Let’s see if I understand leandroc76’s objections.
On the one hand, the earth is supposed to be 4 billion years old, and in that time it took 3.5 billion years to evolve mulicellular life, then another 200 million to evolve life on land, then 65 million for mammals to evolve to their present state since dinosaurs went extinct.
Why didn’t the first life forms on earth evolve into intelligent beings?
The answer to this question is that the first life forms were extremely simple bacteria. They couldn’t evolve intelligence since they didn’t even have brains. So it was nothing but mats of bacteria for billions of years. That bacteria was evolving…some photosynthized, some evolved to use oxygen, they evolved new ways to digest food, but it was all bacteria. For a billion years or more. If a person is lucky, they might live to be 100. Now think of a thousand years, 10 times that long. Back to the middle ages. Now think of 10,000 years, back to the very beginnings of agriculture. Now think of 100,000 years, back to the first people that were really human, but were hunter gatherers with only stone tools. Now think of a million years…and our ancestors then weren’t really human, but Homo erectus, with half our cranial capacity, not much different than bipedal chimpanzees with a penchant for using sticks and flakes of rock. Now back 10,000,000 years, when our ancestors weren’t even bipedal. Now 100,000,000, one hundred million years ago, a million times longer than the oldest humans have lived. Our ancestors then weren’t much different than shrews today. Dinosaurs everywhere. And 1 billion years ago there wasn’t any mulicellular life.
Loooooong time spans. So…with all that time, why doesn’t evolution proceed more quickly? Why didn’t the first dinosaurs evolve big brains and start using tools and invent agriculture and gunpowder and computers? Well, because there isn’t usually a selective advantage in being smarter. Brains take a lot of energy to produce and maintain. If a species doesn’t need a brain they quickly evolve smaller brains. There is no ratchet that makes creatures evolve larger and larger brains. The only ratchet is the one described earlier, in that you can’t get any dumber than a bacteria. So the only direction to move is “smarter”. But there isn’t usually any particular reason to become smarter.
So you have bacteria for billions of years, and dumb animals for hundreds of millions of years. Then along came primates. Primates are smarter than most animals, but why? Well, they evolved larger brains incrementally to help them solve problems…jumping from branch to branch, climbing, finding dispersed food sources, etc. They didn’t start evolving bigger brains so that one day they’d be able to pilot rocketships, but rather to catch more bugs, find more fruit, avoid more snakes, jump farther and climb faster. But those large brains weren’t just bug-finding single purpose modules, but could also be used for other things.
Large brains make more complex social structures possible. You can recognize other members of your species as individuals, and remember their past actions. You can cooperate with them, or compete with them. The better you are at social interactions they more successful you become. But before you can even begin this process you need a brain that is already very very large by the standards of most species. A monkey has a brain much larger than most animals their size. Monkeys are successful, but they aren’t the most successful animals in the world. They didn’t rule the earth with their large brains 10 million years ago, they just did their monkey thing, catching bugs, eating fruit, climbing trees. Some monkeys might not need larger brains, so their brains got smaller, most were adapted to their particular environment and so stayed the same, and a few were more successful with larger brains and got smarter.
But again, they didn’t get smarter with any other purpose than being a better monkey or ape. A smarter monkey could do different things than a dumb monkey, but dumb monkeys weren’t less successful than smart monkeys, in fact on average dumb monkeys were more successful. So to get a creature as smart as a human you have the equivalent of getting heads 100 times in a row from a coin flip. Sure, given a long time you’re bound to get a run of 100 heads. But how long should you expect to wait? Hard to say. It isn’t like waiting for a linear process to where you can measure the current rate and give an estimate for when the process will reach a particular value. To evolve something as smart as a human you had to start with bacteria, then wait till multicellular life formed, then wait for animals, then wait for them to move on land, then wait for them to live in trees, then wait for their major predators to go extinct, then wait for them to evolve to eat fruit as well as bugs, then wait for them to develop complex social structures…and none of the new advances could be predicted from looking at the preceeding species.
