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  • often go belly up before their female counterparts  too. One big reason males live shorter lives than  

  • females might be hidden away in the chromosomes  that help determine sex in the first place

  • Welcome to MinuteEarth. In lots of species, males are more aggressive and  

  • take more risks, so you might expect they'd die  first - and in many species, like humans, they do.  

  • But males aren't always more aggressive, and the  more aggressive sex doesn't always die first.  

  • Instead, when you look across the animal  kingdom, the animals that die earlier,  

  • regardless of their sex, have something else  in common: they have a small sex chromosome

  • Sex chromosomes generally come in two sizesbig and small; part of what determines the  

  • sex of an individual is the combination of  sizes they inherit. In mammals like humans,  

  • females inherit two big sex chromosomes, while  males inherit one big and one small. But in birds,  

  • butterflies, and some reptiles and amphibiansthe opposite is true: males get two bigs,  

  • while females get a big and a small. In most cases, the sex with the small  

  • chromosome tends to die first, regardless  of whether they are the males or females.  

  • There are two possible explanations for why  this trend exists: one is that having more  

  • big sex chromosomes is better, and the other  is that having a small sex chromosome is worse

  • Having more big sex chromosomes might be  better because big sex chromosomes have  

  • lots of genes on them; a human's big chromosome  has 800 or so genes that code for many things  

  • unrelated to sex - from color vision to  proper wound healing to muscular function.  

  • Someone with two big chromosomes has  TWO copies of each of those genes.  

  • So if one big chromosome carries a harmful  mutation, the other is likely to have a working  

  • version of the gene. But someone with only one  big chromosome only has ONE copy of all those  

  • genes - they have no backup copies. That's  why colorblindness, hemophilia, and muscular  

  • dystrophy are much more common in human males. While there may be an advantage to having two big  

  • sex chromosomes, there's also evidence there's  a disadvantage to having a small chromosome.  

  • Small chromosomes happen to be particularly  vulnerable to malicious viral genes called  

  • transposons, which can trigger lots of harmful  mutations in genes on other chromosomes.  

  • So having a small sex chromosome at all may  put a critter at risk for a shorter life

  • These hypotheses - that big chromosomes are  beneficial, and that small chromosomes are  

  • detrimental - are not mutually exclusiveit's  likely that both are true. Scientists are still  

  • debating how these processes interact - and  how big a role they play in animals' lifespans  

  • versus other factors. That may take a whileso if you want to be around when we figure out  

  • X-actly Y all this happens , you should  probably hope you don't have a small chromosome

often go belly up before their female counterparts  too. One big reason males live shorter lives than  

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The Actual Reason Men Die First

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    VoiceTube staff 發佈於 2024 年 03 月 28 日
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