A horizontal gene transfer expert scientist suggests multiple origins of life are possible:-http://www.annualreviews.org/doi/pdf/10.1146/annurev-genet-110711-155529-"CONCLUSION
Let's reexamine one of Charles Darwin's
famous quotes, taken from the final line in The
Origin of Species: “There is grandeur in this
view of life, with its several powers, having
been originally breathed into a few forms
or into one.” This sentence is prescient in
its acknowledgment that life might indeed
have multiple origins. Haeckel was the first to
unambiguously present the modern concept
of the tree of life originating from a common
ancestor. The tree as a pure representation
of vertical evolution was reinforced by the
introduction of Mendelian genetics, which
understandably focused on sexual reproduction
because it is the dominant form of gene flow
among modern eukaryotes. The biological
unities revealed by modern molecular biology
were interpreted as further evidence of the
existence of a common universal ancestor. But
Darwin was wise to finesse this issue because
horizontal gene flow is a recently discovered
variable that needs to be considered."-It is a long and thorough article about HGT and ends with this suggestion that to explain the lack of a genetic tree of life might be explained by HGT and multiple origins.