Your appendix is not useless and you are mostly not human

Plus human photosynthesis, how mosquitoes know who to bite, the hardest problem in solving the climate crisis, and why the world is running out of sand.

The physicist Freeman Dyson speculated that in the future children will create new genetically modified organisms the same way that his generation tinkered with chemistry sets. Whether it is designed proteins or vaccines or new genetic codes, the tools are all in place.

Some of the most fun things to write are those that merge the cutting-edge of science with the imagination and curiosity of childhood.

Asking why something in the universe is the way it is and not some other way…

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Why can’t people photosynthesize?

This month for The Morning Context I took the question of a ten-year-old on why humans can’t photosynthesize to the logical extreme. People can’t make food from sunlight. But why?

In his wonderful book, The Next 500 Years: Engineering Life to Reach New Worlds, geneticist Christopher Mason of Cornell University imagines humans centuries in the future with “chloroskins” that trap light energy during spaceflight. Mason has calculated from the energy requirements of a person and the efficiency of photosynthesis that a chlorohuman would need about 290 hours of midday sun to be able to get through the day. There aren’t that many hours in a day, of course. But there’s another solution: humans with a greater surface area of skin. Mason estimates that with skin the size of two tennis courts, only an hour of sun would be needed. Such genetically modified chlorohumans could unfurl their skin, soak up the sun, and then roll the skin back up!

Other scientists have also calculated the amount of skin we need and have also come up with large estimates in the same ballpark. In an article at The Conversation, plant scientist Lindsay Turnbull of the University of Oxford estimates that only one tennis court’s worth of skin would be needed to satisfy the energy needs of a photosynthesizing woman. 

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How do mosquitoes know who to bite?

I wrote about some of the most recent research on how mosquitoes hone in on people to bite. There’s practical use to this information.

In 2019, researchers found that knocking out a specific smell receptor that let mosquitoes detect a component of human sweat, made them less attracted to people.

Last year, researchers led by Craig Montell at the University of California, Santa Barbara, published a study in the journal Current Biology that showed that when two genes for specific light-sensing proteins were knocked out, mosquitoes could no longer see people.

Now, researchers led by Jeffrey Riffell, a professor of biology at the University of Washington, have found that a certain species of mosquitoes that bites people uses a combination of smell and colour to home in on us. The research, published in the scientific journal Nature Communications on February 4, found that mosquitoes are alerted to the presence of humans by the carbon dioxide that we exhale. Carbon dioxide is a gas that is odourless to humans, but mosquitoes have the ability to smell it. The researchers found that once mosquitoes get a whiff of carbon dioxide, they search for red, orange, and cyan colours. Humans have differing levels of pigmentation, but we all emit a signal in this colour range that mosquitoes can pick up. So, these colours are a reliable indicator of human skin.  

The gist of it is this —

• Mosquitoes smell carbon dioxide that humans and other animals breathe out.

• They also smell volatile compounds in sweat.

• Mosquitoes can sense the heat skin gives off.

• They see orange and red (which is present in human skin regardless of pigmentation).

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We can ignore the hardest problems in decarbonizing the environment

Caring for the environment is a lot like flossing your teeth. A lot of people claim to do it, when they actually don't, and they put it off until their teeth start to fall out.

In climatech there are two major factions —

• we have the technologies particularly in renewables, but we need new infrastructure and scale.

• we need fundamentally new technologies to be developed.

Both views are correct given the magnitude of the challenge of climate change.

Ask anyone who has been looking at climate science or climatech what the hardest sector to decarbonize will be and you'll likely get the same response. It's not agriculture or transportation or even energy. It's from making stuff. There's a lot of stuff and more on the way. I wrote a long column about this problem for Hindustan Times which I’ll summarize below —

Buildings, roads, and factories require a lot of materials to build. In How to Avoid a Climate Disaster, Bill Gates mentions that the world will build the equivalent of a New York City every month for 40 years. For that you need cement, sand, steel, and glass.

Rich countries emitted greenhouse gases building infrastructure. Now, developing countries want to grow economies rapidly by building. China’s economic growth has been fuelled through building projects on a grand scale. Today, China has more skyscrapers than anyone else.

In India's budget there's an ambitious plan to grow through massive infrastructure projects. All of these will result in greenhouse gas emissions. The country needs to increase GDP, but at what cost? India is also at risk from coastal flooding, melting water sources, and unlivable temperatures.

Cement is the most widely used construction material on the planet after water. The world needs a lot of cement and most of it is produced locally. And cement is hard to decarbonize because the emission of carbon dioxide is part of the process of making it.

Steel production also results in massive amounts of carbon dioxide that is not used being released. A full 8% of emissions come from cement making and around 8% from steel production. That's about the same as the entire emissions from some large countries.

Now you can "cure" concrete by forcing in carbon dioxide and you can make steel more efficiently, but these will not be scaled up globally or rapidly to reduce carbon emissions to zero. Ever. That's not a pessimistic opinion, that's a fact.

Now let's talk about petrochemicals. Due to energy transitions, the world will shift away from using fossil fuels as energy sources. But their use in the chemical industry will continue to increase.

