Editing Endosperm (section)

== Evolutionary origins ==
The evolutionary origins of double fertilization and endosperm are unclear, attracting researcher attention for over a century. There are the two major hypotheses:<ref name="Baroux_2002"/>
* The double fertilization initially used to produce two identical, independent embryos ("twins"). Later these embryos acquired different roles, one growing into the mature organism, and another merely supporting it. Thus, the early endosperm was probably diploid, like the embryo. Some [[gymnosperm]]s, such as ''[[Ephedra (plant)|Ephedra]]'', may produce twin embryos by double fertilization. Either of these two embryos is capable of filling in the seed, but normally only one develops further (the other eventually aborts). Also, most basal angiosperms still contain the four-cell embryo sac and produce diploid endosperms.
* Endosperm is the evolutionary remnant of the actual [[gametophyte]], similar to the complex multicellular gametophytes found in gymnosperms. In this case, acquisition of the additional nucleus from the sperm cell is a later evolutionary step. This nucleus may provide the parental (not only maternal) organism with some control over endosperm development. Becoming triploid or polyploid are later evolutionary steps of this "primary gametophyte". Nonflowering seed plants (conifers, cycads, ''Ginkgo'', ''Ephedra'') form a large homozygous female gametophyte to nourish the embryo within a seed.<ref name="pmid11607532">{{cite journal | vauthors = Friedman WE | title = Organismal duplication, inclusive fitness theory, and altruism: understanding the evolution of endosperm and the angiosperm reproductive syndrome | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 92 | issue = 9 | pages = 3913–7 | date = April 1995 | pmid = 11607532 | pmc = 42072 | doi = 10.1073/pnas.92.9.3913 | bibcode = 1995PNAS...92.3913F | doi-access = free }}</ref>
The triploid transition - and the production of [[antipodal cell]]s - may have occurred due to a shift in gametophyte development which produced a new interaction with an auxin-dependent mechanism originating in the earliest angiosperms.<ref name="Friedman-2009" />