Evolution scientists today warn of the spread of a global "pest and weed" environment, with animals and plants such as rats, cockroaches, nettles and thistles flourishing at the expense of more specialized wild organisms.
The scientists say that, in the next 5 million years, short-term evolution will favor those species able to thrive in the margins of human settlement.
They also warned that decisions made in the next few decades will determine the fate of 500,000 billion people, adding that efforts to protect species and wild habitats now will dictate the future course of evolution.
In their startling wake-up call, the group of US, African and British researchers writing in the US journal, Proceedings of the National Academy of Sciences, compared the present mass extinction of species on Earth to past mass extinctions; then, it took roughly 5 million years for biological diversity to reassert itself.
"Suppose that the average number of people on Earth during the future recovery period is 2.5 billion, by contrast with the 6 billion today," said two of the scientists, Norman Myers of Oxford University and Andrew Knoll of Harvard.
"Under these conditions, the total number of people affected by what we do - or do not do - during the next few decades will be in the order of 500 trillion, 10,000 times more people than have existed until now.
"We are thus engaged in by far the largest 'decision' every taken by one human community on the unconsulted behalf of future societies."
The scientists suggested that the world is entering a new period of geological time, the Homogecene, marked by all parts of the planet increasingly coming to resemble each other.
David Woodruff, of the University of California at San Diego, said that between 3,000 and 30,000 of Earth's estimated 10 million species were disappearing each year.
"We live at a geological instant when global rates of extinction are at an all time high for the last 65 million years, and are increasing," he said.
"The biosphere will have fewer species and be subject to more weed, pest and disease outbreaks...the new [habitats] will be more easily disturbed and invaded, and will have an aesthetically unappealing dullness."
None of this means that evolution will stop - just that it might go in an undesirable direction. "Evolution is not over - set back perhaps - but by no means over," Dr Woodruff said.
Scientists who studied evolution, he said, were obliged to abandon their preference for looking backwards and begin considering the future.
"Some of us advocate a shift from saving things, the products of evolution, to saving the underlying process, evolution itself," he said.
"Like it or not, evolutionary biologists have to recognize that the ultimate test of their science is not their ability to solve the riddles of the past and the origin of species, but rather to manage their viability and prevent their premature extinction - to manage the biosphere's future."
DR Myers said that much more emphasis should be put on protecting plants and insects, to protect the evolutionary pool, rather than on preserving big beasts like tigers or elephants, which are too few to evolve.
Environmentalists needed to think not just about saving the species we have, but about protecting the planet's ability to generate the species of the future.
"A lot of people would say, 'no, we don't want creepy crawlies', but if we lost half the mammals, we could get by," DR Myers said.
"If we lost half of all insects, with their pollinating function, our agriculture would be in trouble in just a few seasons.
"We live at a time when, in just the next two decades, we can save some very fundamental processes. If we do that, I think we will be thanked by hundreds of thousands of generations to come, and if we don't, we will be criticized for millions of years."
One of the rarest frogs in the world, Hamilton frogs are small amphibians endemic to Stephens Island in the Cook Strait, New Zealand. First discovered in 1915, about 200 exist. Their future is threatened by stoat invasions
Only one single Diplazium molokaiensis, a member of the wood fern family, has been found in Hawaii during the past two decades, and the species' extinction seems inevitable
Endangered after a reduction of at least 80% of the population in 10 years. Overfishing, and loss of habitat to blame
Dusky seaside sparrow
Became extinct in 1987. It is widely considered to be the most recent, well-documented extinction of a vertebrate in the US. Disappearance due entirely to the loss of a natural habitat, the Everglades
Discovered in Monteverde, Costa Rica, in 1963. Despite being protected, it was presumed extinct when by 1989 the one lone male disappeared
Charco Palma pupfish
Due to falling levels of essential water, the Charco Palma pupfish became extinct in 1994. The species was found at a single spring, Charco La Palma, Aramberri, southern Nuevo León, Mexico.
The 50-70 pupfish disappeared when the spring water was used for human consumption and for irrigation
© Guardian Newspapers Limited 2001