Brains of the Monster-Teeth

Dissopsalis, another member 
of the "monster-tooth" family

Among the distinguishing features of mammals, as compared with other vertebrates are the larger relative size and greater structural complexity of the brain. It's worth pointing out at the outset that many birds are as capable as mammals of complex behaviour despite not possessing the brain structures we'd otherwise associate with such things so that we can't solely use brain anatomy as a proxy for things like 'intelligence'. But, if we're looking only at mammals, brain anatomy can tell us quite a bit and it's probably fair to say that it does distinguish us from, say, reptiles.

Let's Split the Party!

Last week, I described how, over the last few decades, populations of gray seals have recovered from a near-total local extinction in US waters. Clearly, other species facing similar threats, across the world, have not been so lucky. The rapid pace of human expansion simply overwhelms the ability of some species to cope, whether it be through direct effects (expansion of agriculture, cities, transport networks, and so on) or indirect ones (climate change, most obviously).

In the millions of years before humans appeared on the scene the world was changing at a slow enough pace that it was possible for mammal species to evolve their way out of a problem. Many didn't, of course, and went extinct, but others gave rise to newer species that outlived them. Today, it's not just the scale of the changes humans are making that has caused problems for some species, but also their speed.

When it comes to dealing with very rapid changes in the environment - whether human-caused or otherwise - mammals have both advantages and disadvantages compared to some other species. On the negative front, mammals, especially the larger ones, have long generation times, meaning that any effect of evolution, even on a relatively minor scale, is inevitably going to be slow.

The Spikiness of Tenrecs

Being a small mammal (or, indeed, any other kind of animal) can be tough; there's always something out there that wants to try and eat you. There are a whole host of adaptations that animals use to try and avoid this fate. Running fast and being good at hiding or camouflage are, perhaps, the most obvious and widespread defensive methods. Another approach is to live somewhere that it's really difficult for most predators to find you, such as spending your entire life in an underground burrow.

Fighting back, as larger horned animals might do, generally isn't so effective, although skunks (for example) have certainly found a way of doing that. But there is also the option of body armour. It's something we see quite a lot in reptiles and, in living mammals, it's perhaps best developed in armadillos. But body armour doesn't have to be a bony or keratinous shell, for something that wants to avoid being eaten, spines can also be an effective deterrent.

The Social Lives of Elephants

Indian elephant

Elephants are the largest land-dwelling animals alive today. They are also among the most intelligent non-primate species, with complex social lives, and, as I noted in passing a few weeks ago, seem to be able to pass the Mirror Test for self-awareness - the only mammal, other than apes or dolphins, for which there is reasonable evidence of this ability.

There are many reasons that we'd like to know more about the lives and habits of elephants; even leaving pure curiosity aside, on a practical level it might help us to find ways to manage elephant populations so that they can peacefully co-exist with our expanding agricultural and residential footprint.

But there is a problem to really getting to grips with elephant "societies" and how they function. That's because, in addition to being large, elephants are also remarkably long-lived. If you go out into the wild and study a herd of elephants for five years, you will get a lot of information, but it's really just a snapshot of what's going on in the course of their lives. Elephants can live for at least seventy years, and a generation lasts for about 25 years, so getting a really good picture of an elephant's life would take... well, a human lifetime.

Are Horses Self-Aware?

I'd imagine that the first response from anyone who regularly deals with horses to the above would be "well, of course they are!" Your horse shows not just awareness and recognition, and is clearly a fairly intelligent animal, but there seems to be something going on behind those eyes. Horses seem, for example, to be aware of the emotional state of their handlers, and respond appropriately. There is surely more to their actions than simple, pre-programmed instinct.

And, if that is your response, let's face it, you're not wrong.

But then, awareness isn't a simple "all or nothing" phenomenon. All living things respond to their environment in some way; it's part of the definition of being alive. But even once we exclude say, tomato plants, there's still a massive gulf between jellyfish and humans. Once we get specifically to mammals, there is clearly more going in their mental and emotional states than is the case for, say, starfish or parasitic worms. But even then, there is no sharp line between the full consciousness of an adult human and the awareness of every other sort of mammal.

