Today, we’re diving into the amazing world of thumbs! Did you know that the ancient Greeks called the thumb the “second hand”? Thumbs have played a crucial role in our history and evolution. While other animals also have opposable digits, it’s hard to imagine being human without them. So, what can a little blue hedgehog and an ancient fish teach us about the evolution of thumbs? Let’s find out with the help of paleontologist Neil Shubin.
Dr. Neil Shubin is a paleontologist who works at a medical school. You might wonder why a medical school needs a fish paleontologist. The answer is fascinating: some of the best insights into our bodies come from studying other creatures. Our bodies are like a living history book, with each cell, gene, and organ telling a part of the story of life on Earth. Anatomists and geneticists like Dr. Shubin work to untangle this history.
Dr. Shubin studies both modern genes and ancient fossils to understand how life has evolved. One of the most exciting discoveries is a fossil called Tiktaalik, which is 375 million years old. Tiktaalik was found in the Arctic and has features that are a mix between fish and land animals. It has scales and fins, but inside those fins are bones similar to our upper arm, forearm, and wrist. This makes Tiktaalik a key piece in understanding how life transitioned from water to land.
Our arms have a specific structure: one bone, two bones, and many smaller bones leading to our fingers. This pattern can be traced back to Tiktaalik and even earlier fish. By studying these fossils, scientists can see how our arms evolved over millions of years.
So, how do thumbs fit into this story? It all starts with a single cell formed from a sperm and an egg, which divides into trillions of cells. As an embryo develops, small buds form that will become the hands. These buds grow into a paddle shape, and as they develop, cells divide and genes activate to form different fingers.
What makes your thumb different from your pinky? It’s all about how genes are activated in different parts of your developing hand. A specific patch of tissue under where the pinky will form produces a signal that influences finger development. This signal is called Sonic hedgehog, named after the video game character. If there’s too much Sonic hedgehog, you get extra fingers; too little, and you might have fewer than five. This gene is found in many animals and plays similar roles across species.
The study of our “inner fish” and “inner hedgehogs” shows how genetics and paleontology work together to tell the story of life. By understanding these connections, we learn more about our own bodies and the incredible journey of evolution.
If you’re curious to learn more, check out Neil Shubin’s book, Your Inner Fish, and the PBS series of the same name. Stay curious and keep exploring the wonders of science!
Research and create a timeline that shows the evolution of thumbs from ancient fish like Tiktaalik to modern humans. Include key milestones and discoveries, such as the role of Sonic hedgehog in thumb development. Present your timeline to the class and explain how each step contributed to the evolution of thumbs.
Divide into two groups and hold a debate on the importance of thumbs compared to other fingers. One group will argue why thumbs are the most important digit, while the other will defend the significance of other fingers. Use evidence from the article and additional research to support your arguments.
Using clay or other craft materials, create a model of the human arm, highlighting the “one bone, two bones, many bones” structure. Compare your model to the fin structure of Tiktaalik and discuss how these similarities provide evidence for the evolution of limbs.
Use an online simulation or interactive tool to explore how genes like Sonic hedgehog influence the development of fingers. Experiment with different levels of gene activation and observe the effects on finger formation. Discuss your findings with classmates and relate them to the article.
Read selected chapters from Neil Shubin’s book, Your Inner Fish. In small groups, discuss how the book expands on the concepts introduced in the article. Share your insights and any new questions you have about the evolution of human anatomy.
Here’s a sanitized version of the provided YouTube transcript:
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Today on It’s Okay to be Smart, we’re talking about thumbs!
[Intro]
The ancient Greeks referred to it as the second hand. It could play a crucial role in various historical events and has been essential in our evolution. Thumbs are a significant evolutionary adaptation, and while we’re not the only animals with opposable digits, it’s hard to imagine being human without them. So, what can a little blue hedgehog and an ancient fish teach us about the evolution of thumbs? To find out, I spoke with paleontologist Neil Shubin.
I’m here with Dr. Neil Shubin.
N: Great to be here, thank you.
J: You work at a medical school. Why does a medical school need a fish paleontologist?
N: The reality is that some of the best insights into our own bodies can be found in other creatures. An entire branch of the tree of life is embedded in every cell, gene, and organ of your body. Our challenge as anatomists and geneticists is to untangle that history.
