Natural selection

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Across
  1. 2. A difference in color,size or patterns is what?
  2. 4. Whose work did Wallace read?
  3. 5. How many factors affect natural selection?
  4. 6. When water is unhealthy the fish have nowhere to ___
Down
  1. 1. If all offsprings survived what would happen?
  2. 3. What helps reduce the oxygen levels in water?
  3. 4. A natural process in which take place is a?