Some authors are guilty of moving the goal posts back in the debate about the validity of a Holocene Extinction event. The Holocene epoch is the inter-glacial after the Würm glacial which ended about 11,500 years ago given the sudden sea level and temperature rises, but some proponents believe 15,000 years ago marks the start of the Holocene Extinction. Using that earlier date, there is a possibility of including some extinction events which cannot easily be combined in a continuum and undermines a discernable thread since the beginning of the Holocene where the rate of extinction has increased due to a specific single cause, namely the human race.
At the start of the Holocene the global human population was about 5 million. To varying degrees most parts of the world had already been colonised by modern human inhabitants who were still living by nomadic hunting and gathering, although some movement along seashore and river routes suggests maritime skills were developed. The Middle and Near East contained a high proportion of the global population and the first city was founded in Jericho about 12,000 years ago. The Middle East and the Sahara were not deserts, but fertile areas with regular rainfall.
By this time Neanderthals, the American Megafauna and most of the European "Ice Age" animals were already extinct. Ice-free Europe was mostly covered by forest and thinly populated. Islands in the Mediterranean and elsewhere across the globe were in the main uninhabited, although Australia and New Guinea were populated by arrivals who had been able to cross from Asia on foot and by rudimentary boats when sea level was sufficiently low at the height of the Würn glaciation 60,000 BP. Both North and South America had people who had crossed the landbridge Beringia, between Asia and Alaska, perhaps 16,000 years ago or earlier. Northern India had recovered from the Toba erruption and modern humans had reached China and Japan.
As long as the human population was nomadic and survived on hunter-gathering it remained a sustainable element in the ecosystem. Other animal species were able to survive because humans came and went and damage was limited in intensity and any recovery facilitated by time lags. Even a small tribal size meant that humans were unable to stay for long in one place because food resources soon ran out.
Agriculture changed that. Hunting didn't stop, but agriculture provided a food base which allowed a much greater area to be thoroughly exploited. This was the start of civilisation; housing, property rights, laws, community identity and organised religion.

The above graphic²⁴ shows the extent of glaciation in Europe about 12,000 years ago and the probable vegetation cover. Glaciers continued to retreat as temperatures rose. Sea level also rose, eventually isolating Britain.
The environmental changes, retreating glaciers, rising sea levels and warmer climate, encouraged humans to adapt their Stone Age mode of living into more and more permanent settlements where specialisation and the exchange of information could take place. This took place very slowly as the environment changed over hundreds of years with reversals due to crop failures, flooding and probably disease often happening. It is important to remember that this transition did not happen everywhere at the same time, nor at the same speed, and it should not be forgotten that some societies living in the 21st Century have still not made this step.

It would seem fairly obvious from the above graphic that there is a relationship between recent extinctions and the growth in human population. The graph is particularly disturbing because it only refers to the known extinctions of birds and mammals which only represent a small fraction of living species. It is quite illogical to assume the extinction of these species has taken place in isolation and that other genera are immune. Certainly amphibians and reptiles are known to be suffering losses and, even if undocumented, presumably plants and invertebrates must be under pressure too.
Since 1950 the world human population has increased from 2.5 Billion to over 7 Billion in 2008, a rise of 278%. If this rate of growth continues there will be over 30 Billion people on the planet by 2100 - 6,000 times more people than there were at the beginning of the Holocene. The conversion of forest and grassland into arable and pasture land to feed, house and establish industrial and social infrastructure sites for an ever increasing human population will have an inevitable negative impact on all species, including humans.
Homo sapiens, our mammal species, is an omnivore and will eat almost anything and has done so. Humans have been accused of killing off many species in the past, but probably only within the last six hundred years have we caused extinctions. In the dramatised version, humans exterminated the magafauna of Europe and America through over hunting. This is highly unlikely bearing in mind the enormous habitat range of these animals and the number of dedicated hunters. Without doubt, thousands of animals were killed and used for food and clothing, but even with a slow reproductive rate the species should have been able to survive. There are no statistics going that far back, but the European megafauna had been hunted for tens of thousands of years by our ancestral relations (including Neanderthals) who must have braved the very cold, inhospitable northern habitat covering an area of millions of square miles to find their prey. Most human inhabitants did not live near enough to the ranges of the megafauna to hunt them and venturing into the vast recesses of the steppes and tundra in the hope of finding a meal must have been an infrequent option. The contact period between the Amerindians and the American megafauna was perhaps less than a few thousand years, but the huge distances and ranges were similar to those in Europe while the human population size must have been considerably smaller. The humans on both continents were not supermen and had limited means of transport - mostly they had to walk - with primitive weaponry. Had they not found enough food within a few days they would have had to return to where food was known to be available.

Perhaps the Stone Age hunters did play a role in these extinctions²⁵, but even today new large mammals are being found in Asian forests despite humans having lived and hunted there for tens of thousands of years. No, the magafauna extinctions are almost certainly due to a breakdown in the food web, probably caused by climate change affecting the vegetation and it must be more than a coincidence that the megafauna became extinct about the same time. We are beginning to see such a climate change now, man made or not, and this is affecting all sorts of different species. Whereas the Pleistocene megafauna were confronted by a warming climate change covering a few thousand years, we may be seeing the same thing with similar effects over only a few hundred years.
The documented cases where humans were directly responsible for causing extinction are numerous and, in the main, concern island species who had no natural predators. Due to their historical isolation and lack of predators, the Dodo, Moa, Pika and dozens of pigeons, quails and ducks were quite unafraid of humans and were literally eaten into extinction by seafarers and island immigrants in the 15^th, 16^th and 17^th Centuries. These extinctions can be seen on the graph above, particularly between 1550 and 1750. This was the classic age of global seafaring exploration and the travellers made full use of the available resources when they stopped at an island. It is easy to understand how and why these extinctions happened, to some degree even justifiable as the survival of the fittest in evolutionary terms.
Humans on their own were destructive enough, but their baggage and pets have been arguably a worse menace to global species and have caused lots of extinctions. Rats, cats and pigs are probably the worst offenders, but the list of invasive species, wittingly or unwittingly imported, is very long and growing. What may appear as a minor addition to a foreign environment can rapidly turn into a nightmare for resident species, threatening their existence. Pigs in New Guinea, goats, hedgehogs and gorse in New Zealand, rabbits, dogs and toads in Australia, Brown tree snakes on Guam, American Mink in Europe and rats everywhere. As already stated, ecosystems can be fragile and the introduction of non-native species can be disasterous for unprepared endemic wildlife.
It is possible to classify human involvement in the extinction of other species into three groups; the incidental, the careless and the consequencial. The first two I have already briefly dealt with.

Not all human actions causing environmental damage are as straightforward as the nuclear tests by America, Russia and China. In the immediate vicinity of the explosions some species, particularly on Bikini Atoll where several took place, almost certainly became extinct. But this destruction is dwarfed by past and present devastation which does not make such an obvious loud bang, but is ultimately much more serious for wildlife.