Evolutionary History of Female Homo Sapiens

Am I joking? No.

There’s not much material on this topic, because “evolution” and “male” have always been accepted as encompassing “human evolution”. Evolution scientists and amateurs alike still argue over “manly things” as determining what characterizes “being human”. Female Homo sapiens and her ancestors – female apes and archaic homo; Homo sapiens (early and late,) have been all but ignored, hanging around in the mists of time doing nothing important. Which is ironic, since “evolution” cannot occur without the production of successful offspring, which also must reproduce, etc. Sexual reproduction requires male and female. How difficult is that to grasp?

Sadly, topics which might become less “mysterious” in human evolution require understanding the evolution of the female body and brain, and in particular, the literal “growing” of new humans within the female body, and their introduction into the environment. But, reproduction is all but ignored by the “definers of species characteristics and boundaries”. The body of myth, mystery and rumor that surround the process of reproduction today, and in an evolutionary context, is ASTOUNDING.

Much is made of “difficult human birth” but curiosity as to “Why is this so?” generally begins with religious prejudice (God makes women suffer and die in childbirth because women are evil, inferior and weak) and ends in the scientific conclusion that “big-brain=big head” makes delivery difficult. (Gee whiz! Males don’t have to experience this phenomenon, so who cares?)

Gynecologists and other “specialists in human reproduction” care. It’s their job, but that doesn’t mean that there is much curiosity as to the evolution of human childbirth. The literature is jam-packed with the excruciating details of the “problem” of difficult childbirth and how to “deal with” the situation, but not much more than passing concern is directed to “the big picture” of human reproduction as a product of evolutionary process.

Modern women, especially in the U.S., are consumed by the pressure to “have children as proof of their femininity” and become obsessed by the “acquisition” of children in a social context. The changes that have taken place in society, which “allow” women to pursue lifestyles other than “domestic goddess” have produced a backlash, which is in essence a punishment. If women want a “career” they must compensate by also being a “super mother” – a demand something like having to tie one hand behind the back in a boxing match. Any difficulty in conception is taken personally – and any and all “fixes” by medical and technical intervention are required. This fear of bio-social incompetence extends throughout pregnancy, delivery and infant care, and indeed for the life of the child, until “Mom” dies. And in many families, Mom is still responsible for guiding her children’s behavior, but from the afterlife!

It is also astounding how little women know about their own bodies.

Where to start? Who were those female critters that are considered to be enough like us to be species that “led to” us, Homo sapiens. The important characteristic is bipedalism – standing and walking on two legs.

The following is highly simplified and covers a huge span of time – 4+ million years to the present. Needless to say, there is actually very little known that is “definite” due to the scarcity of fossil evidence and competing “arguments” as to interpretation of the evidence. __________________________________________________________________________________________

Pelves in anteroposterior  (front to back) (top row) and axial views (bottom row).

Fig. 2 Changes in female pelvis over 4.4 million year time span in 6 species. Chimpanzees are NOT our ancestors and are not in our evolutionary group. The apes shown are in our group, the Hominins. Note the birth canal first widens transversely (side to side),  but from Au. afarensis to H. sapiens only anteroposterior (front to back) deepening occurs (adapted from Bergé and Goularas40, Lovejoy et al41 and Simpson et al42, with permission). In Darwin’s day, only the specimens far right and far left were known.

From left to right: Chimpanzee (Pan troglodytes), (Anthropoid pelvis)

Ardi (Ardipithecusramidus, (ape species) 4.4 million years ago), (Anthropoid Pelvis)

Lucy (Australopithecus afarensis, (ape species) 3.2 million years ago), (Platypelloid Pelvis – rare in modern females and requires C-section)

Australopithecus africanus (ape species) (2.7 million years ago), (Becoming less Platypelloid as pelvis becomes more narrow)

Homo erectus (human species) (1.2 million years ago) (first “Gynecoid” Pelvis (?)

and Homo sapiens; there are between 2-4 “types” in modern females, according to the Caldwell-Malloy system, from 1933, with various “combination types” in individual women. (There are more human species, such as “Neanderthal” – not shown here.)

The Caldwell-Malloy classification of modern female pelvis types, 1933.

It is the modern Android “male” pelvis type that is  causing problems.

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Below: comparison of lower skeleton, Chimp, the Australopithecine apes and modern Homo sapiens. It’s easy to see that although we share a distant common ancestor with chimpanzees, we are not on the same evolutionary path. Our distinct path began with bipedal apes.

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This illustrates a comparison between an ape pelvis (called “Lucy” – (Australopithecus afarensis) although “she” may be a “he” – misidentified?) and Homo erectus, a “human” species over which there is much disagreement as to whether or not it is our direct ancestor. By the time of this H. erectus fossil pelvis, brain size had increased, and due to more advanced bipedalism, the pelvis is more narrow, producing a more “round” opening – what is today called a Gynecoid pelvis type. (It has been “assumed” that the gynecoid pelvis only appeared when Homo sapiens evolved) This is considered to be the pelvis that best provides for successful vaginal delivery.

Body shape, fat distribution, and body composition: Just as in males who developed a characteristic body shape, girls also respond to rising levels of estrogen. The lower half of the pelvis widens to provide a larger birth canal. This results in a widening of the hips and the characteristic hour glass shape of the female form. Fat tissues increases compared to males…especially in the breasts, hips, buttocks, thighs, upper arms and pubis. On average, by age 10 girls have 6% more body fat than boys. Source: Bacha, Saad, Gungor, Janosky, & Arslanian, 2002.

The “Android” (male) pelvis is the result of a “lack of” female development (widening of pelvis at puberty). The pelvis remains a “male type” pelvis which is obviously not adapted to pregnancy and birth! Vaginal delivery is difficult. A C-section is often required or chosen.

Why does the “Android” pelvis appear in modern Homo sapiens? Next post!

 

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