Necessary? No. Useful? Absolutely. The ability to digest milk and mlik products into adulthood opens up new food sources, and new food sources tend to increase ones probability of surviving to adulthood and passing on genes to next generation. The ability to digest milk is certainly not universal among humans, and those who can not digest milk products in adulthood simply eat alternatives.
You may had learned at some point that increasing temperature increases solubility of solutes in solvents. This is true for solids, but not for gases. As temperatures of water decreases, the easier it is for gases to dissolve into them. The water were icefish live is very cold, so oxygen concentration is high enough for their need. This means there is no longer evolutionary pressure to maintain the ability to produce functional hemoglobin. Additionally, making hemoglobin is metabolically expensive, and it would be an advantage to invest that energy into something more useful for the organism.
Christine M.
The drinking of cows' milk is a modern convenience food. Drinking cows' milk or goats' milk can add necessary nutrients to the diet for some but not all. Many adults from all cultures and some children are lactose intolerant, meaning they do not produce lactulose the enzyyme to digest the lactose in milk. They cannot ingest the nutrients and become ill from ingesting milk or milk products. Prior to modern animal husbandry, Pasterurization and refrigeration liquid milk was rarely drunk . It posed too many dangerous complications, tuberculosis, gastroenteritis, severe diarrhea for example. Cheese was invented as a way to preserve the milk fat from milk and in previous years did not require refrigeration. The drinking of milk came after the invention of disinfectants used to clean udders, modern dairy milking machines, Pasteurization and household refrigeration. Prior to these, milk was rarely drunk. People who are able digest milk and its products do have another source of nutrients , but they are not necessary for humans. There is a wise saying,cows are not a baby's mother unless they are cows, meaning that cows milk or goats milk are a valuable asset but not necessary. There are many other sources of those nutrients, proteins, fats and minerals available to the diet. A good source of information comes from cook books. Look up various common dishes from different cultures and note which ones include a lot of cheeses or milk in them. Not all do, for example how many dishes include cheese as an ingredient in Chinese cuisine? How about Pacific Islanders cuisine? Not many. Two reasons, the areas are not condusive to raising cows and a large number of the population are lactose intolerant.02/06/20