The light of evolution

Discuss the Statement:

Nothing in Biology Makes Sense Except in the Light of Evolution?

Theodosius Dobzhansky was a well known evolutionary biologist, who was born in the Ukraine and later emigrated to the USA. In 1973 he published the paper, ?Nothing in Biology Makes Sense Except in the Light of Evolution?, which opposes anti-evolutionary ideas, namely creationism, and details how evolution links all the separate areas of biology together, explaining how life is the way it is.[1] Dobzhansky himself was a Christian, however he also strongly believed in the idea of evolution, and wrote in his paper how he considered religion and evolution to be perfectly compatible with each other.

To say that ?Nothing? makes sense without evolution is a powerful statement, but is this really true? Or are there things in biology which the evolution theory doesn?t quite explain satisfactorily? Is there even a possibility that Darwin?s theory, which is widely accepted as fact, is incorrect, and that a few centuries from now it will be completely replaced?

In this essay, I will attempt to explain what Dobzhansky originally meant by this proclamation. I will consider how relevant his statement still is today, and I will discuss his arguments in favour of evolution and his belief that creation ?is a process that began some 10 billion years ago and is still under way?.

To begin, I will define exactly what Dobzhansky meant by the key terms ?biology? and ?evolution?. ?Biology? comes from the Greek words: ?bios?, meaning ?life?; and ?logia?, meaning ?study of?. Biology is ?the scientific study of life?, ?posing questions about the living world and seeking science-based answers?.[2]

?Evolution? refers to the idea of ?descent with modification?. Dobzhansky himself, in his book ?Genetics and the Origin of Species?, defines evolution as ?a change in the frequency of an allele within a gene pool?.[3] All organisms alive today are descended from ancestral organisms, beginning with a single universal common ancestor, some four billion years ago.

Dobzhansky?s use of the term ?light of evolution? can be attributed to the French philosopher Pierre Teilhard de Chardin, who wrote of evolution as ?a light which illuminates all facts?. Dobzhansky quotes this in his essay, and argues that without the idea of evolution, the separate areas of biology become interesting but pointless facts, with nothing to link them together.

The original context of Dobzhansky?s essay deals with the typical evolution versus creationism debate, something that is still entirely relevant today. According to the Guardian newspaper, in a recent survey, ?54% of the 973 polled Britons agreed with the view that evolutionary theories should be taught in science lessons in schools, together with other possible perspectives, such as intelligent design and creationism?. This compares to 51% of 991 people polled in the USA.[4]

To define creationism and intelligent design: ?Creationism? is taking the story of creation literally, as it was written in the bible, and believing that the world was created only recently (in 4004 BC), in the space of six days. The theory of ?Intelligent Design? proposes that some things in nature are simply too complex to have occurred by evolution, and therefore they must have been created. Dobzhansky was vehemently opposed to such theories, as there is significant scientific evidence to prove them incorrect. For example, that the earth was created in 4004 BC has been completely disproved by the evidence provided by radiometric dating of rocks. Fossils that span millions of years prove that the earth was most definitely not created as it is today in the space of six days. Furthermore, these fossils are significant in proving the evolution theory to be correct: they provide evidence for the gradual changes of organisms over millions of years.

Dobzhansky himself was a devout Christian; however he believed that his religion was completely compatible with evolution. He describes himself as ?a creationist and an evolutionist?, explaining his belief that ?creation is realized in this world by means of evolution?. My interpretation of this is that Dobzhansky sees evolution and creation as synonymous, that evolution is the ongoing process of creation.

Dobzhansky uses the example of the ?diversity and unity? of life to explain his argument in favour of evolution. Life is infinitely diverse. Organisms have evolved to occupy a huge variety of ecological niches, developing many different modes of life to enable them to do so. Some species are highly specialised and are only found in a single area; Dobzhansky uses the example of drosopholid flies in Hawaii. In his essay he explains how a quarter of the 2000 species of drosopholids are endemic to the Hawaiian Islands, i.e. they are found nowhere else in the world. Other species have become adapted for survival in the most extreme environments: take the archaea that can tolerate temperatures of 85?C and pH 2 in volcanic hot springs. Still others are widely adapted to many different environments; humans for example have colonized the entire globe. However, as Dobzhansky points out; no individual species is able to make use of all possible ?opportunities for living?. Indeed, the only way humans are able to survive in the varied environments that we live in is to physically alter those environments, we as a species have not evolved adaptations to enable us to live in them.

