I am trying to understand why, if the first life on earth appeared so soon after the Hadean between 4 and 3.5 billion years ago, its development since then has been so slow. The fact that life appeared so soon, suggests that the prevailing conditions were favorable. So why didn’t those conditions lead to a faster evolutionary development? Am I perhaps underestimating the difference in complexity between a self replicating RNA strand and a living cell? Still, it took 3 billion years to produce just sponges, corals, and anemones, before the first sea-based life forms ventured onto the land, which is a really huge lapse of time. It then took another nearly 500 million years to produce primates. Genus homo has existed for only about 2.5 million years or about 0.06% of Earth’s history, and nearly all of that has been spent living more or less like erect monkeys. Is it not the case that homo sapiens nearly didn’t evolve at all? Big climatic changes, asteroid impacts and vulcanism can represent setbacks, but they only represent setbacks if there was progress to set back. There have been many long periods of excellent conditions for intelligent life, but all we ever got was a huge amount of unintelligent diversity, until now, after 4 billion years. If brain based intelligence is only a further development of the sense organs, I wonder why it took so long to evolve large sophisticated brains, considering the advantages of intelligence for survival and proliferation. Ouabache wrote in another thread (a few years ago): “Certainly lower life forms (microbes and insects) will adapt more easily to severe stresses on the environment. Because of their shorter life cycles, they respond more quickly to these stresses. This is due to a faster accumulation of beneficial mutations. If the air and land become too inhospitable, life will continue to adapt under water.” In view of this, I have some questions about evolution: 1. Apart from the reproduction rate, what are the other most important factors which drive the frequency of genetic mutations? 2. If lower life forms mutate faster under stress, does this mean that a certain amount of stress should lead to higher life forms? 3. Why do higher life forms tend to have lower reproduction rates, which is detrimental to their proliferation? 4. In more complex life forms, does the mutation process have a higher or lower chance to be beneficial than in simpler life forms? I don’t know if the answers to these questions may help to explain why it took so long for us to get here. Otherwise, what is the reason? Or, if no particular reason, could it easily have happened much sooner, in the conditions actually prevailing on Earth, or are we deluded in our thinking that this is the perfect Goldilocks planet? .