If only one species is considered the 'fittest', why do we still have so many variation among species?

Refer to the family pedigree shown here. in generation i, one parent is affected by the gene mutation and one parent isn't. in generation ii, all three children are affected by the gene mutation. what can you conclude about this gene mutation? a. all children born in future generations will be affected by this disorder. b. this gene mutation is a dominant disorder. c. this gene mutation is a recessive disorder. d. the generation i mother is a carrier of this gene mutation.