The cow bos primigenius (which is bred for meat and milk) has a smaller brain and

they arose by artificial selection. this is because to obtain animal with this traits, there is an interference by humans. i.e these organisms do not result from natural selection. the process of obtaining organisms with increased number of desirable traits is referred to as hybrid vigor. in this process an animal with certain desirable trait is bred with another animal with another different type of desirable trait. the resulting offspring will have both desirable traits. 

horse latitudes (B) hope this helps