Have you ever thought about how different we are from lobsters? Sure, we both live on Earth, but that’s about where the similarities end. Lobsters belong to a group of animals called arthropods, which also includes spiders, insects, and other crustaceans. In fact, 80% of all known animal species are arthropods! They have segmented bodies, jointed legs, and hard exoskeletons. But there’s something even more fascinating about lobsters that sets them apart from us.
In 1822, a French naturalist named Geoffrey Saint-Hilaire made an interesting discovery. When he cut open a lobster, he noticed that its internal anatomy was like a mirror image of ours. In humans, our guts and circulatory system are on the belly side, while our nerve cords run along our backs. But in lobsters, it’s the opposite: they have their nerve cords on the belly side and their guts on the back.
So how did this happen? Imagine you’re a primitive worm, living hundreds of millions of years ago. You don’t have a brain or a central nervous system, just a simple body with a mouth and a tube for food. For a long time, your descendants lived just like you. But then, about 600 million years ago, something changed. Some of these worms started swimming upside down. Maybe it was an accident, or maybe it gave them an advantage. Whatever the reason, these upside-down worms thrived and eventually evolved into creatures with spinal cords, brains, and bones.
Now, let’s fast forward to the early stages of human development. When you were just a tiny cluster of cells, your body was already being shaped by specific patterns. On one side of this cell cluster, a gene was telling cells to become your guts and heart. On the other side, a different gene was blocking the first one, directing those cells to become your spinal cord. Interestingly, this is similar to how it works in invertebrates like lobsters and fruit flies.
Despite our common ancestor living around 700 million years ago, the genes that determine where our nerves and guts end up are surprisingly similar across all bilateral animals. This means that the same genetic instructions guide the development of both human and lobster nervous systems. Somewhere along our evolutionary journey, one of us got flipped!
So, which body plan came first: ours or the lobster’s? It turns out that we’re the newcomers. Studies of a peculiar worm called the acorn worm suggest that our body plan is more recent. On the evolutionary tree, this worm is closer to us than to lobsters, but its embryo shows the lobster pattern. This means that the lobster’s body plan is the original one.
While lobsters might wonder why humans are built differently, it seems like we got the better end of the evolutionary deal. So, next time you see a lobster, remember the incredible journey of evolution that led to our unique body structures. Stay curious and keep exploring the wonders of biology!
Using clay or playdough, create a model of a lobster’s anatomy. Pay special attention to the placement of the nerve cords and guts. Compare your model to a human anatomy diagram and discuss the differences and similarities with your classmates.
Work in groups to create a timeline that traces the evolutionary journey from primitive worms to modern lobsters and humans. Include key events such as the “Great Body Flip” and the development of spinal cords. Present your timeline to the class.
Research the genes involved in the development of nerve cords and guts in both humans and lobsters. Create a poster that illustrates these genetic patterns and explains how they are similar across different species. Share your findings with the class.
Participate in a class debate on the topic “Who Flipped First: Humans or Lobsters?” Use evidence from the article and additional research to support your arguments. Discuss the implications of these evolutionary changes.
Conduct a simple experiment using images of embryos from different species, including lobsters and humans. Analyze the similarities and differences in their development stages. Write a report on how these observations support the concept of a common ancestor.
Sure! Here’s a sanitized version of the transcript:
—
[MUSIC] Consider the lobster. Other than both living on Earth, we don’t have a lot in common with these arthropods, the group of animals that includes everything from spiders to insects to crustaceans like these. 80% of all known animal species are arthropods. They are noted for having segmented bodies, jointed legs, and stiff exoskeletons. But if you ask me, the most amazing difference between us and this lobster isn’t immediately obvious. Let me show you. This, right here. The dorsal intestine. If you’ve ever eaten lobster, shrimp, or crawfish, you’ve probably just thrown this away. This little tube holds more than just lobster waste. It tells a special story of an event, hundreds of millions of years ago, that changed the course of our bodies.
