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Explore the fascinating process of evolution through genes, mutations, and adaptations. Discover how mutations can be harmful, beneficial, or neutral, and how species evolve over time to adapt to new environments. Delve into the evolution of the elephant family as a case study.
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Evolution An overview
DNA is made up of genes. A gene is a short section of DNA which carries the code for production of one protein. gene
Mutations • Permanent change to the base sequence of the DNA molecule. • Can be caused by mutagens such as: • Ionising radiation • Chemicals • Because mutations change the base sequence, the coded message in the genes change.
Remember: Mutations are only inherited if they occur during production of gametes. sperm egg
Each protein has a distinct structure. Enzymes Hormones Structural proteins
Mutations can be harmful. • Results in a phenotype that has poor fitness i.e less able to compete for resources. • Individuals with this phenotype either die before producing offspring, or produce less offspring. • This means that these individuals will be ‘selected against’ and the mutated gene will eventually disappear from the gene pool.
Mutations can be beneficial • These mutations result in a phenotype that benefits the individual. i.e improves fitness. • Individuals with this phenotype are better able to compete for resources or avoid being eaten. • This means that the new characteristic will be ‘selected for’ and over time the new phenotype becomes more common in a population. • They live longer and produce more offspring, so the mutated gene becomes more common in the gene pool.
Neutral mutations • These mutations don’t result in any benefit or harm to the individual under the current environmental conditions. • HOWEVER, if environmental conditions do change, there might be an advantage in having the mutated gene.
If the environment changes • There will be ‘selection pressure’ favouring those individuals with the phenotype that allows them to survive and breed under those new conditions. • This process is called ‘natural selection’ i.e survival of the fittest. • Over a long period of time a new species may evolve.
A case study Evolution of Probosidea – the Elephant family
The Moeritherium is believed to be the ancestor of elephants. They lived about 36 million years ago in Africa when the earth was very warm and wet. They were the size of a pig
Over millions of years, the genes coding for long trunks, tusks and large size were selected for. 4 tusks Gomphotherium lived from about 25 mya until 5 mya and stood about 3 m tall.
The ancestors of modern elephants spread out from Africa and adapted to new environments.
Of course, the continents were in different places millions of years ago. Dinosaurs were wiped out by an asteroid impact.
Mammals evolved very quickly to fill the niches left by the dinosaurs.
Ancestors of the modern elephant were evolving at this time. This period of time was warm even at the poles. Animals were adapted to warm and moist conditions and plant growth was prolific.
The ice ages The sea level dropped and land bridges opened for animals to migrate over.
During the ice ages, the northern hemisphere vegetation changed. summer winter Near the ice sheet tundra developed with freezing winters and cool summers.
Further south, taiga vegetation developed. pine trees
Large size was selected for as it insulated elephants against the cold and protected them from predators. Ambelodon
Smilodon was well adapted to ambushing large herbivores. Sabre toothed cats weighed 300kg Giant ground sloth
Mastodon lived in North America from around 4 mya until 12 500 ya. Weighed up to 5 tonne
Mammoth migrated from Asia to North America while sea levels were low. They lived from about 2 mya until 11 000 ya.
Mammoth were the successful end product of millions of years of evolution. Huge size, a woolly coat and massive tusks were an advantage in a cold climate with large predators.
Massive herbivores were preyed on by massive carnivores. Twice the size of a Grizzly bear
Around 13 000 years ago the first humans arrived in America. The first people were expert hunters and used the most sophistocated and lethal stone spear tips ever made.
The huge herbivores had not evolved behaviours to cope with human hunting.
Within a few thousand years all huge herbivores and the predators that fed on them were gone. extinct extinct extinct extinct
Meanwhile, Africa was still warm and had become much drier. Much of eastern and southern Africa became grassland.
The modern African elephant evolved in this environment. A number of traits were selected for. Large size as protection from predators. Lack of hair to prevent over-heating. Big ears to radiate heat Social behaviours
In Asia the Asian elephant had evolved adaptations for a different environment.
Summary • Mutations result in genetic variety in a species. • Good mutations improve fitness and are passed on to the next generation. • If a group of animals migrate to a new area or if environmental conditions change, only the fittest survive. • Eventually natural selection can result in the evolution of new species.
