? Some survival will be about luck or good fortune. But any offspring’s chance of surviving to adulthood is also influenced by its inherited traits. Any individual with an inherited genetic variation that gives it a survival advantage will have a higher chance of surviving the dangers of infancy and youth and making it to adulthood.

[q]Differential survival is what generates adaptation.

Compare this case of natural selection to what happens during artificial selection.

If you were a shepherd breeding sheep for their wool, you’d select those sheep in your herd with the best wool, and have them breed with one another to create the next generation. You’d prevent sheep with poor quality wool from breeding, and the most likely way you’d do that would be to kill those sheep…and eat them (or sell the meat to others). You’re literally consuming the genes for poor quality wool, while selecting for reproduction those sheep with superior wool. The effect is to reduce the frequency of the genes you don’t want (the ones for poor quality wool), while increasing the frequency of the genes that produce the trait you want (high quality wool).
In the case of the leaf insect, it’s as if the predators were the breeders. By trying to find and eat leaf insects, the leaf insect’s predators inadvertently work to create better and better camouflaged leaf insects.

[q]We’ve just seen that selection for beneficial traits between predators and prey can unleash an evolutionary [hangman] race. In this situation, an [hangman] in one population of organisms forces a counter adaptation in another population, and that feeds back to the first population.

It’s called an arms race because it’s similar to what happens between rival nations. As each one builds a bigger army, the rival is forced to counter by expanding its army. In the 1980, an arms race between the United States and the former Soviet Union led to a situation where each nation had tens of thousands of nuclear bombs aimed at the other.

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[q]Along with selection, there needs to be renewed creation of variation. This renewal of variation is caused by ongoing mutation of the genes within a population. These mutations are random, and provide the raw material upon which natural selection can act upon in each generation. Note also that populations aren’t mutating so that they can adapt. There’s no foresight to evolution, no planning. It’s just random generation of variation, followed by selection, repeating over time.

[q]Variation within a population is renewed by continued [hangman] with a population’s gene pool.

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[q]Adaptations like the camouflage of the leaf insect only come about if selection repeats in the same [hangman] for many generations.

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[/qwiz]

[qwiz]

[h] Adaptation, Artificial Selection, and Natural Selection

[i]Biohaiku

Selective pressure

Wedges pound down; many die

The most fit survive

[q] An[hangman] is a trait that helps organisms to survive or reproduce.

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[q] Adaptations that work in one [hangman] might not work in another one.

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[q] Kale, broccoli, and cauliflower are all domesticated [hangman]  that were bred from the wild cabbage, Brassica oleracea.

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[q] In selective breeding, breeders create a carefully guarded gene [hangman] that only includes organisms with a desired [hangman]

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[q] During the creation of any particular dog breed, breeders selected males and females with [hangman] phenotypes, and bred them together. The breed emerged after breeders repeated this process for many [hangman]

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[q] In animal breeding, the desired phenotype can be a particular body form, but it also might be a specific [hangman].

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[q] The co-discoverers of the process of natural selection were Charles [hangman] and Alfred Russel [hangman].

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[q multiple_choice=”true”] Adaptations arise through

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[q multiple_choice=”true”] The kind of variation that matters most for natural selection is

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[q] All populations have [hangman]. The type that matters in terms of natural selection is caused by [hangman] (or genes) and not by the [hangman]

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[q]A fact about nature is that when organisms reproduce, there’s always over[hangman] of offspring. In other words, parents produce many more offspring than can possibly [hangman].

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[q]One of the main reason why few offspring survive is [hangman] for limited [hangman].

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[q]Competition for limited resources leads to [hangman] survival. Not only will few survive, but there will be differences among the survivors. Any offspring with a phenotype that gives it an [hangman] will be more likely to survive to adulthood and reproduce.

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[q]One ironic result of natural selection is that predators produce prey that are more difficult to [hangman] upon. They do this by killing all of the prey that are [hangman] to catch. In the case of leaf insects, the survivors will be those with the best [hangman].

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[q]The dynamic that unfolds between predator and prey, or between individuals that are competing for the same resource is an evolutionary [hangman] race. Every adaptation in the predator leads to a counter [hangman] in the prey, which feeds back to the predator in the next generation.

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[q]Fill in the blanks for this summary of natural selection.

1. In every population, there’s [hangman]. The type that matters for natural selection is caused by [hangman].
2. In every species, parents produce [hangman] at a rate that exceeds that environment’s ability to support them. In other words, many are [hangman], but few [hangman].
3. Overproduction of offspring leads to [hangman] survival
4. The ones who survive will most often be those with [hangman] traits.
5. [hangman] of this process for many generations leads to [hangman]

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[q]Variation in a population is maintained by ongoing [hangman] of the genes with a population’s [hangman] pool.

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[q]Individuals don’t [hangman]. Rather, individuals are [hangman]. The thing that evolves is the [hangman].

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[q]Natural selection directly acts upon [hangman].

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[q]Natural selection is often summarized as [hangman] of the [hangman]. That last term means the individuals who have the most [hangman] success.

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[q]The criteria for fitness that a population faces within its environment can be described as selective [hangman].

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[x][restart]

[/qwiz]