For the purposes of instructing a jury on the degree of homicide under section 189 of the California Criminal Code, what are the reasons why such instructions were rejected?

There is a second, related reason for rejecting the instructions. As explained in People v. Mendoza (2000) 23 Cal.4th 896, it is inappropriate to instruct on lesser degrees of homicide when the evidence demonstrates a felony murder: "When the prosecution establishes that a defendant killed while committing one of the felonies section 189 lists, 'by operation of the statute the killing is deemed to be first degree murder as a matter of law.' [Citations.] Thus, there are no degrees of such murders; as a matter of law, a conviction for a killing committed during a robbery or burglary can only be a conviction for first degree murder. [] . . . Where the evidence points indisputably to a killing committed in the perpetration of one of the felonies section 189 lists, the only guilty verdict a jury may return is first degree murder. [Citations.] Under these circumstances, a trial court 'is justified in withdrawing' the question of degree 'from the jury' and instructing it that the defendant is either not guilty, or is guilty of first degree murder. [Citation.] The trial court also need not instruct the jury on offenses other than first degree felony murder or on the differences between the degrees of murder." (Id. at pp. 908-909.)