The Ancestor's Tale Part 7

It is more problematical whether all the whales hang together. On the face of it, the toothed whales and the baleen whales might well represent two entirely separate returns to the sea from the land. Indeed, that very possibility has often been advocated. The molecular taxonomists who demonstrated the hippo connection very wisely did take DNA from both a toothed whale and a baleen whale. They found that the two whales are indeed much closer cousins to each other than they are to a hippo. But again, how do we know that 'the toothed whales' hang together as a group? And the same for 'the baleen whales'? Maybe all the baleen whales are related to a hippo except the minke whale, which is related to a hamster. No, I don't believe that, and I really do think the baleen whales are a united clade, sharing a common ancestor which is not shared by anything that is not a baleen whale. But can you see how the hippowhale discovery shakes the confidence?

We could regain our confidence if we could think of a good reason why whales might be special in this respect. If whales are glorified artiodactyls, they are artiodactyls that suddenly took off, evolutionarily speaking, leaving the rest of the artiodactyls behind. Their closest cousins, the hippos, remained relatively static, as normal, respectable artiodactyls. Something happened in the history of the whales that made them flip into evolutionary overdrive. They evolved so much faster than all the rest of the artiodactyls that their origin within that group was obscured, until molecular taxonomists came along and uncovered it. So, what is special about the history of the whales?

When you write it down like that, the solution leaps off the page. Leaving the land and becoming wholly aquatic was a bit like going into outer s.p.a.ce. When we go into s.p.a.ce we are weightless (not, by the way, because we are a long way from the Earth's gravity, as many people think, but because we are in free fall like a parachutist before he pulls the ripcord). A whale floats. Unlike a seal or a turtle, which still comes on land to breed, a whale never stops floating. It never has to contend with gravity. A hippo spends time in the water, but it still needs stout, treetrunk-like legs and strong leg muscles for the land. A whale doesn't need legs at all, and indeed it doesn't have any. Think of a whale as what a hippo would like to be if only it could be freed from the tyranny of gravity. And of course there are so many other odd things about living the whole time in the sea that it comes to seem far less surprising that whale evolution should have spurted as it did, leaving hippos behind, stranded on land and stranded in the middle of the artiodactyls. This suggests that I was unduly alarmist a few paragraphs back.

Much the same thing happened in the other direction, 300 million years earlier, when our fish ancestors emerged from the water onto the land. If whales are glorified hippos, we are glorified lungfish. The emergence of legless whales from within the middle of the artiodactyls, leaving the rest of the artiodactyls 'behind', should not seem more surprising than the emergence of four-legged land animals from one particular group of fish, leaving those fish 'behind'. That, at any rate, is how I rationalise the hippowhale connection, and recover my lost zoological composure.

EPILOGUE TO THE HIPPO'S TALE.

Zoological composure be blowed. My attention was drawn to the following while this book was in its final stages of preparation. In 1866, the great German zoologist Ernst Haeckel drew up a schematic evolutionary tree of mammals (see plate 9) (see plate 9). I had often seen the full tree reproduced in histories of zoology, but I had never before noticed the position of the whales and hippos in Haeckel's scheme. Whales are 'Cetacea', as today, and Haeckel presciently placed them close to the artiodactyls. But the real stunner is where he put the hippos. He called them by the unflattering name 'Obesa' and he cla.s.sified them not in the artiodactyls but as a tiny twig on the branch leading to Cetacea.8 Haeckel cla.s.sified hippos as the sister group to the whales: hippos, in his vision, were more closely related to whales than they were to pigs, and all three were more closely related to each other than to cows. Haeckel cla.s.sified hippos as the sister group to the whales: hippos, in his vision, were more closely related to whales than they were to pigs, and all three were more closely related to each other than to cows.

... there is no new thing under the sun. Is there anything whereof it may be said, See, this is new? It hath been already of old time, which was before us.ECCLESIASTES 1: 910 THE SEAL'S TALE.

Most wild animal populations have approximately equal numbers of males and females. There's a good Darwinian reason for this, which was clearly seen by the great statistician and evolutionary geneticist R. A. Fisher. Imagine a population in which the numbers were unequal. Now, individuals of the rarer s.e.x will on average have a reproductive advantage over individuals of the commoner s.e.x. This is not because they are in demand and have an easier time finding a mate (although that might be an additional reason). Fisher's reason is a deeper one, with a subtle economic slant. Suppose there are twice as many males as females in the population. Now, since every child born has exactly one father and one mother, the average female must, all other things being equal, have twice as many children as the average male. And vice versa if the population s.e.x ratio is reversed. It is simply a question of allocating the available posterity among the available parents. So, any general tendency for parents to favour sons rather than daughters, or daughters rather than sons, will immediately be counteracted by natural selection for the opposite tendency. The only evolutionarily stable s.e.x ratio is 50/50.

But it isn't quite that simple. Fisher spotted an economic subtlety in the logic. What if it costs twice as much to rear a son, say, as to rear a daughter, presumably because males are twice as big? Well, now, the reasoning changes. The choice that faces a parent is no longer, 'Shall I have a son or a daughter?' It is now, 'Shall I have a son or for the same price two daughters?' The balanced s.e.x ratio in the population is now twice as many females as males. Parents who favour sons on the grounds that males are rare, will see their advantage precisely undermined by the extra cost of making males. Fisher divined that the true s.e.x ratio equalised by natural selection is not the ratio of numbers of males to numbers of females. It is the ratio of economic spending on rearing sons to economic spending on rearing daughters. And what does economic spending mean? Food? Time? Risk? Yes, in practice all these are likely to be important, and for Fisher the agent doing the spending was always parents. But economists use a more general expression of cost, which they call opportunity cost. The true cost to a parent of making a child is measured in lost opportunities to make other children. This opportunity cost was named Parental Expenditure by Fisher. Under the name Parental Investment, Robert L. Trivers, a brilliant intellectual successor to Fisher, used the same idea to elucidate s.e.xual selection. Trivers was also the first to understand clearly the fascinating phenomenon of parentoffspring conflict, in a theory that has been carried further in startling directions by the equally brilliant David Haig.

As ever, and at the risk of boring those of my readers not handicapped by a little learning in philosophy, I once again must stress that the purposeful language I have used is not to be treated literally. Parents do not sit down and discuss whether to have a son or a daughter. Natural selection favours, or disfavours, genetic tendencies to invest food or other resources in such a way as to lead eventually to equal or unequal parental expenditure on sons and daughters, over the whole of a breeding population. In practice this will often amount to equal numbers of males and females in the population.

