microcosmos
Looking at Tardigrade Sperm and Other Reproducing Swimmers
YouTube: | https://youtube.com/watch?v=DctfqZFqwgM |
Previous: | The Diversity of Shapes in the Microcosmos |
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View count: | 137,852 |
Likes: | 6,797 |
Comments: | 335 |
Duration: | 10:44 |
Uploaded: | 2021-05-31 |
Last sync: | 2024-12-02 09:45 |
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Not all hypotheses need to be good. In fact, many of them are terrible. It’s just that when you’re trying to understand the world, you might find yourself believing that there are tiny humans living inside the heads of sperm, and we're here to tell you, that's not how it works.
Follow Journey to the Microcosmos:
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Support the Microcosmos:
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More from Jam’s Germs:
Instagram: https://www.instagram.com/jam_and_germs
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Hosted by Hank Green:
Twitter: https://twitter.com/hankgreen
YouTube: https://www.youtube.com/vlogbrothers
Music by Andrew Huang:
https://www.youtube.com/andrewhuang
Journey to the Microcosmos is a Complexly production.
Find out more at https://www.complexly.com
Stock video from:
https://www.videoblocks.com
SOURCES:
https://www.google.com/books/edition/The_Gene/S4nHjgEACAAJ?hl=en
https://www.researchgate.net/publication/49749832_Anton_van_Leeuwenhoek_1632-1723_Father_of_micromorphology_and_discoverer_of_spermatozoa
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1710.0044
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1710.0026
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1700.0062
https://embryo.asu.edu/handle/10776/1924
https://embryo.asu.edu/pages/preformationism-enlightenment
https://link.springer.com/article/10.1007/s00435-002-0066-8
https://www.nature.com/articles/nrmicro1064
https://www.nature.com/articles/nrm3370
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4071627/
Not all hypotheses need to be good. In fact, many of them are terrible. It’s just that when you’re trying to understand the world, you might find yourself believing that there are tiny humans living inside the heads of sperm, and we're here to tell you, that's not how it works.
Follow Journey to the Microcosmos:
Twitter: https://twitter.com/journeytomicro
Facebook: https://www.facebook.com/JourneyToMicro
Support the Microcosmos:
http://www.patreon.com/journeytomicro
More from Jam’s Germs:
Instagram: https://www.instagram.com/jam_and_germs
YouTube: https://www.youtube.com/channel/UCn4UedbiTeN96izf-CxEPbg
Hosted by Hank Green:
Twitter: https://twitter.com/hankgreen
YouTube: https://www.youtube.com/vlogbrothers
Music by Andrew Huang:
https://www.youtube.com/andrewhuang
Journey to the Microcosmos is a Complexly production.
Find out more at https://www.complexly.com
Stock video from:
https://www.videoblocks.com
SOURCES:
https://www.google.com/books/edition/The_Gene/S4nHjgEACAAJ?hl=en
https://www.researchgate.net/publication/49749832_Anton_van_Leeuwenhoek_1632-1723_Father_of_micromorphology_and_discoverer_of_spermatozoa
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1710.0044
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1710.0026
https://royalsocietypublishing.org/doi/pdf/10.1098/rstl.1700.0062
https://embryo.asu.edu/handle/10776/1924
https://embryo.asu.edu/pages/preformationism-enlightenment
https://link.springer.com/article/10.1007/s00435-002-0066-8
https://www.nature.com/articles/nrmicro1064
https://www.nature.com/articles/nrm3370
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4071627/
This episode is sponsored by Fabulous, an app that helps you form healthy habits that stick. Click the link in description to get a free week trial and 25% off a Fabulous subscription! This is not an organism.
At least, it’s not yet anyway. What we are looking at are a lot of zoospores packed together, getting ready to be released so that they can find the right place to grow into themselves.
And this? Well, this is a male tardigrade filled from head to many toes with sperm. Just chock full of it. We did not start this channel with the intent of becoming so familiar with tardigrade mating habits, but tardigrades are easy to find, and their mating habits are straightforward enough to track, so we keep getting drawn back into the details and the drama of tardigrade reproduction. In the past, we’ve talked about the particulars of their mating habits.
