Hi everyone, today will dive into sexual selection we will discover what you can learn about a species behavior just by looking at its skull and
We'll talk about if any of this applies to us. The modern cultured human. Let's go
You probably heard about evolution and its main mechanism natural selection. Let's talk about the basic idea in sixty Seconds
let's put it on the clock. Evolution is the basic idea that species change over time and with enough time and
Gradual slow change those species will become new and different species.
This was a huge idea 250 years ago. Up until that point almost
Everybody thought that the natural world is fixed and created by a God, ever unchanging. As a trained biologist
I'm obligated, by law to immediately shout the name of Charles Darwin, Charles Darwin, the moment
I talk about evolution natural selection. But Darwin wasn't the one who came up with the theory of evolution him and Alfred Russel Wallace
We're the geniuses though who discovered the mechanism by which evolution has happened and that mechanism is natural selection
natural selection means that
Individuals within a species are different from each other and those differences are the reason that some of those individuals survive and others die out
The individual that survives will pass on those
Characteristics or those traits on to the next generation on to their offspring or the individual that died will not those traits
Well, they die out. That's the basic idea
But Darwin had a huge problem on his hands
some smart critics
Rightly pointed out and pointed to animals like the peacock and it's huge feathers in saying what about that, dude?
Those feathers are not adaptive. They do not help that peacock survive
How do you explain that Charles to understand sexual selection humans?
we first have to grapple with Darwin's problem and see how he
Solved it by the means of sexual selection in animals and to that we have to travel to Barcelona vamanos
There was one animal though that Darwin was worried about
The peacock he wrote to his American botanist friend a sir gray, but whenever he thinks about the feather of a peacock
It makes him sick and he was rightly worried because his critics pointed out if natural selection was true
Why would the people have this huge ornaments this huge feathers that make it very cumbersome to walk and to fly?
But let's think about this first second natural selection says the most adapted quote-unquote the most fittest
Individual has the most offspring and therefore spreads the genes within the population but survival isn't the key here. It's leaving offspring
So reproduction is king not survival
It's reproduction of the fittest if you leave the most offspring and then you died you did your part you succeeded
Darwin was aware of this and he came up with a new theory to amend natural selection
Which is sexual selection meaning members of one sex upon species choose
To mate with specific members of the opposite sex within the same species
The key point with sexual selection is whatever sac has the largest investment in offspring care
It's usually the cheesiest and on average. That's mostly the female of a species
Because the female invests more I'm gonna put in a peacock
she invests more in the egg in fat and protein and egg production and also in
Sitting on the eggs and rearing it the male just invested sperm very small investment
Very low energy investment meaning he doesn't have to look for quality
He can look for quantity the more he mates the more offspring
He will have a female peahen doe on the other hand has to be choosy because she can't have ten
Offspring at the same time and then she has to rear them peahen takes days to choose one specific peacock
Usually one with the largest ornaments to mate with what does that have to do with the peacock and feathers the peahen?
starts choosing a male with larger feathers
Peacocks with larger ornaments and larger feathers get more offspring and this will create a positive feedback loop
Leading to more and more males with large and larger ornaments and feathers because they are the ones producing the most
Offspring so it's not only natural selection pushing on them better at predators and environment factors
But there's also sexual selection pressure moving towards larger and larger feathers
So why would the peahens choose?
