Who has human dignity?

The blog of British magazine The Difference has some interesting points regarding human dignity after reading the Academy of Medical Sciences' report on inter-species embryos.

Somewhat ironically, though, in making their case for proceeding with research on other kinds of hybrid and chimeric embryos, they use an argument that could equally undermine respect afforded to people who are disabled or elderly. For they argue that human "dignity arises from the qualities possessed by a creature, rather than species membership per se."

However, they do not define what these mystic "factors of form, function or behaviour" are. If we can justify excluding human rights from individuals who because of their immaturity lack certain undefined "factors of form, function or behaviour," then what is to prevent us from excluding those same rights from individuals who because of physical or mental impairment also lack those same factors?....

Or, to encroach on the abortion debate, at what point of maturity do embryos acquire the necessary "factors of form, function or behaviour" to merit their protection from needless destruction? At present, the creation and use of human embryos for research is not permitted beyond 14 days in vitro. In order to be consistent, should the time frame allowed for human embryo research be extended to 24 weeks to match that for abortions, should the time frame for abortions be reduced to 14 days to match that for in vitro experiments, or should some other compromise be reached?