Evolution

SLC24A5 and the Great Human Divide

SLC24A5 is a gene. The gene finds a special place in human cultural discourse because it produces a protein critical to the production of melanin – the great-divider pigment of human skin.

What is an SNIP?

A single nucleotide polymorphism, or SNP, is a variation at a single position in a DNA sequence among individuals. If it occurs in more than 1% of a population, they are an SNP group. If the SNP occurs in a gene (resulting in what is known as alleles), it can have some consequences – rs1426654 is one of them, as we shall see.

A Quick Tour to the Basics

Imagine that the GENOME is a book. There are 23 chapters called CHROMOSOMES. Each chapter contains several thousands of stories, called GENES. Each story is made up of paragraphs, called EXONS, which are interrupted by advertisements called INTRONS. Each paragraph is made up of words called CODONS. Each word is written in letters called BASES. The words are written on long chains of sugar and phosphate called DNA!

– Matt Ridley in “Genome”
gene tree, tree of life, evolution-1490270.jpg

Allele and Us

As we have seen earlier, a gene has more than one allele if an SNP occurs within a gene. Our SLC24A5 gene also has alleles: the original allele that still dominates in the African and East Asian population (and contains the amino acid alanine), and the variant allele dominates in the Europen population (and contains threonine).

Why Me?

Why do ‘the originals’ have an alanine version, and what does it do? To answer the first part of the question, you should know how nature works. It is not that the originals have alanine, but only the alanine-containing humans survived the test of time in that location. The alanine allele triggers pigment production and defends the lower layers of the dermis from cancer-causing ultraviolet light, giving a small but significant additional life expectancy for people carrying this natural sunscreen.

The case with the sun-starved European side is quite the opposite: to fight Vitamin D deficiency, they must capture as much light (UV) as possible, and the pigment melanin is a potentially fatal blocker!

Does This Change Our Attitudes?

Unlikely. The notion that human complexion is only skin deep may be necessary but never a sufficient argument for people to stop distinguishing others based on colour (racism). Irrational as we are, humans will always keep inventing newer tricks to match their fancies and exercise their territorial powers. But this can, at least, refute one such stupid argument, and I will say I did not waste my page!

[1] SNP Definition: Nature

[2] Human Skin Color Gene: Scientific American

[3] SLC24A5: Science

[4] The Light Skin Allele of SLC24A5: Plos

[5] Skin Color for Indian Population: The Hindu

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Natural Selection

Natural selection does not mean nature selects something. It has no such powers (by the way, what is nature?)! Natural selection is merely the sum of all random activities resulting in an outcome. In other words, nature is what is imposed on it!

The first term is random (/ˈrændəm/; as per OALD: done, chosen, etc., without somebody deciding in advance what will happen or without any regular pattern ). Yes, the processes are random. 

The next up is activities; what are those? They are DNA replication followed by cell division (our life in one sentence). So, how much copying is happening in our bodies? Humans have about 30 trillion cells (30 followed by 12 zeros); on average, each one divides once a day, which is 30 trillion cell divisions per day. Even if you assume a tiny proportion of error during cell division, you could accumulate a few billion (called mutations) daily. 

In simple language, mutations are misspellings of DNA structure while copying. The body corrects most of it, but some may persist. Many of the mutations are neither harmful nor beneficial. So you get away. But, when it happens to the part of DNA that makes up a gene (gene variant), it becomes a serious affair.

Now, let’s come back to natural selection. Some rarer mutations lead to long-lasting consequences (maybe once in a few hundred generations) for an entire species. Say a skin colour change (I will explain that in another blog), a long nose or a pair of wings! 

Let’s take the story of tree frogs. Imagine two treefrogs in a society of treefrogs that got mutations that changed their colour – one got grey and the other green. If they lived in a dark wooded area, the accident enabled the grey variety to camouflage away from predators (snakes and birds). If you return after a few years, you will see the area is full of grey tree frogs. Now, change the scene to a green swamp. The genetic lottery is now with the green variant.  

The actions were random in both cases, but the outcome was specific.

When Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913) came up with the term natural selection, little did they know his grandchildren would give it the opposite meaning.

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Three Books You Must Read

Read these books! I believe every human must read these. Three books by three eminent scholars who own different areas of expertise yet share their passion for unearthing our past and showing what made us the way we are today.

Guns, Germs, and Steel

American geographer and biologist Jared Diamond dives deeper into the sea of human history, mesmerising his readers with the pearls of wisdom to answer basic questions of human inequalities we see in the modern world.

Sapiens: A Brief History of Humankind

This Yuval Noah Harari masterpiece divides the human history of the last 70,000 years into three revolutions: the cognitive, the agricultural and the scientific. He then proves how the marginal and territorial hunter-gatherer, homo sapiens, learned the lessons of cooperation and became the master of the planet, scripting unparallel progress in the last few hundred years.

The Better Angels of Our Nature

Known for his witty and lucid writing style, Steven Pinker, a well-known speaker, linguist and cognitive psychologist, wields his literary sword against the believers of “those good old days”. To choose his own words from the book: “Cultural memory pacifies the past, leaving us with pale souvenirs whose bloody origins have been bleached away”.

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The First Post

Here we start. ‘Thoughtful Examinations’ is about life, knowledge, and happiness. It’s about numbers, rationality, and perspectives. I welcome you to the experience.

The Life of Chances

Probability, the mathematics of chances, is tightly woven into the fabric of life. Our existence started, evolved, and was nurtured by countless unlikely events – some are linked, some are not. We all studied the subject at school, the endless tossing of coins! Yet, it’s rarely applied in life. We will see the subject of probability and statistics as a recurring theme of my posts.

The Gates of Knowledge are Open

The gates have been crashed; the doors are open. The Tree of Knowledge is no longer hidden from your sight. The internet has made access to knowledge to each one of us. The democratization of knowledge is complete! Remember chances: yes, the chances that you reach your goals are better than ever before.

The Happiness Project

This page is for all who enjoy learning new things or getting new perspectives. This piece is for people confused by the volume of information out in public, finding it hard to separate the truth from the sea of junk. This one is a happiness project.

Life is about chances, knowledge, and happiness.

Once again, welcome to this journey. I offer whatever that I can to make it enjoyable. Remember: life is about chances, rationality, and decision-making.

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