Grey aliens clone themselves to survive and Humans have 6 billion.

According to Sitchin, and other researchers, the mysterious ‘bag’ is some sort of box where the ancient Anunnaki deposited the so-called Water of Life”, something like a mobile Gene Bank used in their genetic experiments.
But the Ancient Anunnaki werent the only species that has visited Earth in the distant past. In addition to the Anunnaki, aliens known as the ‘Greys’ also visited Earth in the past, and are said to visit us in the present as well.
The Grey Aliens are one of the most famous aliens species in the 21st century. There are two types of Grey Aliens. The Small Greys are said to possess extremely large heads, almond-shaped eyes, and small bodies. The small greys are said to be clones of the other species known as the Tall Greys. According to ufologists and researchers, their population is in fact very small which is why they have numerous clones among them.
In the last couple of decades, researchers have come across a sheer number of evidence which points to several interesting facts:
Many nations on Earth, among them the United States of America have made several agreements with the Greys. The trade was simple: Alien technology was given to mankind and in return, governments agreed not to interfere with alien operational plans on Earth. These agreements were made in 1934, 1964 and 1972.
The Grey Aliens are said to be responsible for most of the modern-day abductions on Earth.
However, just as the Ancient Anunnaki, Grey Aliens have been visiting Earth for thousands of years. Cave paintings in the Kimberley region of nearly 5,000 years old could be the earliest depictions of the Greys ever discovered.