Sex. We do it, deer do it, dogs do it, cats do it,
lizards do it, turtles do it, frogs do it, fish do it,
worms do it, coral does it, even yeast do it, but why?
What is sexual reproduction good for?
Scientists argue that because sexual reproduction is so wide spread,
and because it has survived for so long, it must serve some beneficial function.
But those opposed to modern scientific thought argue that sex is just too complex to evolve.
You need matched gametes, complex gonads, matched genitals,
and complex mating behaviors for sexual reproduction to work,
and there is no way such a complex multi-component system could have evolved naturally.
Well the origin and evolution of sexual reproduction are topics I've already covered.
Check out these videos to learn how it all happened.
Okay, but there are still costs associated with sexual reproduction.
You need to find a mate, and you never pass all your genes to the next generation.
In other videos I presented a computer simulation discussing the benefits
of sexual over asexual reproduction and why sexual reproduction settled on two sexes,
male and female, but not three or more.
But even if you refuse to acknowledge all that science has discovered over the past century and a half,
and want to believe that all life was magically created in its modern form 6000 years ago,
then you have to acknowledge that god, the intelligent designer
made the majority of complex multicellular life sexually reproducing.
So we can all at least agree that sexual reproduction must be good, but for what?
Well a recent study by Morran and colleagues
published in the peer-reviewed scientific journal Nature
set out to answer precisely this question. Here's what they did.
They started with an isogenic, meaning there is little to no genetic variation,
population of the tiny nematode worm C.elegans.
Now this worm is special in the way it reproduces.
The majority of C.elegans are hermaphrodites,
meaning they have both male and female reproductive structures.
They can therefore either reproduce with each other, called out-crossing,
or they can fertilize themselves, called selfing.
The population was then split in thirds.
In the first group a single gene was mutated forcing the worms
to only be able to reproduce by mating between individuals, out-crossing.
In the second group a different gene was mutated forcing them to only be able to
reproduce by fertilizing themselves, selfing.
And the last group was the wild-type control.
Now what's important to note here is that because these three groups
all come from the same starting population, which itself has little to no genetic variation within it,
any changes seen in the groups over generations, must be due to new genetic mutations,
and because of the large population size of the groups tested any differences that emerge
between them must be due to their different sexual reproductive habits.
Also, self fertilizing is different from pure asexual reproduction,
but in an isogenic population these two forms of reproduction are nearly the same.
Now in the first experiment each group of worms was placed in separate petri dishes.
Their food was placed on the opposite side of the dish.
And between them and their food, the equivalent of a small mountain range,
really just some vermiculite, was erected, well, more like sprinkled,
but to the worms it looked and felt like a mountain range.
For the worms to survive, they would have to scale the mountains
to reach the fertile pastures of yummy E.coli beyond.
Worms would then be collected from the side with the food and placed on a new dish,
again on the side opposite their food, and would again have to cross the mountain range.
After 50 generations the worms that were only able to outcross,
actually improved their mountain climbing ability
while those that were only able to self-fertilize showed a decrease in fitness.
And since these populations were isogenic, these differences must be due to novel mutations
that were selected for during the course of the experiment.
So to those of you out there who claim or believe that evolution has never been observed.
Merry Christmas, because this is another perfect example.
The worms that engaged in normal outcrossing sexual reproduction
evolved an enhanced ability to cross mountains by selecting for beneficial mutations
that in effect added information to their genomes.
In a second experiment they repeated the mountain crossing test, again for 50 generations,
but this time added a chemical mutagen to the environment
that increased their natural mutation rate 4-fold.
Now if all mutations are bad, as some would have you believe,
all groups should show a decrease in fitness.
And while the worms that could only self fertilize
did show a dramatic decrease in their ability to cross the mountain range,
the worms that could only outcross showed no decrease in fitness.
Clearly the ability to outcross, which is to participate in normal sexual reproduction,
somehow protected the worms against the buildup of deleterious mutations
caused by the chemical mutagen.
The study contains a few other interesting experiments
so I encourage everyone to download the paper
from the link in the video description and give it a read.
So what is sex good for?
Why do we spend all this energy searching for a mate?
Why are we willing to only pass on half of our genes to each offspring?
Why is sexual reproduction so pervasive with life on this planet?
The answer is actually quite simple.
Evolution.
Think about it.