Tag Archives: evolution of intelligence

Planet of the apes

22.9-21.6 million years ago

The Miocene (23 – 5 million years ago) is a period of extraordinary success for our closest relatives, the apes. Overall there may have been as many as a hundred ape species during the epoch. Proconsul (actually several species) is one of the earliest. We will meet just a few of the others over the course of the Miocene, as some leave Africa for Asia, and some (we think) migrate back.

Sometimes evolution is a story of progress – not necessarily moral progress, but at least progress in the sense of more effective animals replacing less effective. For example, monkeys and apes largely replace other primates (prosimians, relatives of lemurs and lorises) over most of the world after the Eocene, with lemurs flourishing only on isolated Madagascar. This replacement is probably a story of more effective forms outcompeting less effective. And the expansion of brain size that we see among many mammalian lineages throughout the Cenozoic is probably another example of progress resulting from evolutionary arms races.

But measured by the yardstick of evolutionary success, (non-human) apes — some of the brainiest animals on the planet — will turn out not to be all that effective after the Miocene. In our day, we’re down to just about four species of great ape (chimpanzees, bonobos, gorillas, and orangutans), none of them very successful. Monkeys, with smaller body sizes and more rapid reproductive rates, are doing better. For that matter, the closest living relatives of primates (apart from colugos and tree shrews) are rodents, who are doing better still, mostly by reproducing faster than predators can eat them.

So big brains aren’t quite the ticket to evolutionary success that, say, flight has been for birds. One issue for apes may be that with primate rules for brain growth – double the brain size means double the neurons means double the energy cost – a large-bodied, large brained primate (i.e. an ape) is going to face a serious challenge finding enough food to keep its brain running. It’s not until a later evolutionary period that one lineage of apes really overcomes this problem, with a combination of better physical technology (stone tools, fire) and better social technology (enlisting others to provision mothers and their dependent offspring).

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Ground-up monkey brains

One reason for being interested in monkeys is that they’re brainy mammals. Here’s the conventional graph illustrating that:

brain size

Larger mammals tend to have larger brains, but the relationship is non-linear. Multiplying body mass by x doesn’t multiply brain mass by x. Instead it multiplies brain mass by about x.75. In other words, Brain Mass is proportional to (Body Mass).75. Equivalently (taking the logarithm of both sides) Log[Brain Mass] is equal to .75 times Log[Body Mass], plus a constant. So Log[Brain Mass] plotted against Log[Body Mass] gives a straight line with a slope of .75. That means that if one mammal has 16 times the body mass of another, it’s expected to have 8 times the brain mass. 10,000 times the body mass means 1000 times the brain mass. The thing to note is that primates defy expectations. They have larger brains than would be expected based on their body sizes.

But we’ve recently learned that primates – especially big ones – are even more special than this graph suggests. Susan Herculano-Houzel has pioneered a technique that involves chopping up brains (or parts of brains), dissolving their cells to make a kind of brain soup, and counting cell nuclei. This allows her to estimate how many neurons there are in different brains.

monkey brain soup

Major findings: Among most mammals, the number of neurons increases more slowly than brain size. Increase brain size by x, and you increase number of neurons by about x.67. (H-H shows this flipped around. Increase number of neurons by x and you increase brain mass by x1.5.) But primates are exceptional; the relationship is nearly linear. An x-fold increase in primate brain size corresponds to about an x-fold increase in number of neurons. Humans follow the primate rule here. We have about the same density of neurons as other primates. When you combine the exceptionally large brain sizes of humans with a standard high primate neuron density, you get an animal with an enormous number of neurons. By contrast, a rodent with a human sized brain, if it followed rodent rules for how neuron numbers increase with brain size, would have only 1/7 as many neurons.

Neurons are expensive. Most large animals economize by cutting back on neuron density. A cubic centimeter of cow brain has fewer neurons, and consumes energy at a lower rate, than a cubic centimeter of mouse brain. By contrast, large primates are extravagant, devoting exceptionally large energy budgets to running their brains. And human brains are exceptionally costly. An important question for the study of human evolution is how we paid the bill for such costly brains. That’s a story for later. But another part of the story starts back in the early Cenozoic, when monkeys committed to a different set of rules for building brains.

Where is everybody? Maybe we’re (some of) the first.

5.31-5.03 billion years ago

A followup to yesterday’s post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible.

On its own, it’s not clear this would have prevented intelligent life from arising long ago. The Sun has a high “metallicity” (concentration of heavy elements), but there are stars in the Milky Way older than the Sun with higher metallicities. But metallicity could combine with GRBs (below): toward the center of the galaxy there are more heavy elements but also more GRBs.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out tweets for January 11.) They are probably supernovas or even larger explosions with one pole of the exploding star pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere off Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.

