As we know it:
If someone were to tell you that roughly 100 million years ago, our ancestors were infected by parasitic DNA, which copied and pasted itself throughout their genomes—and that this was linked to the evolution of modern human pregnancy—you might assume they were channeling early L. Ron Hubbard. But this week, in the prestigious journal Nature Genetics, researchers provide evidence for such a theory. Seeking to explain how our ancestors developed a more advanced kind of gestation—including the ability to carry fetuses in the womb until they reached a more developed state—scientists studied the uterine cells of three contemporary mammals. Specifically, they compared opossums (whose young develop largely in pouches) to armadillos and humans (whose offspring spend more time in the womb). They concluded that rogue DNA, which probably arrived by way of a virus or bug, was associated with wild new horizons in baby-making.
The Dish 