Natural Selection – Application of Selective Pressures

The four steps of Natural Selection identified by Charles Darwin: 1) overproduction, 2) genetic variation, 3) survival struggle, 4) successful reproduction. Larger organisms tend to produce less offspring than smaller organisms, so the examples below do not reference the overproduction mechanism of natural selection.

Key Components / Explanation / Example Giraffe / Example: Dinosaurs
1. Variation within a population / Within any population of living things their traits ______from individual to individual. / Ancestors to giraffes had different length ______. / Dinosaurs were large and small ______, there were meat and plant eaters, they lived in many different areas.
2. Environmental Challenge (selective pressure) / When the environment changes available food, shelter, or water are affected and this affects a population’s ability to ______. / The climate ______became drier and there was less and less food available. Animals which could get to food would survive, while the others could not. / There was a ______event, an asteroid hit the Earth. The asteroid caused tidalwaves and sent dust into the air which blocked the sun for months changing he climate and killing plants and animals.
3. Adaptation / The population either has variations that them a competitive ______and they survive or they do not have traits well suited to the new conditions and they die. / The giraffe ancestors with ______necks could reach food higher in the trees and were able to survive where those with shorter necks did not. / Dinosaurs were unable to adapt to the catastrophic changes taking place on Earth and this lead to one of the largest mass ______in Earth’s history.
4. Reproductive success / Living things pass on their characteristic to their ______. The longer they live the more offspring they will produce with that trait. / The giraffe ancestors with longer necks were able to live long enough to ______and their offspring also had long necks eventually evolving into giraffes as we know them today. / Dinosaurs did ______live to reproduce and they became ______.

Name: ______Date: ______Period: _____

Key Components of Natural Selection in Action

1. The Florida Pantheris an endangered species; there are less than 100 left. Because there are so few there is not much variation in the population. Humans are creating an environmental challenge by building on the land in which they live. Explain what might happen to the Florida Panther and why?

  1. What do you think can be done about the Florida Panthers?

Cockroaches in Action

The cockroach is also one of the hardiest insects on the planet, capable of living for a month without food. It can also hold its breath for 45 minutes and has the ability to slow down its heart rate. It is popularly suggested that cockroaches will "inherit the earth" if humanity destroys itself in a nuclear war. Cockroaches do indeed have a much higher radiation resistance than vertebrates, with the lethal dose perhaps 6 to 15 times that for humans. However, they are not exceptionally radiation-resistant compared to other insects, such as the fruit fly. The cockroach's ability to withstand radiation better than human beings can be explained in terms of the cell cycle. Cells are more vulnerable to effects of radiation when they are dividing. A cockroach's cells only divide once when in its molting cycle, which at most happens weekly. The cells of the cockroach take roughly 48 hours to complete a molting cycle, which would give time enough for radiation to affect it but not all cockroaches would be molting at the same time. This would mean some would be unaffected by the radiation and thus survive.

The following statements contain information regarding the roach populations;

A)Roaches that live to maturity may mate and produce offspring.

B)A population of roaches contain some pesticide-resistant roaches and some that are not resistant to pesticides.

C)Many roaches do not survive because they come in contact with pesticides

D)Roaches lay many eggs (100 per mating up to 400 in a lifetime)

  1. Which of the above statements most closely describes genetic variation?______
  2. Which of the above statements most closely describe successful reproduction?____
  3. Which of the above statements most closely describes overproduction?______
  4. Which of the aove statements most closely describes the struggle to survive?_____

Cut out the pictures and place them in the correct place in the table to illustrate the concept of natural selection in giraffes.

Cut out the pictures and place them in the correct place in the table to illustrate the concept of natural selection in giraffes.