Senior Editor Gary Stix talks about the September special issue of Scientific American, devoted to the science of being human. And Brown University evolutionary biologist Ken Miller discusses human chromosome 2 and what it tells us about us.
Welcome to Scientific American’s Science Talk, posted on September 5th, 2018. I’m Steve Mirsky.
Every September, Scientific American publishes an issue devoted in its entirety to a single topic. We cleverly call it our single topic issue. And the 2018 edition is about…you. To explain further, I spoke with Gary Stix. When Scientific American was founded in 1845, Gary was the copy boy. Okay, he hasn’t been here quite that long, but he’s a senior editor, and when I showed up more than 20 years ago he already had big piles of books on his desk. But enough about us, let’s talk about you.
By the way, the theorist I was thinking of who’s done work on the co-evolution of war and altruism is Samuel Bowles. Just do your googling if you’d like more info on that subject. And you can hear Pedro Domingos on the episode of Science Talk about artificial intelligence and health care, which was posted on our Web site on June 18.
Now a bit more with Gary Stix.
Steve Mirsky: Welcome to Scientific American's Science Talk, posted on September 5, 2018. I'm Steve Mirsky. Every September, Scientific American publishes an issue, devoted in its entirety, to a single topic. We cleverly call it our "single topic issue". And the 2018 edition is about you.
To explain further, I spoke with Gary Stix. When Scientific American was founded in 1845, Gary was the copy boy. Okay. He hasn't been here quite that long, but he's a senior editor, and when I showed up more than 20 years ago, he already had big piles of books on his desk. But, enough about us. Let's talk about you.
Gary, the special September issue – single topic issue. Humans – Why We're Unlike Any Other Species on the Planet. What was your role in putting this together?
Gary Stix: So, I came up with this idea about – actually several years ago, because I was playing part in another special issue on evolution, and I did the article on how humans are somehow different from other species. And I realized when I did that that there was so much more that we could do, and that kind of lead to this issue. The thing that really triggered this was the recognition that we, in so many different ways, are not really special. That the more people look, the more they find that humans are, in all of the respects that they were thought to be special in the way they communicate and our cognitive abilities, our abilities to think of what other people are thinking – many other animals – particularly primates – have these abilities. That still begs a huge question.
We do thing that other animals don't. We've spread throughout the planet. We build skyscrapers. We've gone to the moon. So, why is that? And that's what this issue attempts to address.
Mirsky: And you were the overall editor for this issue?
Stix: Yes, I was.
Mirsky: Right. Three parts to the issue. Part one is "Why Us?" What's in that part?
Stix: That part tries to get at the specifics of the question that I just raised. Why are humans still special? And it acknowledges, at every step of the way, that in many ways, we're not. But, it does identify a few things that make us stand out. And the one thing is that we teach, from generation to generation, new things that are then built upon in a new generation.
Other species do that as well, but they don't do it with the same precision that humans do. And an example of that that appears in one article is how the things that are taught are then practiced after they're taught with this high degree of precision. And there are ways that, in that very section, "Why Us?" that's illustrated by taking something that was very ancient – like a flywheel from the Egyptians – and show how it's been adapted over many generations into something like the internal combustion engine.
Mirsky: Okay. And part two, "Us and Them" – what's in the "Us and Them" section?
Stix: So, in the "Us and Them" section, there is an article in there that's entitled "The Last Hominid Standing" – the last human of a number of human species that is the only one remaining subsequent to our breaking off with chimpanzees and other species that went along a different branch of the evolutionary tree. And the answer to that is – we were probably lucky, because those other human species were actually developing in many of the same ways that we were. And it could have been a climate related issue. It could have been that we got to a cognitive stage of development slightly earlier, but not much, and we were just lucky. I mean, it could have been that Neanderthals would have populated the whole planet by now.