And today, we’re going to use this tardigrade as a convenient starting point to talk about the history of our understanding of sperm. Because as absurd as it might seem to be looking at tardigrade sperm, the theories people have had about sperm are much weirder. Humans have been theorizing about the contents of seminal fluid long before the invention of the microscope.
We did not, as a species, need to work out all of the scientific mechanisms underlying sexual reproduction to make babies. But the observation of children who carried traits from their parents naturally raised questions about how those traits were passed on. And those questions inevitably led to some hypotheses.
And look, not all hypotheses need to be good. In fact, many of them are terrible. It’s just that when you’re trying to understand the world, you need to start somewhere, and as long as you’re willing to work with your ideas and challenge them, then hopefully some day, you go from somewhere, to somewhere better. Some of these early ideas about sperm weren’t just bad though, they were, maybe as we should expect, a little self-serving to the male ego. Masturbatory, even, you could say. Like the theory now known as spermism, advocated for by one Pythagorus, yes, that Pythagorus. According to spermism, the information driving heredity came entirely through the semen. Whether that was the color of someone’s hair or their height or whatever other trait— all of that came through the father, and the father’s father, and so on.
The mother’s role was just to provide nourishment to the sperm as it developed and manifested those traits. It’s easy enough to find flaws with this idea. After all, our observed reality, which Pythagorus just chose to ignore, shows us that traits pass from mother and father alike. But this would not be the last theory to overestimate the sperm. Even with the advance of scientific tools over the ages, there was plenty to get wrong.
One of those key scientific tools was, of course, the microscope, which allowed scientists to observe the cells within semen for the first time. But just because microscopists could see sperm now, that did not mean they could make out the details. And this invited speculation, including the idea that we are essentially developed from a much smaller version of ourselves. This theory was called preformationism. At the end of the 17th century, the Dutch scientist Nicolaas Hartsoeker sketched out his spermist vision of preformationism: inside the head of the sperm cell, he speculated, was a very, very, very small human--later called a homunculus--just waiting for a womb to grow in. And look, we have the advantage of centuries of advancements to know that the homunculus was wrong. But maybe take a moment to think about how weird that would be if it were right. Look at this tardigrade, full of sperm.
And then just imagine if we zoomed in further on those sperm cells, and we could see little tiny tardigrades inside of them. And then, if we could zoom in even more on those tinier tardigrades, we’d see even more tinier tardigrades inside of them, and so on and so on. Now, to be clear, that is not what tardigrade sperm looks like.
Their sperm is made up of a slightly globular head connected to a flagellum. But as wrong as both spermism and tiny people inside of sperm turned out to be, they’re not that far off the mark if you think about the zoospores we showed at the beginning of the episode. They are a tool of asexual reproduction in a lot of different organisms, including algae, fungi, and bacteria. They all use zoospores in different ways. And because we don’t know exactly what organism these zoospores come from, there are specific details of their lives we just don’t know. But take, for example, the Phytophthora, a group of oomycetes most notorious for their role in the 19th century potato blight that led to the Great Famine in Ireland.
Phytophthora can reproduce sexually, but they mostly rely on making asexual zoospores, which pack together in a biological enclosure called the sporangia until the conditions are right for their release. And when they emerge from the sporangia, the zoospores start swimming, using their flagella and chemical sensors to find the ideal place to settle and germinate. All of the hereditary information in those zoospores came from one parent, fashioning an organism that resembles the infant form of that parent, and that seeks only nourishment from its new host.
The outlines of that process sound pretty similar to how early philosophers and scientists envisioned their sperm-centric ideas of sexual reproduction. But what those scientists missed—what separates the sperm from the zoospore—is the nature of sexual reproduction itself, of the genetic variation it drives by combining and recombining traits from different parents. Sperm cannot accomplish that on their own. Sperm needs an ovum to fertilize, which scientists would eventually uncover in the 19th century with experiments on rabbits, sea urchins, and starfish eggs that helped to further our understanding of the molecular and cellular collaboration that set the stage for inheritance.
