Why can't elephants grow tusks anymore?

Vocabulary

reproduce disappear

proportion weed out

rhino civil war poaching

Trend (tendency) Ecological chain (ecological chain)

fertilized egg main current

African elephant evolution

Character Dominant gene

Sex chromosome rampant

shark fin (fin) greed (greed) academic paper

Female (female) ecological environment (ecological environment)

Column consultant/ Dr. Zhang Dake, associate researcher at the Center for Advanced Biomedical Engineering, Beihang University

Guest: Tao Yong, Director of Ophthalmology Department, Beijing Chaoyang Hospital

Produced by/ Ke Rongyi, supervised by/ He Na, coordinated by/ Wang Xiaoying

Chief writer: Zhang Zhouxiang Drawing: Vasili Intern: Duan Jiayu

Source: Tutu is the way