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Age structures

In this video Dr. Nathan B. English introduces us to Age Structures.
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<v ->Well now that we’ve had a chance</v> to look at global population, think about how we got to where we are today and just take a quick stab at calculating some growth rates, I want to just touch on another aspect of human demography and that’s age structures. And so we’ve had the chance to look at global population in sort of a spatial context, and we’ve touched a little bit, but indirectly, on human population growth in a temporal or a time-based context. And now I really want to talk about digging into the temporal aspects of population growth and of age structures, because it’s interesting in that different, different populations have different age structures.
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And that means they have a different proportion of old people to middle-aged people, to young people. And that’s really what we’re looking at is we’re looking at the age structure of a population and how the different age people are distributed across that population. And the reason that’s important is because it has impacts not only on what people buy and what people consume and the impact they have on the environment, but it has an impact on what’s going to happen in the future. For instance, if we look at this population age structure on the left hand side, and I’ll just back up a minute. On the Y axis is the age of those people. Okay.
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And on the X axis on the right on the left-hand side is the number of men in that age group. And on the right-hand side is the number of women in that age group. And
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what we find here is that you find in, in populations that are rapidly increasing, they have really high birth rates. And so therefore you have a lot of young people. Children, teenagers, and you can see that here, where you’ve got lots of teenagers and very few old people. Okay. That’s pretty cool. You got lots of middle-aged people what’s important here as well is not just how many young people you have or how many old people you have, but how many people you have of childbearing age. And that’s important because it’s these people who can produce more young and the more you have of child-bearing age, the more young you can produce.
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If you don’t have a lot of people at childbearing age, you’ll might produce fewer young people. Okay. So what’s also interesting is that different countries, depending on their stage of development also have different population structures, age structures. And so in a population, in a country that has a relatively stable population, what you’ll find is you have a relatively large number of older people, and this is really a reflection of that. People are living well, good healthcare. They’re not have an extended life span. And then what you notice here is that the, roughly the same number of reproductive age people, as you have young people and people are choosing to have fewer children or just enough children to replace themselves.
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And so you find this relatively straight stable population structure. In a population that is decreasing, or will soon be decreasing, you see this in Japan quite a bit, What you find is very relatively lots of older people,
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a declining number of reproductive age people, and a declining number of young people. So people who are, who have not yet reached puberty. And so here, what you find is that you’re actually, your population will decrease because remember this cohort at the bottom in five years will be the cohort at the top, at the next stage up. And so the way these things go is they move and you can look at population. I think this is really fascinating. You can look at population structures through time and you can see different cohorts traveling through the population structure. Now, this is the population age structure in the United States from 1952 to 2008 I think.
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Now what’s cool here is you can see the baby boomers coming through as a cohort. Let’s see, what was it? And it ends in 2010 now here in. Okay. So let’s just, so if we look at this, let’s just examine. Starting in 1954, you’ll see this big bump in young people and that’s children being born after world war II, typically called the baby boomers. Now notice that this big bump, every, every five years moves up a step. Okay. And this is my parents moving through middle-age. They had me down here in 1970s, and now I’m moving up through this age population structure as well.
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And so this is a really cool way to look at whether nations are growing or shrinking, and also a really good way to plan on resources. So let’s say you’re going to get a big bump of older people who might need increased healthcare. You can begin to plan 20 years out for this big bump to come through and need that extra health care. Environmentally wise, you can also look at the impact. Maybe some age groups have more impact on environment than other age groups or more affluent or more likely to use energy. And so you can look at population age structures as a reflection of that.
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So it turns out as well that these rapidly increasing populations, stable population and decreasing population age structures also tend to line up with developing versus developed nations, where developing nations tend to have this very youth heavy age structure. And that’s generally a reflection of lower income, lower education, lower, especially with respect, to women’s education and higher child mortality. Whereas in stable populate, in more developed countries, you tend to have a stable population or even a decreasing population where people choose to have fewer children. They have other activities in their life and children just aren’t a priority. And that, and that’s okay. It just ends up being that they’re actually decreasing in population.
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Now these tend to not include immigration or emigration. So these are an interesting way to look at human population.

In addition to the overall size of the population, another human demography factor that is interesting to scientists is age structure.

Watch Dr. Nathan B. English explain how the proportion of young, middle-aged and older people in a population can be studied to understand demographic and environmental impacts.

Now it’s your turn

How do you think the environmental impacts of a rapidly increasing population will differ from those of a stable or decreasing population. Share your thoughts in the comments.

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