Answer: Steps: (They all start on the left side).
(Left side | Right side)
(3 men, 1 Gorilla, 2 Chimps | 0 men, 0 Gorilla, 0 Chimps)
-> Chimp and Gorilla (3 men, 0 Gorilla, 1 Chimps | 0 men, 1 Gorilla, 1 Chimps)
<- Gorilla (3 men, 1 Gorilla, 1 Chimps | 0 men, 0 Gorilla, 1 Chimps)
-> Chimp and Gorilla (3 men, 0 Gorilla, 0 Chimps | 0 men, 1 Gorilla, 2 Chimps)
<- Gorilla (3 men, 1 Gorilla, 0 Chimps | 0 men, 0 Gorilla, 2 Chimps)
-> Two men (1 men, 1 Gorilla, 0 Chimps | 2 men, 0 Gorilla, 2 Chimps)
<- Human and Chimp (2 men, 1 Gorilla, 1 Chimps | 1 men, 0 Gorilla, 1 Chimps)
-> Human and Gorilla (1 men, 0 Gorilla, 1 Chimps | 2 men, 1 Gorilla, 1 Chimps)
<- Human and Chimp (2 men, 0 Gorilla, 2 Chimps | 1 men, 1 Gorilla, 0 Chimps)
-> 2 men (0 men, 0 Gorilla, 2 Chimps | 3 men, 1 Gorilla, 0 Chimps)
<- Gorilla (0 men, 1 Gorilla, 2 Chimps | 3 men, 0 Gorilla, 0 Chimps)
-> Gorilla and Chimp (0 men, 0 Gorilla, 1 Chimps | 3 men, 1 Gorilla, 1 Chimps)
<- Gorilla (0 men, 1 Gorilla, 1 Chimps | 3 men, 0 Gorilla, 1 Chimps)
-> Gorilla and Chimp (0 men, 0 Gorilla, 0 Chimps | 3 men, 1 Gorilla, 2 Chimps)
And they are all safely across.