Natural Selection

1
Natural Selection

• The scientific theory that explains evolution

2

• 1) Species produce more offspring than can
  survive
• Giraffes can produce one offspring every 2 years
  for 20 years. So, each female can produce 10
  offspring in her lifetime.

3

• 2) Variations exist within a species.
• No two giraffes are exactly alike.

4

• 3) There is a struggle to survive.
• One of the giraffes predators is the hyena.

5

• 4) The environment exerts selective pressures on
  individuals.
• The environment changed so that the giraffes
  food is primarily in the trees. The giraffes born
  with longer necks could reach the food in the
  trees.

6

• 5) The organisms that have inherited favorable
  traits survive and reproduce.
• Giraffes with longer necks survive and passed the
  trait on for longer necks to their offspring.
  Giraffes with shorter necks died out.

7

• 6) Overtime, the population changes. Populations
  evolve, individuals do not.
• Eventually, all the giraffes are born with long
  necks.

8
(No Transcript)