Evolution
How did life arise on planet Earth?
The unique conditions on early Earth allowed for the formation of biological molecules -- the building blocks of life. Over time, these biological molecules combined to form the first simple cell. As you complete the activities below, you will see how life on Earth began, evolved and diversified over billions of years.
I: Synthesis of Biological Molecules
II: Earth Viewer
Survival of the Fittest
Evolution occurs due to some organisms in a population having variations that are more suitable for survival within a particular environment. These variations arise due to mutations in the DNA. There are many different ways that DNA can change, resulting in different types of mutations. One type of mutation that can occur is a point mutation. Point mutations are mutations that originate at one spot in the DNA. Below are two types of point mutations.
Type I) Substitution: a change in a single base. These mutations can be silent, harmful, or beneficial.
Silent mutations: A change in a base that still codes for the same amino acid, causing no change in the final protein.
Harmful mutations: A change in a base causing the codon to code for a different amino acid. This causes a change in the final protein shape, resulting in a defective protein.
Beneficial mutations: A change in a base causing the codon to code for a different amino acid. This causes a change in the final protein shape, resulting in a new, more fit phenotype.
Type II) Frameshift: A change in the number of bases in a gene, causing a shift in the reading frame of the codons in the mRNA. There are two types of frameshift mutations.
Insertion: Additional base pairs are inserted into a new place in the DNA.
Deletion: A section of DNA is lost, or deleted.
Mutations can cause changes to a protein's shape, which can cause a change in phenotype. If a mutation results in a more fit phenotype, that individual will be more likely to survive and pass on their genetic information. In the example to the right, imagine that green beetles are easier for birds to spot. If a mutation arose that produced a brown phenotype, this phenotype would increase the brown beetle's chances of survival. These individuals will then pass their genes for brown coloration on to their offspring. In the next generation, brown beetles will be more common than in the previous generation.
Survival of the fittest means that the organisms best suited for their environment are more likely to survive and pass on their genetic information to their offspring. This process is also known as natural selection.