No asteroid hit the Earth. The climate is three degrees warmer on average, and there have been some very bad earthquakes, no-one is quite sure why. The worst, in 2085, destroyed three billion original stored human bodies, nearly 15% of humanity, of which only 200 million were fully backed-up with current-state copies. Although it was of course already easy to replicate a human brain bio-electronically (known as an eclone), the problem was that the brain is not a static object, and relatively few people bothered to use the repetitive and quite arduous 'manual' back-up process, required at least every two hours in order to maintain current state in the eclone. Between 2070 and 2085, people used to make eclones as temporary controllers for RCRs, and abandon them when the task in hand was finished, returning their cognitive awareness to their original brains, which would meanwhile have been receiving streams of sensory and cognitive data from the eclone. Only a current-state eclone is independently viable.
Technology for real-time back-up of eclones was commercialized in the 2090s, but maintaining a fully equivalent copy of a living brain on a continuing basis whether in an RCR, an RCC or just in a bio-electronic host remained complex and expensive for a further 10 years. Since then, costs have reduced and population has stabilized, so that the proportion of un-backed-up human eclones is now thought to have fallen to around 20%. Probably this is close to the absolute minimum that can be achieved. There will always be a certain proportion of people who are too lazy to instal real-time back-up; and about 10% of people are thought have decided to self-terminate, although not necessarily immediately, which will cause them not to bother with back-up.
In the 2110s, there was a move to make back-up compulsory, but civil liberties activists prevented it, in an alliance with the global population council (affiliated to the United Nations), as ever, worried about resources. Nation states were in favour, of course. Another person = another tax slice.
By 2120, with automatic back-up having become cheap and easy, few people were using their original bodies as a permanent base, and now it is almost unheard of. Again, it's a question of cost. While it is possible to maintain a legacy human body in close to optimum condition for even hundreds of years (so they say!) the costs are extremely high compared to the cost of maintaining an e-clone in a bio-electronic host together with a separate current-state back-up. Once people had this choice, it was really amazing how few wanted to stay with their warts, and most people now choose to use a bio-electronic host as their permanent 'home', keeping their original bodies, if at all, in permanent storage. A small and declining proportion of people use their original bodies for physical reproduction, in preference to so-called 'artificial' reproduction, for the legacy Olympic Games and a few other antique spectator sports. Evidently, this requires an upload of a current-state e-clone to the stored body, which then temporarily becomes the person's cognitive home.
By 2100, people were in any event choosing to spend most of their time in Remote Cognitive Collectives (RCCs); once you have experienced the excitement and incredible fertility and productiveness of working or playing in a group cognitive environment, being on your own rather palls.
(NB Appendix Five includes a description of the development, capabilities and uses of RCRs, RCCs and eclones.)