Question: We all know how an electric current causes magnetic fields. But when a single electron is flowing through the wire, how is this electron creating the magnetic field or how are electrons responsible for magnetic field around a wire?

Answer: 
The following graph indicates the amount of radiation, matter (which almost is entirely made of dark matter), and dark energy vs time. We are at a point in time where dark energy has just started to dominate. For instance, if you go back to the first few years, radiation was the most abundant source of energy.

![Density vs time](https://i.stack.imgur.com/MXiov.gif)
I the very early universe there was very little atoms. Atoms are mainly made from exploding stars. I the first pie chart there are less atoms and more photons. This is because that was the initial state and the universe. It was highly fence with photons and neutrinos going in all directions.
They will be more of all materials in the second pie chart. For matter and universe has increased in volume with starts ending and expelling larger atoms. The Higgs field continues to create matter. Its just the ratios that have changed. Its not worth put the photons and neutrinos on the second pie chart. Although there quantity has dramatically increased the ratios now are so much lower that the atom ratio.
More humility learning needs to come before your question about dark matter ratios can be answered.