Why Did Two Sexes Evolve?

Have you ever wondered why there are two sexes? As in, why do we require sexes for sex? The origin of the sexes is actually a very interesting question in theoretical biology, and in today's video I'll be covering my favourite hypothesis for the evolution of the sexes: The Hurst-Hamilton Hypothesis.

The video is structured to cover:
- A simplistic hypothesis for the evolution of the sexes
- The hypothesis I believe to explain the origin of the sexes
- Addressing two of its main criticisms

Alongside answering the question as to why there are male and females, this video is also part of a wider evolution themed collaboration - you can enjoy the whole playlist here!

Also, my apologies for each time I say "theory" instead of "hypothesis" - a rookie error!

Special thanks to Asher Leeks and Alan Grafen for resolving some key doubts in this video.

Inés Dawson is a PhD student and animal flight scientist at the University of Oxford.

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[DrawCuriosity]

As always, feel free to ask any questions on this topic - as I know it's a little more convoluted than usual. :) Also, please pretend I said *hypothesis* each time I said _theory_ (rookie error... I know!).
And last but not least - don't forget to check out the playlist on how and why things evolve - from homosexuality, to facial expressions, to selfies, to words and more!

[StepBackHistory]

I hadn't even considered the organelle thing. That's my novel information of the day.

[Gideon]

Great job making a somewhat technical topic accessible and interesting! I only just found your channel thanks to the collaboration and you definitely deserve a wider audience - subscribing now!

[chmtech]

You're really an amazing creator! So glad I found this channel :)

[ptonpc]

"The exception that confirms the rule"  Ahh so close, I used to have an encyclopaedia as a kid that had "The exception that *proves* the rule" as it's mantra.   Happy days.

[abrtn]

Wow! This was super interesting! I'm curious as to what the other hypotheses are. Maybe a topic for a future video? Or short series?

[upandatom]

Fascinating stuff! You're a great speaker :)

[itisdevonly]

I only discovered you recently, but I love your videos! You do a great job of covering more advanced/interesting topics within science that I rarely see done elsewhere. Please keep it up, I love learning new stuff!

[BlobVanDam]

I'd been wondering about this exact topic recently, although I think I'll have to rewatch this one again to fully grasp these concepts. :D And great work on the graphics and animation!

[LeiosLabs]

I really liked the criticisms at the end! When you say there are species with multiple sexes in the second criticism, are you referring to species with 3 or more parents?

[tone]

The animations in this one are awesome.

I do have a follow-up question, though: Once the destroyer-suppressor-choosy trio becomes fixed, isn't it then incentivized to invest as few resources as possible into maintaining them and, if so, do we see that? Like, it seems like modern ova would have no reason to carry awesomely powerful destroyers when all it has to do is clear out the last couple organelles that a sperm needs to survive, and likewise the sperm probably wouldn't need a suppressor anymore since it could just do away with its destroyer gene altogether and just keep the choosy gene signifier to tell any prospective ova that it's not gonna blow up their organelles. Is that what we see, and if not, is there a working theory as to why not?

[Damage]

Really interesting topic and presented very well. The hats were a nice touch on the organelles lol.

[VyvienneEaux]

(As in, I am a biology enthusiast with a degree in biochemistry who studies biology all day, and I hadn't considered the idea that distinguishing self from non-self was a major reason behind anisogamy, so this blew my mind).

[Alobster]

Interesting video. BTW your new hair color fits you well, looks good.

[Iknash]

Casi nunca comento videos, pero voy a hacer una excepción.

Conocí tu canal al revisar las suscripciones de Simon Clark, y la verdad que me gustaron mucho tus videos, a tal punto que no puedo parar de verlos. Están muy bien producidos, y sobretodo, las explicaciones que llevas a cabo son muy amenas. Agradezco que añadas los subtitulos en español, ya que no tengo muy buen nivel de inglés como para comprenderlo en su totalidad (me pasa con Simon Clark, por desgracia, aunque al gustarme sus videos me esfuerzo por entenderlos, como lo haría con el tuyo si no estuviesen los subtitulos jajaja).

¡Un suscriptor hispanohablante más! :) (porque supongo que a esta altura del canal deben haber muchos más).

¡Saludos!

[FannomacritaireSuomi]

This question's more important: Why did discrimination between sexes come to existence ?

[PlayTheMind]

Now my brain is all worked up about how the HHhypothesis will extend to the sexual reproduction of *robots*. Seriously!

[dianamc]

Video about the 8 hypothesis would be interesting! :)

[Skip]

Loved the video and it was super interesting! One thing I would say, though, is to be more careful when you use the word "theory". That is a very loaded and misunderstood word. Scientists can try and be more careful when using terms in a scientific context to try and separate those terms casual connotations. By equating "theory" and "hypothesis", it gives more perceived credence to people who make statements like "evolution is ONLY a theory"

Keep up the great work!

[leesweets]

"Very rarely more" than two sexes? Name one.