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| · | Intro |
| 0:00 | · | Only around 5% of the world's population have hazel eyes. Yet a 2009 study found that 55.2% |
| 0:07 | · | of their Spanish cohort had hazel-green eyes. This eye color is also more common in Portugal |
| 0:13 | · | than the global average. But why is there such a concentration of hazel eyes in the Iberian |
| 0:18 | · | peninsula compared to most other parts of the world? And is the evolution of hazel |
| 0:22 | · | eyes connected to the genetic history of Iberia? Now there are a two main types of hazel eyes. The |
| · | Hazel Eyes |
| 0:28 | · | first kind has more green hues, and this photo shows hazel-green eyes compared to pure green |
| 0:35 | · | eyes. The second type have stronger brown notes, and are more of a hazel-brown color. Now although |
| 0:40 | · | anyone can be born with hazel eyes, they are most common in people of Brazilian, Middle Eastern, |
| 0:45 | · | North African, or Spanish descent. They are more common in parts of Latin America with |
| 0:50 | · | higher Spanish ancestry for example. Given the Portuguese influence in Brazil and the Spanish |
| 0:56 | · | influence in various parts of Latin America, it's clear to see this connection to Iberia once again. |
| 1:02 | · | But how did hazel eyes evolve and does this connect to the genetic history of the Iberian |
| 1:06 | · | peninsula? Well I should quickly note the makeup of this region itself. Although Spain and Portugal |
| · | Iberian Peninsula |
| 1:12 | · | dominate this area, the small landlocked country of Andorra is also part of Iberia. It sits in |
| 1:17 | · | the eastern Pyrenees between Spain and France. Its capital is Andorra la Vella. Now Gibraltar |
| 1:23 | · | is also technically part of the peninsula. It is classified as a British Overseas Territory, |
| 1:29 | · | although it is at the centre of a long-standing dispute between the United Kingdom and Spain, |
| 1:33 | · | after it was ceded to Britain in 1713. A small part of France is |
| 1:38 | · | also part of Iberia but it's very small. What is interesting about Iberia though is |
| 1:43 | · | that it has been a genetic and cultural crossroad for millennia. On one hand, it has had a strong |
| 1:48 | · | influence from European forces associated more with higher levels of blues eyes, such as Western |
| 1:53 | · | Hunter Gatherers, Celtic & Germanic tribes. On the other hand, it has also had a major north |
| 1:59 | · | African influence as well. This influence is associated more with brown eyes of course. |
| · | Genetics of Hazel Eyes |
| 2:04 | · | And it just so happens that hazel eyes are an intermediate eye color. They sit almost |
| 2:09 | · | perfectly in between blue or gray on one end, and brown on the other. And this intermediate |
| 2:14 | · | status actually speaks to the genetics of hazel eyes themselves... Now this trait is a |
| 2:18 | · | complex one influenced by multiple genes, mainly those involved in the production |
| 2:23 | · | and distribution of melanin in the iris. The key genetic factors involved however include: |
| 2:30 | · | 1. OCA2 & HERC2 Genes (on Chromosome 15) o These genes essentially control |
| 2:35 | · | melanin production in the iris. o People with hazel eyes typically |
| 2:39 | · | have intermediate levels of melanin, meaning they do not produce as much as brown-eyed individuals |
| 2:44 | · | but more than blue-eyed individuals. 2. Now various other genes also |
| 2:48 | · | contribute to eye color. This breakdown shows some examples |
| 2:51 | · | of other genes that could play a role, that influence factors like |
| 2:54 | · | melanin levels and how light scatters in the iris. o SLC24A4 & SLC45A2: Also influence melanin levels |
| 2:55 | · | and eye color variation. o TYR & TYRP1: Affect the |
| 2:55 | · | shade and undertones of eye color. o ASIP & IRF4: Influence how light |
| 2:56 | · | scatters in the iris, which can contribute to the color-changing effect of hazel eyes. |
| 2:57 | · | 3. But are hazel eyes a dominant or recessive trait? Well in general, eye color inheritance |
| 3:02 | · | is more complex than we initially thought. o This is because it is polygenic, |
| 3:07 | · | meaning multiple genes interact rather than following a simple dominant/recessive pattern. |
| 3:12 | · | o While brown eyes are typically dominant over blue, hazel is more variable and |
