0:00:03.906,0:00:07.571 Ehi Vsauce, Michael here and you guys 0:00:07.571,0:00:10.897 are my family. 0:00:10.897,0:00:14.267 Scientifically speaking, geneticists tell us that 0:00:14.267,0:00:19.550 every single person on Earth is at the least 50th cousins with 0:00:19.550,0:00:24.412 everybody else on Earth. It kind of has to be that way. 0:00:24.412,0:00:29.412 Thinkin' of it like this: you have two biological parents and 0:00:29.412,0:00:33.888 four biological grandparents and eight biological great-grandparents and 0:00:33.888,0:00:34.841 it keeps doubling. 0:00:34.841,0:00:38.964 Well, if you follow your family tree all the way back to 0:00:38.964,0:00:42.781 the time of the ancient Romans, 64 generations ago, 0:00:42.781,0:00:49.936 that tree will need one quintillion separate individuals, 0:00:49.936,0:00:52.759 which is a number that is larger than 0:00:52.759,0:00:56.906 the number of humans who have ever existed ever. 0:00:56.906,0:00:58.311 So what does that mean? 0:00:58.311,0:01:01.242 Well I think Bill Bryson put it best when he said 0:01:01.242,0:01:05.852 "You couldn't be here without a little incest -actually 0:01:05.852,0:01:08.435 quite a lot of incest". 0:01:08.435,0:01:10.383 Nothing ridiculous mind you, 0:01:10.383,0:01:12.748 but if you go far enough back in your family tree 0:01:12.748,0:01:15.378 you are going to find that quite frequently people who 0:01:15.378,0:01:18.492 were distantly related had kids. 0:01:18.492,0:01:22.898 In fact, if you are currently dating or married to somebody 0:01:22.898,0:01:26.322 who is from your own country and is of your own ethnicity, 0:01:26.322,0:01:29.508 there is a one in five chance that the two of you share 0:01:29.508,0:01:35.786 a common family member fewer than ten generations ago. 0:01:35.786,0:01:40.075 Furthermore, because our society is becoming more and more mobile, 0:01:40.075,0:01:44.805 our most recent common ancestor is becoming more recent. 0:01:44.805,0:01:48.897 Mathematical models are now showing us that for everybody, 0:01:48.897,0:01:50.792 every human on Earth right now, 0:01:50.792,0:01:53.041 our most recent common ancestor probably lived 0:01:53.041,0:01:57.122 only 2,000 to 4,000 years ago. A recent study 0:01:57.122,0:01:58.527 -it's a great one you should read it- 0:01:58.527,0:02:05.671 found that there was a person alive as early as 300 BC 0:02:05.671,0:02:11.291 who is related to every single person alive on Earth today. 0:02:11.291,0:02:14.131 That study also found that that person most likely 0:02:14.131,0:02:18.070 lived in Taiwan, near a busy port city so that ascendance 0:02:18.070,0:02:21.264 could quickly spread around the world. 0:02:21.264,0:02:24.486 Now all that said, you only receive half of your genetic information 0:02:24.486,0:02:27.241 from your mother and half from your father and 0:02:27.241,0:02:29.846 as you go up your tree it's quite possible that 0:02:29.846,0:02:36.944 distant and distant ancestors had literally no contribution to your genome. 0:02:36.944,0:02:41.103 So, who are you? 0:02:41.103,0:02:45.082 Have said this before but, because bacteria are 0:02:45.082,0:02:48.510 so much smaller than the average human body cell, 0:02:48.510,0:02:54.404 your body contains more bacteria than it contains its own cells. 0:02:54.404,0:02:56.356 And forget about trying to remember 0:02:56.356,0:02:59.209 every individual cell and bacteria in your body, 0:02:59.209,0:03:01.986 they're constantly dying and being replaced. 0:03:01.986,0:03:05.696 Even cells like brain cells which seem to live for a very long time 0:03:05.696,0:03:10.337 still take in new nutrients and expell waste, meaning that 0:03:10.337,0:03:16.176 within about every five years every single atom that 0:03:16.176,0:03:19.864 used to make up your body has been exchanged. 0:03:19.864,0:03:23.106 Do you remember what you were like 5 years ago? 0:03:23.106,0:03:26.741 Well, the atoms that make up your body, they sure don't. 0:03:26.741,0:03:29.753 This is a little existentially scary but 0:03:29.753,0:03:31.241 it leads to a very good question: 0:03:31.241,0:03:35.484 how many atoms are inside my body to begin with and 0:03:35.484,0:03:38.322 how much is a billion atoms? 0:03:38.322,0:03:41.021 Well, here's one way to think about this. 0:03:41.021,0:03:45.138 If you were to count one number greater every second 0:03:45.138,0:03:49.544 it would take you 12 days to count to a million. 0:03:49.544,0:03:56.286 And if you wanted to count to a billion, that would take you 32 years. 0:03:56.286,0:04:01.676 So a billion is a very large number, but not when it comes to atoms. 0:04:01.676,0:04:07.095 Atoms are so inconceivably small that even if you had a billion, say 0:04:07.095,0:04:14.336 Sodium atoms, their entire weight would only be 38 thintograms. 0:04:14.336,0:04:19.145 Each individual cell in your body, too small to be even seen by the eye, 0:04:19.145,0:04:23.060 contains 100 times more atoms 0:04:23.060,0:04:27.343 than there are stars in the Milky Way galaxy. 0:04:27.343,0:04:30.039 Multiply that by the number of cells that make up what 0:04:30.039,0:04:33.139 we call ourselves and each human body 0:04:33.139,0:04:38.870 contains more atoms than there are stars in the known universe. 0:04:38.870,0:04:43.783 Numbers that large lead to some pretty mind-blowing truths, 0:04:43.783,0:04:47.802 for instance, this one mentioned by Bill Bryson. 0:04:47.802,0:04:52.297 Because our bodies contain so many atoms, and because we so 0:04:52.297,0:04:55.639 vigorously recycle them, statistically speaking 0:04:55.639,0:05:02.901 about one billion of the atoms inside your body used to belong to Shakespeare. 0:05:02.901,0:05:06.747 A billion of your atoms used to belong to Beethoven, 0:05:06.747,0:05:09.327 a billion of the atoms in your body 0:05:09.327,0:05:12.244 right now, as you sit and watch this, used to be 0:05:12.244,0:05:15.026 inside the body of Buddha. 0:05:15.026,0:05:19.651 You could also think of it this way. A thousand years from now, 0:05:19.651,0:05:24.432 when humans first land on a planet outside of our Solar System, 0:05:24.432,0:05:29.346 that first person to step under the surface of the alien planet, 0:05:29.346,0:05:36.930 that body will contain a billion atoms, that are in you, right now. 0:05:36.930,0:05:45.148 And as always, thanks for watching.