In 1822, a French naturalist named Geoffrey Saint-Hilaire cut open a lobster and noticed that its arthropod anatomy was essentially a mirror image of our own along what is called the dorsoventral axis. Geoffrey never did figure out why, but his observation was correct. Animals like us have our guts and circulatory system on our belly side and our nerve cords along our backs. But arthropods have ventral nerves and dorsal guts.
Here’s how we think it happened. Let’s imagine for a moment that you’re a primitive worm, so primitive that you don’t have a brain or central nervous system to even do the imagining. You’re pretty much just a mouth, some moving parts, and a tube to pass food through. Up and down and back and belly don’t mean much to you. But hey, it’s a living. For a long time, all your descendants will live and grow like you did. Until one day, 600 million years ago, one of them decided to start doing the backstroke. Maybe its mouth ended up on the wrong side, or maybe it had colors that gave it an advantage. Whatever the case, these upside-down worms not only survived, they flourished. They would go on to develop spinal cords, brains, bones, and heads.
[EMBRYOLOGY 101] Here’s one of your earliest baby pictures. You were basically just a frisbee-shaped wad of cells, but already patterns were in place that would determine precisely the body you’d one day become, everything from your intestines to your epidermis. On either flat side of this disk, a special gene was expressed. Over here, cells were set on course to become your guts and your heart. On the other side, though, the second gene inhibited the action of the first, and instead of being told to become “guts,” those cells were fated to become your spinal cord. Oddly enough, this is exactly how it works in invertebrates like lobsters or fruit flies. Despite the fact our common ancestor lived nearly 700 million years ago, the genes that determine where nerves and guts end up are remarkably similar among all bilateral animals. This means that the same set of instructions define where your nervous system forms and where a lobster’s nervous system forms, but somewhere along our evolutionary history, one of us got flipped.
So which plan came first? Ours or the lobster’s? Sorry to disappoint you, but it’s us. Studies of a rather unfortunate-looking worm suggest that we’re the new kids on the body plan block. [MUSIC] On the tree of life, this acorn worm is closer to us than they are to lobsters, but spine-to-guts, their embryos show the lobster pattern, and not ours. That means that our pattern probably developed more recently. So while lobsters may sit there in their bubbly tanks wondering why all of us humans are built differently, I think we got the better end of the deal. Stay curious. This video is part of a three-part series all about guts! If you want to know more about why your body is organized the way that it is, check out the rest of these videos, if I’ve uploaded them yet.
—
Let me know if you need any further modifications!
Lobsters – Marine crustaceans with long bodies and muscular tails, belonging to the order Decapoda. – Lobsters have evolved over millions of years to develop strong claws for defense and hunting.
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 evolution of species is driven by natural selection, where advantageous traits become more common in a population over time.
Arthropods – A large group of invertebrate animals that have an exoskeleton, a segmented body, and paired jointed appendages. – Arthropods, such as insects and crustaceans, are the most diverse group of animals on Earth.
Anatomy – The branch of biology concerned with the study of the structure of organisms and their parts. – Understanding the anatomy of a frog helps biologists learn how its organs function and interact.
Nervous – Relating to the network of nerve cells and fibers that transmits nerve impulses between parts of the body. – The nervous system of vertebrates is more complex than that of invertebrates, allowing for advanced functions like learning and memory.
Genes – Units of heredity that are transferred from a parent to offspring and determine some characteristics of the offspring. – Genes play a crucial role in the evolution of species by passing on traits that may enhance survival and reproduction.
Embryos – Early developmental stages of multicellular organisms, following fertilization and before becoming a fetus. – Studying embryos can provide insights into the development and evolution of different species.
Bilateral – Having symmetrical arrangement of body parts on either side of a central axis. – Most animals, including humans, exhibit bilateral symmetry, which is an important aspect of their anatomy and evolution.
Development – The process by which an organism grows and develops, involving changes in size, shape, and function. – The development of an organism from a single cell to a complex multicellular entity is a fascinating aspect of biology.
Species – A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. – The concept of species is fundamental to understanding the diversity and evolution of life on Earth.