| 3:16 | · | can result from a mix of genetic factors. Some of you may also be asking why do hazel |
| 3:21 | · | eyes seem to change color? Well there color appears to shift between green, |
| 3:25 | · | brown, and gold due to various factors: · 1 is Rayleigh Scattering. Similar to the |
| 3:30 | · | way the sky looks blue, hazel eyes scatter light in a way that can make them look |
| 3:34 | · | different depending on lighting conditions. · Another factor is Melanin Distribution. |
| 3:39 | · | Hazel eyes often have a brownish ring around the pupil with a greenish or gold outer area. |
| 3:45 | · | The balance of different types of melanin i.e. eumelanin and pheomelanin affects how |
| 3:50 | · | much light is absorbed and reflected. · Colors in clothing and surroundings |
| 3:55 | · | can also enhance certain pigments in the iris, making hazel eyes appear greener or browner. |
| 4:00 | · | · Some people even report their eye color shifts due to mood. When they're upset, they |
| 4:04 | · | turn more green. When they're happy, they are more gold." And please let me know if you have hazel |
| 4:10 | · | eyes in the comments below and if your eyes ever appear to change color depending on your mood. |
| · | First Person with Hazel Eyes? |
| 4:14 | · | Now who was the first person with hazel eyes? Well although this is an important question |
| 4:20 | · | the answer isn't so straight forward. For intermediate eye colors, scientists |
| 4:27 | · | can't predict eye color to a high degree of accuracy. When it comes to brown vs blue eyes, |
| 4:32 | · | scientists can predict eye color with a very high accuracy rate by analysing genetic SNPs, at |
| 4:41 | · | between (~90-95%). Intermediate colors like hazel and green eyes remain more elusive to predict |
| 4:47 | · | however, with accuracy rates of only (~50-80%). The reason for this is because the difference |
| 4:53 | · | between blue and brown eyes is more clear in relation to melanin production, which is |
| 4:57 | · | largely controlled in this OCA2 & HERC2 genetic locus. Intermediate colors such as hazel and |
| 5:04 | · | green are less clear-cut though. There is a bit more mystery to them that we don't fully |
| 5:09 | · | understand yet, and it's perhaps not surprising how many ancient cultures associated hazel eyes |
| 5:15 | · | with mysticism and magic. After all, they are a trait that appear to change color depending |
| 5:20 | · | on lighting, clothing and perhaps even mood. Now this is all to say that because of the less |
| 5:25 | · | clear-cut nature of hazel eyes, pinpointing the earliest person with them is extremely difficult |
| 5:30 | · | given the prediction methods we have today. However we do know that hazel eyes today are often |
| 5:35 | · | found in populations where blue and brown-eyed ancestry has mixed. If we extrapolate this a |
| 5:40 | · | little, we know that brown eyes are very old in homo sapiens, considered the original human eye |
| 5:45 | · | color going back hundreds of thousands of years. We also know that blue eyes are pretty old as |
| 5:50 | · | well. Some argue that blue eyes could have first developed as far back as around 42,000 years ago, |
| 5:56 | · | much older than the 6,000 and 10,000 years ago that a 2008 study first estimated. We |
| 6:03 | · | certainly know that they are older than this though. A 2016 study for instance found this |
| 6:08 | · | mutation in the HERC2 area linked to blue eyes in ancient samples. These individuals lived between |
| 6:14 | · | 14,000-13,000 years ago in the Caucasus and Italy. So a major first merging of blue eyed and brown |
| 6:21 | · | eyed populations in Europe could have been when Western Hunter Gatherers met Early European |
| 6:26 | · | Farmers for the first time. We know that the former largely had blue-eyes and the latter mainly |
| 6:31 | · | brown eyes. This probably happened around 8,000 to 6,000 years ago. This could have produced some |
| 6:37 | · | of earliest people with hazel eyes if they are indeed caused by a mixture of these two genetic |
| 6:42 | · | profiles. This leads to another question though: as this mixing happened across most of Europe, |
| · | Iberia and Hazel Eyes |
| 6:51 | · | why is there such a concentration in Iberia today? Well later episodes would have influenced the |
| 6:57 | · | distribution of hazel eyes, and other factors probably played a role as well. We know that |
| 7:01 | · | the Iberian peninsula has been a melting pot of European and North African ancestry in more |
