Re: Becoming altricial/bipedal

Alex Duncan (
2 Oct 1995 12:29:04 GMT

In article <> Paul Crowley, writes:

>The immediate disadvantages of becoming altricial would appear to be
>catastrophic. The hominid mother, while foraging, must either awkwardly
>hold the infant or put it on the ground. If a predator approaches, she
>must locate it, pick it up and carry it in her arms while trying to run
>or climb a tree. On the other hand, the maternal chimp with her baby
>clinging to her can instantly flee and has unimpeded use of all her limbs
>for running, climbing as well as for foraging.

You're making lots of unwarranted assumptions here:

1) Why do you think early hominids would have been constantly
encountering predators? Humans occupy a diurnal foraging niche, which
means we're active at a time when most big predators like lions and
hyenas (but not crocodiles) are resting.

2) You seem to have forgotten that humans (and presumably our ancestors)
are the most social primates. If you were a lion would you attack a
GROUP of large primates wielding branches and stones? I think not.

>This amazing change had one cause: the development of the bipedal foot.
>Laetoli tells us it took place before 3.6mya.
>This foot is unable to hold on either to the mother or to the branches of
>a tree. At every stage of its development, its selective disadvantages
>would appear to be overwhelming. Those infants with a weaker grasp in
>this limb would be at much greater risk of predation. They would be less
>able to climb out to peripheral branches, and be more likely to fall, or
>be dropped on the ground. Their mothers would suffer constant extra
>burdens and would be less capable of providing for themselves and their

You seem to know a lot more about the Laetoli footprints than most people
who have examined them first hand. With a few exceptions, the consensus
in the anthropological community is that some bipedal creature made them,
and that you can't tell much about pedal anatomy from them. I'm glad
you've been able to resolve these issues. The pedal remains from Hadar
and from Sterkfontein are clearly from an animal that was capable of
substantial grasping behavior with the foot.

>Furthermore, at the same time the anatomy of both infants and mothers
>would have been undergoing massive changes. They were becoming bipedal
>with, essentially, the wrong equipment: short legs, a wrong musculature,
>a weak spine, and the many other defects which Elaine Morgan has
>described so well. With these handicaps, the early hominid mother would
>have found it difficult just to carry the infant; running or climbing
>with it must have been nearly impossible for her. And it is fair to
>assume that the early hominid infant took as long as home sapiens, or
>even longer, to learn to walk.

I have previously accused you of ignorance. The paragraph above
demonstrates the accuracy of my assertion. Have you read anything about
hominids other than Morgan's work?

>Consequently transitional hominids could not possibly have been living
>in trees, nor could they have had any significant contact with them.
>A forest or mosaic environment must be ruled out.

Most paleoanthropologists (who have actually studied the material in
question) would disagree quite strongly with you on this point. The fact
that most of the earliest hominids are found in depositional contexts
that indicate forested or mosaic environments also contributes to the
sense that you don't know what you're talking about.

>Such creatures would be lucky to survive a single night on the ground
>in the open. Some safe refuge must be proposed.

Trees? Would a PRIMATE climb a tree? Nah.....

nonsense deleted

>Heat dissipation would be a serious problem in the middle of the day.
>The hominids would have taken to the water to keep cool. In time the
>species would have put on extra fat to provide buoyancy, and lost its
>fur, leaving hair solely on the head for protection against the sun.

Ever heard of sweating?

>The ability to cling to the mother has such a high survival value that
>its disappearance is still hard to explain.

Unless your mother happens to be a biped whose hands are free.

nonsense deleted

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086