Factors of evolution

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Across
  1. 5. Interchanging of genes between population
  2. 7. Change over time
  3. 8. A naturalist which explored the Galapagos islands
Down
  1. 1. Changes that occur in DNA sequences of an organism
  2. 2. Groups of actually or potentially interbreeding populations
  3. 3. Number of offspring
  4. 4. Survival of the fittest
  5. 5. Changing of allele frequencies in random samples
  6. 6. A unit of heredity