But what about those cases where a minority of males holds the majority of females in harems? Does this violate Fisher's expectations? Or those cases where males parade in front of females in a 'lek', and the females look them over and choose their favourite? Most females have the same favourite, so the end result is the same as for a harem: polygyny disproportionate access to a majority of females by a privileged minority of males. That minority of males ends up fathering most of the next generation, with the rest of the males hanging about as bachelors. Does polygyny violate Fisher's expectations? Surprisingly, no. Fisher still expects equal investment in sons and daughters, and he is right. Males may have a lower expectation of reproducing at all, but if they do reproduce they reproduce in spades. Females are unlikely to have no children but they are also unlikely to have very many. Even under conditions of extreme polygyny it evens out and Fisher's principle holds.

Some of the most extreme examples of polygyny are to be found among the seals. Seals haul themselves out onto beaches to breed, often in huge 'rookeries', heaving with intense s.e.xual and aggressive activity. In a famous study of elephant seals by the California zoologist Burney LeBoeuf, four per cent of the males accounted for 88 per cent of all copulations seen. No wonder the rest of the males are dissatisfied, and no wonder elephant-seal fights are among the fiercest in the animal kingdom.

Elephant seals are named for their trunks (short, by elephant standards, and used for social purposes only), but it could equally be for their size. Southern elephant seals can weigh 3.7 tonnes, more than some cow elephants. Only the bull seals reach this weight, however, and that is one of the central points of the tale. Cow elephant seals are typically less than a quarter the weight of bulls, by whom they, and the calves, are regularly flattened as the bulls charge about fighting each other.9 Why are males so much bigger than females? Because large size helps them to win harems. Most young seals, of whichever s.e.x, are born to a giant father who won a harem, rather than a smaller male who failed to win a harem. Most young seals, of whichever s.e.x, are born to a relatively small mother whose size was optimised to the business of giving birth and rearing babies, rather than the business of winning fights.

The separate optimisation of male and female characteristics comes about through selection of genes. People are sometimes surprised to learn that the genes concerned are present in both s.e.xes. Natural selection has favoured so-called s.e.x-limited genes. s.e.x-limited genes are present in both s.e.xes but turned on in only one s.e.x. For example, genes that tell the developing seal: 'If you are male grow very big and fight' are favoured at the same time as genes that say, 'If you are female, grow small and don't fight.' Both cla.s.ses of genes are pa.s.sed on to sons and to daughters, but each is expressed in one s.e.x and not the other.

If we look at mammals overall, we notice a generalisation. s.e.xual dimorphism meaning a big difference between males and females tends to be most marked in polygynous species, especially those with a harem-style society. As we've seen, there are good theoretical reasons why this should be so, and we've also seen that the seals and sea lions go farthest out along this particular limb.

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Relations.h.i.+p between s.e.xual dimorphism and harem size. Each point represents a species of seal or sea lion. Adapted from Alexander Each point represents a species of seal or sea lion. Adapted from Alexander et al et al. [5].

The graph above comes from a study made by the eminent zoologist Richard D. Alexander of the University of Michigan and his colleagues. Each blob in the graph represents one species of seal or sea lion, and you can see that there is a strong relations.h.i.+p between s.e.xual dimorphism and harem size. In extreme cases, for example southern elephant seals and northern fur seals which are the two blobs at the top of the graph, males may be more than six times the weight of females. And, sure enough, in these species the successful males a minority, to put it mildly have huge harems. Two extreme species can't be used to draw general conclusions. But a statistical a.n.a.lysis of the known data for seals and sea lions confirms that the trend we think we see is real (the odds against its being a chance effect are more than 5,000 to 1). There is weaker evidence in the same direction from ungulates and from monkeys and apes.

To repeat the evolutionary rationale for this, males have a great deal to gain, and also a great deal to lose, from fighting other males. Most individuals born, of either s.e.x, are descended from a long line of male ancestors who succeeded in winning harems, and a long line of female ancestors who were members of them. Therefore most individuals, whether male or female, and whether they themselves go on to be winners or losers, inherit genetic equipment for helping male bodies to win harems and female bodies to join them. Size is at a premium, and the successful males can be very large indeed (see plate 10) (see plate 10). Females, by contrast, have little to gain from fighting other females, and they are only as large as they need to be to survive and be good mothers. Individuals of both s.e.xes inherit genes that make females avoid fighting and concentrate on child-rearing. Individuals of both s.e.xes inherit genes that make males fight against other males, even at the expense of time that could have been spent helping to rear children. If only males could agree to settle their disputes by the toss of a coin, they would presumably shrink over evolutionary time to the size of the females or smaller, with great economic savings all round, and they could give their time to looking after children. Their surplus ma.s.s, which in extreme cases must cost a great deal of food to build up and maintain, is the price they pay to be compet.i.tive with other males.

Of course, not all species are like seals. Many are monogamous and the s.e.xes are much more alike. Species in which the s.e.xes are the same size tend, with some exceptions such as horses, not to have harems. Species in which males are markedly bigger than females tend to have harems, or to practise some other form of polygyny. Most species are either polygynous or monogamous, presumably depending on their different economic circ.u.mstances. Polyandry (females mated to more than one male) is rare. Among our close relatives, gorillas have a harem-based polygynous breeding system and gibbons are faithfully monogamous. We could have guessed this from their s.e.xual dimorphism, and lack of it respectively. A large male gorilla weighs twice as much as a typical female, while gibbon males and females are approximately equal in size. Chimpanzees are more indiscriminately promiscuous.

Can the Seal's Tale tell us something about our own natural breeding system, before civilisation and custom obliterated the traces? Our s.e.xual dimorphism is moderate but undeniable. Lots of women are taller than lots of men, but the tallest men are taller than the tallest women. Lots of women can run faster, lift heavier weights, throw javelins further, play better tennis, than lots of men. But for humans, unlike for racehorses, the underlying s.e.xual dimorphism precludes s.e.x-blind open compet.i.tion at the top level in almost any sport you care to name. In most physical sports, every single one of the world's top hundred men would beat every single one of the world's top hundred women.

