Friday, June 9, 2023
Mitochondrial Health

Sex determination in animals: genetic and environmental (from Livestream #120)

Clip taken from DarkHorse Podcast Livestream #120 (originally streamed live on March 26, 2022):


What is this a clip from?
In this 120th in a series of live discussions with Bret Weinstein and Heather Heying (both PhDs in Biology), discuss the state of the world though an evolutionary lens. Find more from us on Bret’s website ( or Heather’s website (

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Theme Music: Thank you to Martin Molin of Wintergatan for providing us the rights to use their excellent music.


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39 thoughts on “Sex determination in animals: genetic and environmental (from Livestream #120)
  1. Seems like it is possible that the dinosaurs may have entirely died out due to temperatures making it so that the entire population was male or female….if they had environmental sex determination.

  2. OMG, this conversation is golden. I’m one of the people that asked about XX and XY. Thanks for the deep dive. One joke – And people make fun of attorneys for complicating things 😂 (from a pre-law student). I will definitely know the answer to “what is a women” when get asked in class 👍🏻

  3. 5:48 – not true. Androgen Insensitivity Syndrome woud not exist, if only XY system played role in sex determination. While it may rightfully be considered a disease, it can be resulting from a combination of some genes from other 22 chromosomes and not caused by environmental factors. Whichever the cause, you can not call a person with AIS male based on fact that she can not produce eggs. Sorry, but evolution does not work the way you represent. Favouring some combination, even with enormous bias, does not mean completely eliminating the other, not to mention the other can reappear as a result of mutations. The observable "favoured" combination between strategy/behaviour and egg size/motility/2-10 chromosome sex determination, exceptions from which you already mentioned, is just a statistical fact, not a fundamental law. Even if there exists a fundamental law of binary sex and related behaviour, it's been continuously violated and alluding to it is somewhat phylosophical or religious discourse, rather than scientific. Would you call a person with complete AIS male if she knows she's female? Would you be right to lecture her with current understanding of some scientists with limited field of view?
    Even if someone is fully developed sexually, but knows, that belongs to the opposite sex, rather than what biologists would assign to him/her, how or why should you persuade such a person or others that you know better who he/she is?

  4. Can someone please explain where, when & why the word ‘gender’ become an overriding idea of sex? Male / Female – is Man/Woman. The issue is using the term gender ideologically has now blurred that line. And saying it’s a social construct allows it to essentially be meaningless and used to reach the point have arrived at. So WHY was ‘gender’ used? This is the issue as language has become so distorted that things that are logical are warped into illogic and nothingness.

  5. This is a good discussion on sex.
    It was one of the earlier comments that brought these thoughts to mind:
    "In the German language, a turnip has a sex but a young woman doesn't." — Mark Twain (close enough). To be precise, in German, a turnip has a gender, but a young woman doesn't. Sex is biological, gender is a linguistic term. Just because English doesn't use gender for words doesn't mean speakers of English can use "sex" and "gender" interchangeably, as the promoters of the fallacy of "gender is a social construct" do.

  6. There are a MINIMUM of 6 sets of “sex chromosome groupings”: XO, XX, XY, XXY, XXXY, XYY. These groupings can give variants on intersex people but also so can environment in utero such as people born with a Y chromosome but who have some lack of exposure to testosterone (lack of an enzyme to convert it or something). Their genitalia are “female”. They have XY. They are “male”. They may even feel male but have female genitalia etc.

    It is NOT all binary.

  7. ”Male and Female have a meaning in the universe beyond the gametes.”
    This here is something spiritual people have understood profoundly since forever. It’s the ying and yang theory. The duality exists in nature and all throughout the universe. Male vs female. Up vs down. Good vs evil. Hot vs cold. Night vs day. It all exists in duality for a reason. To balance everything out.

  8. 1:30 Yes, chimpanzees have 24 pairs of chromosomes. Lloyd Pye hypothesized many years ago that humans must have been genetically engineered by aliens, because it didn't make sense to him that humans could have evolved from chimpanzees and apes naturally. As he put it, how could humans evolve from apes with 24 chromosomes, and over any length of time lose one pair of chromosomes, and yet be so much smarter, and nowhere near as physically strong. As he put it, one of our chromosome pairs as humans appears to be the fusion of two chromosomes from apes — that is we have all the same genetic information, yet in one chromosome pair instead of two. How could that occur naturally? Not sure if he's right or wrong, but it is kind of interesting, and puzzling.

  9. Have you worked out that it's a created evolutionary process yet, it only matters if you like truth, ultimately your a nice couple you will enjoy eternal life, just trying to help, I GUARANTEE THAT YOUR A CREATION, I WOULDN'T BET AGAINST ME OK

  10. A women who has casual sex is corrected by other women, who don't want the husbands tempted, or don't want to be left with no male attention. Traditionally more so than today maybe.

