This post is a follow-up to yesterday's The Fate Of The Earth's Largest Animals — Dave

In her book Once And Future Giants, Sharon Levy presents two hypotheses to explain the megafaunal (large animal) extinctions in the Americas which occurred as the last Ice Age ended about 13,000 years ago—human hunting and climate change. You might think that human hunting is the obvious choice, but you would be wrong. I laughed out loud when I came across passages like this one on pages 22-23—

Russell Graham, a geoscientist at Pennsylvania State University and a staunch supporter of climate change as the cause of the mass extinctions, believes that too many people, scientists and environmentalists alike, uncritically accept the idea that humans bear responsibility for the die-off. Given our species' accelerating destructive impact on animals and habitats worldwide, he says that its easy to get caught up in a spiral of collective guilt over what our ancient ancestors might have done. Part of the problem with climate-based arguments is that they've become increasingly complex over the last few years...

Only a member in good standing of our twisted species Homo sapiens could go to such astonishing, contradictory lengths to get humans off the hook for killing off the Ice Age megafuauna. Mr. Graham is very, very confused because the subject here is human behavior. It is simply unacceptable for Russell and most other humans to come to grips with who they are. As a result, he puts 2 plus 2 together and gets 5.

It is disappointing that Graham's confused, increasingly complex denial is the default case. Even the scientists who support the human hunting hypothesis do so because, unsurprisingly, the bulk of the scientific evidence indicts humans in the demise of the large animals.

Common sense, experience, and human self-knowledge count for exactly nothing in this debate. It seems that these scientists have metaphorically re-discovered the wheel and, in my experience, they do so over and over again when their subject is human behavior itself.

To decide between the hunting and climate "hypotheses" regarding Ice Age megafaunal extinctions, one only has to know three things, to wit—

The die-off of the Ice Age megafauna coincides precisely with the arrival of the "Clovis" people in the Americas 13,000 years ago.

The Ice Age megafauna of the Americas survived several transitions from glacial to interglacial (warm) conditions during the Pleistocene. What was different about this last transition was that large numbers of humans had arrived on the scene.

And last, but not least—

Contemporary humans are killing large animals off because that's what humans do, given half the chance, and a burning desire to do so (from yesterday's post).

It also might help to know that humans have killed off the large animals everywhere they've traveled during the peopling of the Earth—Australia, Madagascar, New Zealand, and so on. We do have some experience to draw on in this area of study.

We might call that last bullet point above the "self-knowledge" clause. There is no good reason to believe that the Clovis people of thousands of years ago were behaviorally different than modern humans in any significant way. Granted, they weren't nearly as technologically advanced, but otherwise, they could be your friends and neighbors.

Part of the confusion here (as with Mr. Graham above) is the false, self-serving belief that modern humans are somehow qualitatively different (better than, superior to) Ice Age humans. They are not. Our supposed superiority is the myth of "progress" writ large. If you want to know how late Stone Age humans might have behaved in the 21st century, look in the mirror, read a newspaper, watch TV, or browse the internet. They were us, and we are them.

Humans need to get acquainted with themselves. Another telling example serves to drive this point home. I found this example yesterday, but I want to emphasize that I hear this sort of thing all the time. I see this kind of material everywhere I look.

I heard the story on NPR on yesterday's Morning Edition. It is called Your Child's Fat, Mine's Fine: Rose-Colored Glasses And The Obesity Epidemic. The story is about optimism bias, which is why I listened to it. The reporter is Shankar Vedantam. Tali Sharot is a neuroscientist at University College London.

SHAROT: People underestimate their likelihood of experiencing all kinds of negative events, including medical illnesses. And they do that for their family members as well. So not only do we think we are immune more than other people, we think that our kids are also more immune than other kids. VEDANTAM: Sharot and others have called this an optimism bias. SHAROT: The optimism bias is our tendency to overestimate our likelihood of experiencing positive events in our lives, and underestimating the likelihood of experiencing negative events in our lives, such as divorce or cancer. VEDANTAM: Three decades ago, psychologist Neil Weinstein discovered the bias when he asked students about the likelihood of different events in their lives. He found that the students believed they were more likely than their classmates to find a job they loved or get an above-average salary. But they believed their classmates were more likely than they were to commit suicide or to develop a drinking problem. More recent research has found we not only have rose-colored glasses about our future, and the future of our kids, we actually discount negative information.

You might want to look at my post The Optimist's Brain.

Now, let's zero in on this sentence: Three decades ago, psychologist Neil Weinstein discovered the bias when he asked students about the likelihood of different events in their lives.

Discovered the bias? Is this like the paleoanthropologists who have recently "discovered" that human hunting killed off the Ice Age megafauna?

Every day, everywhere I look, I see "optimism bias" in human cognition. Pick a subject, any subject. Global warming? Optimism. The future crude oil supply? Optimism. Future growth in the U.S. economy? Optimism. Future technological advances in energy? Self-driving, flying cars? A robot servant in every home? Optimism.

You get the idea.

The only problem here, the one I'm describing in this post, is that this "optimism bias" is so deeply ingrained, so much a part of who humans are, that they are totally blind to its existence. A fish will always be the last to know the kind of the water it swims around in.

But I've left out the best part of the NPR story. Here it is—

VEDANTAM: In a series of experiments, Sharot has identified a region in the brain that seems to be responsible for this bias. She temporarily disables this region using a magnetic field and then asks people what they think. The bias disappears. People stop being overly optimistic. They start to take risks seriously.

I like it! Now we're talking, that's what I call Progress! Vedantam continues...

Now, this bias isn't a brain defect. In fact, multiple studies have shown the optimism bias produces a variety of positive life outcomes. We do better in life when we expect to do well. The trouble arises when it comes to major public health problems like childhood obesity.

Not a brain defect? Being generally out of touch with Reality is not a defect?

But, no, no, no! — we won't be admitting there are any "brain defects" in the human animal today. Optimsim leads to a variety of positive life outcomes. Optimism helps us do better in life. Optimism is good!

Optimism does not inflate housing bubbles.

And what did Shankar Vedantam unknowingly display in this part of his report? Optimism bias

Humans are clueless about themselves, utterly blind as to who they are, which is why I dubbed them Homo laeviculus — Clueless Man on September 6, 2011.

Later.

Bonus Video — optimism bias in American perception of wealth inequality. Apparently this video is going viral...