Answer :
It is due to evolution.People are migrated to different regions and for adaptation there skin tones changes (sunny regions-dark and cold regions-white).Then gene is another reason for these changes.
ᴛʜᴇ ʜᴜᴍᴀɴ ʙᴇɪɴɢs ᴀʀᴇ ᴅɪғғᴇʀᴇɴᴛ ғʀᴏᴍ ᴇᴀᴄʜ ᴏᴛʜᴇʀ ɪɴ ᴛᴇʀᴍs ᴏғ sɪᴢᴇ, ᴄᴏʟᴏᴜʀ ᴀɴᴅ ʟᴏᴏᴋs ʙᴜᴛ ᴀʀᴇ ᴛᴏ ʙᴇ ᴏғ ᴛʜᴇ sᴀᴍᴇ sᴘᴇᴄɪᴇs (ʜᴏᴍᴏ sᴀᴘɪᴇɴs) ʙᴇᴄᴀᴜsᴇ ᴛʜᴇʏ ᴄᴀɴ ɪɴᴛᴇʀʙʀᴇᴇᴅ ᴛᴏ ᴘʀᴏᴅᴜᴄᴇ ғᴇʀᴛɪʟᴇ ᴏᴅʟɪᴘɴɪɴᴇ
(sᴏɴ ᴀɴᴅ ᴅᴀᴜɢʜᴛᴇʀ). ᴛʜᴇ ᴇᴀʀʟɪᴇsᴛ ᴍᴇᴍʙᴇʀs ᴏғ ʜᴏᴍᴏ sᴀᴘɪᴇɴs ʜᴀᴠᴇ ʙᴇᴇɴ ᴛʀᴀᴄᴇᴅ ʙᴀᴄᴋ ᴛᴏ ᴀғʀɪᴄᴀ sᴜ ᴏғ ᴏᴜʀ ᴀɴᴄᴇsᴛᴏʀs sᴛᴀʏᴇᴅ ʙᴀᴄᴋ ɪɴ ᴀғʀɪᴄᴀ ᴀɴᴅ sᴘʀᴇᴀᴅ ᴀᴄʀᴏss ᴛʜᴇsᴇ ᴄᴏɴᴛɪɴᴇɴᴛs; ᴏᴛʜᴇʀ ʟᴇғᴛ ᴀʟᴍᴀ
sʟᴏᴡʟʏ sᴘʀᴇᴀᴅ ᴀᴄʀᴏss ᴛʜᴇ ᴡʜᴏʟᴇ ᴇᴀʀᴛʜ. ᴛʜᴇʏ ᴍᴏᴠᴇᴅ ғᴏʀᴡᴀʀᴅ ᴀɴᴅ ʙᴀᴄᴋᴡᴀʀᴅ ɪɴ ɢʀᴏᴜᴘs, sᴇᴘᴀʀᴀᴅᴀ ᴏʀ ɪɴ ᴍɪxᴇᴅ ɢʀᴏᴜᴘs ᴀᴛ ᴛɪᴍᴇs. ᴛʜᴇsᴇ ɢʀᴏᴜᴘs ᴏғ ᴀɴᴄᴇsᴛᴏʀs, ʟɪᴋᴇ ᴏᴛʜᴇʀ sᴘᴇᴄɪᴇs, ʟɪᴠᴇᴅ ᴛʜᴇɪʀ ʙʀᴇs
ᴛʜᴇɴ ᴘʀᴇᴠᴀɪʟɪɴɢ ᴇɴᴠɪʀᴏɴᴍᴇɴᴛ ᴀɴᴅ ᴅᴇᴠᴇʟᴏᴘᴇᴅ ɢᴇɴᴇᴛɪᴄ ᴠᴀʀɪᴀᴛɪᴏɴ ᴛᴏ ʙᴇᴄᴏᴍᴇ ᴅɪғғᴇʀᴇɴᴛʟʏ ᴄᴏʟᴏᴜʀᴇᴛ ᴡɪᴛʜ sᴘᴇᴄɪғɪᴄ ғᴇᴀᴛᴜʀᴇs ᴏғ ᴅɪғғᴇʀᴇɴᴛ ɢᴇᴏɢʀᴀᴘʜɪᴄᴀʟ ʀᴇɢɪᴏɴs ɪɴ ᴍᴏᴅᴇʀɴ ᴛɪᴍᴇs.
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