Saturday, 20 June 2009

Human Evolution On Trial - 'Extinctions'

Human Evolution on Trial - Extinctions

Extinctions have been happening on the earth since life began. In fact death is a part of life. Some farmers even say that where you have livestock, you have deadstock. In this section the defence will use as evidence only the extinctions that have happened since modern humans appeared and that we may have had a hand in. But humans are not that special. The expansion of many animal, bird and even plant species into new regions has often led to extinctions in those regions. Environmental and ecological change, and asteroid collisions, also cause extinctions.

When I first took on this case I had a feeling that examining the pattern of animal extinction during the most recent ice age might provide me with some idea of the pattern of human expansion. I found that in fact extinctions and landscape change can be used to independently date human expansion through the world, so much so that where other evidence conflicts or is inconclusive, I’d go with the extinctions.

The defence showed in “Change” [Destruction] that bird extinctions indicate a breeding group of humans didn’t arrive in New Zealand until around 1000 - 1200 AD (and see King 2003). The evidence is overwhelming. Moa died out about then, many seal colonies disappeared, and the landscape of New Zealand changed through an increase in fire (McGlone et al in Sutton 1994). Thirteen or fourteen species of moa and at least 20 other bird species in New Zealand all died out around this time. These extinctions included another flightless bird called an adzebill, a swan, two types of goose (one flightless), a few species of duck, an eagle, a goshawk, a pelican, several species of rail and numerous smaller birds. Remains of many of these species are present in “Moa-hunter” sites. Carbon dating of these sites clusters around 600-1000 years ago.

(see also: Bullockornis - aka the 'Demon Duck of Doom')

Extinctions in Madagascar also occurred about 1000 years ago. Is there a connection with the Pacific Ocean? Both areas were settled about the same time and believe it or not, the language was related (both being members of the Austronesian family, see “Polynesian Origins”). To the surprise of most people, including me when I first heard it, the people of the Malagasay Republic (Madagascar) are not of African origin. They came from Indonesia some time before 1,000 AD. This supports the defence claim that some technological change happened in the chain of islands stretching from Indonesia to Tonga and Samoa that gave the impetus for an expansion of population (“Eastern Polynesia” [The Sail]).

The extinctions in Madagascar included a dwarf hippopotamus, several large flightless bird species called elephant birds, a species of aardvark, a giant land tortoise, a viverid and several species of lemur (Martin and Klein 1984). 40% of the lemur species died out, mainly the larger daytime foraging ones. The flightless elephant birds apparently nested in large colonies on the coastal plains making nest robbing easy. Nest robbing was probably also important in the extinction of moa in New Zealand. Madagascar is about twice the size of New Zealand and extinctions may have taken longer, but in both cases were caused by hunting, fire, introduced pests and diseases and environmental change.

In other parts of the world, a similar thing has happened with the first arrival of people (Diamond 2005). Fire and the decline of large herbivores have altered the landscape, which in turn may have altered the climate. Climate change due to human activity is not necessarily a modern phenomenon. We may not have progressed that much.

What Have We Done?

The most notable changes in animals during the Pleistocene geological epoch (the Ice Age) is the huge reduction in range, or even extinction, of species and the reduction in size of the survivors (Kurten 1971). These changes don’t happen simultaneously around the world but always coincide with the archaeological evidence for the arrival of humans or at least their probable time of arrival in an area. In many cases the animals had survived previous climatic fluctuations and so the changes are unlikely to be simply the result of climate change (Jobling et al 2004).

The drawings in map 10 (mostly from Kurten 1971) give some idea of the kinds of animals that became extinct when modern humans appeared in their region. Most kinds were spread widely around the world and have been classified into a number of genera. The dates on the map indicate how long ago extinctions in each region were completed. (click to enlarge)

The distribution of mammals around the world today is a poor sampling of what it has been in the past. Most living examples are also much smaller than their ancestors were though some smaller mammals, e.g. rats, have actually increased in size. There also seem to be fewer species in all families of large mammals. Many mammals that today have interrupted distributions had virtually continuous distributions earlier. For example lions were found throughout Europe, Turkey, Asia and into China (Tudge 1996). They were also found in Alaska and possibly North America (Flannery 2001). Elephants were present in Northern Syria until as recently as 800 BC (Markoe 2000). The orangutan was found throughout Southeast Asia and into China and was much larger than it is now. Elephants, tapirs, camels, llamas, rhinoceros and large cats were all widely distributed through Africa, Asia and Europe and most were also found in America. The extinctions have interrupted what were almost certainly clines of these animals.