Even so, by the standards of seals and many other animals, we are only slightly dimorphic. Less so than gorillas, but more than gibbons. Perhaps our slight dimorphism means our female ancestors lived sometimes monogamously, sometimes in small harems. Modern societies vary so much that you can find examples to support almost any preconception. The Ethnographic Atlas Ethnographic Atlas of G. P. Murdock, published in 1967, is a brave compilation. It lists particulars of 849 human societies, surveyed all over the world. From it we might hope to count numbers of societies that permit harems versus numbers that enforce monogamy. The problem with counting societies is that it is seldom obvious where to draw lines, or what to count as independent. This makes it hard to do proper statistics. Nevertheless, the atlas does its best. Of those 849 societies, 137 (about 16 per cent) are monogamous, four (less than one per cent) are polyandrous, and a ma.s.sive 83 per cent (708) are polygynous (males can have more than one wife). The 708 polygynous societies are divided about equally into those where polygyny is permitted by the rules of the society but rare in practice, and those where it is the norm. To be brutally precise, of course, 'norm' refers to harem members.h.i.+p for females and harem aspiration for males. By definition, given equal numbers of men and women, the majority of men miss out. The harems of some Chinese Emperors and Ottoman Sultans broke the most extravagant records of the elephant seals and fur seals. Yet our physical dimorphism is small when compared with the seals, and also probably although this evidence is disputed when compared with the australopithecines. Would this mean that australopithecine chiefs had harems even larger than Chinese Emperors? of G. P. Murdock, published in 1967, is a brave compilation. It lists particulars of 849 human societies, surveyed all over the world. From it we might hope to count numbers of societies that permit harems versus numbers that enforce monogamy. The problem with counting societies is that it is seldom obvious where to draw lines, or what to count as independent. This makes it hard to do proper statistics. Nevertheless, the atlas does its best. Of those 849 societies, 137 (about 16 per cent) are monogamous, four (less than one per cent) are polyandrous, and a ma.s.sive 83 per cent (708) are polygynous (males can have more than one wife). The 708 polygynous societies are divided about equally into those where polygyny is permitted by the rules of the society but rare in practice, and those where it is the norm. To be brutally precise, of course, 'norm' refers to harem members.h.i.+p for females and harem aspiration for males. By definition, given equal numbers of men and women, the majority of men miss out. The harems of some Chinese Emperors and Ottoman Sultans broke the most extravagant records of the elephant seals and fur seals. Yet our physical dimorphism is small when compared with the seals, and also probably although this evidence is disputed when compared with the australopithecines. Would this mean that australopithecine chiefs had harems even larger than Chinese Emperors?

No. We mustn't apply the theory in a naive way. The correlation between s.e.xual dimorphism and harem size is only a loose one. And physical size is only one indicator of compet.i.tive strength. For elephant seals, male size is presumably important, because they win their harems by physically fighting other males, biting them or overpowering them by sheer weight of blubber. Size is probably not negligible in hominids. But any sort of differential power, which enables some males to control a disproportionate number of females, can take the place of physical size. In many societies, political clout plays this role. Being a friend of the chief or, better, being the chief empowers an individual: enables him to intimidate rivals in a way that is equivalent to the physical intimidation of a large bull seal over a smaller one. Or there may be ma.s.sive inequalities in economic wealth. You don't fight for wives, you buy them. Or you pay soldiers to fight for them on your behalf. The Sultan or the Emperor may be a physical wimp, yet he may still secure a harem larger than any bull seal. The point I am moving towards is that even if australopithecines were much more dimorphic in size than us, our evolution from them may not, after all, have been a move away from polygyny itself. It may just have been a s.h.i.+ft in the weapons used for male compet.i.tion: from sheer size and brute force to economic power and political intimidation. Or, of course, we also may have s.h.i.+fted towards more genuine s.e.xual equality.

For those of us with a distaste for s.e.xual inequality, it is a consoling hope that cultural polygyny, as distinct from brute-force polygyny, might be rather easy to get rid of. On the face of it, this seems to have happened in those societies, such as (non-Mormon) Christian societies, which became officially monogamous. I say 'on the face of it' and 'officially', because there is also some evidence that apparently monogamous societies are not quite what they seem. Laura Betzig is a historian with a Darwinian turn of mind, and she has uncovered intriguing evidence that overtly monogamous societies like ancient Rome and medieval Europe were really polygynous under the surface. A rich n.o.bleman, or Lord of the Manor, may have had only one legal wife but he had a de facto de facto harem of female slaves, or housemaids and tenants' wives and daughters. Betzig cites other evidence that the same was true of priests, even those who were notionally celibate. harem of female slaves, or housemaids and tenants' wives and daughters. Betzig cites other evidence that the same was true of priests, even those who were notionally celibate.

These historical and anthropological facts have been seen by some scientists as suggesting, together with our moderate s.e.xual dimorphism, that we evolved under a polygynous breeding regime. But s.e.xual dimorphism is not the only clue we can get from biology. Another interesting signal from the past is testis size.

Our closest relatives, the chimpanzees and bon.o.bos, have extremely large testes. They are not polygynous like gorillas, nor are they monogamous like gibbons. Female chimpanzees in oestrus normally copulate with more than one male. This promiscuous mating pattern is not polyandry, which means the stable bonding of one female with more than one male. It does not predict any simple pattern of s.e.xual dimorphism. But it did suggest to the British biologist Roger Short an explanation for the large testes: chimpanzee genes have been pa.s.sed down the generations via spermatozoa that had to battle it out in compet.i.tion with rival sperms from several males inside the same female. In such a world, sheer numbers of spermatozoa matter, and this demands big testes. Male gorillas, on the other hand, have small testes but powerful shoulders and huge resonating chests. Gorilla genes do their competing via male fights and chest-thumping threats to win females, which pre-empts subsequent sperm compet.i.tion inside females. Chimpanzees compete via sperm proxies inside v.a.g.i.n.as. This is why gorillas have p.r.o.nounced s.e.xual dimorphism and small testes, while chimpanzees have large testes and weak s.e.xual dimorphism.

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Relations.h.i.+p between testis ma.s.s and body ma.s.s. Each point represents a species of primate. Adapted from Harvey and Pagel [ Each point represents a species of primate. Adapted from Harvey and Pagel [132].

My colleague Paul Harvey, with various collaborators including Roger Short, tested the idea using comparative evidence from monkeys and apes. They took twenty genera of primates and weighed their testes. Well, actually, they went into the library and gathered published information on testis ma.s.ses. Large animals obviously tend to have larger testes than small animals, so they had to correct for that. Their method was the one explained in the Handyman's Tale for brains. They placed each monkey or ape genus as a point on a graph (above) of testis ma.s.s against body ma.s.s and, for the same reasons as we saw in the Handyman's Tale, they took logarithms of both. The points fell around a straight line, from marmosets at the bottom to gorillas at the top. As with the brains, the interesting question was which species have relatively big testes for their size, and which smaller. Of all the points scattered about the line, which ones fall above the line and which below?

The results are suggestive. The filled black symbols all represent animals that are like chimpanzees in that females mate with more than one male, and where there is consequently likely to be sperm compet.i.tion. The chimpanzee itself is the black blob at the top. The open circles are all from animals whose breeding system does not involve much sperm compet.i.tion, either because they are harem breeders like gorillas (the open circle to the far right) or they are faithfully monogamous like gibbons.

