0:00:08.163,0:00:12.313 The evolutionary tango [br]of animal genitalia. 0:00:12.313,0:00:14.704 Can you guess what you're looking at? 0:00:14.704,0:00:18.465 If you answered "duck vagina,"[br]you'd be right. 0:00:18.465,0:00:22.115 Although the bird's outward appearance[br]may not strike you as especially odd, 0:00:22.115,0:00:24.155 it uses this strange, intricate, 0:00:24.155,0:00:28.150 cork-screw shaped contraption [br]to reproduce. 0:00:28.150,0:00:31.084 We see similarly unbelievable genitalia[br]in insects, 0:00:31.084,0:00:32.005 mammals, 0:00:32.005,0:00:32.883 reptiles, 0:00:32.883,0:00:33.785 fish, 0:00:33.785,0:00:34.583 spiders, 0:00:34.583,0:00:36.576 and even snails. 0:00:36.576,0:00:40.915 Apparently, no organs evolve[br]faster and into more variable shapes 0:00:40.915,0:00:44.055 than those involved in procreation. 0:00:44.055,0:00:49.550 Superficially, it makes sense[br]because evolution works via reproduction. 0:00:49.550,0:00:53.536 When an animal leaves more offspring,[br]its genes will spread. 0:00:53.536,0:00:57.284 And since genitalia are an animal's tools[br]for reproduction, 0:00:57.284,0:01:01.579 any improvement there [br]will have immediate effect. 0:01:01.579,0:01:05.946 And yet, what's the point of having[br]such decorative nether regions? 0:01:05.946,0:01:08.986 After all, the function [br]of genitalia seems simple. 0:01:08.986,0:01:11.107 A penis deposits a bit of sperm 0:01:11.107,0:01:15.156 and a vagina receives it [br]and delivers it to the egg. 0:01:15.156,0:01:17.126 A pipette-like thingy on the male 0:01:17.126,0:01:22.507 and a funnel-like gizmo on the female[br]should do just fine for any animal. 0:01:22.507,0:01:25.686 And yet, that's not what we see. 0:01:25.686,0:01:30.078 The penis of a chicken flea, for example,[br]looks nothing like a pipette, 0:01:30.078,0:01:33.014 more like an exploded grandfather clock. 0:01:33.014,0:01:35.647 And the vagina of a featherwing beetle 0:01:35.647,0:01:39.387 resembles something you'd find[br]in a Dr. Seuss book. 0:01:39.387,0:01:40.837 Throughout the animal kingdom, 0:01:40.837,0:01:43.679 genitalia are very complex things, 0:01:43.679,0:01:48.049 much more complicated than seems[br]necessary for what they're meant to do. 0:01:48.049,0:01:53.036 That's because genitalia do more than just[br]deposit and receive sperm. 0:01:53.036,0:02:00.607 Many male animals also use the penis[br]as courtship device, like crane flies. 0:02:00.607,0:02:02.587 In some South American species, 0:02:02.587,0:02:05.668 males have a tiny washboard and scraper[br]on their penis, 0:02:05.668,0:02:09.989 which produces a song that reverberates[br]throughout the female's body 0:02:09.989,0:02:11.828 when they mate. 0:02:11.828,0:02:15.459 It's thought that if female crane flies[br]enjoy this unusual serenade, 0:02:15.459,0:02:18.876 they'll allow the male [br]to father their offspring. 0:02:18.876,0:02:22.718 This way, the genes of the most[br]musical penises spread, 0:02:22.718,0:02:27.509 leading to rapid evolution[br]of insects' phalluses. 0:02:27.509,0:02:31.820 Similarly, some beetles have two little[br]drumsticks on either side of the penis. 0:02:31.820,0:02:36.680 During mating, they'll rub, slap, or tap[br]the female with these. 0:02:36.680,0:02:40.429 And some hoofed mammals,[br]like rams and bulls, 0:02:40.429,0:02:43.519 use a whip-like extension [br]on the penis's left side 0:02:43.519,0:02:46.820 to create a sensation during mating. 0:02:46.820,0:02:50.277 But how can females really choose[br]between males 0:02:50.277,0:02:53.688 if she can only assess them after mating? 0:02:53.688,0:02:57.978 This is where the power[br]of female adaptation comes into play. 0:02:57.978,0:03:00.968 In fact, insemination is different[br]to conception, 0:03:00.968,0:03:04.481 and the female genitalia exploit[br]this distinction. 0:03:04.481,0:03:06.159 For instance, in some dung flies, 0:03:06.159,0:03:11.050 the vagina contains pockets[br]for separating sperm from different males 0:03:11.050,0:03:14.630 depending on how appealing they were. 0:03:14.630,0:03:16.739 Males using their penises for courtship 0:03:16.739,0:03:19.610 and females controlling [br]their own sperm management 0:03:19.610,0:03:24.855 are two reasons why genitalia evolve[br]into such complex shapes. 0:03:24.855,0:03:25.971 But there are others 0:03:25.971,0:03:30.370 because genitalia are also where[br]a sexual conflict is played out. 0:03:30.370,0:03:34.031 A female's interests are best served if[br]she fertilizes her eggs 0:03:34.031,0:03:36.860 with the sperm of the best fathers 0:03:36.860,0:03:40.901 and creates genetic variability amongst[br]her offspring. 0:03:40.901,0:03:44.381 For a male, on the other hand,[br]this is bad news. 0:03:44.381,0:03:47.524 For him, it would be best if a female[br]used his sperm 0:03:47.524,0:03:51.334 to fertilize all of her eggs. 0:03:51.334,0:03:55.514 So we see cycles of adaptation[br]in an evolutionary arms race 0:03:55.514,0:03:57.975 to retain control. 0:03:57.975,0:04:00.977 Black widow spiders [br]have a disposable penis tip 0:04:00.977,0:04:06.011 that breaks off inside the vagina[br]blocking the attempts of his rivals, 0:04:06.011,0:04:09.522 and bed bug males bypass a female's[br]genitalia altogether 0:04:09.522,0:04:16.762 using a syringe-like penis to inject[br]sperm cells directly into her belly. 0:04:16.762,0:04:18.137 Not to be outdone, 0:04:18.137,0:04:21.254 females have evolved [br]their own countermeasures. 0:04:21.254,0:04:22.772 In some bed bug species, 0:04:22.772,0:04:26.002 the females have evolved an entirely[br]new set of genitalia 0:04:26.002,0:04:30.914 on their right hand flanks[br]where the males usually pierce them. 0:04:30.914,0:04:35.244 That allows them to maintain[br]the power to filter out unwanted sperm 0:04:35.244,0:04:37.404 with their genitalia. 0:04:37.404,0:04:40.698 And duck vaginas are shaped[br]like a clockwise spiral 0:04:40.698,0:04:46.604 so that when the male inflates his long,[br]counterclockwise coiled penis into her, 0:04:46.604,0:04:48.202 and she disapproves, 0:04:48.202,0:04:51.364 all she needs to do [br]is flex her vaginal muscles 0:04:51.364,0:04:55.061 and the penis just flubs out. 0:04:55.061,0:04:59.425 So, genitalia differs so much,[br]not just to fascinate us, 0:04:59.425,0:05:01.334 but because in every species, 0:05:01.334,0:05:05.405 they're the result of [br]a furious evolutionary tango of sex 0:05:05.405,0:05:08.375 that has been going on[br]for millions of years 0:05:08.375,0:05:11.446 and will continue for millions [br]of years to come.