Milk Lines, Mammals and Creation

In February 2011 the Television Program “Embarrassing Bodies” presented a segment on a “Third Nipple“. This draws attention to an intriguing similarity between the human body and other mammals.

All mammals, including humans have  two “milk lines”.

The milk lines are two parallel lines, formed by thickenings of the epidermis (the mammary ridge) along the ventral surface of mammals of both sexes. They extend from the upper limbs (arms) to the lower limbs (legs) and are developed in the embryo. They give rise to the mammary glands and nipples but are otherwise usually not visible in the adult.” 1

In humans these lines begin to develop in the first 8 to 9 weeks of pregnancy and then, apart from the top two, go dormant. In other mammals the number that remain active is related to the number of young generally given birth to by that species.

The following table lists the number and position of visible glands normally found in a range of mammals: 2

Species [23] Anterior
Goat, sheep, horse
guinea pig
0 0 2 2
Cattle 0 0 4 4
Cat 2 2 4 8
Dog [24] 4 2 2 or 4 8 or 10
Mouse 6 0 4 10
Rat 6 2 4 12
Pig 6 6 6 18
Elephants, primates 2 0 0 2

The remarkable similarity of these milk lines between humans and other mammals raises significant questions for Creationists.

If humans were created on day six of the Biblical Creation week as a special act by God, why do we have milk lines? Why do they develop early in pregnancy and then go dormant in different locations for different mammals including humans? Why are they generally found in both male and female of each species?


Vestigial refers to the presence of body parts or behaviors which have little or no practical use. These are most often considered to be “left behind” as a result of the evolutionary process. Here is an example of vestigiality in whales from Talk Origins:

“Modern whales often retain rod-like vestiges of pelvic bones, femora, and tibiae, all embedded within the musculature of their body walls. These bones are more pronounced in earlier species and less pronounced in later species. As the example of Basilosaurus shows, whales of intermediate age have intermediate-sized vestigial pelves and rear limb bones.

Whales also retain a number of vestigial structures in their organs of sensation. Modern whales have only vestigial olfactory nerves. Furthermore, in modern whales the auditory meatus (the exterior opening of the ear canal) is closed. In many, it is merely the size of a thin piece of string, about 1 mm in diameter, and often pinched off about midway. All whales have a number of small muscles devoted to nonexistent external ears, which are apparently a vestige of a time when they were able to move their ears – a behavior typically used by land animals for directional hearing.

The diaphragm in whales is vestigial and has very little muscle. Whales use the outward movement of the ribs to fill their lungs with air. Finally, Gould (1983) reported several occurrences of captured sperm whales with visible, protruding hind limbs. Similarly, dolphins have been spotted with tiny pelvic fins, although they probably were not supported by limb bones as in those rare sperm whales. And some whales, such as belugas, possess rudimentary ear pinnae – a feature that can serve no purpose in an animal with no external ear and that can reduce the animal’s swimming efficiency by increasing hydrodynamic drag while swimming.”

Now what about the human milk lines? Are they left over from a shared evolutionary history and relatedness to other mammals? If we say “no”, then we are hard pressed not only to explain their existence, but why God would create in both male and female parts which appear to have no purpose. Clearly, the lower sections of milk line within humans most likely represents a vestigial part of the body.

It is of interest to note that in the UK up to 1 in 18 people will have at least one extra nipple, so even though the continuation of the lines below the breast is vestigial and serves no purpose, its evolutionary place in the human body is by no means over. It lingers on!

If man was created by a Divine act on day 6 of a Creation week, there is no possible reason for anything but the two mammary glands, and even that is only necessary on the female!

Taken alone this may not be a conclusive argument, but in the context of other evidences for the relatedness of all life through evolution, it provides a powerful pointer to the relatedness of humans to other mammals.

Copyright:  01. 05. 2011

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