The separation between the open circles and the filled blobs is satisfying.10 We seem to have support for the sperm compet.i.tion hypothesis. And now, of course, we want to know where we fall on the graph. How big are our testes? Our position on the graph (see small vertical cross) is close to the orang utan. We seem to cl.u.s.ter with the open circles rather than with the black blobs. We are not like chimpanzees, and probably have not had to contend with much sperm compet.i.tion in our evolutionary history. But this graph says nothing about whether the breeding system of our evolutionary past was like a gorilla's (harem) or like a gibbon's (faithful monogamy). That sends us back to the evidence of s.e.xual dimorphism and anthropology, both of which suggest mild polygyny: a small tendency in the direction of harems. We seem to have support for the sperm compet.i.tion hypothesis. And now, of course, we want to know where we fall on the graph. How big are our testes? Our position on the graph (see small vertical cross) is close to the orang utan. We seem to cl.u.s.ter with the open circles rather than with the black blobs. We are not like chimpanzees, and probably have not had to contend with much sperm compet.i.tion in our evolutionary history. But this graph says nothing about whether the breeding system of our evolutionary past was like a gorilla's (harem) or like a gibbon's (faithful monogamy). That sends us back to the evidence of s.e.xual dimorphism and anthropology, both of which suggest mild polygyny: a small tendency in the direction of harems.

If there is indeed evidence that our recent evolutionary ancestors were weakly polygynous, I hope it needs no saying that this should not be used to justify a moral or political stance, one way or the other. 'You can't get an ought from an is' has been said so often it is in danger of becoming tedious. It is none the less true for that. Let's hasten on to our next rendezvous.

1 I would have liked, at this point, to insert the Bat's Tale, but it would be pretty much the same as a chapter in another of my books, so I won't. Incidentally, I had to exercise similar restraint over 'the Spider's Tale', 'the Fig Tree's Tale' and half a dozen others. I would have liked, at this point, to insert the Bat's Tale, but it would be pretty much the same as a chapter in another of my books, so I won't. Incidentally, I had to exercise similar restraint over 'the Spider's Tale', 'the Fig Tree's Tale' and half a dozen others.

2 By the way, we even had it wrong when we cla.s.sified hippos most closely with pigs within the artiodactyls. The molecules suggest that the sister group to the hippowhale clade is the ruminants: the cows, sheep and antelopes. Pigs lie outside them all. By the way, we even had it wrong when we cla.s.sified hippos most closely with pigs within the artiodactyls. The molecules suggest that the sister group to the hippowhale clade is the ruminants: the cows, sheep and antelopes. Pigs lie outside them all.

3 The molecular evidence for this radical view is what I have referred to in the Gibbon's Tale as a Rare Genomic Change (RGC). Transposable element genes that are highly recognisable are found in particular places in the genome, and are presumably inherited from the hippowhale ancestor. While this is very strong testimony, it is nevertheless prudent to look at the fossils too. The molecular evidence for this radical view is what I have referred to in the Gibbon's Tale as a Rare Genomic Change (RGC). Transposable element genes that are highly recognisable are found in particular places in the genome, and are presumably inherited from the hippowhale ancestor. While this is very strong testimony, it is nevertheless prudent to look at the fossils too.

4 The celebrated Victorian anatomist Richard Owen tried to get the name changed to The celebrated Victorian anatomist Richard Owen tried to get the name changed to Zeuglodon Zeuglodon, and Haeckel followed suit in his phylogeny, reproduced in plate 9. But we are stuck with Basilosaurus Basilosaurus.

5 This idea has a name, the Baldwin Effect, although the idea was independently proposed by Lloyd Morgan in the same year, and by Douglas Spalding earlier. I follow Alister Hardy's way of developing it in This idea has a name, the Baldwin Effect, although the idea was independently proposed by Lloyd Morgan in the same year, and by Douglas Spalding earlier. I follow Alister Hardy's way of developing it in The Living Stream The Living Stream. For some reason it is a favourite of mystics and obscurantists.

6 The fearsome The fearsome Andrewsarchus Andrewsarchus was one of them. was one of them.

7 Actually, blood is not the best source of DNA in mammals because, unusually among vertebrates, their red blood corpuscles don't have nuclei. Actually, blood is not the best source of DNA in mammals because, unusually among vertebrates, their red blood corpuscles don't have nuclei.

8 Haeckel didn't get everything right, however. He put the sirenians (dugongs and manatees) in with whales. Haeckel didn't get everything right, however. He put the sirenians (dugongs and manatees) in with whales.

9 Don't be surprised that bull seals flatten calves of their own species. Any calf squashed is no more likely to be the bull's own child than the child of any rival bull. Therefore there is no Darwinian selection against squas.h.i.+ng. Don't be surprised that bull seals flatten calves of their own species. Any calf squashed is no more likely to be the bull's own child than the child of any rival bull. Therefore there is no Darwinian selection against squas.h.i.+ng.

10 In plots of this kind, it is important to include only data that are independent of each other, otherwise you can unfairly inflate the result. Harvey and colleagues sought to avoid this danger by counting genera instead of species. It is a step in the right direction, but the ideal solution is that urged by Mark Ridley in In plots of this kind, it is important to include only data that are independent of each other, otherwise you can unfairly inflate the result. Harvey and colleagues sought to avoid this danger by counting genera instead of species. It is a step in the right direction, but the ideal solution is that urged by Mark Ridley in The Explanation of Organic Diversity The Explanation of Organic Diversity, and fully endorsed by Harvey: look at the family tree itself and count neither species nor genera but independent evolutions of the characteristics of interest.

Rendezvous 12.

XENARTHRANS.

Rendezvous 12, about 95 million years ago in the time of our 35-million-greats-grandparent, is where we meet the xenarthran pilgrims from South America, which at that time had fairly recently torn itself away from Africa and was a very large island just the thing for fostering the evolution of a unique fauna. The xenarthrans are a rather odd group of mammals, consisting of the armadillos, sloths and anteaters and their extinct relatives. Their name means 'alien joints', referring to the peculiar way their vertebrae join onto each other: they have extra articulations between their lumbar vertebrae, which strengthen the backbone for the digging that so many of them go in for. Among anteaters, only South American ones are xenarthrans. Other mammals such as pangolins and aardvarks also eat ants and are called, respectively, scaly anteaters and ant bears. All 'anteaters', by the way, might just as well be called termite-eaters they are very fond of termites.

The xenarthrans have a tale to tell of South America, and it falls to the armadillo to tell it. We shall cover the diversity of the Xenarthra themselves during the course of the tale.

THE ARMADILLO'S TALE.

