Molecular similarities support the shared common ancestry of life. Comparing the DNA sequences makes it possible to reveal how closely any two species are related. Whereas biogeography, or the study of organisms’ geographic distribution, can disclose information about how and when species evolved.

Homologous structures suggest comparable selected pressures can produce similar adaptations, whereas analogous structures show similar selective pressures can cause similar adaptations (beneficial features). Similarities and differences among biological molecules (for example, in the DNA sequence of genes) can be utilised to assess the relatedness of species.

Over many decades, researchers investigating many areas have identified evidence of common descent of living species, suggesting that all life on Earth descends from a single ancestor. This is significant evidence supporting evolutionary theory, demonstrating that evolution does occur and illuminating the mechanisms that gave rise to Earth’s biodiversity. It backs the modern evolutionary synthesis, the most recent scientific hypothesis explaining how and why life evolves by developing testable predictions, testing hypotheses, and constructing theories that demonstrate and describe its causes.

Similarities between biological molecules, like structural homologies, can indicate a common evolutionary ancestor. 

All living entities, at their most fundamental level, have:

• Same genetic material
• Genetic codes that are the same or somewhat similar
• Gene expression follows the same basic rules (transcription and translation)

These characteristics show that all living creatures had a common ancestor who had DNA as its genetic material, employed the genetic code, and expressed its genes through transcription and translation. Because these characteristics were ‘inherited’ from the ancestor, all current species have them (and because any significant changes in this basic machinery would have broken the basic functionality of cells)

Molecular evidence of common ancestor 

• Biomolecules like DNA (deoxyribonucleic acid), RNA (ribonucleic acid), and proteins are fundamental molecules that all living beings share. Scientists compare these molecules between life forms and investigate patterns of change to understand the evolutionary history of species.

• DNA structure is conserved in all life forms, including Archaea, Bacteria, and Eukaryotes, indicating that all life evolved from a common ancestor. Adenine, thymine, cytosine, and guanine are the nucleotides (base pairs) that encode genetic information in DNA (represented by the letters A, T, C, G). The mutation causes nucleotide changes in the DNA code throughout time.

• It is possible to track genetic change throughout time by comparing DNA from different organisms. The number of nucleotide changes across species in a piece of DNA can determine how long ago they separated from a common ancestor. The greater the nucleotide differences between two species, the longer they have evolved separately.

Nuclear vs mitochondrial DNA-Evolutionary approach

• Nuclear DNA, or nDNA, is DNA found in the nucleus of cells. DNA can also be present in mitochondria, referred to as mitochondrial DNA or mtDNA. Both are employed in evolutionary research.
• In evolutionary investigations, the choice between nDNA and mtDNA is based on the studied genes. Because nDNA codes for many more genes than mtDNA, there is a larger pool of candidate genes. While each mitochondrion contains only a tiny amount of DNA, the massive number of mitochondria in a cell results in a large amount of mtDNA. Differences in mutation rates between the two forms of DNA and the fact that mtDNA is exclusively passed down through the maternal line.

For example

• A chicken and a gorilla’s DNA and amino acid sequences differ more than an orangutan and a gorilla. That suggests the chicken and gorilla shared an ancestor a long time ago, whereas the gorilla and orangutan shared a more recent ancestor.

• This contributes to the evidence that gorillas and orangutans are more closely related than chickens.

Analysis of proteins

Protein amino acid sequences are compared to identify the evolutionary histories of species. For example, the amino acid sequence of beta-globin, a subunit of the protein haemoglobin, reveals only one amino acid difference between humans and gorillas but nearly twenty amino acid changes between humans and horses. Based on this, we can deduce that humans are more closely related to gorillas than horses.

Conclusion

Examining the chemicals and DNA found in all living things may provide some of the most substantial evidence of evolution. Scientists analysing molecules and DNA have been confirming conclusions about evolution gleaned from other sorts of evidence since the 1940s. By counting the number of differences between two species’ DNA or amino acid sequences, molecular clocks can be used to assess how closely two species are related. Gene clocks and evolutionary clocks are two terms used to describe these clocks. The fewer the distinctions, the shorter time has passed since the species separated and evolved into distinct species.