Except that he doesn’t. In “Slaves to evolution,” (ABC Science 06/09/2011) Bernie Hobbs explains it all for you:
Two billion-odd years ago, one of the most important meals in history took place. One bacterium swallowed another one. But instead of being digested, the swallowee survived. And it kept doing what it had always done: using oxygen to rip apart food molecules, and then using the energy released to make ATP. So the bacteria that did the swallowing suddenly had this little lump inside it that leaked ATP, which the swallower could use to power its own cellular reactions. It was a match made in thermodynamic heaven.
And this crazy hybrid was the great (x10n) grandmother cell that all eukaryotic cells evolved from. The mitochondria in your cells, mine and every plant, animal and fungi on the planet are descendents of that meal. It’s like slavery, but with benefits.
[ … ]
Cyanobacteria can photosynthesise, so when a eukaryotic cell swallowed a cyanobacteria somewhere in the distant past, it suddenly had a lump inside it that could make food as long as the sun did shine. Not only that, the lump spat out oxygen at the same time — oxygen that the eukaryote’s now well-established mitochondrian could soak up to release energy. And it was a lovely green to-boot!
Okay, Bernie, so … we know it happened this way because …
There’s no single piece of killer evidence that proves the case for the bacterial origins of mitochondria and chloroplasts, …
He offers enough information to make his position (endosymbiosis, sometimes called symbiogenesis) sound quite reasonable and attractive, but not nearly enough to write it up as a historical narrative. There’s a lot of that about these days, and some of it may end up in the school system.
Here’s a salamander as an endosymbiont with an alga (in this case, we know it happened, and it produced a benefit, but not a dramatic new suite of abilities), such as Bernie Hobbs would need. Here are reasons experts disagree, and here are Jonathan M’s comments. Albert de Roos is a respected critic of within the discipline as well. What unites them is that they don’t know exactly what happened, and can live with that fact while doing research.