Zoologically speaking, South America is a sort of giant Madagascar. Like Madagascar, it split off from Africa, but from the west rather than the east side, around the same time, or a bit later than Madagascar. Like Madagascar, South America was cut off from the rest of the world during most of the period of mammal evolution. Its long purdah, which ended only about 3 million years ago, led to South America becoming a gigantic natural experiment culminating in a unique and fascinating mammal fauna. Like Australia but unlike Madagascar, South America's fauna was rich in marsupials. In South America's case, marsupials filled most of the carnivorous niches. Unlike Australia, South America also had plenty of placental (non-marsupial) mammals, including armadillos and other xenarthrans, and various uniquely South American 'ungulates', now all extinct, which evolved entirely independently of the even-toed and odd-toed ungulates of the rest of the world.

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Xenarthrans join. Of the four major placental mammal groups identified by molecular taxonomists, the two earliest branching are the afrotheres (see Of the four major placental mammal groups identified by molecular taxonomists, the two earliest branching are the afrotheres (see Rendezvous 13 Rendezvous 13) and the South American xenarthrans (approximately 30 species of sloths, anteaters, and armadillos). Conceivably, further data may reverse the order of Rendezvous 12 Rendezvous 12 and and 13 13, but here we draw the current consensus.

Image: six-banded armadillo ( six-banded armadillo (Euphractus s.e.xcinctus).

We have already seen that monkeys and rodents entered South America, probably in separate rafting incidents long after the continent wrenched itself free from Africa. When the monkeys and the rodents arrived, they found a continent already thickly populated with unique mammals. These 'old timers', to borrow from the book Splendid Isolation Splendid Isolation by the great American zoologist G. G. Simpson, belong to three main groups. The Xenarthra are one, and there were some marsupials, which we'll come to later. The remaining old timers can all be loosely called ungulates. As we saw at by the great American zoologist G. G. Simpson, belong to three main groups. The Xenarthra are one, and there were some marsupials, which we'll come to later. The remaining old timers can all be loosely called ungulates. As we saw at Rendezvous 11 Rendezvous 11, 'ungulate' is not a taxonomically precise word. These South American old timers did the same herbivorous job as horses, rhinos and camels, but they evolved independently of them.

Unlike Madagascar and Australia, South America's isolation came to an end naturally, before human travel brought all zoological isolation more or less to an end. The rise of the Isthmus of Panama, as recently as 3 million years ago, led to the Great American Interchange. The separate faunas of North and South America were free to travel along the narrow corridor formed by the Isthmus, to each other's continents. This enriched the two faunas, but then some extinctions occurred on both sides, presumably at least partly as a result of compet.i.tion.

Because of the Great American Interchange, there are now tapirs (odd-toed ungulates) and peccaries (even-toed ungulates) in South America animals that entered from North America even though tapirs are now extinct there and peccaries greatly reduced. Because of the Interchange, there are now jaguars in South America. Before, there were no cats, or any members of the order Carnivora. Instead, there were carnivorous marsupials, some bearing a fearsome resemblance to the sabretooths (true cats) which were their contemporaries in North America. Since the Interchange there have been armadillos in North America, including glyptodonts giant armadillos with what look comically like tweed caps on their heads, and formidably spiked clubs on the end of their tails, perhaps wielded against sabretooths, both marsupial and placental. Alas, the glyptodonts went extinct, surprisingly recently, as did the giant ground sloths, lumbering ground-dwelling cousins of today's tree sloths. Ground sloths are often depicted rearing up on their hind legs to feed on trees, and they may also have knocked them down, as elephants do today. The largest of them were, indeed, comparable in size to elephants, six metres long and between three and four tonnes in weight. Ground sloths (though not the very largest of them) penetrated North America as far north as Alaska.

Coming the other way, llamas, alpacas, guanacos and vicunas, all members of the camel family, are now confined to South America, but camels originally evolved in North America. They spread into Asia and then Arabia and Africa quite recently, presumably via Alaska, where they gave rise to the Bactrian camels of the Mongolian steppe, and the dromedaries of the hot deserts. The horse family, too, did most of their evolving in North America but then went extinct there, which makes poignant the baffled surprise with which the Native Americans responded to the horses, reintroduced from Eurasia under the infamous conquistadores.

The anteaters don't seem to have made it into North America, but three genera survive in South America, and very unusual mammals they are. They have no teeth at all and the skull, especially in the case of Myrmecophaga Myrmecophaga, the large ground-dwelling anteater, has become little more than a long, curved tube, a kind of straw for imbibing ants and termites which are chivvied out of their nests by means of a long sticky tongue. And let me tell you something amazing about them. Most mammals, like us, secrete hydrochloric acid into our stomachs to aid digestion, but South American anteaters don't. Instead, they rely upon the formic acid from the ants that they eat. This is typical of the opportunism of natural selection.

Of the other 'old timers' of South America, the marsupials survive only in the form of the opossums (which are also now common in North America), the very different 'shrew opossums' (confined to the Andes), and the single mouse-like monito del monte (which, strangely enough, seems to have emigrated back to South America from Australia). We shall meet them properly when we get to Rendezvous 14 Rendezvous 14.

The old South American 'ungulates' are all extinct, and more's the pity because they were amazing creatures. Simpson's name 'old timers' only means that their ancestors have been in South America for a very long time, probably since that continent broke free of Africa. They evolved and diversified during the same long period as our more familiar mammals were evolving and diversifying in the Old World. Many of them flourished up to the time of the Great American Interchange and, in some cases, beyond. The litopterns split early into horse-like and camel-like forms, which probably (from the position of the nose bones) had a trunk like an elephant. Another group, the pyrotheres, also probably had a trunk, and may have been quite elephant-like in other respects. They were certainly very large. The South American mammal fauna rather ran to ma.s.sive rhino-like forms, some of whose fossil bones were first found by Darwin. The notoungulates included huge rhinoceros-like toxodons, and smaller rabbit-like and rodent-like forms.

The Armadillo's Tale is the tale of South America in the Age of Mammals. It is the tale of a gigantic raft, like Madagascar, Australia and India cut adrift by the breakup of Gondwana. Madagascar we have already dealt with in the Aye-Aye's Tale. Australia will be the subject of the Marsupial Mole's Tale. India would have been a fourth raft experiment, except that it travelled north so fast that it reached Asia rather early, and so its fauna became integrated with that of Asia during the latter half of the Age of Mammals. Africa, too, was a gigantic island during the rise of the mammals, not so isolated as South America and not for so long. But long enough for a large and very diverse group of mammals to go their own way in isolation, closer cousins to each other than to the rest of the mammals, though you'd never guess it to look at them. These are the Afrotheria, and we are about to meet them at Rendezvous 13 Rendezvous 13.