As an oil company executive said, "we'll always have plastics."

There are 100,000s of everyday products around you that are derived from petroleum including paints, solvents, and drugs. And plastics are everywhere- in clothes, electronics, packages (and unfortunately in our oceans and inside our bodies too).

The chemical industry is actually the most energy intensive industrial sector, but only the third in emissions (after cement and steel). The reason? Most of that carbon is in the product. Plastics are carbon polymers. If you burn them, you get energy, but you also release carbon dioxide.

By now, you see the problem that we're mostly ignoring. Riding a Tesla or getting your energy from solar panels is not going to be enough to prevent a climate disaster. Cement, steel, and plastic production will always be net positive carbon emitters on a global scale. So, we have to capture carbon and reuse it or store it. Otherwise, the world will never achieve the goal of net-zero carbon emissions. And we will speed disastrously past no-return to hothouse earth.

Here’s where trees come in. Green plants such as trees pull carbon dioxide naturally through the process of carbon fixation by photosynthesis. But as many others have said, tree-planting only works as a carbon store if the right trees are planted and taken care of. We should plant a lot of trees, but they’re not a perfect solution. I’ll talk more about trees at a later date.

You can also pull carbon dioxide from the air and store it underground or under the ocean. A plant in Iceland gets a lot of media coverage for this, but it's costly and difficult to scale up globally without significant financial incentives. I won't get into the details of the catalysts or materials here, but as any materials scientist, engineer, or chemist knows you also need a cheap and clean energy source. On the bright side, you can pull carbon dioxide anywhere on the planet, because it's in the air.

My favorite technologies in this sector are the ones that are part of the "circular" green economy. There's a proof-of-concept just out a few days ago in Nature Biotechnology. The idea is ingenious. Instead of using fossil fuels, use industrial gases (like syngas) as feedstock to make precursors of chemicals and materials like plastics. This study took the carbon dioxide released during steel production to make acetone and isopropanol. You can use chemical catalysts or biocatalysts (enzymes) to do this work. Here researchers used synthetic biology to genetically modify a microbe that was already eating carbon dioxide to excrete out useful chemicals.

The world is never going to stop making stuff. But through carbon capture, use, and storage by multiple approaches we can solve the hardest problems in decarbonizing the world economy.

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Your appendix is not useless…

Despite learning the word "vestigial" in school, your appendix might not be useless after all. And the appendix isn’t the only part of the body that is undergoing a radical rethink in recent years. I’ve written about what exactly the appendix might be good for here.

In a research article published in Nature Immunology, Gabrielle Belz at Walter and Eliza Hall Institute in Melbourne, Australia, and her colleagues reported that the appendix might be a storehouse for good bacteria. These bacteria normally inhabit the gut, and they help to prevent infections. The team showed that a class of white blood cells in the appendix have a role in the immune response of the body. 

…and you are mostly not human.

Picture yourself. What you imagine are features of your body made of human cells. But what you do not see, and what children do not read about in school yet, is that there is an essential, invisible part of the body called the microbiome. And the microbiome is no less integral to the body than organs or tissues. In fact, the microbiome influences health from birth until death.

The microbes that make up the microbiome are tiny, but they outnumber human cells. That’s right. A human body is made up of around 30 trillion human cells and anywhere from 40-100 trillion microbial cells. There are more microbial cells than human cells inside us!

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The world is running out of useful sand.

As crazy as it might sound, it is true: the world is running out of useful sand. That's why pirates and mafia are murdering for sand and Dubai is importing sand from Australia. I wrote about this dilemma as well.

The fact is that there are various kinds of sand, each suitable for different purposes. For example, a small town in South Carolina no one has heard of is the source of the purest quartz in the world which is used to make silicon chips in computers, phones, tablets, and cars.

Some black sand is made from ground up volcanic rock. Then there's pristine white sand found in the beaches of the Caribbean which is actually the poop of parrotfish that eat coral. Surprisingly, sand doesn't have a hard definition.

In his wonderful book, The World in a Grain: The Story of Sand and How It Transformed Civilization, journalist Vince Beiser travels the world in search of sand. Beiser extols its virtues. “Sand is the main material that modern cities are made of. It is to cities what flour is to bread, what cells are to our bodies: the invisible but fundamental ingredient that makes up the bulk of the built environment in which most of us live.”

Beiser’s book is a wonderful read.

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What else I’ve read:

• Manu Prakash is one of the smartest people I've ever met so it is always cool to read about what textbook-changing work his lab is up to.

• One of the most provocative papers on the effects of climate change I've seen is this one by Matthew Liao, a bioethicist, who argues for human engineering. Liao says we should create drugs to make people kinder, engineer humans to make them smaller, lower the birth rate by making people smarter, and make people nauseous through drugs that make red meat intolerable.

• And here’s a great article. Animals are already adapting to climate change.
  

Endnotes…

I’ve only recently started traveling again. It’s felt weird and yet familiar after two years of sitting at home. Here’s a photo I took in San Diego last week with an important message.