So, if all life is this diverse, how is it possible to prove that all species present today have evolved from a single common ancestor? It is because life is also remarkably unified in the most fundamental ways. All organisms need to carry out the same processes in order to survive ? respiration and metabolism for example. All species follow the same basic drive to reproduce, even though the mechanisms for achieving this are as diverse as the species themselves. Advances in molecular biology have provided much evidence for the universal cell chemistry of organisms. In all living organisms, their genome is stored in DNA, transcribed into RNA, and translated into protein. The genetic code is the same for every species; the four DNA bases give rise to the same amino acids. Even viruses, for which it is debateable whether they are really living, follow this same genetic code in RNA and protein. Cellular processes are carried out by very similar enzymes in many organisms, with only a few variations in amino acid sequence. As remarked in The World of the Cell (Becker et al.); ?The more closely related two different organisms are, the more similarities we see in their sequences of particular DNA, RNA and protein molecules?.[5] Hence it is easy to see how similar species could have evolved from a common ancestor by natural selection, and this idea can be extended far back in time, explaining how all species have evolved from the same common ancestor, no matter how different they appear now.

Without the theory of evolution it would be impossible to explain the similarities of organisms at a cellular level, and their diversity in appearance and mode of life. In this regard I would certainly agree with Dobzhansky that biology would not make sense without evolution.

So, is there anything in biology that can?t be explained by evolution? The question of how life itself originated is still an enigma: we have no solid evidence for how living cells first appeared. Evolution is based on random mutations in DNA that give specific advantages to organisms, but how did DNA form in the first place? The current hypothesis on the origin of life is that the environmental conditions on earth 4 billion years ago could have caused the formation of simple organic molecules, such as amino acids. In certain conditions these molecules could have spontaneously polymerised, and perhaps had the ability to act as catalysts. ?Protobionts?, small droplets of organic molecules with a primitive membrane, could have acted as a kind of ?cell?. The formation of self-replicating RNA could provide the first genetic material. If certain RNA sequences were more stable than others, they would be more likely to self-replicate. And so natural selection is born. In time, more stable DNA could replace RNA, and protobionts could evolve into proper cells, with the ability to divide and reproduce.[6] However there is no proof of any of this. Lab experiments have shown that amino acids can form abiotically in certain atmospheric conditions, but how can we possibly prove events that happened 4 billion years ago? In this case, evolution is useless in explaining how ?biology? even came to exist; the principles of natural selection cannot be applied to inanimate matter before life even began. Evolution is not illuminating anything about the origin of life. However, having said this, it doesn?t by any means disprove the theory of evolution. Once the formation of DNA and cells had occurred, evolution could proceed as we know it; it just doesn?t explain how DNA and cells came to exist in the first place.

In conclusion, I largely agree with Dobzhansky?s statement that ?Nothing in biology makes sense except in the light of evolution?. Evolution can be used to explain the vast diversity seen in the natural world, and yet the incredible unity of organisms at a cellular level. However, as pointed out above, it can?t universally explain everything, as the mechanism of the origin of life is still unknown to us. We can only hypothesise about how life came to exist, and for all we know, the creationists may be right after all!

But while all the mechanisms of evolution may not be fully known to us yet, the central theory of descent by modification remains solid. There is no scientific evidence for theories like creationism and intelligent design, and significant evidence to disprove them. Evolution is the single concept which links all the separate areas of biology together, it explains why and how things are the way they are.


1.Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. The American Biology Teacher, 35, 125-129.

2.Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., et al. (2008). Biology (eighth (International) ed.). USA: Pearson Benjamin Cummings. Pg 1

3.Dobzhansky, T. (1937). Genetics and the origin of species. New York: Columbia University Press.


5.Becker, W. M., Kleinsmith, L. J., Hardin, J., & Bertoni, G. P. (2009). The world of the cell (Seventh (International) ed.). USA: Pearson Benjamin Cummings. Pg 75

6.Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., et al. (2008). Biology (eighth (International) ed.). USA: Pearson Benjamin Cummings. Pg 507 - 510

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