4.2.2 (e) Evidence of evolution

To include the contributions of Darwin and Wallace in formulating the theory of evolution by natural selection AND fossil, DNA (only genomic DNA at AS level) and molecular evidence.

Meaning of evolution

can be distinguished into 2 key ideas:

• the general theory of evolution - the way in which species have changed over time and continue to change

• the shorthand way of referring to the theory of evolution by natural selection - the specific process by which evolution occurs

Darwin’s several key observations that helped him to develop the theory of evolution by natural selection

• All organisms produce more offspring than could ever actually survive (i.e. not all offspring survive)

• Populations of organisms do fluctuate (change over time) but not significantly (i.e. their numbers usually stay fairly constant)

• Populations of the same species of organisms show variation in characteristics between individuals (known as intraspecific variation)

• Offspring inherit characteristics from their parents

Two key sources of evidence for the theory of evolution by natural selection:

• Fossil evidence

• Molecular evidence (characteristics are passed on to offspring in genes)

Fossil evidence for the theory of evolution by natural selection

• are preserved remains of organisms or other features left by organisms, such as footprints, burrows and faeces

• We can tell from fossils that environments (and the organisms living there) have changed significantly over millions of years

• Fossils and rocks they are found in, can be dated, allowing us to accurately put fossil organisms into a sequence from oldest to youngest (i.e to see how the organisms changed through evolutionary time)

• Fossils also allow us to show similarities between extinct species (i.e. how related they are) and even between now-extinct, ancestral species and present-day species

Molecular evidence for the theory of evolution by natural selection.

• DNA found in the nucleus of cells can be sequenced and used to provide evidence of evolutionary relationships between species and how the genetic code of species has changed as they have evolved

• The differences between the nucleotide sequences in the analogous genes of different species can provide a lot of information:

  • The more similar the sequence the more closely related the species are

  • Two groups of organisms with very similar DNA will have separated into separate species more recently than two groups with less similarity in their DNA sequences

• As a result, DNA sequence analysis and comparison can be used to create phylogenetic trees that show the evolutionary relationships between species