  11. I wonder if any or all of trans people were ever exposed to some chemical or drug like atrazine at some point in their lives, prior to transitioning, without being notified or otherwise made aware of it.

  12. Wait. Stop. There is nothing patriarchal about the Trans stuff and men competing in women's sports or going into women's prisons. "The Patriarch" ain't doing that, honey. Ok? Seriously stupid

  13. Another fascinating discussion. I think Heather and Brett would be amazing professors to study science under. It's unfortunate they're no longer professors, but grateful to listen to their fascinating discussion online here. I like that they make it understandable for normal folks.

  14. Get rid of prisons. Male guards are already in women’s prisons, sometimes impregnating inmates. The children of inmates are sentenced to foster care or the care of relatives that may not be especially caring. The oligarchy, chock full of the most heinous crooks is exempt from prosecution, and they use the prisons as profit centers. Slavery has been reinvented within prison walls, with a strike proof workforce producing to maximize the corporate take and suppress wages for those not incarcerated.with plea bargaining, a huge percentage of the imprisoned are innocent of the charges brought against them, and relatively few defendants get an actual trial.

  15. I don't think it's viable to say that if a person is unable to reproduce, that they don't have a sex. I think if you can have sex, or even just have sexuality, then you have a sex.

    I was afraid you two would dismiss anomalous sexual dimorphism as non-viable, and that's exactly what you're doing. That's very disappointing. An individual life is not non-viable, my friends, it's still alive, and has feelings and experiences. Many of these non-viable lifeforms, as you call them, can even have sex while they're alive. And many organisms which are biologically capable of reproduction fail to reproduce at all. Are people without children non-viable to you as well? Are women past menopause no longer women, since they can no longer produce large gametes? Are men with their testes removed no longer men because they can no longer produce small gametes. Sounds like you would say "yes" to those cases, and that's very disturbing.

    This lowers my opinion of both of you considerably, because it shows me that you look at the entire world through the lens of biological reproduction. First of all, as a physicist I find that amusing, since biology is but a minor facet of the multi-faceted lens of physics. To me, all of existence is equally viable because it exists. Only what does not exists lack viability. I don't mean this in the dismissive sense that the character Dr. Manhattan says in the movie Watchmen – "A live body and a dead body have the same number of particles…" First of all, that's not even true, since the cells lyse and the body releases a lot that it was holding in, fairly rapidly after death. But, more importantly, life is about a dynamic of processes and patterns, not just numbers of particles. They only put that line in the movie to make scientists seem cruel and a-moral… although I have to say that the thinking you two displayed here today does lend that notion credence. This kind of thinking is where eugenics movements come from.

    Again, very disappointing. I can no longer value your opinions as highly as I once did. I encourage you both to stop merely looking at life as a series of biological processes, with reproduction being the most important one, so that all things are valued for their contributions to reproduction, and have no value if they brook no contribution. That is not a healthy perspective of reality. Sex as you define it, is a briefly transient phenomenon that will soon be replaced by designer babies in test tubes, and then by fabricated replication of robotic lifeforms, which will live for vastly longer epochs than biological lifeforms. We are the blink of an eye, my friends. We do not encompass all of what "life" is, your dualistic notion of sex does not encompass all of what sex is.

    Biology attempts to define life, but it does NOT define life. It only tries its best to put an approximation to paper. And you are guilty here of the Paper Indian fallacy. You have taken the page for the real thing, and forgotten that it was only ever a flattened representation of real life, which you cannot define.

  16. Wait! You two 👩🏻‍🔬👨‍🔬 have the temerity to assert differences between women & men that are neuropsychobiochemical anatomic physiologic and deoxyribonucleic acid based?! MISOGYNISTS! 🔬🧬

  17. As a child born to a mother who was pregnant on a farm that used DDT …. An Endocrine disruptor, to control mosquitoes, and all the water came from one font, my development was going to have the fate of the frogs and crocodiles down stream. 50+ years I figure this out, and it's implications.

    I don't think people realise the IA problem that is everywhere thanks to phalates, it's in all the tiny taint children in all the schools in every country across the world

    Ps I'm gay and have no skin in this game, I think IA is a separate thing to the lbgtq

    Too figure out if you have skin in this game…

    Did you breed/birth or have an IA tiny taint child?

    PPS cannabis is much like humanity 40% male 40% female 10% who can't decide, the other 10% didn't survive long

  18. In simple terms, life is a 'big accident' waiting on 10,000 variations to occur (which it does), and then trying to undo the 10,000 at age eighteen to be 'something' else….leaves you mostly in a spiral….wondering about the rest of your life. The 'accident' was a roll of the dice.

  19. Hello Heather and Brett this has nothing to do with this video but i have a crazy question and dont know how to find the truth therefore i'd love both your opions…is it normal for these tornadoes to come in the middle of the night. As opossed to diring the day when you are awake and can prepare or run? So many lies I'm waking up too i geel crazy! Also isnt it obvious not to cover your mouth from fresh sir???? Help please

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