Ben Kiernan Defines Genocide
Well, I believe that the international law does cover crimes against humanity, which could be committed against social or political groups who aren't technically covered by the Genocide Convention. And war crimes, also, do cover many of the cases that some might consider genocide but aren't legally genocide under the Convention.
My view is that genocide is a more serious crime even than other crimes against humanity. It is a crime against humanity, but it's an aggravated crime against humanity. It's necessary for a case of genocide to prove the intent to kill in whole or in part in order for a verdict of genocide to be reached. So therefore, it's a very difficult case to prove, and therefore it's a more serious crime than other crimes against humanity. But they are very serious, also.
Well, there hasn't been enough legal investigation, because the Genocide Convention was never implemented for so long after its initial passing by the United Nations General Assembly in 1948, and then its slow ratification -- for instance, the United States didn't ratify it until 1988, and it wasn't until the 1990s that it was implemented as international law with the Bosnian and Rwandan International Criminal Tribunals.
And so there hasn't been enough discussion in the legal literature and judgments based on legal reasoning to determine any number limit that might be required by a judge to convict a person or a group of genocide. Technically, it's not necessary for killings to take place for genocide to occur; it can be done by dispersing a population, separating the children from parents, to prevent them from reproducing themselves as a community. But it's unlikely that courts would take that reasoning, in the absence of any killing.