At present, the function of mammoth tusks is not fully understood, but it is generally believed that their length (up to five meters) and curved shape are to enable mammoths to remove debris from the ground when foraging for plants. However, some evolutionary paths eventually came to a dead end, because the ivory of some animals became too long and too heavy. Asian elephants are different from African elephants. Not all male Asian elephants have ivory, but Asian elephants with ivory are often killed by illegal hunters. Environmentalists worry that if this hunting continues, ivory elephants will disappear forever. Normally, only 50% to 60% elephants have ivory. However, researchers recently found in Sri Lanka that more than 90% elephants have no ivory, which may be related to rampant illegal elephant hunting activities. "Whether elephants can grow ivory is determined by a gene," said Gan Stojin, a protected species of WWF. Elephants with ivory have dominant genes, while those without ivory have recessive genes, which are usually passed on to the next generation. After the ivory male elephant is hunted, there is no chance to inherit the dominant gene. " Review the hottest pictures this week. Angela Zhang's new album depicts the miserable life of premature aging children. The online video of a Swedish 4-year-old drummer became famous in one fell swoop. KOLOC-Go Ara, a 0/8-year-old innocent girl, has a lovely pet turtle. Go to the knowledge gallery to see more good pictures.