Human Longevity: The Influence of Genetic & Environmental Factors

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  • 0:01 Life Span
  • 1:58 Gender & Longevity
  • 3:54 Individual Genes
  • 5:18 Environmental Factors
  • 7:01 Lesson Summary
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Lesson Transcript
Instructor: Devin Kowalczyk

Devin has taught psychology and has a master's degree in clinical forensic psychology. He is working on his PhD.

Here we will discuss the human life span, with specific interest in average life span by gender, as well as what factors are likely contribute to lengthening and shortening a life span.

Life Span

We never know when we're going to go. Some people will survive four separate diagnoses of cancer; some people won't survive a cold. Longevity is defined as the length of one's life. Most often we measure this in chronological years, but we could also measure it in life events (like the number of children and grandchildren born), or accomplishments (such as the number of degrees and impact on the world) or other ways.

Each person's life span will be different. Some people don't live past the first year of age; some people will live past 115 years. The average lifespan is 78 years right now. This is, of course, an average. You could die at 115; you could die right now.

Still alive? Good, let's keep moving. Males and females have different life span expectations, and each individual has different life expectancies based on their individual genetic makeup. Unfortunately, not enough information is collected on inter- and trans-gendered people to make good statements about their life expectancies. Male average life expectancy is 76 years. Female average life expectancy is 81 years. Let's examine these differences in a little more detail.

Gender and Longevity

We can expect women to live about five years longer than men, on average. It is difficult to tell exactly why this happens, and it is likely a result of many individual points interacting.

One aspect that causes male life expectancy to be shorter is males compete for female attention. If you've ever driven past a high school parking lot, you will see the cars with the spoilers, big rims and expensive equipment all likely bought by their parents. This is a flashy version of that. Other ways males might attempt to get females' attention is by doing things that are dangerous and stupid, like jumping off a cliff on a bike.

Men just have this urge to make the ladies pay attention to them. We can't say that more or less testosterone causes males to be more competitive since it is a combination of sensitivity, size and production. What we can say is that how a male goes about getting the attention is very much a learned behavior from peers and media.

Another reason might be rooted in natural selection by way of childbirth. Let's look back through human history. One of the most dangerous times for a woman was giving birth, due to a lack of basic sanitation and a high level of complications. Those women who were stronger and able to survive the infections would have more kids. The women who had weaker immune systems or died due to complications had fewer children. Generation after generation saw the number of stronger women increase and the number of weaker ones decrease. Males only have to provide the genetic material; there is no process like this for them.

These are two very easy to understand and fairly common arguments about the difference between males and females. Let's look at the individual genetic differences now.

Individual Genes

Current research suggests that 20%-30% of a life span length is determined by genes. That means around one-quarter of what determines when you'll kick the bucket was present inside of you when you were born. This is why my grandmother, who smoked from the age of 11 until she died in her 80s, lived so long. We would label this as a genetic factor, defined as a gene, encoded in the DNA, that influences you based on its activation.

Information on genetic factors can be found using a twin study, in which twins are studied to determine the effects of genes and the environment. Twins come in two types, monozygotic, which means one egg and translates into identical twins, and dizygotic, which means there were two eggs and you have fraternal twins.

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