Memory Tests for Mouse Lemurs

The ability to learn and remember things is a vital ability for just about any animal, albeit the sort of things that (say) monkeys are able to learn can be a good deal more complex than those flatworms can manage. There are, however, multiple different types of memory, rather than it being a single process that takes place in our brains and works the same way every time. There is the difference between short-term and long-term memory, for one thing (and there's actually more than two of those), but also between what are termed procedural and declarative memory.

Procedural memory is the ability to remember how to do something. Once you've learned whatever the task is, you don't need to think about it, it just comes automatically, like riding a bicycle. Exactly like riding a bicycle, in fact. Declarative memory, on the other hand, is the sort of thing you have to think about, such as remembering what happened to you the last time you were in a specific situation. If you're a human, this includes the ability to remember things like Vespertilio being a genus of bat (well, it is if you're me), but it also encompasses a much wider range of knowledge about the world and your own experiences in it.

How Clever is a Baboon?

Humans were long considered quite different from the rest of the animal kingdom based on the fact that they're considerably smarter. While we now know that, biologically speaking, we're no different from any other animal, there remains no question that we are quite a bit more intelligent. This is why we're the dominant species on Earth - at least, assuming you happen to use human-biased definitions of 'dominant'. (There are other senses in which, say, bacteria have us beat hands down).

Anatomically, the clearest sign of this higher intelligence is the size of our brains. Relative to the rest of our bodies, they are huge, and they're also considerably more complex than those of many other mammals, let alone reptiles, fish, or insects. The 'relative' part is important, though. An elephant's brain is much larger than that of a human, and those of whales are larger still. Now, granted, elephants and whales are among the most intelligent of mammals, but it's not as if they've discovered quantum mechanics or (that we know of) have composed the equivalent of Dante's Divine Comedy. Their brain is large in part because they are large, and, when you allow for the size of the bodies, it's really not all that big in proportion to the rest of them.

On the other hand, when it comes to brains, as with certain other organs, size does matter. The brain of a mouse is, in proportion to it's body, almost exactly the same size as our own. (And something like, say, a chaffinch, has a brain that's even larger). Clearly, there is a minimum size below which you just can't fit all that much into a brain, in terms of neural connections and the like.  Smaller animals, therefore, will have proportionally larger brains, just in order to function.

Cultural Traditions of the Spider Monkey

One of the distinguishing features of humanity is the great cultural variation that we exhibit across the globe. The traditions and practices of, say, the Masai of Africa, are quite different from those of western Europeans. In animals, by contrast, behaviour tends to be firmly dictated by genetics. Even where there is clear learning, with mothers teaching their offspring to hunt, for example, the end results of that learning are often fairly similar across a given species.

But, as is so often the case, the dividing line between humans and our closest relatives is not so clear as that broad generalisation would imply. Traditions have been observed in other animals, even including some that aren't primates, such as dolphins and killer whales. When we talk about 'traditions' in these animals, we are referring to behaviours exhibited by some populations of a species that are, for no obvious reason, not seen among other populations. The behaviours are obviously not genetic, or everyone would perform them, but on the other hand, neither are they simply the result of some lucky discovery by a single individual that was never passed on to their peers.

Most research on such traditions has been carried out on chimpanzees, and has tended to focus on the way that they use tools. This has obvious relevance to our own origins, as well as having the advantage of being easily identifiable. Chimpanzees do seem to learn at least some of their behaviour by copying others in their local cultural environment, and this sort of learning may extend quite a way back in our evolutionary family tree, since such tool-using cultural traditions have also been seen in orangutans.

But tools do nor represent the entirety of culture. To look further back into the origins of traditions, it may be useful to look at our more distant relatives, and to consider behaviour that is more relevant to the way they live their lives. Geoffroy's spider monkey (Ateles geoffroyi) is native to the Americas, placing it firmly on a branch of monkey evolution entirely separate from that which eventually gave rise to humans in Africa. They appear to be remarkably intelligent animals - perhaps even more so than gorillas - but they don't have opposable thumbs, and since the main thing they want to do in life is pick fruit off trees, they really don't need much in the way of tools, anyway.



