theory of evolution

About 3 billion years ago life started forming on Earth. They were very simple life forms such as prokaryotes (bacteria) which were single celled. Over time these organisms changed into to many different other organisms. All of Earth’s first life lived in water, it was only 450 million years ago the first plants started to grow and that the organisms started to come out the water and started to live on land. This change is called evolution. Who founded the theory; what is it and why it happens will all be explained in the following paragraphs.
Charles Darwin is the man who is most famously associated with the theory of evolution. In 1859 he published a book a called ‘the Origin of Species’ which explained his theories on evolution. Darwin received lots of criticism and his theories caused much debate when he first mentioned it. This is because his theory of evolution did not match up with religious views which said that God had made all the animals and plants on Earth. Also, Darwin did not have much evidence to go by and he had only discovered the tip of the iceberg of evolution. It took a further 50 years to discover how inheritance and variation worked. But Darwin was not the only man to come up with this absurd idea. Around the same time as Darwin a French scientist, Jean-Baptiste Lamarck, had come up with a theory about evolution. This theory was slightly different from Charles Darwin’s. Lamarck believed in use and disuse, he thought that the long necks of giraffes evolved as generations of giraffes used their necks to reach for leaves which were higher and higher on the trees. There was one major flaw to Lamarck’s theory, it says that all simple organisms will eventually become complex, but this is not the case as there are simple organisms on earth. This is why Darwin’s theory is better as it explains the presence of simple organisms.
Darwin observed that:
1. All organisms over produce
2. But populations remain fairly constant, so some offspring must die.
3. All organisms show variation, the ones who are the best adapted to their environment are more likely to survive and breed
4. Some characteristics are inherited. Well adapted parents may pass on useful characteristics to future generations which can eventually evolve into species
This is called natural selection and this is what he is most famous for. Darwin believes that evolution is a consequence of natural selection. The organism with the best characteristics will be able to reproduce and hence they will be able to pass on their genes. But the thing is that you cannot be 100% sure that the good characteristics of the parent will be passed on to the offspring. This is why evolution takes such a long time to take place. Even in the same species there is variation, this is because of the difference in type of genes in an organism. Adaption and the environment play a huge role in evolution.
This is proved when Charles Darwin goes to the Galapagos Islands in South America from December 1831 to October 1836. He studies the different type of finches that live there on the island. This is called micro-evolution. The large ground finch (geospiza magnirostris) and the medium ground finch (geospiza fortis) both live on the ground and eat shrubs and seeds. They have quite short stout beaks which are well adapted to do this. However the small tree finch (camarhynchus parvulus) has sharp and more slender beaks which are ideal for catching insects and green warbler-finch (certhidea olivacea) has Long, pointed beaks made some of them more fit for picking seeds out of cactus fruits. Even though all these birds are within the same species there are variations. Animals have to change to suit the environment they are in otherwise they will become extinct; it is essentially the survival of the fittest. This is probably why the dinosaurs became extinct. They had had millions of years to evolve the necessary features which were needed for them to survive. So, when the meteor hit the earth it caused a massive change in the environment but the dinosaurs could not survive because they were too suited to the previous environment and they could not cope with the changes. This allowed for mammals to dominant the earth, evolve and get bigger as the dinosaurs were wiped out. Competition also has a role to play in the theory of evolution. In a group of animals each will have a different trait and animals with the best trait will be able to reproduce with more success. However sometimes there are mutations, this can either be good or bad for the animal. If bad it will not be passed on successively and it will eventually become extinct. Conversely, if the mutation is good, then it will be inherited by the next generation. These mutations are purely by chance and random. An example of this is shown in early humans whom all lived in Africa where it was very hot and so they had very dark skin. This meant they could not survive in places which were too cool/cold because they needed vitamin D. But as time went on some humans developed lighter skin which meant that they could live in cooler/colder habitats where there was less competition.
Evidence for evolution is in the fossils which are being discovered in the ground. These fossils can be dated due to the age of the rock in which they were found and the we can see how the animal is changing over time. There are disadvantages to this as not all fossils have been found and that not all animals have been fossilised. Another evidence for evolution is that sequence DNA can be used to see how closely related two organisms are. The most obvious evidence for evolution is the physical mutations/changes we can see, or in other words comparative anatomy, how similar/different two animals physically look. In conclusion evolution is a change in the frequency of an allele, this is random. An allele is an alternative form of a gene, which is caused by mutation and is found in the same place on a chromosome.