The more technologically advanced a human culture is when it is first introduced to a region, the more rapid the extinction of animals. The two facts are probably related. In Africa the extinctions happened long ago and may have taken half a million years to complete. Extinctions in Southern Asia also took a long time though how long, I don’t know. Australian extinctions were extended over maybe 5000 to 10,000 years. In America maybe 1000 years and in New Zealand it took just 200 years, probably due to the late arrival of people to the country and their fairly advanced technology.

Almost 40% of the different genera of large animals in Africa had become extinct by 60,000 years ago and most were extinct long before then (Kurten 1971). Interestingly this fits human Y-chromosome evidence more closely than the mitochondrial DNA evidence (“MtEve” [The Trees]). Extinctions in Africa included three-toed horses, a giant deer, an antlered giraffe, giant baboons, sabre-tooth and scimitar-toothed cats, a bear, many types of pig and various kinds of elephants, hyenas, antelope and buffalo. Remains of these animals are found with Lower Palaeolithic (early Old Stone Age) cultural artefacts throughout Africa but are absent from Middle Palaeolithic sites. The sites span about one million years, indicating extinctions were not rapid and may not have been caused by humans, but I’m suspicious.

Extinctions were also early below about latitude 40° north in Asia and Europe. Presumably because the warmer climate allowed humans to live in these areas even during ice ages. The timing of extinctions in India would be especially interesting. This might give us some idea of when a population expansion indicated in gene maps started from there. We will come back to this expansion much later in “MtEve” [Interpretation] and “Out of Africa” [Genes Again]. Anyway, extinctions in Sri Lanka are dated at 37,000 years ago.

In Australia a mass extinction of large animals was completed by 40,000 to 50,000 years ago but extinctions in Tasmania are more recent. Tasmania may have been cut off from the mainland until the ice age really started to hit and sea level dropped. Humans may not have been able to get there until 25,000 years ago. Anyway, the prehistoric extinctions in Tasmania were completed by 20,000 years ago ,indicating humans had arrived by then. The extinctions in Australia included land crocodiles, giant lizards, kangaroos and wombats, several marsupial carnivores, a large animal the size of a rhinoceros called Diprotodon and a huge flightless duck.

Mammoths were extinct in North China by 20,000 years ago and may have first been hunted there about 35,000 years ago. In Crimea and the Northern Caucasus remains of mammoth are common in Middle Paleolithic Neanderthal sites but not in Upper Palaeolithic sites (from about 30,000 years ago). In Part V the defence will use this to date the human expansion into the Americas (“North to Alaska”).

Only about 50% of the large animals survived the extinctions in Northern Europe, which were completed about 15,000 years ago. Extinctions include elephants (including mammoths) woolly rhinoceros, large deer, hyena, large cats and cave bear. Mammoth extinction is surprisingly late in France, probably because animals were able to recolonise France from areas to the north. Hunters couldn’t exploit that region until late in the Ice Age, after they had invented warm clothing. Mammoths survived on Wrangel Island in the Arctic until 7000 and possibly even 4000 years ago (Wade 2001).

All the above extinctions were relatively protracted. In America they were sudden, occurring a little before 10,000 years ago (Martin and Klein 1984). Included are horses, camels, several species of deer, an antelope related to the modern pronghorn, several species of giant sloth, giant armadillo, giant beaver, large cats (including the sabre-tooth), cheetah, two types of peccary, a tapir, three types of elephants, and a type of large wolf. Several species of giant tortoises and many birds also disappeared. 70% of the large animals of America died out ,and most there today came in from Asia at about the same time as humans. These animals had learned how to survive human presence (Flannery 2001).

The point is that these extinctions occur everywhere in conjunction with the arrival of humans. If climate alteration was responsible, then the possibility humans themselves were partly responsible for that change cannot be ruled out.

How Did We Do It?

