That’s the case for most species.

As a very specific and highly functional example of critical viral proteins in other organisms, there wouldn’t be any placental mammals without viruses. https://en.m.wikipedia.org/wiki/Placenta

Mammalian placentas probably first evolved about 150 million to 200 million years ago. The protein syncytin, found in the outer barrier of the placenta (the syncytiotrophoblast) between mother and fetus, has a certain RNA signature in its genome that has led to the hypothesis that it originated from an ancient retrovirus: essentially a virus that helped pave the transition from egg-laying to live-birth.