Life History Theory & the Role of Natural Selection in Traits

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  • 0:01 Life Histories
  • 1:21 r-Selection
  • 3:42 K-Selection
  • 4:42 Lesson Summary
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Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Natural selection doesn't just influence an organism's physical traits, it also influences their life history traits. In this lesson, we'll explore various life history patterns and how they are shaped by different environmental demands.

Life Histories

Life is all about tradeoffs. 'Should I go to the movies and have fun or stay home and study so that I do better on my test?' 'That salad is a healthier option, but that cake will taste so much better!' These are conscious decisions that we make every day. When it comes to evolution and natural selection, the tradeoffs come in a different form, helping to shape our life histories. A life history is an organism's schedule of growth, reproduction, and death and includes things like how many offspring an organism will have, at what age it will first reproduce, and how much care will be given by the parents. For example, a frog produces a lot of eggs, but those eggs are then left to hatch and fend for themselves. One mother frog can't take care of so many children so, instead of providing care, she devotes her energy into producing a large amount of offspring quickly. In contrast, humans generally have only one or two babies at a time and can, therefore, devote a large amount of energy to raising them. This is the type of evolutionary tradeoff we're talking about with life histories. But it's not just one or two tradeoffs that make up an organism's life history, it's the balance that's created through numerous life history traits. This balance is based on the environmental demands of both reproduction and survival, and because there are so many different organisms on earth, there's also a wide variety of life history patterns that are shaped by natural selection.

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