Reproduction: Crash Course Zoology #9 - Free Educational videos for Students in K-12

Reproduction: Crash Course Zoology #9 - By CrashCourse

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00:0-1	one of the most enduring questions of humanity is what
00:03	is the meaning of life ? Well , spoiler alert
00:07	, we won't be answering all of your existential questions
00:10	today , but as far as evolution is concerned ,
00:13	the most important thing that animals can do is make
00:16	more of these . No no no not just the
00:19	baby's genes without passing down our D . N .
00:23	A . Through sexual reproduction . There would be no
00:26	adorable spring baby bears , No beetles , No us
00:30	. Sexual reproduction is part of the very definition of
00:34	what it means to be an animal . Even though
00:36	life has found other more efficient methods of reproducing ,
00:39	like cloning , which just takes one individual , most
00:44	living animals and the last shared ancestor of all animals
00:48	pass on their genetic makeup with sexual reproduction . I'm
00:52	Ray Wynne Grant and this is crash course psychology .
01:01	Yeah . Mhm . Let's lay down some ground rules
01:06	because sexual reproduction is complicated . All animals have some
01:10	sort of biological sex which is harder to define than
01:13	you think because it's a combination of our DNA hormones
01:17	and physical characteristics . Unlike other animals , humans can
01:22	also have a separate concept called gender , which involves
01:25	how people can view themselves in the context of our
01:27	society and culture . Today , our focus will be
01:30	on non human animals will use mail for animals that
01:34	produce reproductive cells , or gametes that don't take a
01:37	lot of energy to make like sperm and female for
01:41	animals that produce high energy investment . Gametes like eggs
01:44	and sexual reproduction is a process that happens when male
01:48	and female gametes fuse to form offspring , combining the
01:51	genetic material of both parents . Nonhuman animals whose biological
01:56	sex characteristics don't fit . The male female binary are
02:00	hama frenetic . We'll talk about hermaphroditic animals to refer
02:04	to the many non human animals that can produce both
02:08	types of gametes throughout their lives , like earthworms ,
02:11	land snails or our old friend C . Elegans .
02:15	The nematode binaries like yes or no or male or
02:20	female are actually pretty rare in nature . So let's
02:24	start by sorting through the puzzle pieces of biological sex
02:28	which varies across animals . It's a combination of a
02:32	lot of biological signals and structures that make sperm eggs
02:36	or both . Or neither genetically various biological instructions made
02:41	of DNA called genes influence animals , biological sex .
02:46	And in many species these genes , along with plenty
02:50	of other non sex genes , are found on Alice
02:53	OEMs or one particular pair of chromosomes , which are
02:56	big chunks of DNA . Like some animals , including
03:00	humans , have an xy sex determination system . We
03:04	don't all share the exact same X . And Y
03:07	chromosomes , but similar alyssum combinations produce similar biological sex
03:12	characteristics . So in the X . Y . System
03:16	, individuals that get two of the same Alice OEMs
03:19	produce high investment gametes and are called female . And
03:23	individuals with two different Alice OEMs produce low investment gametes
03:27	and are called mail . Other animals evolved a Z
03:31	. W . Sex determination system here , biologists picked
03:36	different letters because the patterns work differently . Animals with
03:40	two different Alice OEMs produce eggs and are called females
03:45	and males producing sperm have two Z's . And to
03:50	be clear not all Z . Or W chromosomes are
03:54	the same across animal species . Either just like not
03:57	all exes and wise are the same Z . W
04:00	. X . Y . And other chromosome systems evolved
04:04	independently multiple times from different non sex chromosomes throughout animal
04:09	evolution . Like the X . Zero sex determination system
04:13	, which shows up in our friends C elegans ,
04:15	the nematode and see elegance , the tarantula . This
04:18	system only has one type of Allison and biological sex
04:22	is determined by how many copies the animal gets .
04:26	Males get just one X . And individuals with X
04:30	. X . Are female or hermaphroditic depending on the
04:33	species very efficient . But like I said , genetics
04:37	is only one piece of the biological sex puzzle for
04:41	some animals . The environment they happen to be in
04:44	as they develop plays a bigger role than genetics .
04:48	The most famous example is temperature dependent sex determination ,
04:52	which shows up in some reptiles and fish under normal
04:55	conditions , some parts of the nest are cooler than
04:57	others and a mix of males and females hatch .
05:00	But if the nest is too hot or too cold
05:03	even by just a few degrees , we get only
05:05	one sex . All of the animals we've talked about
05:08	so far whether their biological sex is determined by their
05:11	genetics or their environment stay one sex . But many
05:16	animals are serially hermaphroditic and switch which type of gammy
05:20	they produce based on cues in their environment . Let's
05:24	live a day in the life of one of the
05:25	most famous examples allow me to introduce the clownfish .
05:31	Our clownfish is the largest male and leads his small
05:36	group with his mate , the female fish , cute
05:39	by the moon . These two are the only ones
05:43	to reproduce , laying their eggs on a flat surface
05:46	near their anonymity . The father takes good care of
05:50	his eggs , fanning them with his fins and chasing
05:53	off predators . Like all other clownfish , our clownfish
05:58	began life as an undifferentiated juvenile who are neither truly
06:03	male nor female because they don't make gambians and don't
06:08	mate with the leader fish . He spent his early
06:12	years tending to his an mne home , but even
06:16	big dominant clownfish don't live forever , and every once
06:21	in a while , the largest female gets eaten by
06:24	a predator or dies of natural causes , losing their
06:29	only reproductively active female would be a disaster for the
06:33	fitness of the colony . But our clownfish has a
06:36	creative solution . He grows rapidly and his biology changes
06:43	, taking her place as the largest female , The
