Evolution and speciation

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Evolution is where the species change slowly over time.

Only the fittest survive.

Charles Darwin came up with the theory of evolution.

It’s called the theory of natural selection.

Darwin knew that organisms in a species show wide variation. He also knew that organisms have to compete for limited resources in n ecosystem.

Darwin concluded that organisms that are best adapted (the fittest) would be more successful competitors and would be more likely to survive. This idea is called ‘survival of the fittest’.

The successful organisms that survive are more likely to reproduce and pass on their adaptations that made them successful offspring.

The organisms that are less well adapted would be less likely to survive and reproduce, so they are less likely to pass on their characteristics to the next generation.

Over time, successful adaptation become more common in the population and the species changes – it evolves.

New discoveries have help to develop the theory of natural selection.

Darwin’s theory wasn’t perfect – he still couldn’t give a good explanation to why new characteristics appeared or exactly how individual organisms passed on their beneficial adaptation to their off spring.

That’s because DNA wasn’t discovered until 50 years after his theory was published.

We now know that adaptations ae controlled by genes. New adaptations arise because of mutations (changes in the DNA. Successful adaptations are passed on to future genes that parents contribute to their offspring.

The development of a new species is called speciation.

Over a long period of time, organisms might change so much because of natural selection hat a completely new specie if formed. This is called speciation.

Speciation happens when a populations of the same species change enough to become reproductive isolated – this means they can’t interbreed to produce fertile offspring.

Reproductive isolated can be caused by geographic isolation. Here’s how:

• A physical barrier divides a population of a species, e.g. a river changes its course. The two new populations are unable to mix.