Do Fermions and Bosons Produce the Same Gravitational Field?
  We examine some cosmological consequences of gravity coupling with different strength to fermions and bosons. We show that this leads to a different perturbation of the standard picture of primordial nucleosynthesis than the addition of extra neutrino types or overall scaling of the value of G. Observed abundances of deuterium and helium-4 place bounds on the ratio of the bosonic gravitational constant (G_B) to the fermionic gravitational constant (G_F) of 0.45 < G_B/G_F < 0.92 at 1-sigma, and 0.33 < G_B/G_F < 1.10 at 2-sigma. A value of G_B < G_F can reconcile the current "tension" between the abundances of deuterium and helium-4 predicted by primordial nucleosynthesis. We comment briefly on other cosmological effects. 
John D. Barrow and Robert J. Scherrer