Today, November 2nd, my brother Colas and I are releasing a comic book about romantic biology. 190 pages of pure pleasure that sticks to your finger to answer fundamental questions such as: Why do we have sex, first of all, actually To tell you about the diversity of how living beings have sexe and to get you to realise that the human way is actually kinda boring. That was a big project of ours, and we're very proud and happy that we've finished it, and that we can as of today share this beautiful object with you. Anyway ! I'll tell you a few details about the comic at the end of the video, and here we go ! Hi everyone, welcome in You Ask, a new format designed to answer your scientific questions quickly, in the most simple and intelligible terms, and above all quickly, cause, who's got time to finish senten... To begin with this show, let's answer Colas's interrogation as he was drawing the comic: why are there males and females Let's start with a revelation: There's a 50% chance that you're parasitising the other half of the human species. Nothing serious! I'm personally one of those, and I'm fine! But it's still interesting to understand why males are parasites. The answer to this question is a biological evolution which took place about a billion years ago: the invention of males and females. So. Let's start from the beginning. Life appears a bit more than 4 billion years ago, not so long after our planet itself formed. Simply put, at the beginning of the History of life, organisms reproduced without sex. They just split: POOF! Reproduction = Copy. You can still find this mechanism today with bacteria for which sex, as a way to mix your DNA with other individuals, is a process which takes place during all their life, but is not necessary at all for their reproduction. It's a bit like if we humans cloned ourselves and sometimes had sex to acquire different versions of our genes, and to have new properties. No males or females here, everyone's the same. With our ancestors a new way of doing things appeared: sexual reproduction. Here, reproduction and sex become linked. To clone yourself, you gotta have sex too. The idea is that each partner gives half of their DNA, everything gets mixed together, and POOF! a third individual is made. Of course, this is less efficient than cloning in terms of gross number, because to double your number of "self" you have to have sex twice, whereas you only needed to clone yourself once when we weren't doing sexual reproduction But sexual reproduction offers other very interesting advantages, we will just not talk about them here What is interesting here, is the consequence of sexual reproduction Since both individual gives half their DNA to create a third one, the easiest solution that was found is that each partner create a specialised cell, containing the DNA. These specialised cells are called "gametes", and, all of our very distant ancestors' gametes were the same size. Still no males or females here. Over time, our ancestors' sexual cells started changing. One became smaller, which by definition is called a "spermatozoon", and the other one became bigger, which by definition is called an "ovum". And, still by definition, the individual producing the bigger gamete is female, and the individual producing the smaller one is male Disclaimer: I am not talking here about gender differences or other cultural constructions, just biology. Males and females are, for millions of species joyfully copulating on Earth, defined with the size of the gametes they produce. It's just their biological definition. Alright. But the question is: How did these gametes go from an identical size at the beginning to such an obvious size difference And this is when parasitism comes in. One the major mechanisms of evolution is selection. An individual with genes allowing him/her to have more descendants will produce children with the same genes too, and they too will have more descendants on average than the rest of the population Over time, and if this advantage persists, They will be everywhere in the population Imagine that one individual, one day, decides to make gametes that are a bit smaller than the others'. Since they are smaller, he can produce more. Advantage: with more gametes, he can find more partners, and therefore, reproduce more. His descendants too will make smaller gametes on average, and reproduce more, etc etc Every time a genetic mutation will head towards smaller gametes, it will allow its bearers to have more descendants, and it will be selected along evolution. The first organism lucky enough to mutate into having 200 million gametes instead of a single big one had a lot of fun. Those were the first spermatozoa, and therefore the first male. The problem is, the offspring is of less good quality because it has less resources to begin with. One field of mathematics, Game Theory, enables to show that, when enough individuals have very small gametes, it is interesting to adopt the opposite strategy: Making BIG gametes in very few quantity. And that's the invention of the ovum, a gamete full of resources, making sure that the offspring's gonna be totally lame. Therefore, the male is biologically a parasite It reproduces off another individual, it does not provide any resources, it cheats. So, why are there two sexes Because the ovum and the spermatozoon are two opposite but stable strategies Any deviation from these two strategies is unlikely to be as successful in terms of number of descendants and their quality, so, let's keep it to two sexes. Of course, there are many exceptions Species where males/females disappear, species which reinvent intermediate sexes in another way, and all of this we'll discuss another day, because The living world is a merry chaos after all. Thank you all for watching this episode up till the end I hope you liked it! Feel free to subscribe if you like this concept, or to share the video or even, and most importantly, to comment to propose awesome questions to answer Secondly, if you want more details about the comic book that Colas and I did, you can find some on his channel; he's just published a video on that topic. So I'll let you go ahead and click here. There you go! Fee free to say what you thought of the comic book if you've read it, and anyway, let's meet again for another video!