  With the experimental evidences of $\overline B {}^0\to p \overline{p}$ and
$B^-\to\Lambda\overline p$ decays, it is now possible to extract both tree and
penguin amplitudes of the charmless two-body baryonic $B$ decays for the first
time. The extracted penguin-tree ratio agrees with the expectation. Using the
topological amplitude approach with the experimental results on $\overline B
{}^0\to p \overline{p}$ and $B^-\to\Lambda\bar p$ decay rates as input,
predictions on all other $\overline B_q\to {\cal B} \overline {\cal B}$, ${\cal
B} \overline {\cal D}$, ${\cal D} \overline {\cal B}$ and ${\cal D} \overline
{\cal D}$ decay rates, where ${\mathcal B}$ and ${\cal D}$ are the low lying
octet and decuplet baryons, respectively, are given. It is non-trivial that the
results do not violate any existing experimental upper limit. From the analysis
it is understandable that why $\overline B {}^0\to p \overline{p}$ and
$B^-\to\Lambda\bar p$ modes are the first two modes with experimental
evidences. Relations on rates are verified using the numerical results. We note
that the predicted $B^-\to p\overline{\Delta^{++}}$ rate is close to the
experimental bound, which has not been updated in the last ten years. Direct
$CP$ asymmetries of all $\overline B_q\to {\cal B} \overline {\cal B}$, ${\cal
B} \overline {\cal D}$, ${\cal D} \overline {\cal B}$ and ${\cal D} \overline
{\cal D}$ modes are explored. Relations on $CP$ asymmetries are examined using
the numerical results. The direct $CP$ asymmetry of $\overline B {}^0\to p
\overline{p}$ decay can be as large as $\pm 50\%$. The $CP$ asymmetries of
$\Delta S=-1$ pure penguin modes are constrained to be of few $\%$. These modes
are expected to be sensitive to New Physics contributions and are good
candidates to be added to the list of the tests of the Standard Model.
