  Whereas well-studied galaxies at cosmic noon are found to be baryon-dominated
within the effective radius, recent JWST observations of $z\sim6-7$ galaxies
with stellar masses of only $M_*\sim10^{8-9}\,{\rm M_\odot}$ surprisingly
indicate that they are dark matter-dominated within $r_{\rm e}\approx 1\,$kpc.
Here, we place these high-redshift measurements in the context of the TNG50
galaxy formation simulation, by measuring the central (within $1\,$kpc)
stellar, gas, and dark matter masses of galaxies in the simulation. The central
baryon fraction varies strongly with galaxy stellar mass in TNG50, and this
$M_*$-dependence is remarkably constant across $0<z<6$: galaxies of low stellar
mass ($M_*\sim10^{8-9}\,{\rm M_\odot}$) are dark matter-dominated, as $f_{\rm
baryon}(<1\,{\rm kpc})\sim0.25$. At $z=6$, the baryonic mass in the centers of
low-mass galaxies is largely comprised of gas, exceeding the stellar mass
component by a factor $\sim4$. We use the simulation to track the typical
evolution of such low-mass dark matter-dominated galaxies at $z=6$, and show
that these systems become baryon-dominated in their centers at cosmic noon,
with high stellar-to-gas mass ratios, and grow to galaxies of
$M_*\sim10^{10.5}\,{\rm M_\odot}$ at $z=0$. Comparing to the dynamical and
stellar mass measurements from observations at high redshifts, these findings
suggest that the inferred star formation efficiency in the early Universe is
broadly in line with the established assumptions for the cosmological
simulations. Moreover, our results imply that the JWST observations may indeed
have reached the early, low-mass regime where the central parts of galaxies
transition from being dark matter-dominated to being baryon-dominated.
