Out of Tibet - Origins of the First Sheep

The argali is a species of wild sheep still found in Tibet

Sheep, as I have noted before, are members of the goat subfamily within the much larger group of the bovids. They are, in essence, a special kind of goat that has adapted to living in the foothills of higher mountains, rather than on the steeps-sided peaks themselves. The exact number of species of sheep is debatable, but there are at least five wild ones, plus the domestic animal, for a total of six.

When I discussed the evolutionary history of the goat subfamily a few years back, I talked primarily about the goats themselves, and about the muskoxen, and said very little about how the sheep became separated from the goats, and how they evolved since. A new paper, however, goes into much more detail about the origin of sheep and their fossil history. It is, in fairness, based on just one pair of fossilised horns, but, nonetheless, this is as good a starting point as any, and a sound excuse for me to summarise what we do know about sheep evolution.

Invasion of the Fire Ants

Small, herbivorous mammals have a hard time of it when it comes to being attacked by larger carnivorous ones. Life expectancies are generally short in the wild, counter-balanced by the ability of most animals to breed like... well, rabbits. Many of their behavioural traits are also shaped by the need to avoid being eaten, including, not just general watchfulness, but trying to do things like foraging where (or when) predators are least likely to be a problem.

On the other hand, predators naturally have an interest in getting round this problem, and the result is a never-ending battle between the habits and skills of predators and prey alike. Over the course of thousands of years, this settles into a sort of equilibrium, changing perhaps only as new species evolve and as the geography or climate change on even longer time scales. Unless, of course, we humans get involved.

Humans can mess up the balance of life among wild animals in quite a number of ways, but the one we're concerned with today is that of invasive species. We purposefully carry species from one part of the world to others, especially when it comes to domesticated animals. Pre-Columbian America had no cows, no domestic sheep (although, of course, two native wild species), no pigs, and no horses or cats. There were dogs, but only because humans had brought them across much earlier. The introduction of all of these animals, and the changes in land use required to support them, have had significant effects on the local wildlife in at least some parts of America, and that's before we include animals deliberately introduced for other reasons, such as fur-farming or hunting, never mind those that we didn't introduce purposefully at all, such as rats.

Whispering Bats on the Hunt for Nectar

Southern long-nosed bats (L. curasoae)

There are likely three things that most of us think of when we think of bats: they fly, they're nocturnal, and they can echolocate using inbuilt sonar. In fact, only the first of these is universally true of bats; there are (and never have been, so far as we can tell) any flightless bats in the way that there are flightless birds. The other two statements, while broadly correct, are not absolutely true of all living bat species.

Indeed, the bats are the second largest order of mammals, in terms of number of species, after the rodents. This, as might be expected, leads to a remarkable variety in their habits and ecology, even if much of it is not immediately obvious to the layman. There are, under the most common present scheme, no less than nineteen different families of bat, and while many other mammal families have names that can easily be rendered in regular English ("cats", "deer", "marmosets", and so on), those of bats are have to rely on more obscure terms ("funnel-eared bats", "sheath-tailed bats", etc.)

Bovines: Bongos in the Jungle

Bongo

Broadly speaking, the more cow-like bovine species tend to be found wild in forested habitats, often with quite dense foliage. In contrast, the antelope-like bovines tend to prefer more open wooded country or scrubland. But these are both very crude generalisations. Plains bison and yak, for example, both live in open terrain, and, on the other side of the coin, there are bovine antelopes that prefer forest to savannah.

Among these is the bongo (Tragelaphus eurycerus), which can be found in three, entirely separate, regions of equatorial Africa. The two main populations live along the southern coast of West Africa, from Guinea to Benin, and across the heart of the Congo Basin and surrounding jungles, from Cameroon and Gabon in the west almost to the Ugandan border in the east. The vast majority of bongos live in these two areas, which are nonetheless separated by over 1,000 km (620 miles) of intervening land (much of which is Nigeria). The third population is found only in a couple of tiny mountain refuges in Kenya, where they cling to the forested slopes, migrating up and down them each year as the weather changes.

Pliocene (Pt 13): The First Carnivorans in South America

Macrauchenia

For most of the Pliocene, South America was an island continent. Over the millions of years of its isolation, it had evolved some strange forms of mammal unknown elsewhere. Some, such as the anteaters, armadillos, and sloths, survived the continent's eventual collision with its northern counterparts; most did not. A time traveller visiting the continent during this epoch would find much that was vaguely familiar, to be sure - there were monkeys, rodents, and bats, for example - but also much that was not. This is especially true when it comes to the larger animals of the day.

Even today, South America has no antelopes, zebras, or native goats; the role of "large hoofed herbivore" is taken jointly by deer and by llamas and their kin. Both are introductions from the north, arriving only after the rise of the Panamanian Isthmus in the very latest part of the Pliocene. Their appearance did not spell immediate doom for the native hoofed animals, some of which struggled on until the arrival of humans at the end of the last Ice Age, but the end result was the same, and they are all long extinct.

Flesh-eating Hippos

Hippopotamuses (Hippopotamus amphibius) are amongst the largest of all land-dwelling animals alive today, beaten only by the elephants, and some of the larger species of rhino. They are also distinctive creatures, with their only close relative today being the pygmy hippopotamus, an animal that many people are likely familiar with, if only because they're popular in zoos. While there are, of course, many extinct species, these two are the only living members of the hippo family, the Hippopotamidae.

In the grander scheme of things, hippos belong to the order Artiodactyla, most of the other members of which, such as deer and cattle, are cloven-footed ruminants. Hippos are neither. Like their fellow artiodactyls, the pigs, they are not ruminants, and they have four functional toes. Unlike pigs, however, the toes of hippos are all more or less equal in size and weight-bearing (in pigs, especially warthogs, the two side toes may be used to help steady the animal on slippery or uneven surfaces, but bear little if any of its weight during regular walking).

Do Gorillas Have Culture?

Animal behaviour is generally instinctual. Their behaviour is, in some way, wired into their genetics, and doesn't vary from one animal to another. Particularly in mammals and birds, individual animals may be shaped by their life experiences, learning new things as they go. But what they can't do, as a rule, is pass that information on to others. Mothers may teach their young how to do certain things, but that teaching process is itself instinctual, so that all animals of a given species learn more or less the same thing as infants.

A large part of the success of our own species is down to our ability to circumvent this, to build on the knowledge of previous generations. This results, among other things, in the development of culture, differences in behaviour based not on the experiences of only one individual, but of their ancestors, in a way that isn't genetic. Britain and Japan are different culturally, not just because of environmental variation (Japan has earthquakes, for example, and has different mineral resources than Britain) but simply because of the vicissitudes of history, the separate evolution of their languages, and so on.