SINGAPORE - Everything about us is the result of evolution, says science historian Dr John van Wyhe.

This ranges "from the organisation of our internal organs, our biochemistry, and our susceptibility to diseases".

Tuesday (Nov 24) marks Evolution Day, 161 years since the initial publication of Charles Darwin's "On the Origin of Species" in 1859.

Two pages from Darwin's handwritten draft were recently unearthed, offering glimpses into the making of the book which "changed the world", said Dr van Wyhe, senior lecturer at the National University of Singapore's Department of Biological Sciences and who helms the Darwin Online website.

Another page of Darwin's reading notes which examined slaving-making ants was also uncovered. This eventually became a segment of his book which was widely discussed.

Slave-making ants are a type of parasite which manipulates other similar species to increase the size of its own colony.

Scans of these artefacts, from a private collection in the United States, were given to Dr van Wyhe and uploaded on Darwin Online.

Darwin's theory of evolution posited that all living things change over time and developed characteristics to adapt to their environments.

However, the diversity of living things meant that some species possess characteristics that render them "stronger" than others. These species will survive, and those who are weaker will die.

"Such a theory was considered radical at that time, as people knew that species had appeared and disappeared throughout history, but they did not know why," Dr van Whye said. "Darwin explained that these species had, in fact, evolved over time."

Evolution of the pandemic

Today, this theory has been widely understood as the "bedrock of all living things", and it remains even more important especially amid the Covid-19 pandemic.

During the pandemic, two living organisms - the Sars-CoV-2 virus and human beings - compete with one another for survival. The virus, which causes the disease Covid-19, propagates by infecting host cells in human beings to reproduce.

To survive, they mutate and evolve along the way to infect larger segments of the population.

Yet, on the other side of the battlefield, human beings protect themselves from viruses by developing antibodies. These antibodies lock onto the virus' host cells.

However, the diversity of human beings means that some are more susceptible than others. Those with a stronger immune system "defeat" the virus, while the weaker ones may succumb to it.

Taking a look at the past few pandemics that have plagued human history, it can be seen that viruses must have certain characteristics to remain infectious and continue reproducing.

This is why deadly viruses, which kill the host quickly before they can infect other people, will eventually disappear.

For instance, the Spanish flu in 1918, known to be the deadliest flu in history, killed between 50 and 100 million people.

Back then, scientists knew little about the virus. However, by 1919, the flu pandemic had come to an end as those who were more susceptible to it had died, while those who survived developed immunity to the virus.

In the present day, we are armed with various forms of technology to counteract the virus, with therapeutics, contact tracing tools to control its spread, and even the promise of a vaccine, but we remain in the same game, said Dr van Wyhe.

He added: "As long as living things continue to evolve and change, we will always have to be on our guard for new mutations that come along the way".

On evolution & the Galapagos Islands

Evolution refers to the way things change over time. During one of his voyages on the HMS Beagle ship, Darwin visited the Galapagos Islands, an archipelago comprising 13 main islands and many smaller ones.

He theorised that these species likely migrated from South America to these remote islands in the Galapagos archipelago, and over time, they adapted to the unique environment of each island, and evolved into new species.

Here are four unique types of animal species native to the Galapagos Islands:

Finches

• A diagram of the four beaks has been commonly used in textbooks to show the finches' evolution into different types of species.

• Their different types of beaks are said to be adapted so that they can consume different types of food. For instance, fruit-eating finches have parrot-like beaks, whereas finches that eat insects have narrow beaks.

• Many had the misconception that this sighting helped Darwin explain evolution, but it was in fact British biologist David Lack who discovered this in the 1940s.

• He drew upon Darwin's theory of evolution and named his book Darwin's Finches, which explains the confusion.

Mockingbirds

• The three species of mockingbirds that Darwin collected from three different islands in the Galapagos gave him his "eureka" moment.

• He realised that each of the birds, though they belonged to the same genus, Mimus, had variations in their characteristics, such as the birds from each of the islands sporting feathers of a different colour.

Iguanas

• There are two types of iguanas in the Galapagos, the land and marine iguanas. Marine iguanas are the only modern lizards that can forage in the sea, and are adapted to survive on scarce food on the islands.

• They are able to scrape algae off rocks, and use their large claws to grip the rocky seafloor.

Tortoise

• The famed Galapagos tortoise, Chelonoidis nigra, is one of the largest tortoises in the world, weighing up to 220kg.

• However, its shell size and shape vary across populations. For instance on islands with dry lowlands, the tortoises are smaller, with "saddleback" shells and long necks, which help them reach for vegetation that grows above ground.

SOURCES AND PHOTOS: DARWIN ONLINE, WILLIAM HUXLEY DARWIN, PRIVATE COLLECTORS, RUBEN HELENO, JAMES P. GIBBS, SUNY-ESF, MARTIN WIKELSKI