| 7:07 | · | recent history, unlike many other parts of Europe, such as Scotland. Climate may also |
| 7:14 | · | be involved though in traits being selected for. From the perspective of geography, Iberia sits not |
| 7:19 | · | too far north and not too far south. Hazel eyes are generally more common in temperate climates |
| 7:25 | · | where moderate melanin levels are beneficial. From a logical perspective, it makes sense |
| 7:30 | · | that they not more common in Scandinavia or sub-Saharan Africa. Sexual selection could be |
| 7:36 | · | another factor in hazel eyes evolving. Rihanna has hazel eyes after all, but I do go into |
| 7:40 | · | more details on the reasons for hazel eyes in a previous video I made that you should check out. |
| 7:47 | · | But what about the genetic history of the Iberian peninsula? What impact has all these forces down |
| 7:52 | · | through history, from Celtic tribes to Germanic peoples, the Romans to the Al-Andalus period, had |
| 7:57 | · | on the genetics of this land? Well the goods news is that there has been specific research on this |
| 8:02 | · | very topic. Before we look at this though, please consider subscribing if your enjoying this video. |
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| 8:16 | · | a link in the description below. Or if you prefer to have everything on one platform, check out the |
| 8:21 | · | members area of this channel on YouTube. Just click the join button to get more information. |
| 8:26 | · | I recently posed a member-only video on the DNA and the fascinating role that hair played amongst |
| 8:31 | · | royalty in the Merovingian dynasty of medieval Europe, that is exclusively available either |
| 8:36 | · | on Patreon or the YouTube members area. Thank you for your support and now on with the video. |
| 8:41 | · | Now let's look at how the genetics of the Iberian Peninsula has changed over the past 8000 years. |
| · | The Genetic History of Iberia |
| 8:47 | · | This study analysed the genetics of 271 ancient Iberians and compared them to thousands of ancient |
| 8:53 | · | and modern individuals. For reference, before 8000 years ago, Iberia was obviously home to |
| 8:58 | · | hunter gatherer populations. This study really starts around the time of the first farmers. |
| 9:04 | · | They reached Iberia around 5500 BC, or just under 8000 years ago. Now these first farmers brought |
| 9:10 | · | Anatolian-like ancestry into Iberia, as they moved across Europe from around modern-day Turkey. |
| 9:16 | · | Around 4,000 BC, this study notes that there was somewhat of a resurgence of hunter-gatherer |
| 9:21 | · | ancestry. This is similar to many other parts of Europe around this time. Now if we move |
| 9:26 | · | on a little into the copper age in Iberia, there was sporadic contact with North Africa, |
| 9:32 | · | however this North African ancestry only became widespread in the last ~2000 years or so. |
| 9:38 | · | We will discuss this again shortly. Now during the Bronze Age, from around 2200–900 BC, there |
| 9:44 | · | was a massive change in Iberian DNA, with around ~40% of ancestry coming from incoming groups. |
| 9:51 | · | This was driven by a massive inflow of ancestry from the Pontic-Caspian steppe, |
| 9:55 | · | known as steppe ancestry. The Y-DNA haplogroups changed dramatically around this time. Previously |
| 10:02 | · | common Y-DNA haplogroups in Iberia, such as I2, G2, H, were almost completely replaced by |
| 10:09 | · | R1b-M269. This was a lasting change as we will soon see as well. Findings from this study also |
| 10:16 | · | indicate that there was more incoming males than females during this time, which other studies have |
| 10:21 | · | found similar evidence for a male-biased migration from the steppe. Or is invasion a better way to |
| 10:27 | · | frame it? Let me know your thoughts below... But what happened to Iberian DNA during the |
| 10:32 | · | Iron Age? Well there was an increase of ancestry related to North/Central European populations. |
| 10:39 | · | This increase was anywhere between 10% & 43% depending on the individuals analysed. |
| 10:45 | · | The study notes that this introduction could be related to the Urnfield culture, |
| 10:49 | · | with Celtic tribes also probably involved with this spread. Now this leads us up to the Romans. |
| 10:54 | · | But what impact did they have, if any? Well during the Roman period, there was a shift |
