Humans Are the Only Mammals That Drink Another Animal’s Milk

Humans are unusual in that we routinely drink another species’ milk, especially in adulthood, but the statement “humans are the only mammals that drink another animal’s milk” needs a couple of important clarifications.

1. The claim is mostly cultural, not absolute biology

Among mammals in the wild, humans are the only species known to systematically obtain, store, and regularly consume the milk of other species as a normal, culturally transmitted behavior (milking cows, goats, sheep, etc.). This is what most scientists mean when they say humans are “unique” in this regard: it’s about sustained, organized use of other animals’ milk, not rare or opportunistic events.

2. Lactase persistence is the real evolutionary oddity

Biologically, the striking part is not that humans drink milk, but that many humans can digest it as adults.

• All mammalian infants produce the enzyme lactase to digest lactose, the main sugar in milk. In most mammals — including most humans — the gene for lactase is switched off after weaning, leading to lactose malabsorption.
• Multiple human populations independently evolved lactase persistence: genetic variants that keep lactase “on” into adulthood, strongly associated with histories of dairying and animal husbandry.​
• Globally, an estimated ~68% of humans have lactose malabsorption, meaning only a minority of adults can drink large amounts of unfermented milk without symptoms.​

So evolutionarily, the odd thing is that some adult humans can digest fresh milk easily, not that humans try to drink it.

3. Other animals can and do drink other species’ milk

Your excerpt already names some non-mammal examples, which are good counters to the absolutist claim:

• The red-billed oxpecker has been observed perching on the udders of impalas and actively sucking milk.
• Seagulls and sheathbills have been seen pilfering milk directly from the teats of elephant seals.​​

These are birds, not mammals, but they show that cross-species milk drinking is not uniquely human in the animal kingdom.

Among mammals:

• Many domestic and feral animals — cats, dogs, pigs, even some wild mammals in captivity — will readily drink cow’s milk or formula when offered by humans.
• These are usually considered opportunistic or human-mediated behaviors, not evolved, species-typical feeding strategies. That’s why scientists still say humans are unique “when it comes to mammals” drinking another species’ milk as a regular, culturally embedded practice.​​

4. A more accurate way to frame your paragraph

If you’re writing or revising content, you might phrase it like this (short and accurate):

Humans are the only mammals that systematically produce, collect, and consume the milk of other species into adulthood, thanks to dairying cultures and genetic mutations for lactase persistence. Although many mammals will drink another species’ milk when humans provide it, and some birds have been observed stealing milk from mammals in the wild, no other mammal relies on another species’ milk as a regular, culturally transmitted part of its adult diet.

This keeps the strong, attention-grabbing claim, but builds in the nuance your sources point to:

• Humans are behaviorally unique in how we use other animals’ milk.
• Genetically, only some human groups can digest it well as adults.
• Biologically, we are not the only animals ever to drink another species’ milk.

James  Eckburg

REDOX HEALTH