Fire. It could even be argued it is the possession of fire that actually distinguishes humans from other animals. It was probably used both to chase and to cook game. Both at the same time would have been good. Fire can also be used to keep travelling routes open. It seems to have been used in the central North Island of New Zealand for that purpose. In other parts of the world it has been used to burn off old vegetation to allow new growth, and encourage grazing animals.

This reminds me of a saying I heard when I was living in Australia: “there are three main causes of bush fires. These are men, women and children”. There is always a huge increase in the amount of fire when humans arrive, indicating few fires are actually started by natural causes such as lightning (probably less than 20%) and they certainly don’t keep recurring in the same place. Some people just like watching fires. The first evidence for fire associated with humans was once believed to be near modern Beijing in north China about 500,000 years ago. The evidence has been contested though and it now seems unlikely. There is some evidence for fire in Europe 200,000 years ago but by 60,000 years ago evidence for use of fire is definite (Tattersall and Schwartz 2000).

Kangaroo Island is only 14½ kilometres from mainland Australia and people had been living on it before sea level rose at the end of the ice age. But when Europeans first saw it about 1800 AD they could tell from a distance the island was unoccupied because of the lack of smoke. On the nearby mainland the skies were constantly full of smoke from Aborigines burning the vegetation (Flood 1988). The island itself was full of extraordinarily tame kangaroos and seals. The present vegetation of Australia has been profoundly affected by fire. In fact it has been referred to as an “Aboriginal artifact”.

Some people suggest burning off vegetation is the first step towards farming (Tudge 1996, Flannery 1994 and Flood 1988). Fire stick farming is not a very efficient method of farming. Fire destroys the humus and life in the soil, each very necessary for both moisture retention and nutrient recycling.

People who study the vegetation change at the end of the last ice age all agree that until that time there generally were not the large expanses of either grassland or forest that existed later. For example there is evidence the treeless prairie of North America didn’t exist until 11,000 years ago (Paul Martin quoted in Flannery 2001) and Late Pleistocene epoch (ice age) forests were more open and patchy. It has even been suggested the tropical forest didn’t exist until five thousand years ago but most people believe it is at least as ancient as this (Cavalli-Sforza 1995). Even the Arctic tundra seems to have had more variety (mosaic vegetation). Many plant species present in the Late Pleistocene tundra are now not found so far north even though the climate is much warmer today. This indicates the ancient tundra was a mix of warm and cold loving species. Plants today separated geographically were then able to grow in close proximity, presumably because of more varied microclimates. It has been assumed the change to a more monocultural type cover was a result of climate change.

Cox and Moore (1985) mention in their book “Biogeography” that a tree in grassland collects dust and rainwater. This, and dung from sheltering animals, results in increased fertility under the tree allowing the expansion of more trees into the grassland. The whole process is gradual and is easily interrupted by fire.

Large herbivores have the opposite effect. They break up forestland with their destructive browsing (feeding off high branches). This is shown by the modern destruction of forest in areas of Africa where elephants have been protected in reserves and allowed to reach very high numbers. Usually plants with prickles, such as thorns and blackberries, can provide some protection for palatable plants until they are fairly mature. This all results in a constant recycling of vegetation from grassland to forest and back again.

The combination of the extinction of large animals and the increase in fire may have been responsible for the disappearance of mosaic vegetation. Many conservationists think we should be trying to re-establish this mosaic vegetation. It may be the most productive vegetation for both agriculture and wildlife. Open grassland with trees scattered through it has probably also been our preferred environment since we first evolved.

The Results

A rapid adaptive radiation (increasing numbers of species) of ruminants occurred during the Pleistocene epoch as grassland expanded. Ruminants (cud chewing animals) are the animals most effective at digesting grass (Tudge 1996) and the greatest diversity of these animals is in Africa. More than ninety of the hundred or so antelope and gazelle species in the world live there. It may be that the early impact of humans on the land has encouraged their diversity. Perhaps Homo erectus used fire.