 Spider        Woolly      Howler
 monkeys       monkeys     monkeys
    ^             ^           ^
    |             |           |
    |             |           |      Other American
    ---------------           |         monkeys
           |                  |            ^
           |                  |            |
           --------------------            |       Apes & Old
                    |                      |      World monkeys
                    |                      |            ^
                    ------------------------            |
                               |                        |
                               |                        |
                               --------------------------
                                           |
                                           |

They also have a relatively unusual social structure among mammals. They live in groups, but individuals often wander about different groups, and the groups themselves are always merging and splitting. In contrast, most group-living mammals tend to stick to herds where the females stay with their relatives and the males wander off to find and dominate new groups elsewhere, and then stick with them. The more complex arrangement among spider monkeys means that it will be relatively common for individuals to encounter past 'friends' that they haven't seen in a long time, and perhaps to develop their own greeting rituals for that purpose. It's worth noting that, although they belong to a different part of the primate family tree, chimpanzees are among the few other mammals to live like this (along with humans, of course).

It can be difficult to demonstrate that particular behaviours are not genetic in origin, since even within a species, there could well be genetic differences we are not aware of. However, the usual way of looking for cultural traditions, as used for chimpanzees and orang utans, is to examine the behaviour of animals in different locations, and see how much it differs. This was recently performed for an array of 62 different types of behaviour in Geoffroy's spider monkeys in Costa Rica, Panama, Belize, and Mexico.

Most of the behaviours turned out not to fit the definition of a 'tradition'. Around 20 were performed by monkeys in all the study sites, making it difficult to rule out these being genetically programmed habits. Others were very rare, suggesting that even if one animal had learned that this was a useful thing to do, it never (or at least, hadn't yet) passed the information on to its fellows. For a few, there were obvious reasons why the behaviour couldn't be carried out just anywhere - for example, its difficult to eat the fruit of cohune palms if there aren't any where you live.

But that still left 22 behaviours that just didn't fit the obvious pattern. Some of these were related to the choice of foods. In two sites, almost all the monkeys were seen happily eating the fruit of the elephant ear tree (which, despite being a tree, is also a really big legume). Yet, in the others, they never touched the plant, apparently not realising it was edible, even though there were plenty around. One Costa Rican population had even figured out that they could eat mushrooms, something not normally associated with this fruit-eating species.

Other behaviours, however, were more complex. In some areas, monkeys would climb onto the shoulders of their fellows in piggy-back style in order to appear larger and more threatening to an intruder, while in others it never seemed to occur to them to do this. The monkeys in Panama were often seen to walk upright on their hind legs, something that the monkeys in Belize never did, and was quite rare elsewhere.

As predicted, many of these more social behaviours were related with greeting outsiders, perhaps to determine whether they were long lost friends who shared the same traditions. These included various forms of scent marking, and whether or not they rubbed fig roots on their bodies (presumably to give themselves a distinctive smell). Although all of the groups greeted outsiders in the usual manner for their species - which includes a lot of embracing each other - some of them also kissed each other lightly on the cheeks. Yet the Panamanian monkeys, while they would blow kisses at each other from a distance, never actually kissed each other directly.

The same Costa Rican population that ate mushrooms also had an unusual habit of sometimes climbing to the tops of tall trees and facing into the wind with their mouths open. Presumably this felt pleasant, and probably helped them cool down, but again, its significant that none of the monkeys elsewhere did this, despite the obvious opportunity to do so.

All in all, there was significant variation among the different populations in terms of which practices they performed and which they didn't. Every population had at least some unusual practice that at least one other didn't possess. It's hard, as I mentioned earlier, to be sure that none of these are due to some minor genetic difference, especially since the communities are isolated from each other by the increasing fragmentation of Central American jungles (which has led, sadly, to the species becoming endangered). But that also reduces the chance for cultural communication across large distances, allowing particular traditions to develop and survive in isolated areas. That there was no pattern to which behaviours were exhibited where also tends to count against the genetic theory. If that were the case, then, since one might expect monkeys closer together geographically to be more related, one would also expect them to have more habits in common, and they don't.

Culture and learning are things that humans have developed far beyond any other species on Earth. But we are not entirely separate from the rest of the animal kingdom. The brains of our closest relatives are not simply hard-wired with everything they need to know, and sometimes animals can discover a way of doing something that other members of their species elsewhere have not. When they do, at least some of the time, they can pass this information on to their relatives and neighbours, something that requires the sort of cognitive powers that we tend to think are purely human.

