In the Holy Qur’an, Ya’juj and Ma’juj have been described as the mischievous people, who horrified other human beings repeatedly. The majority of Mufassirin (Qur’anic Commentators) are of the opinion that Ya’juj and Ma’juj were two ancient tribes from the descendants of Japheth bin Noah. So, more likely, Ya’juj and Ma’juj are human beings, but a study of the hadiths shows that they are very different from ordinary human beings. The Qur'an also mentions in the story of Dul-Qarnain the Great (Al-Kahf:83-100), that Ya’juj and Ma’juj are very savage and bloodthirsty tribes. There is sufficient evidence in the ancient history and some clues in the Quran and Hadith to conclude that Ya’juj and Ma’juj are cannibals (man-eating tribes). We mentioned in our paper Dhul-Qarnain the Great: A Modern Review that Ya’juj and Ma’juj might be present in Siberian mountains, where Dhul-Qarnain build an iron-barrier to stop their attacks.
The important question is why Dhul-Qarnain, despite being the king of the world's largest empire and the commander of the world's most powerful army, could not defeat Ya’juj and Ma’juj? On the contrary, instead of eliminating them, why he considered it enough to block their way of attacking?
This clearly means that Dhul-Qarnain and his army did not have the strength and courage to fight Ya’juj and Ma’juj. After all, what characteristics of Ya’juj and Ma’juj made them unbeatable? Even then, the most powerful king was helpless before them? Let us try to find the answer to these questions from the hadiths.
It is narrated on the authority of Nawas bin Samaan (may Allah be pleased with him) that the Holy Prophet (peace and blessings of Allah be upon him) said: When Jesus (peace be upon him) kills Dajjal (the antichrist), Allah will reveal to him that I am sending to you people, no one is able to fight against them. Take these (believing) servants of mine away to mountains. Then Allah will send Ya’juj and Ma’juj.
The main reason behind the invincible powers of Ya’juj and Ma’juj seems to be their man-eating habit. Imam ibni Jarir At-Tabri quotes Imam Saeed bin Abdul Aziz Ad-Demashqi (90 -167 H) who said while interpreting the mischief spread by Ya’juj and Ma’juj:
Imam Saeed bin Abdul Aziz said the Allah’s word ( إِنَّ يَأْجُوجَ وَمَأْجُوجَ مُفْسِدُونَ فِي الأرْضِ )means they (Ya’juj and Ma’juj) used to eat people.
Ya’juj and Ma’juj’s same bloodthirsty nature and man-eating habit has been mentioned in Imam Wahab bin Munabbih Al-Yamani’s narration in Tafsir Ibni Jarir. Though, this narration is somewhat weak,supports the previously mentioned saying of Imam Saeed bin Abdul Aziz Ad-Demashqi.
The oldest language spoken in Siberia is the Samoyedic language, the language of the indigenous Samoyedic people. In Russian language, Samoyed means self-eaters.The Samoyedic people are the closest relatives to Ya’juj and Ma’juj. Since, the Samoyedic people live in the same region, where Ya’juj and Ma’juj once have lived; the Samoyedic people were also thought to be cannibals, by the European historians. The eating habits of the Samoyedic people are somewhat similar to those of the man-eating tribes. The Samoyeds are accustomed to eating raw meat and drinking blood. The reindeer is a Siberian pet. Its raw meat and blood is their favorite food. Probably the Ya’juj and Ma’juj tribes also become savages and cannibals because of their food habits. The famous Greek historian Herodotus, in his book Histories, mentions the man-eating tribes which invaded Greek lands, from the northeast. Herodotus used the term Androphagi for them, which in modern language is called anthropophagus or cannibal. Herodotus notes:
“The manners of the Androphagi are more savage than those of any other race. They neither observe justice, nor are governed, by any laws. They are nomads, and their dress is Scythian; but the language which they speak is peculiar to themselves. Unlike any other nation in these parts, they are cannibals.” 
Encyclopedia Britannica observes:
“ANDROPHAGI (Gr. for “man-eaters”), an ancient nation of cannibals north of Scythia (Herodotus iv. 18, 106), probably in the forests between the upper waters of the Dnieper and Don. They were most likely Finns (Samoyed has the same meaning) and perhaps the ancestors of the Mordvinians (q.v.).”
This is what the Greek and other European experts guessed about the land of the cannibals, located in the northern region of Caucasia. Existence of cannibals is not a myth or a folk tale alone. Archaeological sites have shown signs of scratching flesh and breaking or crushing human bones, at certain burials, indicating that those people were attacked and eaten by some other ferocious human beings. 
How did Ya’juj and Ma’juj turn into cannibals?
Due to eating of raw meat and drinking of blood constantly, their DNA had undergone such dramatic changes that they have developed extraordinary traits and strange eating behaviors. These behaviors are inherited through generations and become an inevitable, coincidentally consistent with laws of genetics. Genetic mutations make their way in the large but isolated populations, through centuries and muted traits become dominant over time.
“The development and function of an organism is in large part controlled by genes. Mutations can lead to changes in the structure of an encoded protein or to a decrease or complete loss in its expression. Because a change in the DNA sequence affects all copies of the encoded protein, mutations can be particularly damaging to a cell or organism. In contrast, any alterations in the sequences of RNA or protein molecules that occur during their synthesis are less serious because many copies of each RNA and protein are synthesized.” 