In previous geological ages animal species have generally become larger over time. This provides protection from predators. It also provides heat conservation in cold climates. During the last ice age size reduction was the norm. In many species this may have been due to the later general climate warming. Smaller size allows greater heat loss. The European brown bear, lynx, red deer, moose and bison are all smaller than they were during the ice age (Kurten 1971). The polar bear is smaller today than it was 100,000 years ago and the North American black bear was as big as a modern grizzly. These size reductions may all be due to climate warming but the Pleistocene size decrease is not confined just to the period of climate warming or only to animals in the arctic regions. Tigers, lions and the Malay tapir are all tropical creatures and are now smaller than their ancestors were. Many size reductions have probably been a result of selection pressure by human hunting favouring smaller, more mobile, less obvious animals (Flannery 2001). Humans hunt by sight rather than smell, unlike most predators.

On the other hand the isolated Mediterranean Islands provide good examples of the sort of miniaturization mentioned in “Hybrid Vigour and Inbreeding” [Survival] (Attenborough 1987). The elephants that lived there were only three feet high and there were dwarf deer, small hippos, etc. All the unusual animals began to die out about eight thousand years ago (“The Last Point” [Islands Again]). The mammoths that survived on Wrangel Island were also fairly small, merely about the height of a human (Wade 2001).

How do species become extinct?

Environmental change can isolate animal species to virtual islands in the form of small areas that suit them ecologically. This may also have happened for several species through human interference and it has probably even happened at times for various ancestral human populations. Small populations are vulnerable to extinction by disasters such as drought or hurricane and can die out through inbreeding (Tudge 1996). This same process may account for the fact the moa died out even in fairly inaccessible parts of New Zealand.

During the last ice age major human interference may have broken up herds of herbivores into isolated populations. The defence has mentioned that some human populations have also died out through inbreeding, when they have become isolated because of rising sea level, climate change or extinction of resources. Indications of such extinctions have been found in some Indonesian and Pacific Islands. In the Pacific people died out on Pitcairn, Norfolk, the Phoenix and Line Islands and some Hawai‘ian islands (Bellwood 1978, Kirch quoted by McGlone et al in Sutton 1994 and King 2003). People also became extinct on Henderson and Pitcairn (Diamond 2005). At other small populations survived to make a genetic or cultural contribution to incoming times, populations.

Perhaps we should assume similar reductions, or even extinctions, of isolated human populations have happened many times throughout the evolution of our species.

Countries such as New Zealand, Australia, Hawai‘i and Madagascar have an apparently bad conservation record in modern times. The reason is simply that they are the most recently settled areas (Australia was actually settled fairly early but by people with what we would call a primitive stone technology). Humans achieved extinctions and environmental destruction elsewhere long ago. Whenever humans arrive in any region the environment changes and animals get smaller or become extinct through human activity. You will see in Part V we can use this change to date elements of modern human expansion. But first the defence needs to show the jury where humans came from.

See next :: Human Evolution On Trial - Human Star - The First Point

Witnesses Called

Attenborough, David (1987) The First Eden. Guild, London.

Bellwood, Peter (1978) Man’s Conquest of the Pacific. Collins, Auckland.

Cavalli-Sforza, Luigi Luca and Cavalli-Sforza, Francesco (1995) The Great Human Diasporas. Addison- Wesley

Cox, Barry C. and Moore, Peter D. (1985) Biogeography. Blackwell, Great Britain.

Diamond, Jared (2005) Collapse. Penguin Books, London.

Flannery, Tim (1994) The Future Eaters. Reed, New Holland.

Flannery, Tim (2001) The Eternal Frontier. Text Publishing, Australia.

Flood, Josephine (1988) Archaeology of the Dreamtime. Collins, Australia.

Jobling et al (2004) Human Evolutionary Genetics. Garland Science, New York.

King, Michael (2003) The Penguin History of New Zealand. Penguin Books, New Zealand.

Kurten, Bjorn (1971) The Age of Mammals. Weidenfied and Nicholson, London.

Markoe, Glenn E. (2000) Phoenicians. The British Museum Press, London.

Martin, Paul S. and Klein, Richard G. ed. (1984) Quaternary Extinctions. University of

Arizona Press

Sutton, Douglas G. ed. (1994) The Origins of the First New Zealanders. Auckland University Press, New Zealand.

Tattersall, Ian and Schwartz, Jeffrey H. (2000) Extinct Humans. Westview Press, New York.

Tudge, Colin (1996) The Time Before History. Scribner, New York.

Wade, Nicholas ed. (2001) The New York Times Book of Fossils and Evolution. The Lyon Press, New York.

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