Humans are animals, and the line between us and 'them' is sometimes a very blurred one.

[Picture from Wikimedia Commons]

The Intelligence of Chimps

Our closest living relatives are, of course, the chimpanzees. There are, in fact, two species of chimp: the common chimpanzee (Pan troglodytes), and the bonobo (Pan paniscus). The latter is sometimes called a "pygmy chimpanzee", although, frankly, there's not a lot of difference in size between the two species. Both species are equally related to humans, having diverged from a common ancestor less than two million years ago, long after that common ancestor diverged from the line that eventually led to us.

Common
Chimp    Bonobo   Human   Gorillas
  |         |       |
  |         |       |
  -----------       |        ^
       |            |        |
       |            |        |
       --------------        |
             |               |
             |               |
             -----------------
                    |
                    |

Both species live in fairly similar environments in the jungles of tropical Africa, and eat more or less the same kinds of food, so we might expect that their behaviour would also be similar. But that's clearly not the case; common chimps are significantly more aggressive than bonobos, while the latter are renowned for their frequent sexual exploits. Common chimps are also more likely than bonobos to use simple tools to extract food from difficult to reach places.

Do these differences in behaviour reflect real differences in intelligence between the two species? A recent large-scale analysis, published in PLoS ONE, aimed to find out. "Intelligence" is a fairly tricky thing to pin down, even in humans, so "which species is the more intelligent?" wasn't the sort of question that the study could answer. Rather, the researchers tested members of both species on a range of tasks designed to look at different aspects of intelligence. Would they perform the same, or would one species prove better at some tasks than the other?

Of course, the study was not conducted in the wild; the animals in question were orphans raised by humans in ape sanctuaries - their parents, in most cases, presumably having been killed by bushmeat poachers. Nonetheless, they had not previously experienced these kinds of tests, so they would have to solve the problems on their own.

For the most part, there wasn't a great difference. The researchers tested spatial awareness by placing food under cups and then rotating the table, moving the cups about, and so on, to see if the chimps could figure out where the food had ended up. Members of both species got this right a little over two thirds of the time. To test their ability to count and perform simple addition, the experimenters placed differing amounts of food under covers and watched to see which one the chimp went for first. Again, both species got this right about two thirds of the time. (This does not, incidentally, imply actual arithmetic - just that the animals could recognise that, say, six peanuts is more than three).

In tests of communication - could the chimps either understand an experimenter trying to tell them where the food was, or could they themselves indicate to the experimenter where hidden food was located - they still managed to get it right over half the time, but again, there was no difference between the two species.

The most difficult test was one in which the food was placed inside a container that required a relatively complex method to open. The researchers showed the chimp how to get the food, and saw if the animals could successfully copy them. In most cases, they couldn't - and, in previous trials elsewhere, no chimp had ever solved these particular problems on their own - although, interestingly, in both species, the females were far more likely to succeed than the males.

However, in tests designed to see whether the chimps could use clues to find hidden food, or could use tools to obtain food, although both species got it right more often than not, the common chimps were significantly better than the bonobos. Tool use, in particular, is something we particularly associated with human intelligence, so we might think that this makes common chimps the more "human-like" of the two species in this respect.

But, of course, using tools isn't really the be-all and end-all of human intelligence. Our ability to work together as a species relies, in part, on our ability to understand the minds of others and to bond together socially. The final set of tests evaluated the chimps' abilities to grasp concepts such as attention and intentionality. For example, a piece of food would be hidden beneath one of two cups; the chimp could not see which cup it was, but a second human could. When the second human tried (and failed) to grab one of the cups, would the chimp work out that this was because that was where the food was hidden? On this test, the bonobos did better, succeeding just over half the time.

So, given that they scored similarly on all the other tests, it seems plausible that the basic intelligence of the two species isn't all that different. Yet the way that they use that intelligence, or the particular skills that they possess, is different. Common chimps are better at physical tasks and understanding the operation of the physical world. But the peaceful and relatively shy bonobos scored higher on tests of social awareness and the ability to understand the minds of others. Both of these are important aspects of human intelligence. Our closest relatives have evolved along paths parallel to our own, and each, perhaps can show something of how we rose to our present position of power over our planet.

[Pictures from Wikimedia Commons - upper image is a common chimp, lower image is a bonobo (both males)]