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　　[00:00.00]Man Is Altering the Balance of Nature

　　[00:05.68]The balance of nature is a very elaborate

　　[00:09.66]and very delicate system of checks and counterchecks.

　　[00:13.60]It is continually being altered as climates change,

　　[00:16.66]as new organisms evolve,

　　[00:18.74]as animals or plants permeate to new area.

　　[00:22.68]But the alternations have in the past,

　　[00:25.95]for the most part,

　　[00:27.49]been slow, whereas with the arrival of civilized man,

　　[00:31.09]their speed has been multiplied many fold:

　　[00:33.83]From the evolutionary time scale where change

　　[00:37.66]is measured by periods of ten or a hundred thousand years,

　　[00:41.58]they have been transferred to the human time scale

　　[00:44.67]in which centuries and even decades count.

　　[00:47.38]Everywhere man is altering the balance of nature.

　　[00:51.65]He is facilitating the spread of plants and animals into new regions,

　　[00:56.79]sometimes deliberately,

　　[00:58.44]sometimes unconsciously.

　　[01:00.31]He is covering huge areas with new kinds of plants,

　　[01:04.24]or with houses, factories,

　　[01:06.75]slagheaps and other products of the civilization.

　　[01:10.26]He exterminates some species on a large scale,

　　[01:13.97]but favours the multiplication of others.

　　[01:16.91]In brief, he has done more in five thousand years

　　[01:20.65]to alter the biological aspect of the planet

　　[01:23.38]than has nature in five million.

　　[01:25.79]Many of these changes

　　[01:27.64]which he has brought about have had unforeseen consequences.

　　[01:31.79]Who would have thought that

　　[01:34.09]the throwing away of a piece of Canadian waterweed

　　[01:36.81]would have caused half the waterways of Britain to be blocked for a decade?

　　[01:40.88]Or that the provision of pot cacti for lonely settlers' wives

　　[01:45.36]would have led to Eastern Australia

　　[01:47.53]being overrun with forest of Prickly Pear?

　　[01:50.29]Who would have prophesied that the cutting down of forests

　　[01:54.11]on the Adriatic coasts,

　　[01:55.98]or in the parts of Central Africa,

　　[01:58.04]could have reached the land to semi desert,

　　[02:01.11]with the very soil washed away from the bare rock?

　　[02:04.50]Who would have thought that improved communications

　　[02:08.10]would have changed history

　　[02:09.86]by the spreading of disease-

　　[02:11.62]sleeping sickness into East Africa,

　　[02:14.01]measles into Oceania,

　　[02:16.13]very possibly malaria into ancient Greece?

　　[02:19.73]These are spectacular examples;

　　[02:22.34]but examples on a smaller scale are everywhere to be found.

　　[02:26.30]We make a nature sanctuary for rare birds,

　　[02:29.68]prescribing absolute security for all species;

　　[02:33.18]and we may find that some common

　　[02:35.48]and hardy kind of bird multiplies beyond measure

　　[02:39.31]and ousts the rare kinds in which we are particularly interested.

　　[02:43.13]We see, owing to some little change brought about by civilization,

　　[02:47.72]the startling spread over the English countryside in hordes.

　　[02:52.22]We improve the yielding capacities of our cattle;

　　[02:55.50]and find that now they exhaust the pastures

　　[02:58.88]which sufficed for less exigent stock.

　　[03:01.63]We gaily set about killing the carnivores that molest our domestic animals,

　　[03:06.44]the hawks that eat our fowls and game-birds;

　　[03:09.49]and find that in so doing we are also removing the brake

　　[03:13.75]that restrains the multiplication of mice

　　[03:16.28]and other little rodents that gnaw away the farmer's profits.