Evolution in
Biology
In biology, evolution is the change in the
characteristics of a species over several generations and relies on the process
of natural selection.
- The theory of evolution is based on the idea that all species are related and gradually change over time.
- Evolution relies on there being genetic variation in a population which affects the physical characteristics (phenotype) of an organism.
- Some of these characteristics may give the individual an advantage over other individuals which they can then pass on to their offspring.
- The mechanisms of evolution operate at the genomic level. Changes in DNA sequences affect the composition and expression of our genes, the basic units of inheritance.
- To understand how different species have evolved we have to look at the DNA sequences in their genomes.
- Our evolutionary history is written into our genome. The human genome looks the way it does because of all the genetic changes that affected our ancestors.
- When DNA and genes in different species look very similar, this is usually taken as evidence of them sharing ancestors.
- For example, humans and the fruit fly, Drosophila melanogaster, share much of their DNA. 75 per cent of genes that cause diseases in humans are also found in the fruit fly.
- DNA accumulates changes over time. Some of these changes can be beneficial, and provide a selective advantage for an organism.
- Other changes may be harmful if they affect an important, everyday function. As a result some genes do not change much. They are said to be conserved.
Different types of evolution
Convergent evolution
- When the same adaptations evolve independently, under similar selection pressures.
- For example, flying insects, birds and bats have all evolved the ability to fly, but independently of each other.
Co-evolution
- When two species or groups of species have evolved alongside each other where one adapts to changes in the other.
- For example, flowering plants and pollinating insects such as bees.
Adaptive radiation
- When a species splits into a number of new forms when a change in the environment makes new resources available or creates new environmental challenges.
- For example, finches on the Galapagos Islands have developed different shaped beaks to take advantage of the different kinds of food available on different islands.
Dr. M. Gomathi,
HOD of Biotechnology,
MKJC.
