Hi there! I’m here to help you understand a fascinating topic about life expectancy. You might have heard that humans live around 72 years, dogs about 14 years, and loggerhead sea turtles around 80 years. But did you know these numbers aren’t directly comparable? That’s because they are calculated using different definitions of “life expectancy.”
For humans, we use something called Life Expectancy At Birth. This means if a group of people are born in the same year, their average age at death is calculated. If we used this method for dogs and sea turtles, we’d get 10 years for dogs and 3.5 years for turtles, which is quite different from the usual numbers.
For dogs, we often use Life Expectancy After Babyhood. This means we ignore the ones that die young and calculate the average age of those that survive past infancy. This is because pet owners are usually interested in how long their dogs will live once they get past the early stages of life.
For sea turtles, “life expectancy” often means Maximum Life Expectancy, which is how long the oldest individuals live. This is because people are curious about the potential lifespan of less familiar species. If we used this definition for humans and dogs, we’d get 122 years for humans and 29 years for dogs.
These different definitions can make it tricky to understand how animals live and die. Instead of focusing on just one number, we can learn more by looking at graphs showing the ages at which animals die. These graphs can be turned into survival curves, showing what percentage of individuals are expected to survive to any given age.
Each green bar on the graph represents individuals still alive after a certain age. The way these bars drop can tell us a lot about the animals. For example, the drop between the first and second bars shows the infant mortality rate. Humans have a small drop, meaning parents take good care of their babies. Dogs have a slightly bigger drop, indicating larger litters with some losses. Sea turtles have a big drop, showing high infant mortality due to little parental care.
The middle part of the graph represents early adulthood. For humans and dogs, the bars stay stable, as they are less likely to die once they can defend themselves and aren’t yet affected by aging. However, for sea turtles, the decline continues, suggesting this stage is still dangerous.
At the end of the graph, we see a rapid decline for humans and dogs, showing that health worsens quickly with age. In contrast, the curve for sea turtles flattens out, suggesting that those who reach old age are less likely to die than when they were younger.
The final data points show the oldest individuals—the maximum life expectancy group. To truly understand the life and death of these animals, we shouldn’t just focus on one type of life expectancy. Instead, we should consider the whole picture and look at the different survival curves.
There are many other animals to explore, like cats, whales, and robins. If you’re curious to learn more, you can check out the “Survival Curves” lab at minutelabs.io, where you’ll find many other fun and interactive activities!
Using graph paper or a digital tool, plot a survival curve for a species of your choice. Research the life expectancy data for that species and draw the curve based on the ages at which individuals typically die. Compare your curve with those of humans, dogs, and sea turtles. What differences do you notice?
Divide into groups and hold a debate on which definition of life expectancy is most useful for understanding animal lifespans. Each group should represent a different definition (e.g., Life Expectancy At Birth, Life Expectancy After Babyhood, Maximum Life Expectancy) and argue why their definition provides the most valuable insights.
Choose an animal not mentioned in the article, such as a cat, whale, or robin. Research its life expectancy using different definitions and present your findings to the class. Discuss how these definitions affect our understanding of the animal’s life and survival.
Visit the “Survival Curves” lab at minutelabs.io and explore the interactive graphs. Experiment with different species and observe how their survival curves change. Write a short reflection on what you learned about life expectancy and survival curves from this activity.
Create a short story or comic strip that illustrates the life journey of an animal, using the concept of survival curves. Highlight key stages in the animal’s life, such as infancy, adulthood, and old age, and show how these stages are represented in the survival curve.
Sure! Here’s a sanitized version of the transcript:
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Hi, this is David from MinuteEarth. If you look up the life expectancy of a human, you’ll find that it’s about 72 years. For a dog, it’s about 14 years, and for a loggerhead sea turtle, it’s about 80 years. However, these numbers can’t actually be compared because they were calculated using three different definitions of the term “life expectancy.”