Neil studies both the past and the present. By examining modern genes, he can explore how living chemistry shapes the diverse forms of life that Darwin described. By uncovering ancient fossils, he can see how our bodies have changed over time. One fossil, in particular, has significantly redefined our understanding of our journey out of the water.
N: This is a cast of a skull from a creature that’s 375 million years old, found in the Arctic. It’s called Tiktaalik. It has a paired set of nostrils and, while it has scales and fins, if you look inside the fins, you’ll find elements that correspond to your upper arm, forearm, and even parts of your wrist. Tiktaalik is a remarkable fossil find, a transitional form between fish and land animals. By studying these ancient bones, we can see how the arms that helped this fish move onto land are not so different from our own.
N: Here’s the fascinating part: Your arm has a structure with one bone, two bones, and many smaller bones leading to your fingers. When we look at the fossil record, we see this same pattern. Tiktaalik has a fin, but if you remove the fin rays and scales, you can see versions of your upper arm, elbow, forearm, and wrist. We can trace this all the way from Tiktaalik to modern land animals and back to earlier fish.
J: Wow, this is 375 million years in the making! So, what does this have to do with thumbs? To develop thumbs, you need to start from a single cell formed from a sperm and an egg, which then divides into trillions of cells.
N: Think about it. This begins as a small bud. Four little buds emerge as an embryo, and those buds develop into a paddle where the hand will form. As this paddle develops, cells divide and genes are activated, orchestrating the formation of different fingers.
J: But what makes my thumb different from my pinky?
N: One reason is that genes are activated in different ways in various parts of your developing hand. A specific patch of tissue under where the pinky will form produces a signal that influences how the fingers develop.
J: What’s that signal called?
N: It’s called Sonic hedgehog, named after the video game character.
J: That’s really cool!
N: If there’s too much Sonic hedgehog, you get extra fingers; too little, and you might end up with fewer than five. This gene is found in many animals, including fish, frogs, and chickens, and it plays similar roles across species. Of course, Sonic hedgehog works in harmony with many other genes, contributing to the complex orchestration of development.
The exploration of our inner fish and inner hedgehogs illustrates how genetics and paleontology come together to tell the story of life.
J: Thank you so much for joining me today. I’ve learned a lot about my inner fish, and I hope you have too. If you want to learn more, check out Neil’s book, *Your Inner Fish*. It’s filled with great stories, and PBS has a special three-part series premiering on Wednesday, April 9th, at 10 PM Eastern, also titled *Your Inner Fish*.
N: Stay curious!
J: Who’s got two thumbs and wants you to subscribe? This fishy guy! Also, check out the info below to watch Neil’s new series, *Your Inner Fish*, premiering on PBS this week, and find a link to his book in the description.
[Preview]
My 165 millionth great-grandparent isn’t even a mammal; it’s a prehistoric lizard that predates the dinosaurs. Every species has its own lineage that branches off somewhere down the line.
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This version maintains the essence of the original transcript while removing any informal language or references that may not be suitable for all audiences.
Thumbs – The short, thick first digit of the human hand, which is opposable to the other four fingers and allows for grasping and manipulation of objects. – The evolution of thumbs in humans has allowed us to use tools effectively.
Evolution – The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. – The theory of evolution explains how species have changed over millions of years.
Genes – Units of heredity that are transferred from a parent to offspring and are held to determine some characteristic of the offspring. – Genes play a crucial role in the evolution of species by passing on traits that may be beneficial for survival.
Fossils – The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock. – Fossils provide evidence of how species have evolved over time.
Fish – A limbless cold-blooded vertebrate animal with gills and fins, living wholly in water. – Fish are believed to be one of the earliest forms of vertebrate life, playing a significant role in the study of evolution.
Arms – The upper limbs of the human body, extending from the shoulder to the hand. – The development of arms in primates has been crucial for climbing and manipulating objects.
Development – The process of growth and differentiation by which an organism or any of its parts changes from a simpler to a more complex form. – The development of complex eyes in some species is a remarkable example of evolutionary adaptation.
Anatomy – The branch of science concerned with the bodily structure of humans, animals, and other living organisms. – Studying the anatomy of different species helps scientists understand evolutionary relationships.
Species – A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. – The discovery of a new species can provide insights into the evolutionary history of life on Earth.
History – The study of past events, particularly in human affairs, but also applicable to the development of life on Earth. – The history of life on Earth is documented through the fossil record, showing the evolution of species over time.