Yes, my friends, as Napoleon drove to conquer Europe, we had no idea that sperm and eggs came together to make the next generation. There are a lot of different types of spores out there, used for both sexual and asexual reproduction. And in contrast, sperm might seem more narrow and focused, both in diversity and purpose. But the function of sperm is so specialized that it requires its own diversity.
Even among tardigrades, there are different morphologies to the head and middle structures of the sperm, small differences that distinguish between species. And that’s because however weird our theories about sperm have been, the reality is also very strange. Of all the cells in the body, sperm cells are maybe the only ones that are expected to navigate and survive in two different beings. The homunculus was wrong, but the idea of there being an image of our life passed on within sperm and in spores, it isn’t absurd at all. It’s just too literal.
Instead, that image is abstracted and tucked away into genetic information. And zoospores and sperm alike are just packets of that information, swimming off to new and different futures. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you to Fabulous for sponsoring this episode. Fabulous is an app that was born at Duke University and uses behavioral science research to gently support your personal goals. Habit changing and habit building is hard. So, if you’re looking for ways to add a new thing to your routine, Fabulous is the way to go. It’s the #1 self care and habit forming app in the app store with over 20 million users, and it can help you whether you’re looking for ways to stay focused at work or you just need a reminder to take a break once in a while to stretch and drink some water. The app is 100% personalized to your goals and you can start building your ideal daily routine today! The first 100 people who click on the link in the description will get a free week trial and 25% off a Fabulous subscription!
Thank you to all of the people on the screen right now. Our Patreon patrons are amazing and they’re the reason that we can make this show. If you would like to join them and be a part of that and also get some access to some special stuff that is only available to Patrons, you can go to patreon.com/journeytomicro.
If you want to see more from our Master of Microscopes James Weiss, you can check out Jam & Germs on Instagram, and if you want to see more from us, there’s always a subscribe button somewhere nearby.
At least, it’s not yet anyway. What we are looking at are a lot of zoospores packed together, getting ready to be released so that they can find the right place to grow into themselves.
And this? Well, this is a male tardigrade filled from head to many toes with sperm. Just chock full of it. We did not start this channel with the intent of becoming so familiar with tardigrade mating habits, but tardigrades are easy to find, and their mating habits are straightforward enough to track, so we keep getting drawn back into the details and the drama of tardigrade reproduction. In the past, we’ve talked about the particulars of their mating habits.
And today, we’re going to use this tardigrade as a convenient starting point to talk about the history of our understanding of sperm. Because as absurd as it might seem to be looking at tardigrade sperm, the theories people have had about sperm are much weirder. Humans have been theorizing about the contents of seminal fluid long before the invention of the microscope.
We did not, as a species, need to work out all of the scientific mechanisms underlying sexual reproduction to make babies. But the observation of children who carried traits from their parents naturally raised questions about how those traits were passed on. And those questions inevitably led to some hypotheses.
And look, not all hypotheses need to be good. In fact, many of them are terrible. It’s just that when you’re trying to understand the world, you need to start somewhere, and as long as you’re willing to work with your ideas and challenge them, then hopefully some day, you go from somewhere, to somewhere better. Some of these early ideas about sperm weren’t just bad though, they were, maybe as we should expect, a little self-serving to the male ego. Masturbatory, even, you could say. Like the theory now known as spermism, advocated for by one Pythagorus, yes, that Pythagorus. According to spermism, the information driving heredity came entirely through the semen. Whether that was the color of someone’s hair or their height or whatever other trait— all of that came through the father, and the father’s father, and so on.
The mother’s role was just to provide nourishment to the sperm as it developed and manifested those traits. It’s easy enough to find flaws with this idea. After all, our observed reality, which Pythagorus just chose to ignore, shows us that traits pass from mother and father alike. But this would not be the last theory to overestimate the sperm. Even with the advance of scientific tools over the ages, there was plenty to get wrong.
