Do all living organisms belong to the same ancestor?

According evidence discovered by scientists over many decades

“All life on Earth comes from a single ancestor”

Yes, you heard that right we all living organisms including human beings have a single common ancestor. This evidence is not from just one disciple, this discovery is supported by various disciples such as physiology and biochemistry, anatomy, paleontology, biogeography, speciation, mathematical modeling, selection, and coloration. This evidence is an important part of evolution theory and also demonstrates that evolution does occur that leads to the creation of biodiversity on earth. Let’s look at some of these disciples and their evidence.

One of the strongest evidence for common ancestor comes from physiology and biochemistry that examines the relationship of DNA sequence from different species. It supports the original hypothesis of Darwin that all species share a common ancestor. The most powerful evidence is provided by phylogenetic reconstruction in which protein sequences are slowly evolved to reconstruct the evolutionary history of modern organisms. A classic example of biochemical evidence for evolution is the presence of protein Cytochrome C which all living organisms have because it performs very basic life functions.

Endogenous retroviruses (or ERVs) are remnants of ancient viral infections that get marked into DNA and passed from one generation to the next generation. Finding the identical chromosomal position of a virogene in two different species suggests that the two species belong to common ancestry.

Evidence from anatomy also supports the discovery of common ancestors. A large number of species contain a small fraction of genes called hox genes that control the development of organisms. These genes are universal and suggest the origin of common ancestry. Based on taxonomy, Darwin described how common descent could provide a logical basis for classification:

All the foregoing rules and aids and difficulties in classification are explained, if I do not greatly deceive myself, on the view that the natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, …

— Charles Darwin, On the Origin of Species, page 577

Finding evidence from paleontology can be difficult as the existence of most of the organisms gets vanished because when they die, their body decomposes rapidly or gets consumed by scavengers. However, sometimes some organisms get preserved as they get embedded in rocks by natural processes. Due to all these difficulties still, there is abundant evidence that different species are related in the form of transitional fossils.

Insect trapped in amber

According to biogeography, the presence and absence of species on various continents and islands can provide evidence of common descent and evolution. History of camel provides fossil evidence for the evolution of camelids which started in North America about 6 million years ago. Then, these species migrated to different continents such as Asia and Africa. Once isolated, they evolved in their way to adapt climate conditions and gave rise to Bactrian camel and dromedary in Asia and Africa. Then, Camelids became extinct in North America at the end of the last ice age.

Three major coloration evidence: camouflage; mimicry; and aposematism were found in second half of the 19th century that provided evidence for evolution by natural selection.

Mathematical modeling has enabled us to provide hidden evidence of evolution by measuring changes in DNA of different species. And in the future also it will help us to build models to solve a more complex tree of life.


Professor Atom

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Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )

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