But, that section also deals with other issues such as the fact that as humans built upon their unique abilities, their groups became much larger. So, to accommodate that, they had to develop a whole set of rules and norms to be able to deal with that, and that is commonly what we think of as morality. And another aspect of that is when groups got to a certain size, they tended to split off into separate groups. And at a certain stage, that resulted in the advent of warfare – that humans, early on, were not innately belligerent, but that's something that developed as group sizes grew.
Mirsky: I forget which evolutionary theorist it was, but I recall some years back – maybe 10 years ago – somebody wrote a paper about the fact that you can't have war without altruism and you can't have altruism without war. They have to co-evolve. Does that ring a bell with you at all?
Stix: There are so many theories about this. And the idea that humans are not innately warlike is highly controversial. This is one take on that. And it's a very cogent take, but I don't think it's, by any means, the last word. I think that if you gathered together a panel on this, even people who initially thought that they would agree, by the end, would be arguing like crazy.
Mirsky: They'd start to fight and maybe somebody would throw themselves in front of somebody else to save them.
Mirsky: Part three of this special issue is "Beyond Us" – and some tantalizing stuff in there.
Stix: So, the question is – what happens now that we are such a dominant presence on the planet? And one of the things that is happening is that it's causing all of the rest of the animal kingdom to kind of adapt to humans. And probably the best example of that – and the most severe example of that – is life in cities for other animals. And plants, as well. Having spiders who avoid sunlight to protect themselves.
Dandelions, instead of being spread to the wind, actually have their seeds fall straight down. Some insects turn color. So, the rest of the animal kingdom and the plant kingdom is kind of at a stage where they're adapting to us. In addition to that, perhaps the most – or one of the most discussed issues in our realm of science and technology, is whether machines are gonna take over from us at some point. And the author that we have – Pedro Domingos – answers that in the negative, primarily because machines don't have any goals. They don't have any intentions.
And we're a long way away from creating machines with a multifaceted goal that any human child or adult or any human really has. So, Domingos' take is that as artificial intelligence continues to develop, what's gonna happen is that artificial intelligence will become like, an alter ego. It will be kind of a companion. You can see that today in its very early stages with things like Siri or Alexa. But the picture that he puts forward is one in which they will have a much greater level of sophistication.
And a lot of the routine things that we do for ourselves will be done by our machine companions. And the issue ends with a look at something that I kind of referred to earlier – the role of luck in all of this. Because it's quite possible, according to the view put forward by the author John Gribbin in the article Alone in the Milky Way, that we may be the only technological civilization in this galaxy and perhaps, even in the universe. And he issues that as a call for us to take better care of ourselves and the planet in an age of climate change and partisanship and what not.
Mirsky: He's not arguing that there's no other life out there; just no other intelligent, developed, technological civilization.
Stix: Yeah. That's basically what he's saying. His argument is very sophisticated. He puts forward a set of arguments about how we are in a very special place in the galaxy, we're in a very special place in the solar system, and we also came about relatively late in the existence of life. Life was around for billions of years before the Cambrian explosion that led to many other creatures springing forth. And again, that could have been pure luck.
Mirsky: We'll be right back after this.
By the way, the theorist I was thinking of – who's done work on the co-evolution of war and altruism – is Samuel Bowles – B-O-W-L-E-S. Just do your Googling if you'd like more info on that subject. And you can hear Pedro Domingos on the episode of Science Talk about artificial intelligence and health care, which was posted on our website on June 18th. Now, a bit more with Gary Stix. Gary, so, a few months ago, I spoke to Brown University evolutionary biologist, Ken Miller, about his new book, The Human Instinct, and he goes into some of these issues.
That's a podcast that we ran earlier this year. He talks about the uniqueness of humanity, even though we're on a spectrum with a lot of other animals in terms of things that we used to think were uniquely human – like, tool making or language, things like that. But, one thing we talked about, he and I, that I did not include in that podcast is human chromosome 2, which is a fascinating example of what makes us unique and how we became different from the other great apes. And I have saved that to run along with our discussion of this issue. So, would you like to hear about human chromosome number two from Ken Miller, Gary?
