[thedoc (OP)]

Mohammed Laher  asked the Naked Scientists:
   Good day. A Cow eats  grass and drinks water and producers pure wholesome milk and it resides  in the body close to the  the intestines and yet the smell does not penetrate it. Man with all his achievements of being able to fly into space cannot produce fresh milk with these gradients, it has been attempted since 1921 yet  we still await. Makes you think doesn't it? Is it a fluke of nature?

 
What do you think?

[chris]

Most people think that cows eat grass. That's not actually true. In fact, cows exist on a diet of microbes that they feed on grass. The proteins and lipids produced by those bugs are chemically dismantled in the intestine of the cow and transported via the bloodstream to the mammary glands - udders - where the glandular tissue extracts from the blood the relevant raw materials. These are assembled, using the recipe dictated in the cow's DNA code, into the composition corresponding to the mixture we call milk. This is achieved by secreting the chemicals, at the right concentration, across the membranes of the cells that line the milk ducts. In this way the milk composition is accurately controlled. Few other chemicals are able to make it across to taint the milk. That said, this is not exclusively true and certain substances, particularly fat-soluble ones and small proteins, as well as some microorganisms can also cross into the milk.

[Bored chemist]

" Man with all his achievements of being able to fly into space cannot produce fresh milk with these gradients, it has been attempted since 1921"
Roughly a hundred years to get it to work, compared to mammals which had billions of years.

[chris]

compared to mammals which had billions of years

Just to clarify, mammals have been around for about 100-200 million years. Life as a whole has been evolving for about 4 billion years (4.1 billion years, if recent findings from the Jack Hills conglomerate in Western Australia can be reproduced)