Twenty million years ago, an ocean covered the area where the country of Panama is now located. There was a gap between the continents of North America and South America through which the waters of the Atlantic and Pacific Oceans flowed freely. The porkfish, Anisotremus sp, lived in this area between North America and South America. Fig. 8.1 shows a porkfish. [Figure 8.1] About 3 million years ago, volcanic activity and sedimentation formed a narrow strip of land, Panama, joining North America and South America. Fig. 8.2 shows the area 20 million years ago and now. [Figure 8.2] Twenty million years ago, porkfish in the Atlantic and Pacific Oceans were able to breed successfully and produce fertile offspring. Explain why Atlantic porkfish and Pacific porkfish are now not able to breed successfully to produce fertile offspring.