Generally, mutations occur spontaneously and cause abnormalities in an organism, especially humans. However, over a larger time scale, these mutations may develop certain abnormal traits in an individual and population. So development of cannibalism in Ya’juj and Ma’juj is the product of genetic mutations.
Do Ya’juj and Ma’juj exist today?
In Dhul-Qarnain’s account, it is mentioned that Ya’juj and Ma’juj were blocked or imprisoned between two mighty mountains and an iron-wall was built as a barrier against them. According to authentic Hadiths, they not only existed in Prophet Muhammad’s life (May Allah shower His blessings and peace on him), but the said barrier was intact. Only a small hole of the size of a coin was made in that wall.
Narrated Zainab bint Jahsh (may Allah be pleased with her)
That the Prophet (ﷺ) once came to her in a state of fear and said, "None has the right to be worshipped but Allah. Woe unto the Arabs from a danger that has come near. An opening has been made in the wall of Ya’juj and Ma’juj like this," making a circle with his thumb and index finger. Zainab bint Jahsh (may Allah be pleased with her)said, "O Allah's Messenger (ﷺ)! Shall we be destroyed even though there are pious persons among us?" He said, "Yes, when the evil person will increase."
As it has been mentioned in Abu Hurairah’s Hadith, Ya’juj and Ma’juj would be released after assassination of Dajjal. It indicates clearly that Ya’juj and Ma’juj ont only existed in Prophet’s time but at present as well.
Where are Ya’juj and Ma’juj
It is an important question if Ya’juj and Ma;juj really exist today, then, where are these cannibals? In our previous paper Dhul-Qarnain the Great: A Modern Review, we did mention that the possible place of residing Ya’juj and Ma’juj might be Siberian forests. Despite the latest technology, a number of mysteries are waiting for being solved including Bermuda Triangle, Stonehenge and Egyptian Pyramids etc. The Arctic Siberia is extremely cold with lowest recorded temperature as 90 degrees below freezing point.Such an extreme cold environment makes it harder if not impossible to investigate the forests in this region.
Possibly, Dhul-Qarnian's wall might be covered by some glaciers; due to global warming glaciers tend to melt; so the said wall might be revealed after melting glaciers.
When would the Dhul-Qarnain’s Barrier breach?
Read this Hadith again:
It is narrated on the authority of Nawas bin Simaan (may Allah be pleased with him) that the Holy Prophet (peace and blessings of Allah be upon him) said: When Jesus (peace be upon him) kills Dajjal (the antichrist), Allah will reveal to him that I am sending to you people, no one is able to fight against them. Take these (believing) servants of mine away to mountains. Then Allah will send Ya’juj and Ma’juj.
This Hadith clearly mentions that Ya’juj and Ma’juj will be released from their captivity after the assassination of Dajjal by the Jesus’ blessed hands (En sha Allah). Definitely, this forecast is awaiting to be witnessed. So the claims that Dhul-Qarnai’s wall has been already breached; are not consistent.
The following hadith is noteworthy regarding Ya’juj and Ma’juj.
It is narrated on the authority of Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: Ya’juj and Ma’juj dig the wall in their path every night, even when the sun is about to rise; their leader says: Let's just dig the rest tomorrow, but Allah makes this wall harder than ever. Until when their captivity is over and Allah wants to allow them to attack the people, Ya’juj and Ma’juj are digging the wall and the sun is about to rise, their leader will say, " Let's just dig the rest tomorrow Inshallah”, then they come the next day, they will find the wall in the same condition in which they left. Then they will be able to dig it out completely and attack the people. They will drink the water of the lakes and the people will take refuge in their forts. Then they will shoot arrows into the sky, which will return with blood on them. They will say, "We have driven out the people of the earth and defeated the people of the heavens as well." Then Allah will send some insects (like grasshoppers) which will enter their necks and kill them. Animals of the earth will eat their flesh and become very fat and fresh.
Why Ya’juj and Ma’juj dig the wall only at night? There is a clear indication in this hadith that Ya’juj and Ma’juj come to the open space only at night, because, they are afraid of light. It seems that they are suffering from photophobia. The Qur'an al-Hakim states that they live in narrow and dark valleys between high mountains. Having been away from light for thousands of years, their eyes could not withstand the bright light. As a result, they have developed photophobia.
These Hadiths evidently reject the misconceptions regarding Ya’juj and Ma’juj that different groups are spreading for their political agenda. The following points can be easily deducted from the aforementioned Hadiths:
1.Ya’juj and Ma’juj are not normal humans.
2.They are permanently, suffering a medical problem called photophobia.
3.Despite modern technology, people would not be able to eliminate them.
4.They would be released from their captivity after assassination of Dajjal.
5.They would be killed by a sort of worms in a short time period.
These implications, deducted from authentic Hadiths, neither could be applied to the Turks, nor Khazar Jews. It is a matter of fact that these misconceptions could not withstand the authentic Hadiths.
This is what we comprehended and Allah s.w.t knows the best.