The connecting link between the fishes and amphibians are the:
1. Seymouria
2. Peripatus
3. Cartilaginous fishes
4. Coelocanths [lobe finned fishes]

Variation in gene frequencies within populations can occur by chance rather than by natural selection. This is referred to as 
1. Genetic flow
2. Genetic drift
3. Random mating
4. Genetic load