06:47	largest juvenile then moves up and becomes a sexually mature
06:51	male and mates with the new female leader . The
06:55	new breeding pair takes over the colony and starts having
06:59	their own eggs . Finding Nemo would have been a
07:02	very different movie if it were 100% scientifically accurate ,
07:08	have a nice day clownfish so animals can end up
07:12	producing different gam . It's based on their genetics ,
07:15	their environment and even what their social group needs to
07:18	survive . But the challenges of sexual reproduction are just
07:22	getting started to get their gametes together . Animals still
07:26	have to find mates and do the whole sperm and
07:29	egg combining thing to help them find mates . Lots
07:33	of insects have special sensory organs . Like the male
07:36	silk moth has huge bushy supersensitive antenna that can sense
07:41	chemical signals from female moths from nearly three miles away
07:45	. Other animals , like deep sea anglerfish who live
07:48	in the vast , empty deep sea , are very
07:52	clingy . Once they find a mate , the male
07:54	latches onto his mate and doesn't let go eventually fusing
07:59	with her body and providing her with a reliable supply
08:01	of sperm . Once an animal knows where its potential
08:04	mate is . The next step is to get there
08:07	and actually combine gametes , which for some animals ,
08:10	like those with a rooted in place lifestyle is a
08:13	lot more complicated than it looks . One strategy is
08:17	to let the gametes do most of the traveling like
08:20	once a year when the moon and water temperature are
08:23	just write entire colonies of coral reefs , release their
08:27	eggs and sperm into the ocean , creating an underwater
08:30	blizzard of gametes once animals needed to mate on land
08:35	, many evolved a system with a gametes meet inside
08:38	one of the individuals , since they couldn't count on
08:40	their gametes floating in water anymore , which requires the
08:43	animal producing the low investment gamut like sperm to have
08:46	an intermittent organ to deliver those gametes , like spiders
08:50	, use their petit alps , their chemo sensitive front
08:54	limbs , although their testes containing the sperm are all
08:58	the way in the back of their abdomen , so
09:00	they have to first put their sperm on the ground
09:02	and then pick it up again with their pelts before
09:05	being ready to mate . Besides the actual logistics ,
09:09	many animals also have to contend with convincing a member
09:12	of the opposite sex to be there mate . This
09:15	is where sexually selected traits or traits that affect an
09:19	individual's ability to mate come into play like antlers to
09:23	fight off rivals or brightly colored ornaments or an impressive
09:27	song to attract a mate . Many of these traits
09:29	show up only in males because typically the sex that
09:33	has to invest more time and energy into reproducing gets
09:36	to choose the mate . And often that's females ,
09:39	since eggs take more energy to make . So in
09:42	many species , females choose mates , but it's the
09:46	opposite in seahorses , some spiders and others where only
09:50	males protect the eggs , that's assuming offspring are the
09:54	goal for offspring to be produced , Both high and
09:58	low investment gametes are needed , but that's not the
10:01	only mate pairing we see in nature . Same sex
10:04	sexual behavior happens all across the animal kingdom and has
10:07	been observed in 1000 species and counting . In fact
10:12	, it could be an evolutionary adaptation passed down from
10:15	a common ancestor , like red flower beetles engage in
10:19	same sex behavior where two males will couple with each
10:23	other , and we think this behavior helps the Beatles
10:25	get rid of old , low quality sperm , lots
10:28	of social animals , like dolphins and bonobos engage in
10:32	same sex sexual behavior to which may help maintain bonds
10:36	within their group . Whatever gambits you have , the
10:39	whole process of sexual reproduction is complicated , messy ,
10:43	inefficient and even dangerous . So we might wonder why
10:46	haven't we evolved something better . Actually . Some animals
10:50	have evolved to reproduce a sexually where sex isn't needed
10:54	to make offspring , but these species are way outnumbered
10:58	by sexually reproducing animals , which suggests that sex is
11:02	evolutionarily better . We're still exploring why that is ,
11:06	but there are lots of interesting hypotheses , including two
11:09	big ideas all about shuffling jeans around since sexual reproduction
11:14	results in offspring with a mostly random combination of genes
11:18	from their parents , It increases the genetic diversity or
11:22	the number of unique combination of genes in a population
11:25	. This can prevent harmful gene mutations from becoming widespread
11:29	and might lead to potentially helpful combinations of other mutations
11:33	. But there's also the red queen hypothesis , mixing
11:37	and matching jeans through sexual reproduction might be super important
11:41	for evolving defenses against external factors like parasites , viruses
11:46	and disease causing bacteria . But since these threats are
11:49	also constantly evolving animals are locked into sexual reproduction just
11:53	to keep up . And at the end of the
11:55	day , the work of sexual reproduction isn't really over
11:59	. Many animals put a lot of time and energy
12:02	raising their fused gametes into fully developed offspring by feeding
12:06	, protecting and even teaching their babies until they can
12:09	take care of themselves , sometimes with substantial costs .
12:13	But all that effort is worth it to pass their
12:15	genes down to the next generation . Sexual reproduction is
12:19	one of the four key parts of being an animal
12:22	, so it's maybe not so surprising that animals do
12:25	all sorts of interesting things to make it happen .
12:28	Next episode will keep with the theme of animals interacting
12:31	with other animals by covering how they work together in
12:34	colonies and societies to do things they couldn't do alone
12:39	. Thanks for watching this episode of Crash Course ideology
12:42	which was produced by complexity in partnership with PBS and
12:45	Nature . It is shot on the team Sandoval Pierre
12:48	stage and made with the help of all of these
12:50	nice people . If you'd like to help keep Crash
12:52	Course free for everyone forever , you can join our
12:54	community on Patreon . Yeah .

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