Rendezvous 13.

AFROTHERES.

The Afrotheria are the last placental mammals to join our pilgrimage. They originated in Africa as their name suggests, and they include the elephants, the elephant shrews, the dugongs and manatees (also known as sea elephants or sea cows), the hyraxes, the aardvarks or ant bears, and probably the tenrecs of Madagascar and the golden moles of southern Africa. The next pilgrims we shall greet will be our far more distant cousins the marsupials, so the Afrotheria all of them equally are our most distant non-marsupial cousins. Concestor 13 lived 105 million years ago, and was our 45-million-greats-grandparent, or thereabouts. Once again, it looked similar to Concestor 12 and Concestor 11, all pretty much like shrews.

I never saw an elephant shrew until I revisited the beautiful country of Malawi which, as Nyasaland, had been my childhood home. My wife and I spent some time in the Mvuu Game Reserve, just south of the great Rift Valley lake which gave the country its name and on whose sandy beaches I had spent my first bucket-and-spade holidays long ago. In the game reserve, we benefited from our African guide's encyclopaedic knowledge of the animals, his sharp eye for spotting them, and his engaging turns of phrase in calling them to our attention. Elephant shrews always elicited from him the same joke, which seemed to improve with each repeating: 'One of the small five.' (See plate 11.) (See plate 11.) Elephant shrews, which are named for their long trunk-like noses, are larger than European shrews, and they run higher, on longer legs a little suggestive of miniature antelopes. The smaller of the 15 species jump. Elephant shrews used to be more numerous and diverse, and included some plant-eating species as well as the insectivorous ones that survive today. Elephant shrews have the prudent habit of devoting time and attention to making runways for themselves to use later when escaping predators. This sounds like foresight and so, in a way, it is. But it should not be taken to imply deliberate intention (although, as always, that cannot be ruled out). Animals often behave as if they know what is good for them in the future, but we must be careful not to forget that 'as if'. Natural selection is a beguiling counterfeiter of deliberate purpose.

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Afrotheres join. The new phylogeny of placental mammals recognises the split between the 70 or so afrothere species and all other placentals as the earliest division within the group. However, the order of The new phylogeny of placental mammals recognises the split between the 70 or so afrothere species and all other placentals as the earliest division within the group. However, the order of Rendezvous 12 Rendezvous 12 and and 13 13 is not entirely resolved. Within the Afrotheria, there is still debate about the order of branching between the elephants, sirenians, and hyraxes; the position of the aardvark; and the tenrecs and golden moles. is not entirely resolved. Within the Afrotheria, there is still debate about the order of branching between the elephants, sirenians, and hyraxes; the position of the aardvark; and the tenrecs and golden moles.

Images, left to right: Cape elephant shrew ( Cape elephant shrew (Elephantulus edwardii); Grant's golden mole (Eremitalpa granti); aardvark (Orycteropus afer); West Indian manatee (Trichechus manatus); African elephant (Loxodonta africana); rock hyrax (Procavia capensis).

In spite of their dear little trunks, it never occurred to anyone that elephant shrews might be particularly close to elephants. It was always a.s.sumed that they were just African versions of Eurasian shrews. Recent molecular evidence, however, astonishes us with the information that elephant shrews are closer cousins to elephants than they are to shrews, and some people now prefer their alternative name, sengi, to distance them from shrews. By the way, the 'trunks' of elephant shrews are almost certainly incidental to their relations.h.i.+p to elephants. From the small five to the big, we come next to the elephants themselves.

Today the elephants are reduced to two genera: Elephas Elephas the Indian elephant, and the Indian elephant, and Loxodonta Loxodonta the African elephant, but elephants of various kinds including mastodons and mammoths once roamed through almost every continent except Australia. There are even tantalising hints that they may have made it to Australia too. Fragments of elephant fossils have been reported, but perhaps they were flotsam from Africa. Mastodons and mammoths were in America until around 12,000 years ago when they were exterminated, probably by the Clovis people. Mammoths died out so recently in Siberia that they are occasionally found frozen in the permafrost and have even, poets sing, been made into soup: the African elephant, but elephants of various kinds including mastodons and mammoths once roamed through almost every continent except Australia. There are even tantalising hints that they may have made it to Australia too. Fragments of elephant fossils have been reported, but perhaps they were flotsam from Africa. Mastodons and mammoths were in America until around 12,000 years ago when they were exterminated, probably by the Clovis people. Mammoths died out so recently in Siberia that they are occasionally found frozen in the permafrost and have even, poets sing, been made into soup: THE FROZEN MAMMOTHThis Creature, though rare, is still found to the EastOf the Northern Siberian Zone.It is known to the whole of that primitive groupThat the carca.s.s will furnish an excellent soup,Though the cooking it offers one drawback at least(Of a serious nature I own):If the skin be but punctured before it is boiledYour confection is wholly and utterly spoiled.And hence (on account of the size of the beast)The dainty is nearly unknown.HILAIRE BELLOC As with all of the Afrotheria, Africa is the ancient home of elephants, mastodons and mammoths, the root of their evolution and the site of most of their diversification. Africa has also become the home of lots of other mammals such as antelopes and zebras, and the carnivores that prey on them, but those are laurasiatheres, who came into Africa later, from the great northern continent of Laurasia. The Afrotheria are the African 'old timers'.

The elephant order is called Proboscidea, after their long proboscis or trunk, which is an enlarged nose. The many purposes for which the trunk is used include drinking, which may have been its primitive use. Drinking, when you are a very tall animal like an elephant or a giraffe, is a problem. Food, for elephants and giraffes, mostly grows on trees which may be partly why they are so tall in the first place. But water finds its own level, which tends to be uncomfortably low. Kneeling down to the water is a possibility. Camels do it. But it is hard work getting up again, even more so for elephants or giraffes. Both solve the problem by sucking the water up through a long siphon. Giraffes stick their head on the end of the siphon the neck. Giraffe heads therefore have to be rather small. Elephants keep their head which can therefore be bigger and brainier at the base of the siphon. Their siphon is, of course, the trunk, and it comes in handy for lots of other things as well. I have elsewhere quoted Oria Douglas-Hamilton on the elephant trunk. Much of her life has been devoted, with her husband Iain, to the study and preservation of wild elephants. It is an angry pa.s.sage, prompted by the horrifying sight of a ma.s.s 'cull' of elephants in Zimbabwe.

