"Dark matter was invoked decades ago to explain why galaxies hold together. Given regular matter alone, galaxies might never have formed, and today they would fly apart. So there must be some unknown stuff that forms invisible clumps to act as gravitational glue. Dark energy hit the scene in the late 1990s when astronomers discovered the universe is not just expanding, but racing out at an ever-faster pace. Some hidden force, a sort of anti-gravity, must be pushing galaxies apart from one another in this accelerated expansion.
K-essence (kinetic-energy-driven quintessence) changes behavior over time in Scherrer’s (theorist) model, clumping early on to help form galaxies, and now forcing the universe apart. Right now, dark matter has a density that decreases as the universe expands, he explained, while dark energy has a density that stays constant as the universe expands.
There is one glaring problem with the idea, which Scherrer admits to. It implies that we live at a very special moment in time when the energy densities of dark matter and dark energy are roughly equal. Scientists hate coincidences.

Britt, Robert Roy. Dark Matter and Dark Energy: One and the Same?
July 12, 2004. Space.com - Science
I like the comment about scientists hating coincidences. There are so many coincidences in nature that forces our common sense to acknowledge the existance and presence of God.