evolve

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Across
  1. 4. Tiny internal blood pipe
  2. 5. Heavy body skeleton frame
  3. 6. Engine for body movement power
  4. 8. Long distance running power
  5. 9. Natural animal milk sugar
  6. 11. Gas for breathing and energy
  7. 12. Random genetic code change
Down
  1. 1. Natural skin sun umbrella
  2. 2. Dangerous space sun rays
  3. 3. Survival of the fittest
  4. 7. Internal blood oxygen tank
  5. 10. Heavy planet pulling force