[Music]
Wouldn't you like to come for a
ride in my sexy red sports car?
Truth is that this nice car isn't mine.
This battered sedan
here is my car.
It has a lot of advantages,
it has more space,
my son can scratch it and it takes
me places conveniently and efficiently.
So why are people attracted
to beautiful cars?
This story of the car is an
analogy to sexual selection
we will discuss in this video.
So far, we discussed useful traits.
An impala that it fast
will survive and reproduce,
while a slow one will be eaten
and will leave no offspring.
There is a great number
of selected traits.
Darwin formulated the rules of natural
selection and everything was fine
until he saw a tail of a peacock,
which made him feel sick.
This tail does not promote survival.
To the contrary, it requires a lot
of energy to produce and carry around.
It makes the peacock
conspicuous to predators
and it slows down its
already ungainly flight.
And the peacock is not alone.
There are lots of other animals
with such peacock-like properties
that are expensive to produce and
maintain and that attract predators.
Darwin thus formulated the
rules of sexual selection.
The logic is simple and we will demonstrate
it by looking at the peacock's tail.
Sexual selection is, like natural
selection, based on variability.
In this case, of the length of the tail.
It is further based on heritability.
Males with a long tail pass on
this property to their offspring.
This is, however, not sufficient.
For sexual selection to work,
another property is to be passed on.
The attraction of females
to males with long tails.
If females won't prefer
males with long tails,
these tails will not have any advantage.
To the contrary, long-tailed males
that have a higher chance of
falling victim to predators
will gradually disappear.
However, if females love long tails
and this preference is passed
on to their daughters,
as seems to be the case in peacocks,
we will get a runaway
positive feedback loop
that will cause the tails to get
longer and longer due to sexual selection.
Let us see how this happens.
The female benefits from
mating with long-tailed males,
because her long-tailed male offspring
will be popular with females,
resulting in many popular
long-tailed grandchildren.
In this manner long tales in males,
as well as the attraction of
females to long-tailed males,
will increase over the generations.
Peacocks are only one example of many.
For example, this
Long-tailed widowbird
is a small bird with a tail
that is half a meter long.
When the tail was either trimmed
or artificially elongated,
it turned out that females would
go with males with the longest tales.
Sexual selection is thus the
result of two inherited traits:
The trait itself in one sex,
usually the male,
and a preference for this trait
in the opposite sex, usually the female.
To some extent,
this is a chicken and egg question,
“What appeared first?
The trait or the preference?”
Michael Ryan studied a range of
sexual selection phenomena
and concluded that the
preference preceeded the trait.
Until the trait appeared
by chance in the male,
the preference remained hidden.
Ryan studied the
courtship call of toads.
He discovered that while the call
itself exists only in a single species,
females of many other species
that live in far away locations
are attracted to this call.
Like many other beauty traits,
this call has a price,
as it attracts, as you can see here,
bats that eat these noisy toads.
Other studies looked
at the Swordtail fish.
When Researchers glued an artificial
sword to males in a sword-less species,
the females of these species
were attracted to it.
These observations show
that the preferences
existed before the trait.
But why?
In swordfish,
the sword makes the male look bigger,
and females prefer bigger males.
In Guppy fish,
females prefer bright orange males.
These fish feed on orange food.
The attraction to orange food might have
become a general attraction to this color,
not only for food,
but also for mate choice.
In most cases we have no clue about
the source of the preference.
In certain cases,
it could represent something.
For example,
the expensive sports car shows
that its owner is likely to be rich.
If he is rich, he might be able
to care better for his offspring.
The prominent Israeli Researcher
Amotz Zahavi,
who recently passed away,
proposed a highly controversial
handicap principle.
Zahavi surmised
that for a single to be authentic,
it has to be as costly as possible.
If a certain individual can survive
in spite of carrying a long tail,
or some other costly feature,
it signals to the female that he has
good genes and is particularly successful
and thus, a worthy mate.
In the text following this video,
we'll explain why
I, like most Researchers in the field,
do not think that the handicap
principle can explain sexual selection.
I mention it here, however, due
to my great respect to Zahavi,
who was one of the founding fathers
of nature conservation in Israel.
Moreover, even if flawed,
the handicap principle played an important
role in the discussion of sexual selection.
While the tail of birds and
the croaking of toads
might sound like a marginal phenomenon,
they represent an important question
“What is beauty,
visual, acoustic, aromatic or tactile?”
We as humans, are of course,
also attracted to beauty.
An attraction that supports a huge industry
that enhances beauty artificially.
Fashion, plastic surgery,
makeup and perfume,
as you can see in my local drugstore.
No matter how and why
sexual selection evolved,
it fills our world with beautiful animals
and plants in all colors of the rainbow.
