While sexual reproduction the way we do it may be rare – using specialized gamete cells with gender differences, like our sperm and eggs – there are plenty of microorganisms with other means of swapping genetic material, some of which may be very similar to the origins of our own form of sexual reproduction, but other forms may very we have evolved independently.
No, the trick is to find a molecule that can kinda reliably reproduce itself. Perfect reproducability is a dead end, the end of evolutionary change. So you want a molecule that reproduces correctly most of the time, but screws up fairly often.
Eh, while there are errors in copying of DNA, they’re much rarer than you’d expect. Imperfections in copying is not something that you need to try hard to attain. Almost certainly, the first replicators had much higher error rates than current life, and had to evolve a lot to get the rate down as low as it is.
Yes. The DNA copying error rate — estimated at one nucleotide per billion — is impressively low.
But note that, just as annealing (and simulated annealing) start off at high temperatures, so a higher error rate very early in life’s evolution would have been advantageous — a vast space needed to be searched to move the genome toward a well-functioning cell.
Since there’s roughly three billion nucleotides in the human genome, when cells divide, there’ll be on average three differences in the DNA of two daughter cells from their progenitor cell. That is, three different changes in each. Which means it’s pretty rare for any two cells in your body to have the exact same DNA. And that’s not even considering the likely different amounts of telomeres in the various cells.
I think the step from prokaryotic cells to eukaryotic was HUGE, while from there to multi-cellularity is tiny by comparison. But also consider that intelligent life has evolved (at most) once. The dinosaurs were around for 165 my but didn’t get there. And many of them were bipedal with hands not used for much.So that might also be a giant step. Of course it could have happened more than once. Human intelligence might, absent hands, give you cetaceans.
Most of human DNA is “junk.” Even in coding regions there’s a fair chance that an SNP will code to the same amino acid, or that the alternate amino acid will yield a functioning protein. Even if a gene is defective, the alternate allele may “come to the rescue.”
The error rate of one nucleotide per billion gives excellent fidelity … as is needed.
(Is “at most once” a snide commentary on human intelligence? 
)
Don’t forget octopuses — highly intelligent on a different evolutionary branch. (And the “hive brains” of ants might be ponderable.)
Depends on how intelligent you call “intelligent”, but there’s only a fairly small gap. On the one hand, as Colibri noted, octopodes are comparable to primates, and the common ancestor of the two was something merely wormlike. So evolution on this planet has gone from wormlike to primatelike at least twice, on completely independent paths.
On the other end, Neanderthals, Floresiens, and possibly Denisovans were all as intelligent as we are. So if you look at the common ancestor of all of us (H. erectus?), evolution has also gone from that level to us-level multiple independent times.
The only thing that has only (so far as we know) happened once, was going from general primate level to H. erectus level.
Genetic variation through mutation always seemed like an inelegant method of evolution to me.
Sure, it’s pretty successful. It lead to intelligence with the ability to manipulate the environment and sally forth beyond our solar system and created cats that land on their feet and Sophia Loren.
But it also created cystic fibrosis, sickle cell anemia, mosquitos, and Paulie Short.
Surely, there must be alternate, more elegant methods to drive evolution on more progressive, alien planets?
For shits and giggles, can you think of any?
This is GQ so I’d best not post my speculations on applying Maxwell’s Demon, divine [del]wrath[/del] guidance, the steeplechase method, or magnets.
Evolution is the survival of change. How to drive that elegantly? How to apply power steering and course correction to evolution? I’ll go with “planned obsolescence.” 
Indeed. I was going to cite the Great Oxidation Event / Oxygen Holocaust which not only changed the planet’s dominant life forms but also affected iron in the earth’s crust worldwide. But your post is more comprehensive.
It’s worth noting that despite our best efforts to the contrary there are substantially more (about twice as many!) species of dinosaurs alive today than mammals, and far more individual dinosaurs than mammals.
Yes, but beetles put us all to shame.
Is there any chance we will find some pocket of ancient life somehow protected for billions of years? I’ve read how scientists have found pockets of water believed to be a billion years old in very deep mines. When they test the water, they find worms and other tiny organisms. Is it theoretically possible that there’s a pocket of water somewhere on Earth which is ~4 billion years old and might have life in it from before our current DNA-based life?
“He is inordinately fond of beetles.”
(Attributed to JSB Haldane, in answering whether his studies of natural history led him to make any conclusions about God.)
I suppose it’s theoretically possible, but it’s more possible that if such life exists, we’ll find it elsewhere in our solar system, carried there by impact ejecta.
There is a long-standing mission proposal to search the oceans of Enceladus for precisely such life. It is thought that liquid water lies beneath the ice-crust and that life could have begun or been sustained there for a very long time indeed.
It is some way off but preliminary testing on the mechanism has been carried out in antarctica. Exciting stuff. They’ll either find nothing (important but disappointing) earth-related life (important and remarkable) or non-earth related life (mindblowing!).
I do hope we do it in my lifetime.
The thing with animal attributes (any evolutionary attribute) is the cost trade-off. Our brain costs about 20% to 30% of the nutrition we consume. Brain development to create something usable requires ongoing nutrition to prevent stunted development. It better produce some survival advantage for that. Being superhuman has serious advantages, but big muscles require food. (Larry Niven’s short story Brenda has an interesting discussion of breeding supermen. Fast-clotting blood causes strokes in mid-life; night vision can cause day-time blindness; etc.) So everything is a trade-off. Moderately smart wolves or whales will survive just as well as ones that can do calculus, and need less food when things are tough. Huge men need a lot more food than small ones (Andre the Giant was known for how much he ate). The pygmy “hobbit” fossils in Indonesia suggest that food became scarce and the species was trapped on an island; similarly the pygmy elephants of Malta - the smaller versions survived better as food supplies dwindled.
So presumably the road to smart took a predictable turn. We evolved the same smarts as wolves who cooperated to hunt - but with hands free to manipulate things, also managed to create tools of increasing complexity, thus challenging our intelligence to select for smarter individuals who could devise tools to do what evolution did not equip us for. A raptor with vicious front claws does not need to learn to use rocks and pointy sticks; if they evolved with fangs and carnivore teeth rather than eating scavenged well-aged meat of carcasses left by others - no need for sharp rocks to cut flesh and smash bones, nor fire to soften fresh meat.
So we evolved very smart brains because we used them, and needed them.