Cosmos: you can thank microbes for sex

FOX’s “Cosmos: A Spacetime Odyssey” hosted by Neil deGrasse Tyson premiered this past Sunday. The show is an ambitious remake of the highly successful 1980s series “Cosmos: A Personal Voyage” with Carl Sagan. Carl Sagan was launched into stardom as an approachable scientist, and inspired the next generation of astronomers including Neil.

Astrophysicist Neil deGrasse Tyson is the Host of Cosmos Bulletproof Coffee http://bit.ly/BulletProofCoffee SUBSCRIBE: http://bit.ly/SubscribeToLondonReal Neil deGrasse Tyson is...well, a dude! Dressed in cowboy boots and an embroidered shirt he represents the essence of ultracool nerdiness. Trained as a wrestler in high school he soon became the self-appointed "Defender of the Geeks."

The show hopes to cover a wide range of topics related to the latest and greatest findings in the field of astronomy. For example, we have discovered a ton of new planets

Although I am not an astronomer, I do like to apply my knowledge of microbiology to astronomical topics as you can see in my post about the possibilities of microbes in space.

Two points were made during the premiere that caught my attention:

1) We owe sex to microbes

2) What if dinosaurs didn’t get wiped out by an asteroid? Would humans still have evolved?

Here, I will focus on the evolution of sex and what these statement means. You can read my thoughts on the reproducibility of evolution and the science of testing fate in a previous post.

Why sex is a big deal, evolutionarily.

Why is sex such a big deal? That is, why is the evolution of sex so important and still studied extensively today?

First off, asexual reproduction works really well. Most bacterial species can grow in number extremely quickly through a process called binary fission. This process creates two new identical individuals through the division of one cell’s cellular contents into different bodies that go their separate ways. Fast growth through asexual reproduction allows some bacterial species to go from one cell to billions of cells in a single day. That would be equivalent to populating the earth with all of humanity in 24 hours.

Some pioneering microbes decided to opt for sexual reproduction or conjugation as an alternative to an already success strategy of asexual reproduction through binary fission. Why would this be? Photo credit: Kenny Flynn

Some pioneering microbes decided to opt for sexual reproduction or conjugation as an alternative to an already success strategy of asexual reproduction through binary fission. Why would this be? Photo credit: Kenny Flynn

An impressive feat, indeed.

The success of asexual reproduction is seen everywhere; bacteria are essentially found in all environments and all over the planet and inside us.

I hope now you see the conundrum: if asexual reproduction works so well, why would organisms switch to the sexual mode of reproduction (besides the obvious recreational benefits)?

Currently, there are several competing hypotheses as to why an organism would want to become sexual but I will argue they all revolve around one central need for more genetic variation.

Genetic variation or variability in the composition of DNA provide opportunity for organisms to adapt and deal with changing conditions.

Don’t put all your eggs in one basket.

For example, imagine I tell you that you won an all expenses paid vacation, but the location isn't revealed. Packing for the trip suddenly becomes difficult. Do you need warm clothes to deal with a winter getaway, or will you be relaxing by the pool in your bathing suit? Packing for a variety of potential outcomes allows you to be prepared no matter what the destination.

Sex essentially accomplishes the same thing.

Diagram for en:Evolution of sex. Sex helps the spread of advantageous traits through recombination. The diagrams compare evolution of allele frequency in a sexual population (a) and an asexual population (b). The vertical axis shows frequency and the horizontal axis shows time. The alleles a/A and b/B occur at random. The advantageous combination AB arises rapidly with recombination (a), but must arise independently in (b).

Diagram for en:Evolution of sex. Sex helps the spread of advantageous traits through recombination. The diagrams compare evolution of allele frequency in a sexual population (a) and an asexual population (b). The vertical axis shows frequency and the horizontal axis shows time. The alleles a/A and b/B occur at random. The advantageous combination AB arises rapidly with recombination (a), but must arise independently in (b).

Now, let’s imagine a more biological relevant example: two genetically identical birds hatch in the same nest at the same time. Being identical, these siblings are equally good at catching flies and only alright at breaking open hard to eat seeds. Since they have the same capabilities, these siblings will spend a lot of energy competing for the same flies to eat. If flies become rare, both siblings might not survive. Meanwhile, neither sibling may survive if suddenly the fly population goes extinct.

Now, let’s introduce sex. Sexual reproduction takes 50% of the genes from one parent and combines it with 50% of the other. However, which 50% you get varies. Back to our siblings, now they are not identical. This time around, one sibling is better at breaking open seeds while the other is better at catching flies. The siblings co-exist better and if flies or seeds suddenly go away, this bird species has options to survive through the success of either sibling.

Why do organisms that do not sexually reproduce get credit for creating it?

Pioneering microbes were the first life on Earth. Some of these asexual pioneers evolved sex and did well, potentially giving rise to our ancestors. Meanwhile, other microbes did fine asexually and eventually became most of the bacteria we know today. The end result is the diverse world of species that can be sexual and/or asexual. Both strategies are good at producing the genetic variation needed to survive nature’s unpredictable challenges.

Stay hungry and make sure to tune into the next episode of Cosmos this Sunday at 9 pm EST.

Got questions about the show? Want more explanations about the details behind Cosmos? Leave a comment or send a message and we will help you feed your data monster.