arguments over natural selection
At first many people disagreed with Darwins ideas;
-some people thought he did not have enough evidence to back up his theory
- many people disagreed because they thought god had created all species
Now Darwins theory is much more widely accepted, this is because; - it explains lots of observations and it has been discussed and tested by a wide range of scientists
There have been other attempts to explain evolution. Before Darwin; Jean Baptiste de Lamarck had a different theory, called the law of acquired characteristics. This said, for example, that giraffes acquired long necks to feed, and this characteristic was passed on.
As we discovered more about how genes are passed on, theories like Lamarcks have been proved incorrect and Darwins theory has become more widely accepted.
There are many different types of pollution. Three that have caused much concern are;
-carbone dioxide, from increased burning of fossil fuels, which may increase the greenhouse effect, and global warming.
-CFCs, from aerosols, which destroy the ozone layer
-sulfur dioxide, from buning fossil fuels, which causes acid rain.
Population and pollution
The human population of the world is growing at an ever-increasing rate. This is called exponential growth.
This growth in population is happening because the birth rate is exceeding the death rate.
The greatest rise in world population figures is occurring in under-developed land masses, such as africa and india. However, the developed world uses the most fossil fuels (principally the USA and europe)
The amount of pollution caused per person or organisation is called the 'carbon footprint'. This measures the total greenhouse gas given off by a person or organisation with a certain time.
Pollution in water or air can be measured using direct methods or by indicator organisms.
Direct methods include oxygen robes attached to computers that can measure the exact levels of oxygen in a pond. Special chemicals can be used to indicate levels of nitrate pollution from fertilisers.
The presence or absence or an indicator species is used to estimate levels of pollution. For example, - the mayfly larva is an insect that can only live in clean water, -the water louse,bloodworm and mussels can live in polluted water, -lichen grows on trees and rocks but only when the air is clean. It is unusual to find lichen growing in cities, because it is killed by the pollution from motor engines.
There are advantages to the different methods of measuring pollution;-using indicator organisms is cheaper, does not need equipment that can go wrong and monitors pollution levels over long periods of time,-using direct methods can give more accurate results at any specific time.
Conservation involves trying to preserve the variety of plants and animals and the habitats that they live in. People think that it is important because it can;
- protect our food supply,- prevent any damage to food chains, which can be hard to predict,- protect plants and animals that might be useful for medical uses,- protect organisms and habitats that people enjoy to visit and study
Species are at risk of extinction if the number of individuals or habitats falls below critical levels.
When trying to conserve species the important factors to bear in mind include;
-the sixe of the population (if the population is below a critical level there is unlikely to b enough genetic variation in the population to enable it to survive), -the number of suitable habitats that are available for the organism to live in, -how much competition there is from other species.
Whales have been hunted for hundreds of years for their body parts. Which are used in many products. Live whales are also important for the tourist trade.
Some whales are kept in captivity for research or captive breeding programmes or just for our entertainment. However,many people object when whales loose their freedom.
It has been difficult to set up police international agreements on whaling and some countries want to lift the ban on whaling.
Scientists believe there is a need to kill some whales to help find out more about how whales can survive at extreme depths. However, they could study the whales without killing them. Migration patterns and whale communication can only be investigated if the animal is alive.
sustainable development means taking enough resources from the enviroment for current needs, while leaving enough for the future and preventing permanent damage. For example; -fishing quotas are set, so that there are enough fish left to breed, -woods are replanted to keep the up the supply of trees.
As the world population increases it is crucial to carry out sustainable development.
-Fossil fuels will run out. As there is an increase in demand for energy, we must alternative fuels, such as wood.
-we need to supply increasing amounts of food for growing populations without destroying large areas of natural habitats.
-large amounts waste products must be disposed of so as to prevent of minimise pollution.
If all of this is achieved it should help to save endangered species.