Untitled

Where is everybody?

5.62 – 5.32 billion years ago

Today in Logarithmic History, January 17, covers a period beginning over a billion years before the origin of our solar system. Back then, stars were forming at a fast clip in the Milky Way and other spiral galaxies. So let’s suppose… Suppose one of those older stars resembled the Sun, and had a planet like Earth orbiting around it – call it Urth. And suppose life originated on Urth more or less as on Earth and followed more or less the same evolutionary path. With this head start, intelligent life could have evolved a billion years ago, and today there could be intelligent Urthians (or their robot descendants) a billion years ahead of us.

There’s an urban legend that says that Einstein called compound interest the strongest force in the universe. Einstein didn’t actually quite say this, but it’s not a crazy thing to say. For example, consider how compound interest works, backward, on our Logarithmic History calendar. December 30 covers a period 5.46% longer than December 31, December 29 is 11.2% longer (because 1.0546 * 1.0546 = 1.112), and so on. At this rate of compounding we wind up with January 1 covering 754 million years. The same math implies that if we invested 1 dollar at 5.46% interest, compounded annually, then after 364 years we’d have 754 million dollars.

With even the slightest compound rate of increase, a billion year old Elder Race would have plenty of time to fill up a galaxy, and undertake huge projects like dismantling planets to capture more of their suns’ energy. Which raises the question, posed by Enrico Fermi in 1950: “Where is everybody?” There are more than 100 billion stars in our galaxies, more than 100 billion galaxies in the visible universe (actually, according to recent estimates, the number may be more than  1 trillion). If there are huge numbers of billion year old Elder Races around, why hasn’t at least one of them taken the exponential road and made themselves conspicuous?

There’s a large literature on the Fermi paradox. One possible explanation is that we’re one of the first intelligent species to evolve because the universe was somehow less suitable for the evolution of complex life before now. I’ll take that one up tomorrow.

Learn This One Weird Trick (Part Two)

… that humans use, and now you can too! (Continued from the previous post.)

recursion 3) Recursion. What if you have one mirror facing a second mirror, so the first mirror shows what’s in the second mirror, which shows what’s in the first mirror …? What if you take a chameleon, which tries to take on the color of its surroundings, and put it on a mirror? What if you point a video camera at the very screen that’s showing what the video camera is pointing at? What if (getting mathematical) you use a function in defining that same function? What if you use the cleaning attachment from your vacuum cleaner to suck dust off the vacuum cleaner itself? (Okay, the last one is a bit lame.) The basic idea in each of these cases is called recursion, which is a major concept in mathematics and computer science. Douglas Hofstadter’s Gödel, Escher, Bach is all about recursion. Some people think recursion – nesting ideas about ideas inside one another in a potentially infinite hierarchy, or (for syntax) phrases inside phrases — is central to human uniqueness. Noam Chomsky has lately been pushing a hard-core version of this argument. Here he is with Robert Berwick defending his view.

Related to the idea of recursion is the idea of “meta-representation”: not just having ideas about the world but having ideas about ideas, being able to put a box around a proposition, and then attaching a tag to it that says the equivalent of “This is true” or “This is false” or “This will be true later” or “Suppose this were true,” and then manipulating it accordingly. A nice little essay in “imagination,” elaborating this idea, is here from Simon Baron-Cohen, best known as an authority on autism.

4) Shared intentionality. Suppose you and I are friends with a couple, Fred and Wendy Smith. I tell you “I saw Wendy Smith kissing a man in the park yesterday.” Logically speaking, there’s nothing to say the man wasn’t Fred. But you’ll probably assume that I meant she was kissing someone other than Fred. Why? Well if the man had been Fred I could just as easily have said “I saw Wendy Smith kissing Fred in the park yesterday.” Since I didn’t say that, you assume I mean to convey the man wasn’t Fred. Note this only works if both of us try to pack as much relevant information into our sentences as possible and know the other person is doing the same. (If you think this sounds like recursion, you’re right.) Back in the 1950s, Paul Grice, a philosopher, worked out a lot of how we pack non-literal meanings into sentences. But the same principles are at work even when people are communicating non-linguistically. This leads to another theory of human uniqueness: human beings are uniquely good at developing shared intentions with one another: each party knows the other party is trying to communicate something, so they converge on the correct answer. People may have been doing this even before language evolved. Following up on this can quickly get you into game theory, where a central concept is “common knowledge”: not just “I know X” and “You know X,” but “I know X,” and “I know X is common knowledge,” and similarly for you. Here’s a philosophical treatment.

scleraBut you can skip the philosophy if you want and move on to a telling little piece of anatomy that’s relevant here. In most mammals, including chimpanzees, the sclera (white of the eyes) is not visible. It’s hard to tell where a chimpanzee is looking, easy for a human. Human eyes make it easy to cooperate in sharing attention, a first step in developing shared intentions. If you know your card games, chimpanzees are playing poker, humans are playing bridge.

