Humans and their Atypical Reproductive Patterns

By Jack Hartigan

In 1859, Charles Darwin illuminated the people of the world with the truth behind the behavioral and reproductive tendencies of organisms. On the Origen of Species delves into how organisms tend to react to improved circumstances, whether it is a disappearance of a predator, an abundance of food, a change in season, etc., by producing more offspring and expanding their population. This is done because organisms are naturally wired to do whatever is in their power to prevent the extinction of their species, and what better way to accomplish this than to reproduce as much as possible. While this trend is arguably the most biologically pragmatic truth established by scientists, it is not a completely universal truth. Homo sapiens, the genus that includes all humans, react to improved circumstances by curtailing reproductive rate rather than raising it.wolfersimage012

Figure 1 from http://freakonomics.com/2011/06/10/the-rich-vs-poor-debate-are-kids-normal-or-inferior-goods/

This behavioral pattern of humans is shown in Figure 1, where the inversely proportional relationship between reproductive rate (TFR) and occupational income is displayed by year, with lower TFRs in high-income families and higher TFRs in low-income families. This trend is essentially the reason behind the shape of the demographic transition, in which humans are shown to lower their reproductive rates as their respective country becomes more and more developed. Dr. Anna Goodman of the London School of Hygiene and Tropical Medicine offers an explanation to this phenomenon by categorizing the reproductive tendencies of humans into two categories; r-selection and K-selection. R-selection applies to humans who produce many offspring but do not invest themselves fully in each child. This is used in conditions that cause high infant mortality rates. The other strategy, K-selection, applies to humans who produce very few offspring, but dedicate themselves fully to their nurturing and well-rounded development. This is used in conditions where contraceptives, medical attention, and food is handily available.

The demographic transition essentially shows that, as a country advances through the chronological stages of the transition, the reproductive rates of people in the country begin to spiral. This is because as countries advance through the stages of the demographic transition, they become more developed and the economical situation of the countries improves.

Bibliography:

http://www.economist.com/node/21561112

http://freakonomics.com/2011/06/10/the-rich-vs-poor-debate-are-kids-normal-or-inferior-goods/

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2 thoughts on “Humans and their Atypical Reproductive Patterns

  1. I found the r selection and k selection reference was fascinating but unfamiliar to me. So, I did some research on the theory. As you said in your blog post, the r- selection is for organisms that have lots of “cheap” offspring. Whereas, k- selection is from species that produce “expensive” offspring. The evolutionary pattern of r- selection is most often found in unstable environments whilst k-selection is found in stable environments. R-selection usually exhibits a population with a type three survivorship whereas k selection generally exhibits more of a type 2 or 1 survivorship curve. So developing countries that are in the beginning of the demographic transition would probably have more people following the r-selection model. Whereas, countries like America and Canada that are later in the transition would follow the k-selection model. To read more about this you can go to this article I found:
    http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html

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  2. Jack, I found the r/k selection theory you mentioned really interesting. I like how you draw the connection between this theory with demographic transition.

    I did some research on the theory, too. It is interesting to know that this theory can not only be used to categorize humans but also be used to categorize different animals. I found this youtube video (http://www.youtube.com/watch?v=Bu6ouKt9zhs) that explains theory really well. r stands for growth rate and r- selection is used to categorize those organisms that live upon growth rate while K stands for carrying capacity and k- selection is used to categorize those that live upon carrying capacity. The video mentioned that r- selection organisms tend to have a low parental care which is also true for r- selection humans who has a high infant mortality rate.

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