Your Inner Fish by Neil Shubin is a book in three parts:

  • How a team of humans discovered our ancient ancestor: a fish with arms!
  • How scientists use cellular manipulation of animal embryos to discover the fundamental building blocks of development.
  • A primer on the evolutionary biology of our senses.

Each part is connected with the insight that we're not so different when it comes down to it. We're all made of cells which have evolved over time to make us humans, chickens, frogs and sharks. I finished Your Inner Fish thinking about how similar we are to other animals and how we should probably treat our cousin the pig with a little more love and respect. After all, we've all got the same fish bits in our genetic history.

...our new creature broke down the distinction between these two different kinds of animal. Like a fish, it has scales on its back and fins with fin webbing. But, like early land-living animals, it has a flat head and a neck. And, when we look inside the fin, we see bones that correspond to the upper arm, the forearm, even parts of the wrist. The joints are there, too: this is a fish with shoulder, elbow, and wrist joints. All inside a fin with webbing.
— Neil Shubin, Your Inner Fish

Tiktaalik was a swole fish. Shubin and a team discovered the fossil of this ancient fish on Ellesmere Island in Canada's Arctic. Way back in the day (millions of years ago) the arctic was actually a tropical paradise with many interesting creatures, including a fish who liked to do push-ups.

The theory goes that Tiktaalik evolved arms in order to push themself up off of creek beds to look around for potential threats. The arms are in a perpetual push-up position similar to crocodiles or other lizards. Those arms eventually brought Tiktaalik up onto land and animals out of the ocean. Before Tiktaalik, all creatures lived in water. Tiktaalik is thought to be our common ancestor with all other land-based animals.

Scientists have very cool jobs. One cool part of being a scientist is that if you discover something new, you get to name it. Now you could go the thoughtful route and consult with the indigenous people in the area of the discovery to come up with a rad name like Tiktaalik. Or, you could name something after a video game. And this is why we all carry the Sonic hedgehog protein.

If Sonic hedgehog hadn’t turned on properly during the eighth week of your own development, then you either would have extra fingers or your pinky and thumb would look alike.
— Neil Shubin, Your Inner Fish

From what I understand Sonic hedgehog is responsible for making our thumbs and pinkies show up on the correct side of our hands. It was first discovered as a little group of cells in chicken embryos. By copying the cells from one place to another in a developing chicken, a wing would grow in the wrong direction, or a double wing would form. This was the time, while reading, where I felt bad and wanted us humans to leave animals alone.

They then took some of these cells and moved them from a developing chicken into a developing frog. Guess what happened? No, the frog didn't grow chicken wings, it grew extra frog legs. This proved that the cells were a common factor. You could move them into an entirely different species and see the same results.

Eventually, they discovered this in humans and named it Sonic hedgehog. Because naming things is one of the perks of the job.

At conception, we start as a single cell that contains all the DNA needed to build our body. The plan for that entire body unfolds via the instructions contained in this single microscopic cell.

I learned a lot about human development while reading Your Inner Fish. My favourite fact is that, after the egg implants on the uterine wall, we are basically one tube inside another tube. I spent an entire day after reading this annoying my partner by saying "we're tubes in tubes!".

We may be more complicated than we were at twenty-one days after conception, but we are still a tube within a tube.
— Neil Shubin, Your Inner Fish

If you think about it, we're still just tubes in tubes. A mouth sphincter connected to a butt sphincter with a whole lot of tubing in the middle. Our outer tube keeps our inner tube safe.

Once we get past the tube phase of development humans grow gills. Ok, so we don't grow gills, but we do grow some bumps that look a lot like they could be gills. Shubin explains how these bumps turn into different parts of the human head. At one point there was a claim that a human embryo goes through all our evolutionary phases while growing into a baby. This turns out to not be entirely true, but it does seem that one can glimpse a bit of Tiktaalik in our cellular development. We're all connected, you and I.

The sound waves enter the ear and make the eardrum rattle. The eardrum is attached to three little bones, which shake along with it. One of these ear bones is attached to the snail-shell structure by a kind of plunger. The shaking of the ear bone causes the plunger to go up and down. This causes some gel inside the snail shell to move around. Swishing gel bends nerves, which send a signal to the brain, which interprets it as sound.
— Neil Shubin, Your Inner Fish

The final part of the book focuses on the different human sense organs and explains a bit about their evolutionary journey. I found this part fascinating as I never studied biology in school. I remember biology students in high-school dissecting eyeballs of some animal and telling me retinas are like bouncy (I think some of them even bounced retinas in the school gym). I'm not into cutting things up, so avoided any biology classes. I took chemistry because I thought the word “stoichiometry" was fun to say. Let's just say I wasn't an "A" student in high-school.

The several parts of the inner ear are filled with a gel that can move. Specialized nerve cells send hairlike projections into this gel. When the gel moves, the hairs on the ends of the nerve cells bend. When these hairs bend, the nerve cells send an electrical impulse to the brain, where it is recorded as sound, position, or acceleration.
— Neil Shubin, Your Inner Fish

My favourite facts from this part of the book were about the human ear. There are these weird hair-type things in the ear that sense a gel-like liquid sloshing around. That's how we understand how our head is orientated and at what speed we're moving. I imagine that's why being is space can be so disorientating. There is no up or down for the little sensors to understand.

Bones that support the upper and lower jaws in sharks are used in us to swallow and hear.
— Neil Shubin, Your Inner Fish

My other favourite ear fact is that one of the bones that make up the tiny instrumentation that allows us to hear is the same bone that a shark can use to extend its jaw out of its mouth. First, just the fact that sharks can do a super-bite beyond the confines of their mouth is pretty rad. But what is really rad is that through evolution that same function turned into a tiny bone that allows us to hear today. That is just incredibly cool.

Your Inner Fish made me want to go dig up fossils on an arctic island, feel compassion for animals we run experiments on to find out how the world works, and left me awed at just how interconnected we all are.

The fact that life evolved at all is a pretty magical thing. That life managed to grow arms and drag itself up off the creek-bed is mind boggling. The subsequent evolutions through reptilian and mammalian forms is, frankly, unbelievable. And yet, here we are. Able to write newsletters on technology that didn't exist 100 years ago. If that isn't awe inspiring, I'm not sure what is.

Take the entire 4.5-billion-year history of the earth and scale it down to a single year, with January 1 being the origin of the earth and midnight on December 31 being the present. Until June, the only organisms were single-celled microbes, such as algae, bacteria, and amoebae. The first animal with a head did not appear until October. The first human appears on December 31.
— Neil Shubin, Your Inner Fish

it took 13.8 billion years for our species to show up. We should probably do a better job of managing ourselves before we cause our own mass extinction. More importantly, in my mind, we should do a better job of protecting all of the other species on this beautiful world. It is our duty to do so. Without them, there would be no us.


I hope you enjoyed this first issue of Booked. If you did, please share it with your friends. I'd love to grow a bit of an audience. Feel free to leave me a comment. I'll definitely respond!

Next week, we dip into another area of interest: philosophy. I'll write about what I learned from Ultimate Questions by Bryan Magee.