how did one simple single-celled organism began to reproduce, become multi-cellular and began to change shape if it was not by accident?? how would you say it happened?<quoted text>
NEXT TIME you address abiogenesis and NOT your own devises, OK?
Genetic drift is not the only factor in genetic variation.
Genetic drift is even not a very strong factor.
Genetic drift is pure RANDOM process. Pure random processes do not AUTOMATICALLY cause decrease of genetic variation. Genetic drift MAY cause gene variants to disappear completely and thereby reduce genetic variation. When the genetic variation has declined, it does not mean that the species gets extinct.
The only thing happening is that the surviving population will be vulnerable to any new selection pressures such as disease, climate change or shift in the available food source, because adapting in response to environmental changes requires sufficient genetic variation in the population for natural selection to take place.
But the first species we are talking about here, did not have a predator. There was no disease by infections because there were no other species to infect them. The food source would have been abiotic. If the abiotic food chain was still there and didn't change, there were no problems there. As the first life forms were sea borne, climate wasn't much of a problem. For instance, when they lived near undersea fumeroles as basic source for chemicals as 'food' and energy, they could have well survived even ice ages.
Please read a little bit more in the things you are talking about.
keep in mind unless you are claiming that life started with a large population, there would not be a sufficient population to change the population over time. remember evolution is on a population level, not an individual level. small populations don't fair well for they lose genetic variation due to genetic drift and founder effect when a new population is established by a very small number of individuals from a larger population.