The definition we use for humans is Life Expectancy At Birth. Essentially, it means that if a group of individuals are all born in the same year and die whenever they die, what would their average age of death be? If we applied that formula to dogs and loggerheads, we’d get 10 and 3.5, which is quite different from what you’d find in general references. For dogs, we use Life Expectancy After Babyhood. Instead of averaging the age at which every individual dies, we ignore animals that die early in life and average the age at which all the non-infants die. This is likely because pet owners are mostly concerned about how long their dogs are expected to live, given that they’ve already survived infancy.
If we used this formula with humans and sea turtles, we’d get 75 and 7, which is somewhat similar for humans but not for the turtles. For them, “life expectancy” usually refers to Maximum Life Expectancy—how long the oldest individuals live. This is probably because when we discuss less familiar species, we’re mostly curious about their potential lifespan. If we applied that definition to humans and dogs, we’d get 122 and 29.
These varying definitions of “life expectancy” complicate our understanding of how these animals live and die. Instead of focusing on a singular number, we can learn much more about animals by graphing all the different ages at which they die. This can be converted into a graph showing what percentage of individuals are expected to survive to any given age. Each green bar represents individuals from the group that are still alive after a certain age, and the way the bars drop can provide insights into the animals they represent.
For example, the drop-off between the first and second bars represents the infant mortality rate. Some animals, like humans, have a small drop-off, indicating that parents provide intensive care, resulting in fewer baby deaths. Other animals, like dogs, have a slightly larger drop-off, suggesting that parents have larger litters and occasionally lose pups. Sea turtles, on the other hand, show a significant drop-off, indicating that parents provide little care, leading to high infant mortality.
The bars in the early middle part of the distribution represent early adulthood. For humans and dogs, the bars remain relatively stable, as they are less likely to die once they are old enough to defend themselves and not yet affected by aging. However, for sea turtles, the trend continues to decline, suggesting that this life stage is still fraught with dangers.
The end of the distribution can be difficult to see, so let’s zoom in on a few examples. Humans and dogs tend to experience a rapid decline near the end of their lives, indicating that health deteriorates quickly with age. In contrast, the distribution curve for some animals, like sea turtles, flattens out, suggesting that those few individuals that reach advanced age not only avoid illness but may also be better protected from death than when they were younger.
These final data points represent the oldest humans, dogs, and sea turtles—the maximum life expectancy group. To gain a better understanding of the life and death of all these animals, it’s important not to focus solely on maximum life expectancy or just on life expectancy at birth or after babyhood. Instead, we should look at the broader picture and consider the various survival curves.
The lab also features a variety of animals that we didn’t have time to cover in the video, such as cats, whales, robins, and more! To explore this further, just click the link below, or visit minutelabs.io to find the “Survival Curves” lab, along with many other engaging interactives.
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Let me know if you need any further modifications!
Life – The existence of an individual human, animal, or plant. – In biology class, we learned about the different forms of life on Earth, including plants, animals, and microorganisms.
Expectancy – The predicted amount of time a living organism is expected to live. – Scientists study life expectancy to understand how long different species, like humans and turtles, typically live.
Humans – Members of the species Homo sapiens, characterized by higher intelligence and complex social structures. – Humans have a longer life expectancy compared to many other animals due to advances in medicine and technology.
Dogs – Domesticated mammals known for their loyalty and companionship to humans. – The life expectancy of dogs varies by breed, with smaller breeds often living longer than larger ones.
Turtles – Reptiles known for their hard shells and long lifespans. – Turtles can have a life expectancy of over 100 years, making them one of the longest-living animals.
Graphs – Visual representations of data used to show relationships and trends. – In statistics, we used graphs to display the survival rates of different animal species over time.
Survival – The ability of an organism to continue living and avoid death. – The survival of a species depends on its ability to adapt to changing environments.
Mortality – The state of being subject to death; often used to describe the death rate in a population. – The mortality rate of a species can be affected by factors such as disease and habitat loss.
Stages – Distinct phases in the life cycle of an organism. – Frogs go through several stages of development, starting as eggs and eventually becoming adult frogs.
Average – A statistical measure that represents the central or typical value in a set of data. – The average life expectancy of humans has increased over the past century due to improvements in healthcare.
