The word evolution can be used in many ways, but in biology, it means descent with modification. In other words, small modifications occur at the genetic level (i.e. in DNA) when a new generation originates from an ancestral population of individuals within a given species. Over time the modifications basically change the characteristics of the whole population. When the population gathers a large number of changes and conditions are right, a new species may appear.
Evolution in Australia
- The theory of plate tectonics holds that the continents and oceans are carried on the large crustal plates of the Earths surface, which move on top of the semi-molten interior
- Evidence for this includes the age of the sea floor around mid-oceans ridges, the matching edges of continents, and fossils of similar organisms found in different parts of the world.
- Megafauna are large animals, such as elephants and whales
- Megafauna are not the ancestors of present animals, e.g. kangaroos didn’t come from giant kangaroos, rather they both evolved from a common ancestor.
- Over the last 50k years most of the world’s megafauna have become extinct
- Two theories have been put forward to explain this:
Climate Change: Megafauna were mainly suited to glacial conditions. Their large bodies enabled them to live in extreme conditions. In Australia, the temperature changed from cold-dry to warm-dry. As a result, water sources began to dry up, and many animals lost their habitat and died out.
Human Expansion: The time of the extinction of megafauna matches very closely the pattern of human migration into these areas. Megafauna are also large and slow, which makes them susceptible to hunting. In Africa, humans evolution occurred there, so hunting increased slowly, allowing animals to adjust. That is why there are still megafauna there. However, in places where humans arrived as skilled hunters, the most extinction occurred.
Evidence of Evolution
It was said that humans evolved from apes. Darwin supported that and even wrote books about it he had many supporters, but even some of his fellow supporters did not initially agree.
In 1858, both Charles Darwin and Alfred Wallace proposed the same method for evolution, the mechanism of natural selection. Their theory of evolution by natural selection is based on four main points.
1. Variation—individuals within a population that reproduce sexually; show variations that can be passed from one generation to the next 2. Natural selection—selective pressure (e.g. change in the environment) puts constraints on organisms (e.g. resources become limited). These constraints are called selective pressures and…