Could it be Willie Green?
Since Brand's been hurt, he's seen plenty of starts in the Sixers small-ball lineup. His overall minutes haven't really increased though, nor have his stats.
Could it be the Sixers team?
In games Brand doesn't play in, the team is 10-8, compared to 10-13 with him. That said, it's been a season of streaks for this team, so things could swing at any time.
Could it be his old team, the LA Clippers?
Quite the opposite. Brand may have been injury-prone, but at least he doesn't work for Jenny Craig.
In the absence of Elton, Speights has really managed to shine, dominating rookies in John Hollinger's PER stat, and nearly matching the resurgent Chauncey Billups.
It's tough to figure out how the PER number is attributed between Brand and Brand-less time, so lets take a different approach (on a per-minute basis, of course) to see how this jump from 12 to 19 minutes per game has affected his game:
Fouls and Turnovers: A big man is only useful if he can stay on the floor, out of foul trouble. In Brand's absence, the amount of time Speights sees per foul has gone up almost 50% (from 6:00 to 8:44), moving him from a liability to around average for a forward/center. A similar story for turnovers, with a 25% increase (from 20:20 to 24:21).
Scoring: A slight increase, from 0.50 to 0.52 points per minute, which still keeps him in the league of Pau Gasol and Amar'e Stoudemire in scoring frequency.
Rebounding: The only negative, possibly as a result of smaller lineups, Speights drops from 0.30 to 0.22 rebounds per minute, dropping him from the league of Tim Duncan and Al Jefferson to the league of Rasheed Wallace and Andray Blatche.
Blocks: Leaps and bounds here, jumping from a rate of 1.8 per 48 minutes up 78% to 3.2 per 48, a rate trailing only a former D-POY Marcus Camby and Ronny Turiaf. Perhaps a product of the system, teammate Samuel Dalembert also saw a 75%+ jump in block rate without Brand.
I think it's safe to say that Marreese Speights is thriving in Elton Brand's absence, with amazing productivity and efficiency. Will he be included in rookie of the year discussion? No, because he doesn't shoot fifteen or sixteen times per game on a team that hinged all their hope upon him.