The African Elephant is the largest terrestrial mammal. Elephants live in tightly knit family groups led by a matriarch. The bulls remain solitary or may band together to form bachelor herds. A fully grown elephant weighs between 6,000 and 7,000 kg. When there are young in the herd the adult female may become aggressive and it is advisable not to venture too close to the herd. The majestic elephant's strength, enormous size and stature have always captured the imagination of man. Elephants have a lifespan of sixty to seventy years. Strikingly similar to those of humans are their development stages. During their lifespan, the stages of naughty and inquisitive childhood, rebellious youth, refined intelligent adulthood and proud majestic old age can be discerned. Also peculiarly humanlike, the birth of a calf is a joyous occasion for the family, with all members taking care of and fussing over the calves. Big bulls have even been observed nudging greetings to youngsters at water holes and other meeting places.