Stix: I absolutely would. What is it about human chromosome 2?
Mirsky: Well, I'm gonna let Ken Miller tell that story right now.
[KEN MILLER SEGMENT BEGINS]
Ken Miller: One of the things that I always like to emphasize when I give public talks on evolution is that the evidence for human evolution is not just in fossil jaw bones and teeth and so forth. That's what everybody thinks about. Everybody thinks paleontologists are still looking for what they call "the missing link". But paleontologists will tell you – we've discovered so many missing links, pre-human ancestors to our species, in the last three or four decades, that they're no longer missing. We have an embarrassment of riches in terms of pre-human ancestry.
In fact, the embarrassment is actually confusing, because it's difficult to tell which of these many organisms was our direct ancestor, which was sort of our distant cousin, and which, if you will, was sort of like the crazy uncle up in the closet. There are some dead ends, but there are some lines leading, we think, directly to us. But, to me, I'm not a fossil person. I am a – you might say I'm more of a DNA and RNA biologist than a fossil prospector. And I think the most spectacular evidence for human evolution is actually written in the human genome.
There are many examples of this. And, in my book, I tried to give several. These include a pseudo gene known as NANOG, which is scattered around our chromosomes in a pattern that matches that of our closest relatives in a remarkable way. They include the fact that even though we, like other placental mammals, don't lay eggs, we still actually have the broken remnants of the genes for the yolk proteins in eggs scattered around our genome. And, of course, the reason we have them is because we, like all mammals, did evolve from what were once egg-laying organisms – namely the mammal-like reptiles. And I go into that as an example as well.
But, to me, the clearest and the most straightforward example of this is right there sitting in one of our chromosomes. Now, we human beings have 46 chromosomes. We each got 23 from mom and 23 from dad. The organisms most closely related to us are the other great apes. And I say "other" 'cause we are actually one of the great apes.
And the other great apes include gorillas, bonobos, chimpanzees, orangutan and so forth. The curious thing is – all of them have 48 chromosomes, not 46. So, if we share a common ancestry with them, how did we get down to 46? Did we lose a pair of chromosomes? Well, the answer is – any geneticists will tell you – is no.
The loss of what biologists call a homologous pair of chromosomes would be fatal. It wouldn't even get throughout embryonic development. So, the only answer that would be consistent with evolutionary common ancestry is the following – and that is – two chromosomes, which are still separate in the other great apes, must have fused together to form a single chromosome in our species, and that would have dropped us from 24 pairs down to 23. Now, that's not evidence; that's just basically an analysis. But, the cool thing about evolution is that conjecture is testable. And if that was really true, if one of our chromosomes was formed by the recent fusion – about a million years ago, maybe two million years ago – of chromosomes that are still separate in the other primates, we ought to be able to find it in the human genome.
Now, how could we find it? Two ways. Every chromosome has, on its tips, a series of repeated sequences known as telomere repeats. They're at the tips of chromosomes. If we carry a chromosome that was formed recently by the fusion of two other chromosomes, we should have head to head telomere repeats at the point where those two chromosomes got stuck together.
It would be almost like finding a piece of scotch tape holding the two of them together. And every chromosome also has a special region – somewhere near the middle – called the centromere. The centromere is where chromosomes attach to what we call the mitotic spindle when they're separated during cell division. If we have a recently fused chromosome, it ought to have two centromere regions. Enter the human genome project, completed in 2002.
People start scanning through it and lo and behold, in 2005, what did we find? We do have a chromosome that has head to head telomere sequences right in the middle and also has two centromere sequences. It's human chromosome number two. And the sequences – DNA sequences – on either side of that fusion site correspond to what we used to call chromosomes 12 and 13 in the other great apes – gorillas and chimpanzees. That similarity – that homology – is so perfect and so compelling, that geneticists working on the chimpanzee genome, the gorilla genome and so forth, they no longer call those chromosomes in the other primates 12 and 13.
