  Recently, Majorana's spirit returns to modern condensed matter physics -- in
the context of topological Majorana zero mode that represents a local half
degree of freedom carrying non-Abelian statistics.In this paper, we investigate
the topological nature of a Majorana fermion by assuming that it is made up of
four Majorana zero modes at cutoff energy scale. First, we show that a pair of
Majorana zero modes can realize a $T^4=-1$ time reversal symmetry, a $P^4=-1$
parity symmetry and even a nontrivial $\overline C^4=-1$ charge conjugation
symmetry. Next, we propose a $\overline CPT$ super algebra for the Majorana
fermion made up of four Majorana zero modes. Furthermore, the origin of three
generations of neutrinos(assuming they are Majorana fermions) can be naturally
explained as three distinguishable ways to form a pair of (local) complex
fermions out of four Majorana zero modes. Finally, we compute the neutrino mass
mixing matrix and mass ratios of the three mass eigenstates from a first
principle at leading order(in the absence of $CP$ violation and charged lepton
corrections). We obtain $\theta_{12} =31.7^\circ$, $\theta_{23}=45^\circ$,
$\theta_{13}=0^\circ$ and $m_1/m_3=m_2/m_3=3/\sqrt{5}$. We predict the
effective mass in neutrinoless double beta decay to be
$m_{\beta\beta}=m_1/\sqrt{5}$.
