I recently read an article that claimed that snakes once had full arms and legs until something caused
them to genetically mutate about 150 million years ago. There are two new studies that address the
mutation of snake DNA, specifically ZRS, or Zone of Polarizing Activity Regulatory Sequence. This is the
DNA that is responsible for limb-altering change. The first study is titled, Progressive Loss of Function in
a Limb Enhancer during Snake Evolution, published in the Journal Cell. The second is Loss and Re-
emergence of Legs in Snakes by Modular Evolution of Sonic hedgehog and HOXD Enhancers, in Current
Biology.

It is interesting that the two studies used different approaches to prove the same thing. The first study
used mice. They took mice embryos and removed their ZRS DNA and replaced it with the ZRS section
from snakes. This interchange was devastating for the mice. The mice barely grew any limbs at all. This
proves that the ZRS element is absolutely necessary for the development of limbs.
The second study differentiated two sorts of snakes. Snakes closer to the base of the snake family tree,
meaning that they were closer to ancient snakes, still have vestigial legs, or tiny bones buried within their
muscles. These snakes are represented by boas and pythons. More advanced snakes, such as the viper and
cobra, have no physical traces of limb structures. In this study, research focused on a gene called hedgehog
which is essential in embryonic development. Hedgehog is also a key in limb formation. What the
researchers discovered was that that the sonic hedgehog regulators in snakes had mutated. The researchers
validated their claims by applying a DNA editing technique called CRISPR to extract the ZRS stretch in
mice embryos and replace it with the ZRS from other animals, including that of snakes. When the mice
had ZRS DNA from other animals, including fish and humans, they developed limbs, just as any normal
mice would. But, when researchers replaced it with ZRS from pythons and cobra, the limbs of mice failed
to form. In further examination of the snakes’ ZRS, researchers discovered that there is a deletion of
seventeen base pairs. They performed another experiment in which they meticulously repaired the 17 base
pairs of snakes and inserted these into mice embryos. Astonishingly, the mice grew legs.
Both studies showed that the ZRS of the DNA chain is responsible for limb development. The ZRS
component contains the DNA instruction for making limbs in humans and other legged vertebrates. This is
interesting because it is not that snakes lack the ZRS component. Rather, it is clear that their ZRS has been
altered through evolution. That the ZRS component of differing species can be interchanged and be
functional is absolutely astonishing for me because it supports an important concept expressly taught in the
Lotus Sutra.

That snakes and people had once shared limbs supports the concept of equality as is found in Chapter
two of the Lotus Sutra. As much as we may abhor snakes, we cannot deny the above data that snakes and
humans both have the ZRS gene. The second chapter of the Lotus Sutra, Hoben-pon, in essence, claims the
same thing. Hypothetically, when we disperse our bodies and minds into small bits and pieces, and analyze
them, we should be able to find components that are similar between people who we think are different
because they are of a different sex, height, weight, skin color, or demeanor. The Buddha encourages us to
see deep within people to find their commonality, thus invalidating any minor differences that we may have
on the surface.

(Rev. Eisei Ikenaga)