Our discussion of human uniqueness on Logarithmic History has been frustratingly short on specific dates. But human sclera are probably a fairly simple trait genetically, and we may soon enough discover the genes involved and even tell how long ago they mutated.

Where is everybody? Maybe we’re (some of) the first.

A followup to yesterday’s post on the Fermi Paradox, some reasons the Universe could have been less suitable for the evolution of complex life until recently, making us one of the first intelligent species to evolve.

1) Metallicity. Chemical elements heavier than helium are formed inside stars, after the Big Bang. Elements heavier than iron are formed in exploding supernovas. These elements have been building up over time. Maybe they had to reach a threshold abundance to make complex life possible.

On its own, it’s not clear this would have prevented intelligent life from arising long ago. The Sun has a high “metallicity” (concentration of heavy elements), but there are stars in the Milky Way older than the Sun with higher metallicities. But metallicity could combine with GRBs (below): toward the center of the galaxy there are more heavy elements but also more GRBs.

2) Gamma Ray Bursts (GRBs). GRBs are bursts of gamma rays (high frequency radiation) lasting from milliseconds to minutes, like GRB 080319B. (Check out tweets for January 11.) They are probably supernovas or even larger explosions with one pole of the exploding star pointed at the Earth. A major GRB could irradiate one side of the planet, and also affect the other side by destroying the ozone layer, causing mass extinctions. GRBs may have swept the Milky Way frequently in the past. The good news is they’re probably getting less frequent. This could be the first time in the history of the Milky Way that enough time has passed without a major GRB for intelligent life to evolve. If true, we should think about how to protect ourselves from the next one – lots of sunblock recommended.

If GRBs are such a threat, we might expect to find evidence that they have caused mass extinctions in the past (not wiping out all life obviously). For more on this, check out upcoming blog posts and tweets for the end-Ordovician, March 3.

3) Panspermia (life from elsewhere). Pretty much as soon as Earth could support life, we see evidence of single-celled organisms. Then life evolves slowly for a long time. The usual story about this is that the origin of life is easy, and it happens as soon as possible. But there is another possibility (illustrated below). It may be that the transition from simple replicating chemical systems to bacteria with genomes of tens of thousands of DNA base pairs is a slow process that happened over many billions of years somewhere off Earth. Then newly forming planets in the nebula that gave rise to Earth were “infected” by this source, by meteorites carrying early cells. (It would have been easier for meteorites to carry life from star system to star system when the Earth was first formed than it would be today.) Back when our hypothetical “Urth” was forming, a billion years before Earth, there might not have been any planets with cellular life on them as potential sources of life-bearing meteorites.

Untitled

Where is everybody?

Today, January 16, covers the period 5.62 to 5.31 billion years ago in Logarithmic History, beginning a billion years before the origin of our solar system. Back then, stars were forming at a fast clip in the Milky Way and other spiral galaxies. So let’s suppose… Suppose one of those older stars resembled the Sun, and had a planet like Earth orbiting around it – call it Urth. And suppose life originated on Urth more or less as on Earth and followed more or less the same evolutionary path. With this head start, intelligent life could have evolved a billion years ago, and today there could be intelligent Urthians (or their robot descendants) a billion years ahead of us.

There’s an urban legend that says that Einstein called compound interest the strongest force in the universe. Einstein didn’t actually quite say this, but it’s not a crazy thing to say. For example, consider how compound interest works, backward, on our Logarithmic History calendar. December 30 covers a period 5.46% longer than December 31, December 29 is 11.1% longer (because 1.0546 * 1.0546 = 1.112), and so on. At this rate of compounding we wind up with January 1 covering 754 million years. The same math implies that if we invested 1 dollar at 5.46% interest, compounded annually, then after 364 years we’d have 754 million dollars.

With even the slightest compound rate of increase, a billion year old Elder Race would have plenty of time to fill up a galaxy, and undertake huge projects like dismantling planets to capture more of their suns’ energy. Which raises the question, posed by Enrico Fermi in 1950: “Where is everybody?” There are more than 100 billion stars in our galaxies, more than 100 billion galaxies in the visible universe (actually, according to recent estimates, the number may be more than  1 trillion). If there are huge numbers of billion year old Elder Races around, why hasn’t at least one of them taken the exponential road and made themselves conspicuous?

There’s a large literature on the Fermi paradox. Here I consider just one sort of explanation. Maybe we’re one of the first intelligent species to evolve because the universe was somehow less suitable for the evolution of complex life before now. (To be continued).