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Did you ever stop to wonder why life on earth is the way it is? Of all the questions human beings have tried to answer, it might be the biggest.
Science can provide some answers, but the topic is still mysterious in many ways.
The earth is about 4.5 billion years old. In those terms, humans just got here.
Most estimates put early humans on the planet for a few million years, but in geologic terms, that's just a few seconds.
"It's amazing how much we actually know about human evolution now, compared to what we did 10, 20, much less 50, 100 years ago," CU Boulder anthropology expert Matt Sponheimer said. "Despite all this knowledge, it's remarkable how mysterious much of it remains."
Most experts believe human beings first appeared in Africa. For millions of years, we lived and died in a frightening world, surrounded by beasts and weather that could easily kill us without much of a fight.
"I think it's very possible throughout most of our existence, we were hanging on by a thread metaphorically," Sponheimer said.
But we did hang on by that thread and thrived. We have no idea how many people there were a million years ago but in 10,000 BC, maybe a million or two. Ten-thousand years later, by the year one, we were up to 200 million and grew gradually until the Modern Age. Then, a billion people in 1804, two billion in 1927, three billion in 1963, and almost five billion in 1983. In 2015, seven billion and counting.
In other words, human beings have been amazingly successful at conquering the planet. But how?
"Between 100,000 and 50,000 years ago, humans spread out from the area where they evolved to all of the earth," said CU Boulder archaeologist Scott Ortman, who says when that happened, humans needed technology to survive, which is why we're where we are today.
Think about the role technology plays in your life: cars, electricity, refrigerators, microwave ovens, computers, cell phones. We're so used to technology we can't even imagine life without it.
But in the beginning, technology was less about fun and more about something much more basic, like survival.
Think of human history as a long road. The first stop on the technology highway, millions of years ago: tools made of stone, wood, antlers and bones that helped us use animals for food and protect us from the world. Then, just yesterday, we gradually started making all the things we take for granted today.
Estimates as to when vary, but the control of fire by humans was an important early discovery.
Then, 50,000 years ago: clothes. 12,000 years ago: boats. 10,000 years ago: agriculture. 8,000 years ago: bricks. 5,000 years ago: the wheel. 3,000 years ago: iron tools.
CU's Matt Sponheimer says that's when things really picked up.
"If you really think about it, most of the things that we think of as what defines us, computers, space travel, cars -- these are things within the last few hundred years, not even a thousand," Sponheimer said.
Three hundred years ago, the Industrial Revolution produced machines, steam engines, typewriters, submarines, the internal combustion engine, cars, planes, spaceships and computers. They are now everyday features of life on earth.
But Sponheimer says human development is about much more than technology.
"I think that's taking a three dimensional argument and looking at it in two dimensions. We are so, so much more than that," he said.
Things like art, music, architecture, and games are all the things we don't need but want in order to make life interesting.
As for technology, is it always for the better?
"I would not say that technology itself is intrinsically bad, because it is an artifact of our creation. And it is a manifestation of whatever the user's intentions really are," CU Boulder expert on the development of technology Revi Sterling said.
"So if ISIS uses technology, they are probably thinking it's for a good goal. Where we're going, this is terrible that they have so much technology," he added.
In the end, Sterling says, human nature determines how and why we use technology.
"You know there's greed, there's favoritism, there's envy, there's fear. All the things that make us human are the things that make us messy, and technology isn't messy," Sterling said.
It also wasn't easy to invent. But CU Boulder archaeology expert Scott Ortman says population growth is one of the main reasons for the rise of technology: more people, more ideas, more solutions to complicated problems.
"A society at the scale of a hunting and gathering group could not maintain enough knowledge of the world to make a cell phone," Ortman said. "If the world population were suddenly cut in half, we would lose a lot of our technology within a couple of decades. We would probably no longer be able to have cell phone networks as we have them today."
To most of us, the earth seems enormous. Most of us will only see a small fraction of it in our lifetime. But it's really just a tiny speck of life floating in the harshness of space. However, the earth can also be a scary place sometimes: fires, floods, storms. They are just of a few of the things that all threaten to wipe us off the planet. And yet, the earth is also an amazing place to live.
"I think the more you know about how the planet functions, the more you're amazed at how well it functions," said Jim White, a CU Boulder expert on the environment. "The more you understand it, the more you realize that maintaining it as a wonderful place is not a simple thing to do."
That's because we're constantly changing the world simply by living on it.
"I think we're going to change climate regardless of the fuels we use. We're going to change the planet's surface regardless of what we do, because we have to," White said
So far, earth appears able to support seven billion people, maybe even more. But somewhere there's a limit to the food, water and land necessary to keep that many of us alive. The question is: do we reach what experts call sustainability in a good way or painfully through disease, starvation and war?
"Personally. I think we're smart enough and sophisticated enough and have enough technology to get there elegantly. But there's no guarantee of that," White said.
It's one of the reasons White says the Pentagon spends money studying climate change. It can force large numbers of people to move away from rising oceans and join extremist movements out of desperation.
"We know what happens when you bring people together who are desperate, that are poor. These are breeding grounds for extremists," White said.
The earth is crowded, and we're living on it longer.
