Take a lineage of microscopic marine animals known as bdelloid rotifers.Most rotifers reproduce sexually, but bdelloid rotifers abandoned sex about 100 million years ago.

• 就拿海洋中的微小动物蛭形轮虫来说，大部份轮虫行有性生殖，但是蛭形轮虫已经把性丢开约一亿年了。