| 10:59 | · | in the ancestry of Iberia more to the east, in the direction of present-day Italians and Greeks. This |
| 11:06 | · | shift was probably a result of increased movement across the Mediterranean because of the Romans. |
| 11:11 | · | And on this topic, during the Roman period there was also a major influx of North African ancestry, |
| 11:18 | · | again probably related to this increased mobility. Some of this ancestry though could be also related |
| 11:23 | · | to an earlier Phoenician-Punic presence as well. Y-DNA haplogroups associated with the Phoenicians |
| 11:29 | · | like J2 became more common around this period. The Punic capital of Carthage in North Africa |
| 11:35 | · | developed out of a Phoenician colony of course, with the Phoenicians originally from the Levant |
| 11:40 | · | around modern Lebanon. Today, this haplogroup of J2 is still high in the eastern Mediterranean. |
| 11:47 | · | Now after the collapse of the Western Roman Empire, it was the turn of Germanic groups, |
| 11:51 | · | such as the Visigoths. The genetic impact of this seems to be limited overall however, |
| 11:56 | · | although some samples shifted a little in the direction of north/central Europe. Around this |
| 12:01 | · | time as well, this study found that an Asian mtDNA haplogroup appeared, called C4a1a. This may be |
| 12:09 | · | related to the Huns in some way, or some other factor, but I will leave this for another day. |
| 12:14 | · | Now in the last section of this study the authors looked at a broad period between the 3rd-16th |
| 12:19 | · | centuries AD. 45 individuals were analysed from this time. As well as the findings already noted, |
| 12:26 | · | they found additional Levantine-related ancestry that could reflect Jewish contributions as well. |
| 12:32 | · | And obviously during this time, there was ongoing gene flow from North Africa. This |
| 12:36 | · | was largely a result of the Al-Andalus period of Muslim-rule between 711 and 1492. Present-day |
| 12:44 | · | populations from southern Iberia have less North African ancestry than the samples from this |
| 12:49 | · | period of Muslim rule however. This was probably the result of later expulsions and repopulations. |
| · | Main Haplogroups of Iberia Today |
| 12:55 | · | So we have seen how the genetics of Iberia has changed over thousands of years, from |
| 13:00 | · | steppe ancestry, to the Celts, the Romans, Muslim rule and much more. But what about today? What |
| 13:01 | · | haplogroups are most common in Iberia? Well R1b is the most common Y-DNA marker in Iberia, found |
| 13:11 | · | in around 60-70% of Iberian men. The subclade R1b-DF27 is especially common in Iberia as this |
| 13:19 | · | map shows. This R1b marker was first introduced in a major way with this steppe ancestry during the |
| 13:25 | · | Bronze age. Other genetics legacies are still felt though. Branches of E1b1b are at around 5-15% in |
| 13:32 | · | Iberia today, such as E-M81 & E-V13. This mostly reflects this North African ancestry. The Y-DNA |
| 13:41 | · | haplogroup J is also found at around 5–10% of the male population, both J1 and J2. This probably |
| 13:48 | · | reflects various influences, including during the Roman period. I2 is also found in around 5-10% of |
| 13:55 | · | men, and this is a very old haplogroup in Europe that likely goes back to early hunter gatherers. |
| 14:00 | · | On the maternal side, H is the most common mt haplogroup, at around 40-50%. H1 and H3 |
| 14:07 | · | are especially dominant in Iberia, reflecting European Mesolithic and Neolithic ancestry. |
| 14:13 | · | Branches of U are the second most common maternal marker. U5 is linked to ancient Hunter-Gatherer |
| 14:18 | · | ancestry in Europe, whereas U6 is associated with North African Berbers. K, T, J, X & V are |
| 14:26 | · | among other mt haplogroups found in Iberia. Now I have made individual videos on the |
| 14:31 | · | genetic history of Spain and Portugal that I would recommend for those looking for |
| 14:35 | · | more information. But to find out more about the origin and reason for hazel eyes, please |
| 14:40 | · | click here... Thanks for watching. Please check out my Patreon page or members area on YouTube |
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| 14:58 | · | for exclusive perks and let me know your thoughts below and I'll see you next time.... |
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