They call them 2a and 2b because they correspond to the two halves of our chromosome number 2. Now, this is much better explained on the black board or with a Power Point slide, but I always try to tell audiences – DNA sequences are not theories. They're not hypotheses. They're not conjectures.
DNA sequences are facts. And this is a fact that is only explicable in terms of our common ancestry with the other great apes. And when I present this to lay audiences who are simply interested in knowing what's the evidence behind evolution, I gotta tell you; it blows them away. I see the look on their faces and they go, "Wow." And sometimes, I will challenge – especially a college audience. I'll say, "Okay. I just told you the chromosome 2 story. How many of you knew this before you came to the lecture tonight?"
And three or four hands will go up and you know who's holding those hands up? Professors of genetics. They knew it. And then, I'll say something to indict my own profession. "Do you know whose fault it is that everybody doesn't know that?
Know whose fault it is why you weren't taught that in school? It's my fault. And it's the fault of everybody else in the scientific community, because we have such overwhelming and compelling and easy to understand evidence for evolution and we don't popularize it. We don't make people aware. We don't go around saying, 'Look how clear the case is.'
And that's really the fault – the indictment of the entire scientific community." And that's one of the reasons I put the chromosome 2 story in this book.
Mirsky: You know, it's – to me, it's thrilling. It's a thrilling story that we were able to figure that out – that we were able to come up with an idea about it and then look for it and find it and it fits exactly the way it should.
Miller: And that's exactly how science is supposed to work.
Mirsky: And you also mention in the book – now, this I didn't know – that there are actually perfectly healthy human beings with 44 chromosomes.
Miller: Yes. Every now and then, someone will tell me, "Well, that must've happened first. That fusion must've happened first in a few individuals. And wouldn't it interfere with fertility, with cell division and so forth?" And the answer turns out to be – there is a slight effect on that.
But, it turns out – and I'm gonna take the easy part first – the closest thing that we have on this planet to a truly wild horse are horses in Mongolia called Przewalski's horse. Przewalski's horse has 66 chromosomes. Domestic horses – Equus caballus, if you will, has only got 64. Why is it that all domesticated horses, again, are missing a pair? Well, the answer is chromosome fusion.
And we can see exactly where it happened, and it happened at some point – probably in central Europe or Asia – during the domestication of horses. So, that's a very interesting thing. Now, here's the next thing. The argument that if this had happened in one of our ancestors, they wouldn't have been fertile, they wouldn't have left descendants – there are now two scientific reports of families with 44 chromosomes. And, in each case, it has resulted of a fusion between two chromosomes.
The one I can recall immediately was the fusion between chromosomes 14 and 15 to form a single combined chromosome. This must've happened a couple of generations ago. The people are healthy. They're still viable. And that shows that there's not a problem of mechanism here.
Chromosome fusions, in fact, happen so common that there's a jargon term for them. They're called Robertsonian Translocations. And they are well-known in mice and other experimental animals, and it's not surprising what happened in our ancestry as well.
Mirsky: I'll be back in a moment.
That's it for this episode. Get your science news at our Web site, www.ScientificAmerican.com, where you can also check out Evelyn Lamb's article on how math – specifically abstract algebra – helped her learn early music. And follow us on Twitter where you'll get a tweet whenever a new item hits the website. Our Twitter name is @SciAm. For Scientific American's Science Talk, I'm Steven Mirsky. Thanks for clicking on us.
That’s it for this episode. Get your science news at our Website, www.scientificamerican.com. Where you can also check out Evelyn Lamb’s article on how math, specifically abstract algebra, helped her learn early music.
And follow us on Twitter, where you’ll get a tweet whenever a new item hits the Web site. Our twitter name is @sciam. For Scientific American’s Science Talk, I’m Steve Mirsky, thanks for clicking on us.