"Survival of the fittest"
The world inhabited by living things is very harsh. They have to compete for everything such as light, food, shelter and mates.
All this and they have to avoid getting eaten!
Only the best suited will survive long enough to reproduce, and so pass on their genes to the next generation.
Organisms try to ensure that their offspring have advantages in survival. Many strategies are used to ensure this; some produce huge numbers of them so that at least a few will survive, others try to protect and shelter them for a long time - and care for them through school!
Charles Darwin is the one who is credited with coming up with the idea of natural selection, although there were others too, notably Alfred Wallace.
Darwin noted four things from his observations:
- All organisms produce an abundance of offspring, many more than is necessary.
- There is a fairly constant population size over time for any particular organism
- Within a species there is a wide range of features, due to different alleles
- Some variations are passed on and inherited by the offspring
From these Darwin decided that all organisms struggle for survival and so have to produce many offspring to ensure that some do survive.
He also concluded that for a species to survive, the best (or 'fittest') of them must survive long enough to reproduce and pass on their genes.;
s usual, someone else had a different idea.
Jean Baptiste de Lamarck had the idea that plants and animals evolve features according to how much they use them.
Lamarck's idea means that giraffes evolved long necks by reaching up for leaves in trees. At one time they would have had short necks but then they got longer.
Why didn't all the other animals get longer necks too?