0_Apprentice
Do you happen to know any twins?
1_Wizard
I have some friends who are fraternal twins - one a boy and one a girl
0_Apprentice
What is the difference between fraternal and identical?
1_Wizard
Identical twins develop from one zygote, while fraternal develop from two different eggs
0_Apprentice
So I guess then boy/girl twins are always fraternal.
1_Wizard
That would be correct.  Each egg has its own sperm cell
0_Apprentice
It's very interesting how twins seem to run in certain families - is it hereditary?
1_Wizard
It seems to be - the yoruba people have the highest rate of twins in the world - 90 to 100 twins per 1000 live births
0_Apprentice
Wow - that is amazing - perhaps it also gives them a way to re-populate faster if there is some other kind of environmental reason
1_Wizard
Yes it is believed it might because they have a high consumption of a type of yam which stimulates eggs to be released from each ovary