One of those key scientific tools was, of course, the microscope, which allowed scientists to observe the cells within semen for the first time. But just because microscopists could see sperm now, that did not mean they could make out the details. And this invited speculation, including the idea that we are essentially developed from a much smaller version of ourselves. This theory was called preformationism. At the end of the 17th century, the Dutch scientist Nicolaas Hartsoeker sketched out his spermist vision of preformationism: inside the head of the sperm cell, he speculated, was a very, very, very small human--later called a homunculus--just waiting for a womb to grow in. And look, we have the advantage of centuries of advancements to know that the homunculus was wrong. But maybe take a moment to think about how weird that would be if it were right. Look at this tardigrade, full of sperm.
And then just imagine if we zoomed in further on those sperm cells, and we could see little tiny tardigrades inside of them. And then, if we could zoom in even more on those tinier tardigrades, we’d see even more tinier tardigrades inside of them, and so on and so on. Now, to be clear, that is not what tardigrade sperm looks like.
Their sperm is made up of a slightly globular head connected to a flagellum. But as wrong as both spermism and tiny people inside of sperm turned out to be, they’re not that far off the mark if you think about the zoospores we showed at the beginning of the episode. They are a tool of asexual reproduction in a lot of different organisms, including algae, fungi, and bacteria. They all use zoospores in different ways. And because we don’t know exactly what organism these zoospores come from, there are specific details of their lives we just don’t know. But take, for example, the Phytophthora, a group of oomycetes most notorious for their role in the 19th century potato blight that led to the Great Famine in Ireland.
Phytophthora can reproduce sexually, but they mostly rely on making asexual zoospores, which pack together in a biological enclosure called the sporangia until the conditions are right for their release. And when they emerge from the sporangia, the zoospores start swimming, using their flagella and chemical sensors to find the ideal place to settle and germinate. All of the hereditary information in those zoospores came from one parent, fashioning an organism that resembles the infant form of that parent, and that seeks only nourishment from its new host.
The outlines of that process sound pretty similar to how early philosophers and scientists envisioned their sperm-centric ideas of sexual reproduction. But what those scientists missed—what separates the sperm from the zoospore—is the nature of sexual reproduction itself, of the genetic variation it drives by combining and recombining traits from different parents. Sperm cannot accomplish that on their own. Sperm needs an ovum to fertilize, which scientists would eventually uncover in the 19th century with experiments on rabbits, sea urchins, and starfish eggs that helped to further our understanding of the molecular and cellular collaboration that set the stage for inheritance.
Yes, my friends, as Napoleon drove to conquer Europe, we had no idea that sperm and eggs came together to make the next generation. There are a lot of different types of spores out there, used for both sexual and asexual reproduction. And in contrast, sperm might seem more narrow and focused, both in diversity and purpose. But the function of sperm is so specialized that it requires its own diversity.
Even among tardigrades, there are different morphologies to the head and middle structures of the sperm, small differences that distinguish between species. And that’s because however weird our theories about sperm have been, the reality is also very strange. Of all the cells in the body, sperm cells are maybe the only ones that are expected to navigate and survive in two different beings. The homunculus was wrong, but the idea of there being an image of our life passed on within sperm and in spores, it isn’t absurd at all. It’s just too literal.
Instead, that image is abstracted and tucked away into genetic information. And zoospores and sperm alike are just packets of that information, swimming off to new and different futures. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you to Fabulous for sponsoring this episode. Fabulous is an app that was born at Duke University and uses behavioral science research to gently support your personal goals. Habit changing and habit building is hard. So, if you’re looking for ways to add a new thing to your routine, Fabulous is the way to go. It’s the #1 self care and habit forming app in the app store with over 20 million users, and it can help you whether you’re looking for ways to stay focused at work or you just need a reminder to take a break once in a while to stretch and drink some water. The app is 100% personalized to your goals and you can start building your ideal daily routine today! The first 100 people who click on the link in the description will get a free week trial and 25% off a Fabulous subscription!
Thank you to all of the people on the screen right now. Our Patreon patrons are amazing and they’re the reason that we can make this show. If you would like to join them and be a part of that and also get some access to some special stuff that is only available to Patrons, you can go to patreon.com/journeytomicro.
If you want to see more from our Master of Microscopes James Weiss, you can check out Jam & Germs on Instagram, and if you want to see more from us, there’s always a subscribe button somewhere nearby.