We Bengalis (Eastern Bengalis) have a lot of Asiatic Mongoloid blood. Especially the further South in Bangladesh you go. Lot of seafaring and trade went on in the early days, as well as Buddhist Religious expeditionary activity in between our land and the kingdoms of Myanmar, Thailand, Cambodia and China and vice versa.
The fact that we look different than the rest of Indian Hindus is also because of Muslim migrations to Eastern Bengal (in addition to Mongol blood). Detractors try to make jokes about it but I have seen this myself when I visited Gulf countries.
IMHO, the more diverse the mix, the stronger the bloodline. The more talent.
In any case - this is off topic, back to our regular programming...
However, there can be many reasons for our somewhat Mongoloid features. Please note that there was no political entity called Eastern Bengal before 1947. So, we cannot just generalize that Turkic blood is responsible for that.
If you analyze the political history, you will see not only Khilji/ Khaliji Turks but also other Turkic and Pashtun people also were part of the expedition in 1200 AD and the sources of subsequent migration.
Please read "Bangalar Itihash" written by Rakhaldas Bannerjy during British time. He wrote, "আদি যুগে উত্তর থেকে এলো মঙ্গোলগোষ্ঠীও লোকজন, দক্ষিণ থেকে এলো দ্রাবিড়, আর ছোট নাগপুর থেকে এলো নিগ্রো জাতীয় লোকেরা। এদের সংমিশ্রনে সৃষ্টি হলো আদি বাঙালি। কোন পদ্ধতিতে এদের সংমিশ্রণ হলো এ তথ্য ইতিহাসে কোথাও পাওয়া যায়না। পাশাপাশি একসঙ্গে বাস করার জন্য আর একই বিগ্রহে পূজো দিতে দিতে না কি পরস্পর যুদ্ধবিগ্রহের মাধ্যমে তারা একে অপরের মধ্যে বিলীন হয়ে গিয়েছিলো এই তথ্য ইতিহাস দেয়না। তবে, ভালোমতো পরীক্ষা করে দেখলে বাঙালিদের মধ্যে এই তিন জাতের সংমিশ্রণ পরিলক্ষন করা যায়"।
Here, he was talking about the origin of the Bangali people. Aryan people immigrated at a later time. It was about 1,000 years after their arrival that the caste system was introduced in India including Bengal. It was because of intermixing with the locals.
Men have always been polygamists by nature. So, an Aryan male would marry one Brhmani lady but many would take other wives from the local Hindus. Aryan society did not accept the mixed offspring as their own. So the sons and daughters remained segregated from the Aryan society and became part of what we say low-caste people.
These offsprings carried Aryan blood but mixed with local blood. Since they were mixed, therefore, many of the local low caste people are not purely the mixture of pre-historic three groups because they also carry Aryan genes.
During the long Muslim period, many people migrated from the western and central parts of Asia. Many people took Islam as their religion during the Mughal period. During the course of time, all these migrant and local Muslims mixed with each other through marriages.
It happened more during the British period because many of the old families lost their properties and forgot also the old-time family status. So, finally, we became all a mixed group of people where religion played a great role, both in the pre-historic time and after the Muslim immigration.
I wrote a long post. But, my intention was to say that there is no difference between the people of Eastern Bengal and Western Bengal. If you watch carefully, you will find similar variations in any small village.
By the way, with all our propaganda the reality is in Bengal proper the
percentage of Muslims was somewhere near 35% that was found in the 1880 census of population. Muslim population increased rapidly compared to the Hindu Bangali population. So, in reality, conversion was less than we think, and the production of children has been more.
I think it is also true even now. But, this phenomenon created a new nation, good or bad.