Ancient life expectancy is difficult to measure, but life was often short and hard.
Before 1800, we lived between 20 and 30 years. By the 1850s, the average life expectancy was up to a little less than 40 years.
By the 21st century, that increased to 67 years globally and nearly 80 in developed countries like the United States. All of which means we're healthier and better able to cure ourselves when we get sick.
"It wasn't long ago, you know 1960s, 1970s, there was a real genuine thought that we could eradicate infectious disease essentially from the planet," CU Boulder physiology expert Matthew McQueen said.
McQueen says our brushes with Ebola and measles recently make it clear that we are still vulnerable.
"I think that the one mistake that humankind tends to make throughout history is, sort of a lack of humility, particularly with these problems as they related to health," McQueen said.
Religion and politics are the two topics we're all supposed to avoid at Thanksgiving. Yet the search for God is one of the biggest stories in the history of humanity, and it never seems to go away.
Most Americans and billions of others around the world believe in one God. Just, not always the same God. Why?
"There's not a simple answer to that question, although people have tried to give simple answers to that question," CU Boulder religious studies expert Deborah Whitehead said.
In America, Christianity is the most common religious belief, but there are literally dozens of different denominations for Christianity alone. Which is one reason why the search for God never seems to end.
"There was a thesis called the secularization thesis that was prominent for a time in the later part of the 20th century, which said, yes, as we're entering the modern era. As we're becoming more and more modern, religion is going to be on the decline," Whitehead said. "We're not going to need religion any more. We're going to have science. We have more secure political systems, ostensibly at that time. So, religion is going to wither away. And in the 21st century, we see that's not the case. That hasn't happened. Religion isn't going away. Religion is still thriving."
Even in America, a land where we often measure happiness and peace in dollars and cents.
"The United States still sees one of the highest rates of religious participation among western industrialized nations in the world. That's a product of our own unique heritage as a country," Whitehead said.
Of course, not everyone believes in God. Atheism is a strong belief system of its own. An atheist's belief in the lack of God depends on inconsistencies in religious stories, while the Christian belief in a virgin birth and a resurrection from the dead requires faith in something that can't be proven using science.
The question then becomes, what explains the willingness of believers to believe whatever they believe?
"I don't think we want to say there's one primary reason why people profess a faith. We need to take each person on a case by case [basis]. And I think if you look closely at a person, you'll come up with a lot of different things," said Loriliai Biernaicki, another CU Boulder religious studies expert.
"A lot of religions will claim and their followers will attest, that they provide, you know, a sense of meaning, and a sense of purpose, large purpose, in an often confusing and painful existence," Biernaicki said.
One of the great ironies of religious belief is that in addition to providing meaning and purpose, it also creates confusion and pain or worse.
Sept. 11 and ISIS are our most recent examples of radical Islam leading to shocking and barbaric behavior.
"We have to ask ourselves: what is the threat of ISIS coming from?" CU Boulder ethnic studies expert Daryl Maeda said.
"Does it come from the fact that those militants, those extremists are Muslim? Clearly not. There are millions of peaceful Muslims across the globe and millions of peaceful Muslims in the United States. Does it come from the fact that they're brown-skinned? That's obviously not the case. It comes from their ideology. And so the enemy for the United States is not Muslims; it's not Arabs; it's not brown-skinned people. It's the ideology of ISIS, which is to impose its will on other people."
"My own experience with this is that it's never really just religion that causes people to become intolerant. It's often politics of some sort or another," Biernaicki said.
In spite of that, Biernaicki is actually optimistic that fighting over God may come to an end, sooner than many might expect.
"The short answer is 'yes.' I even see it in the fairly near future as humans evolve and get to know themselves better and know what it's like to be human. Then eventually humans will not fight over religion."
If there's one thing human beings have proven over and over, it's that we love to disagree: about religion, politics and especially about each other.
People have a natural desire to categorize. We're categorizing machines! That's how we make sense of the world," CU Boulder ethnic studies expert Daryl Maeda said.
We call it diversity, gender, skin color, language, and culture. All those differences make the world an interesting place. But then, those same interesting differences can somehow become a bad thing.
So the question of why does skin color cause so many problems?
The answer is because humans make those categorizations," Maeda said. "And then use those categorizations to create categories of people who receive certain rights or are denied certain rights, who are at the top of the socioeconomic ladder or at the bottom."
It has happened again and again throughout history. Our most vivid and painful example is nearly 250 years of American slavery that ended only after a civil war that almost destroyed the country. It did not end the difficulties created by our differences.
"So, of course we don't have the buying and selling of people based on their skin color in the United States anymore," Maeda said. "And we don't have legally segregated schools. But racism has morphed. It's changed and it's reappeared, as we can see in the events of the past few months."
In 2014, the deaths of Michael Brown in Ferguson and Eric Garner in New York brought the national conversation about our differences back to the top of the list. And it has not been an easy conversation.
"It illustrates that some of us really don't respect each other. [We] really don't value each other," said CU Boulder ethnic studies expert Hillary Potter, who does see one benefit from the painful racial disagreements in recent American history.
"People are being made uncomfortable, which is good to make people uncomfortable, because that's how we have change, when we make people uncomfortable," Potter said.
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