I looked at one of the discarded trunks and wondered how many millions of years it must have taken to create such a miracle of evolution. Equipped with fifty thousand muscles and controlled by a brain to match such complexity, it can wrench and push with tonnes of force. Yet, at the same time, it is capable of performing the most delicate operations such as plucking a small seed-pod to pop in the mouth. This versatile organ is a siphon capable of holding four litres of water to be drunk or sprayed over the body, as an extended finger and as a trumpet or loud speaker. The trunk has social functions, too; caresses, s.e.xual advances, rea.s.surances, greetings and mutually intertwining hugs ... And yet there it lay, amputated like so many elephant trunks I had seen all over Africa.

Proboscideans also run to tusks, which are greatly enlarged incisor teeth. Modern elephants have tusks only in the upper jaw, but some extinct proboscideans had tusks in the lower jaw as well, or instead. Deinotherium Deinotherium had large down-curving tusks in the lower jaw and no tusks at all in the upper jaw. had large down-curving tusks in the lower jaw and no tusks at all in the upper jaw. Amebelodon Amebelodon, a North American member of the large group of early proboscideans called gomphotheres, had elephant-like tusks in the upper jaw and flat, spade-like tusks in the lower jaw. Perhaps they were indeed used as spades, to dig up tubers (see plate 12) (see plate 12). This speculation doesn't, by the way, conflict with the one about the evolution of the trunk as a siphon to obviate the need to kneel for a drink. The lower jaw, with its two flat spades on the end, was so long that a standing gomphothere could easily have used it to dig in the ground.

In The Water Babies The Water Babies, Charles Kingsley wrote that the elephant 'is first cousin to the little hairy coney of Scripture ...' The primary meaning of coney in the English dictionary is rabbit, and two of the word's four occurrences in the Bible are explanations of why the rabbit is not kosher: 'And the coney, because he cheweth the cud, but divideth not the hoof; he is unclean unto you' (Leviticus 11:5 and the very similar pa.s.sage in Deuteronomy 14:7). But Kingsley can't have meant rabbit, because he goes on to say that the elephant is 13th or 14th cousin to the rabbit. The other two biblical references refer to an animal that lives among rocks: Psalm 104 ('The high hills are a refuge for the wild goats; and the rocks for the conies') and Proverbs 30:26 ('The conies are but a feeble folk, yet make they their houses in the rocks'). Here, it is generally agreed, coney means hyrax, da.s.sie or rock badger, and Kingsley, that admirably Darwinian clergyman, was right.

Well, he was right at least until those tiresome modern taxonomists burst in. Textbooks say that the elephants' closest living cousins were the hyraxes, which agrees with Kingsley. But recent a.n.a.lysis shows that we must also include dugongs and manatees in the mix, perhaps even as the closest living relatives of the elephants, with hyraxes the sister group. Dugongs and manatees are purely marine mammals who never come ash.o.r.e even to breed, and it looks as though we were misled in the same way as over the hippos and the whales. Purely marine mammals are freed from the constraints of terrestrial gravity and can evolve rapidly in their own special direction. Hyraxes and elephants, left behind on the land, have remained more similar to each other, just as hippos and pigs did. With hindsight, dugongs' and manatees' slightly trunk-like nose and small eyes in a wrinkled face give them a faintly elephantine appearance, but it is probably an accident.

Dugongs and manatees belong to the order Sirenia. The name comes from their supposed resemblance to the sirens of myth, although this is not, it has to be said, very convincing. Their slow, sleepy-lagoon style of swimming could perhaps have been thought mermaid-like, and they suckle their young with a pair of b.r.e.a.s.t.s under the flippers. But one can't help feeling that the sailors who first spotted the likeness must have been at sea for a very long time. Sirenians are, with whales, the only mammals that never come on land at any time. One species, the Amazon manatee, lives in freshwater; the other two manatees are found in the sea as well. Dugongs are exclusively marine, and all four species are vulnerable to extinction, which inspired my wife to design a T-s.h.i.+rt: Dugoing Dugong Dugone. A heart-rending story concerns the fifth species, the enormous Steller's sea cow, which lived in the Bering Straits and weighed over 5 tonnes. It was hunted to extinction a mere 27 years after its discovery by Bering's ill-fated crew in 1741, showing how vulnerable sirenians can be.

As with whales and dolphins, the front limbs of sirenians have become flippers and they have no hind limbs at all. Sirenians are also known as sea cows, but they are not related to cows and they don't ruminate. Their vegetarian diet requires an immensely long gut and a low energy budget. The high-speed aquabatics of a carnivorous dolphin contrast dramatically with the lazy drifting of the vegetarian dugong: guided missile to dirigible balloon.

There are small afrotheres, too. Golden moles and tenrecs seem to be related to each other, and most modern authorities place them within the afrotheres. Golden moles live in southern Africa where they do the same job as moles do in Eurasia, and do it beautifully, swimming through the sand as if it were water. Tenrecs live mostly in Madagascar. There are some semi-aquatic 'otter shrews' that are actually tenrecs in western Africa. As we saw in the Aye-Aye's Tale, Madagascan tenrecs include shrew-like forms, hedgehog-like forms and an aquatic species which probably returned to the water independently of the African ones.

Rendezvous 14.

MARSUPIALS.

Here we are, 140 million years ago, at the base of the Cretaceous when Concestor 14, in round figures our 80-million-greats-grandparent, lived in the shadow of the dinosaurs. As the Elephant Bird's Tale will recount, South America, Antarctica, Australia, Africa, and India, which had been part of the great southern supercontinent of Gondwana, were just starting to break apart (a map of approximately this period is shown in plate 19). Consequently, changes in climate had plunged the world into a (geologically) short-lived cold period, with snow and ice blanching the poles during the winter months. Only a few flowering plants grew in the temperate forests of coniferous trees and the plains of ferns that covered the northern and southern parts of the globe, and there were correspondingly few of the pollinating insects that we know today. It is in such a world that the entire ma.s.sed pilgrims of the placental mammals horses and cats, sloths and whales, bats and armadillos, camels and hyenas, rhinoceroses and dugongs, mice and men all now represented by a small insectivore, greet the other great group of mammals, the marsupials.

Marsupium means pouch in Latin. Anatomists use it as a technical term for any pouch, such as the human s.c.r.o.t.u.m. But the most famous pouches in the animal kingdom are those in which kangaroos and other marsupials keep their young. Marsupials are born as tiny embryos equipped only to crawl crawl for their tiny lives through the forest of their mother's fur, into the pouch where they clamp their mouths to a teat.