So at some point you have Homo erectus, which stayed at the same brain size and level of technology for a million years. Why didn’t they immedieatly evolve into modern humans? They just didn’t, modern humans weren’t the goal when Homo erectus evolved from Australopithecus, Homo erectus was. Then for unclear reasons about 100,000 years ago modern humans evolved? Why then and not earlier or later? There isn’t any real answer to that question. If it happened earlier, we’d still have the question of why particularly then, why not even earlier, or later, or at all?
So 100,000 years ago we have modern humans. So it took 100,000 years to evolve from living hunting and gathering and using stone tools to building skyscrapers and piloting spaceships? No, of course not…since there are modern people even today who hunt and gather and use stone tools, living a lifestyle essentially identical to the lifestyle those first humans did 100,000 years ago.
Technological progress is not inevitable, and it isn’t a ladder. Inventions get made, but they don’t always get adopted. In a hunter-gatherer band people have to learn to build and use a tool every generation or the technology will be lost. Since pretty much every person has to learn all the technology that the band uses, there’s only room for so much. You can learn a new design for arrows, but you can only learn to make so many types of tools, and a tool that isn’t used for a generation is gone forever.
For 90,000 years human technology was essentially static. Sure, we had technological change, but these were simple changes…new types of stone tools, new fishing techniques. And the new techniques might be improvements, but they weren’t radical improvements. We might find evidence for a new tool type…nets, or bone needles, or what have you, but the technology tool kit of a hunter-gatherer is inherently limited.
Then along comes agriculture 10,000 years ago. Why then and not earlier or later? Well, that was around the time that the Ice Ages ended. Climates had changed. Perhaps that had something to do with the precise time. But the real answer is that it just did happen then, and if it hadn’t happened then we’d still be hunter-gatherers. So how did we get from agricultural villages to cable television? Agriculture doesn’t mean more food exactly, but it does mean more storable, transportable food…and more importantly, more expropriatable food. Farmers can’t move away from aggressive neighbors, they’ll lose their farms and starve. So the only choice is to fight back or see them take your grain. If you fight back you need soldiers, those soldiers need food, so you have to give them your food, or the soldiers from the other side take your food anyway. Pretty soon the difference between the soldiers from your village and the soldiers from the other village isn’t much, they all take a percentage of your food in return for not hitting you with their swords.
But surplus food means artisans can specialize. Butchers, bakers, candlestickmakers, etc. Ah, so why didn’t this specialization lead to an explosion of knowledge and the beginning of the industrial revolution thousands of years ago? Because artisans didn’t have much incentive to share their knowledge, there wasn’t an advantage to sharing a family’s secret method for making blue glass, so the method didn’t spread. Some inventions are simple enough that anyone can copy them given an example, so there was some technological progress, but it wasn’t linear improvement, it wasn’t universal improvement, and it often went backwards.
Then sometime around 500 years ago we have a change…the beginning of the modern era. Why then and not earlier? Why then and not later? Why in Europe and not in China or India or MesoAmerica? Hard to say. We know the industrial revolution happened, but why? A good first look might be Jared Diamond’s “Guns, Germs and Steel” which asks this particular question. But if we were going to be sitting on a message board asking this question it had to have happened already, so asking why not later is kind of answered. As to why not earlier, there wasn’t any particular reason. The earlier agricultural civilizations weren’t striving to achieve an industrial renaissance, there was some progress but not enough for most people to even have the idea there was such a thing as progress. Progress happened over centuries, not people’s lifetimes. Empires arose and fell apart, but for most people their lives didn’t change much.
And during all this, the move from agriculture, to industry, to the Straight Dope, there was no detectable evolution of human intelligence. A hunter-gatherer from the Pleistocene was just as intelligent (on average) as a modern hunder-gatherer from New Guinea, who is just as intelligent as a modern subsistance farmer from Central America, who is just as intelligent as a modern industrial worker from China, who is just as intelligent as a suburban service worker from New Jersey. There wasn’t any physical evolution going on, just cultural change.
Does that answer some of your objections?