Males with large feathers and ornaments Darwin himself had one theory and it's one of the two main
Hypotheses for this question. He thought because of arbitrary beauty standards different in every species
He thought the peahens choose the brightest and the largest feathers just because they quote unquote like them
They just fancy them they like bright shiny symmetrical colors and feathers
So it's purely arbitrary beauty standards as a peahen if you then all of a sudden
choose to go against the grain and not choose a mate with the brightest and largest cause
Which will mean your son's all of a sudden do not get the genes for beauty and your sons will leave less offspring
So it is a runaway effect a positive feedback loop also called the sexy Sun hypothesis. Yes evolutionary biologists
love their funny nicknames
But it's literally called the sexy Sun hypothesis because you want to make sure your sons get the genes
For the beauty standards within your species. So that's
Hypothesis number one hypothesis number two was that the beauty standards within species are not entirely arbitrary
But communicate certain fitness standards as in it's extremely hard to be very have large feathers and have high
symmetry and beauty within your feathers if you're sick or if you have
parasites or if your genes aren't good it's way easier or way more probable that you have a symmetrical features in
animals than symmetrical beauty features
You really have to be quote unquote extremely healthy for those Beauty standards to be a case
So in other words beauty is a proxy measure for fitness and health and therefore female choose pretty or beautiful
peacocks not alone
Because they're pretty but because it tells them that these are the best genes you can get
So those are the two theories the sexy Sun hypothesis and the good gene hypothesis. So you might ask yourself and rightly, so
Why is any of this useful anything about behavior? Let's do a thought experiment
I give you the skull of a female and a male of a species, you know
Nothing about so just armed with the tools in the knowledge of sexual selection
You will be able to infer a lot of behavioral traits from that species. Especially you look at the sexual dimorphism
We call it the difference in size from this male skull to the female skull for instance bonobos and gorillas
The males are double or triple the size of the female and that allows you to say a lot about their social behavior for instance
Aggression in males is high in those species
Life expectancy or a difference in life expectancy is larger males live a shorter life
Have a shorter life expectancy than females we know about parental behavior of the dad of the of the males
Which usually is almost non-existent the higher the sexual dimorphism
Species where there's almost no sexual dimorphism and the female and male are almost indistinguishable from each other. Those are usually
Pair-bonding species and they have low aggression males. The life expectancy is almost the same parental behavior of the dad is more involved
So by just looking at the skulls of a species, you know
Nothing about and using the tools we learn about sexual selection
you have very high probability cause of making an inference about what the behavior of that species will be like and I think
That's freaking amazing. That's really cool. So the main question now is what about us? What about humans?
Are we a tournament species? Do we have sexual dimorphism or are we pair bonding species?
Was it really necessary to fly to Barcelona to watch some peacocks?
No was this weekend trip or a plant before I thought about a video topic of the month?
Maybe the point is what the sexual selection tell us about human behavior
So where do we land on the spectrum of sexual dimorphism sexual differences?
Are we more tournament species or more pair-bonding species?
You might have guessed it already humans are smack in the middle on average male and female are distinguished from each other by appearances
It's not as obvious as with gorillas or baboons, but we're not identical either when we talk about male and female and humans
I'll be talking about biological sex and usually differences on a group level
So averages number one life expectancy life expectancy is pretty straight forward
Almost every study in every country in the world shows that women live longer than males
On average the larger the life expectancy within a country the larger the difference between women and men in life expectancy
Those differences in life expectancy are different between countries
It can be large as in Russia or United States or Western Europe up to twelve ten eight years
But it can be lower like in in Bangladesh. It's almost zero or 1 year difference
There are two main factors to this its behavioral and resistance to disease on the behavioral front men are more likely to take risks
They're two times as likely to die during accidents on the other hand. It's also
Resistance to disease men are more likely to die because of cancer cardiovascular diseases liver disease
One of the explanations could be first hospital first our stone doesn't only influence brain development in males more than females, especially
prenatally but also during puberty and therefore influences risk-taking behavior, but also has an influence on disease resistance, especially
cardiovascular disease behavior number two aggression and violence
This is another extremely robust finding and there's only one way to interpret the data men are on average across all countries and continents
way more likely to be the victim and the perpetrators of
Aggressive behavior or violence looking at the most recent available statistics in the United Nations
We find this picture men are always more likely to be the victim of homicides in every region
But more importantly they're the perpetrators 90 to 95 percent of the time. That is an insane
One-sidedness. Let's talk about the third and last one marriages and infidelity and this is an issue one because it becomes even more personal we
Can look at infidelity rates in cheating, even though these data are not perfect because not everybody honesty reports in the behavior of cheating
they give us a rough estimate on where we are on the spectrum from qurbani species and
tournament spaces on average and meta-analyses
we find numbers between 5 10 and 25 and 30% on the upper ends depending on the age group and
Sex or the gender of the person men are usually more likely to cheat and in the last 30 50 years the numbers have also
Gone, this can just be reported but it could also be the actual numbers go
So what have you learned?
Sexual selection is an extremely powerful tool to explain much of evolutionary change in
Behavior in animals in humans it becomes bit more complicated
We're neither clearly a tournament species with huge extremes in
differences in sexual dimorphism
Well, we're not identical in behavior or aggression or life expectancy either and we're not perfectly playable in it man are more aggressive
And violent and live shorter lives make sense. Right? We see the same pattern in males of tournament species
Males have to compete with other males were accessed for females
So we do see dimorphism in bone structure muscle mass and levels of aggression violence
I think sexual selection is an amazing tool to understand human behavior
It doesn't explain everything
but it is a great start just like our bodies our brains and minds have been molded for eons of sexual selection and
Competition to leave us what what we have today
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