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Marsupials join. Three major lines of living mammals are recognised, based upon their method of reproduction. These are the egg-laying mammals (monotremes), the pouched mammals (marsupials) and the placental mammals (including ourselves). Morphology and most DNA studies agree in grouping the marsupials and placentals together, making Three major lines of living mammals are recognised, based upon their method of reproduction. These are the egg-laying mammals (monotremes), the pouched mammals (marsupials) and the placental mammals (including ourselves). Morphology and most DNA studies agree in grouping the marsupials and placentals together, making Rendezvous 14 Rendezvous 14 the divergence of the 270 or so species of marsupial from the 4,500 or so placental mammals. It is generally accepted that marsupials fall into the seven orders shown here. Their interrelations.h.i.+ps are not firmly established: particularly problematic is the position of the South American 'monito del monte'. the divergence of the 270 or so species of marsupial from the 4,500 or so placental mammals. It is generally accepted that marsupials fall into the seven orders shown here. Their interrelations.h.i.+ps are not firmly established: particularly problematic is the position of the South American 'monito del monte'.

Images, left to right: red kangaroo ( red kangaroo (Macropus rufus); Tasmanian devil (Sarcophilus harrisii); southern marsupial mole (Notoryctes typhlops); bilby (Macrotis lagotis); Virginia opossum (Didelphis virginiana).

The other main group of mammals are called placentals because they nourish their embryos with various versions of a placenta: a large organ through which miles of capillary blood vessels belonging to the baby are brought into close contact with miles of capillary blood vessels belonging to the mother. This excellent exchange system (for it serves to remove wastes from the foetus as well as to feed it) enables the baby to be born very late in its career. It enjoys the protection of its mother's body until, in the case of hoofed herbivores for example, it is capable of keeping up with the herd on its own legs, and even running away from predators. Marsupials do it differently. The pouch is like an external womb, and the large teat, to which the baby becomes attached as a semipermanent appendage, works a bit like an umbilical cord. Later, the joey detaches itself from the nipple and sucks only occasionally like a placental infant. It emerges from the pouch as if in a second birth, and uses it less and less frequently as a temporary refuge. Kangaroo pouches open forwards but many marsupial pouches open backwards.

The marsupials, as we have seen, are one of the two great groups into which the surviving mammals are divided. We normally a.s.sociate them with Australia which, from a faunistic point of view, can conveniently be deemed to embrace New Guinea. It is unfortunate that no widely recognised word exists to unite these two landma.s.ses. 'Meganesia' and 'Sahul' are not memorable or evocative enough. Australasia won't do because it includes New Zealand which, zoologically, has little in common with Australia and New Guinea. I shall coin Australinea for my purpose.1 An Australinean animal hails from mainland Australia, Tasmania or New Guinea, but not New Zealand. From a zoological point of view, though not a human one, New Guinea is like a tropical wing of Australia, and the mammal faunas of both are dominated by marsupials. Marsupials also, as we saw in the Armadillo's Tale, have a long and older history of a.s.sociation with South America, where they still occur, mostly in the shape of some dozens of species of opossums. An Australinean animal hails from mainland Australia, Tasmania or New Guinea, but not New Zealand. From a zoological point of view, though not a human one, New Guinea is like a tropical wing of Australia, and the mammal faunas of both are dominated by marsupials. Marsupials also, as we saw in the Armadillo's Tale, have a long and older history of a.s.sociation with South America, where they still occur, mostly in the shape of some dozens of species of opossums.

Although present-day American marsupials are nearly all opossums, it hasn't always been so. If we take fossils into account, most of the range of marsupial diversity is in South America. Older fossils have been found in North America, but the oldest of all marsupial fossils is from China. They went extinct in Laurasia but survived in two of the main relics of Gondwana, namely South America and Australinea. And it is Australinea which is the main stage for modern marsupial diversity. It is generally agreed that marsupials came to Australinea from South America via Antarctica. Those fossil marsupials that have been found in Antarctica are not in themselves plausible ancestors of the Australinean forms, but this is probably just because so few Antarctic fossils have been found anyway.

It happens that Australinea, for much of its history since it split off from Gondwana, has had no placental mammals. It is not unlikely that all Australia's marsupials stem from a single introduction of an opossum-like founder animal from South America, via Antarctica. We don't know exactly when, but it can't have been much later than 55 million years ago, which is approximately when Australia (more especially Tasmania) pulled far enough away from Antarctica to be inaccessible to island-hopping mammals. It could have been much earlier, depending upon how inhospitable Antarctica was to mammals. American opossums are no more closely related to the animals that Australians call possums than they are to any other Australian marsupials. Other American marsupials, mostly fossils, seem to be more distantly related. Most of the major branches in the marsupial family tree, in other words, are American, which is one reason why we think the marsupials originated in America and migrated to Australinea, rather than the other way around. But the Australinean branch of the family diversified mightily after their homeland became isolated. The isolation came to an end around 15 million years ago when Australinea (specifically New Guinea) reached close enough to Asia to allow the arrival of bats and (presumably island-hopping) rodents. Then, much more recently, dingos arrived (in trading canoes, we must suppose) and finally a whole host of other animals, such as rabbits, camels and horses, introduced by European immigrants. Most ridiculously of all, these included foxes in order that they should be hunted an eloquent comment on the claim that this pursuit can be justified as pest control.

Together with the monotremes who join us next, the evolving Australian marsupials were carried, on the great raft that Australia became, out into South Pacific isolation. There, for the next 40 million years the marsupials (and monotremes) had Australia to themselves. If there were other mammals at the beginning2 they died out early. Dinosaur shoes were waiting to be filled, in Australia as well as in the rest of the world. From our point of view the exciting thing about Australia is that it was isolated for a very long time, and it had a very small founder population of marsupial mammals, conceivably even a single species. they died out early. Dinosaur shoes were waiting to be filled, in Australia as well as in the rest of the world. From our point of view the exciting thing about Australia is that it was isolated for a very long time, and it had a very small founder population of marsupial mammals, conceivably even a single species.

And the results? They were dazzling. Of approximately 270 surviving species of marsupial in the world, about three-quarters are Australinean (the rest are all American, mostly opossums plus a few other species such as the enigmatic Dromiciops Dromiciops, the monito del monte). The 200 Australinean species (give or take a few depending on whether we are lumpers or splitters)3 have branched to fill the whole range of 'trades' formerly occupied by the dinosaurs, and independently occupied by other mammals in the rest of the world. The Marsupial Mole's Tale goes through some of these trades, one by one. have branched to fill the whole range of 'trades' formerly occupied by the dinosaurs, and independently occupied by other mammals in the rest of the world. The Marsupial Mole's Tale goes through some of these trades, one by one.

THE MARSUPIAL MOLE'S TALE.

There is a living to be made underground, a living which moles (family Talpidae) have made familiar to us in Eurasia and North America. Moles are dedicated burrowing machines, their hands modified into spades, their eyes, which would be useless underground, all but completely degenerate. In Africa, the mole niche is filled by golden moles (family Chrysochloridae). These are superfici