See Midrash Rabba Besraishis 22:7

וַיֹּאמֶר קַיִן אֶל הֶבֶל אָחִיו וַיְהִי בִּהְיוֹתָם וגו' (בראשית ד, ח), עַל מָה הָיוּ מִדַּיְּנִים, אָמְרוּ בּוֹאוּ וְנַחֲלֹק אֶת הָעוֹלָם, **אֶחָד נָטַל הַקַּרְקָעוֹת וְאֶחָד נָטַל אֶת הַמִּטַּלְטְלִין**, 


“And Cain spoke to Abel his brother, and it came to pass when they were in the field…” (Genesis 4:8) What were they arguing about? They said: come let’s divide up the world, **one will take the land and one will take the moveable property**. 


By this division Hevel became the sole owner of all the sheep in the world.