Evolutionary Anatomy – Walking Upright and Childbirth

A message from UCLA professor, Dr. Tony Friscia.
A message from UCLA professor, Dr. Tony Friscia.

In the last installment of our evolutionary anatomy series, we talked about vestigial structures, those hold-overs from our evolutionary ancestry. This time we’re going to talk about some specific adaptations of the human body, and how often seemingly unrelated aspects of our biology are linked.

The example I will use are those features of our skeleton that are adaptations to walking upright. Our ape-like ancestors mainly used all four limbs to support their body weight while walking, probably similar to the way modern chimpanzees move. The transition to upright walking in the hominid lineage was accompanied by many anatomical changes that made our unique form of locomotion more efficient:

A figure showing the curvatures of the vertebral column (from eOrthopod).
A figure showing the curvatures of the vertebral column (from eOrthopod).

The curvatures in our lower backs and necks keep the majority of our weight over our hips and legs. Gorilla and chimps have a spinal curvature that is concave forward along the entire length – like a c-shape (also called a kyphosis). This is fine for them, because all the limbs are supporting their weight. We have the same shape to our vertebral column when we are born, but as we learn to walk, we develop the reverse curvatures (lordoses) in the lumbar (lower back) and cervical (neck) regions. So, although we say we walk with a straight back, it actually has 4 curvatures in it (2 in each direction) which give us the appearance of a straight back.

A figure showing the shape of the pelvis in a chimpanzee (left) and a human (right). In the center is the pelvis of one of our earliest upright-walking ancestors (from TalkOrigins).
A figure showing the shape of the pelvis in a chimpanzee (left) and a human (right). In the center is the pelvis of one of our earliest upright-walking ancestors (from TalkOrigins).

Our pelves are short, along with the shortened lumbar region of our vertebral column (with it’s lordosis). This is another feature that enhances stability. In apes, the pelvis and lumbar regions are very long, and the ilium (the ‘hip bone’ you put your hands on when they are on your hips) extends far up the vertebral column, almost to the rib cage. The shortened pelvis of human acts like a bowl for the abdominal organs, and the ilia are flared laterally, giving better mechanical advantage to the muscles that stop us from falling over when we walk (the main one being the gluteus medius).

A figure showing the Q-angle (from Physiopedia).
A figure showing the Q-angle (from Physiopedia).

Our femurs slant inward from the hips to the knees making all humans a little knock-kneed (the angle they form at the knee is called the Q-angle). This keeps the knees under the weight of the torso, which prevents the body from swaying side-to-side while walking. This slant is so distinctive that some hominid fossils preserve only the distal end of the femur and from this we can tell that they walked upright.

There are a number of other adaptations to walking upright – the orientation of the foramen magnum (down, not back), the loss of the opposable big toe, the lack of curvature in the fingers and toes, etc. But there was a cost to these adaptations to walking upright – many of these features often had direct implications for childbirth.

You don’t need to tell any mother (and most fathers) than human childbirth is painful. For most other mammals this is not the case. Think of a mother gazelle on the plains of Africa – it stands for the whole birthing process, and barely seems to notice that it dropped a newborn. The reason for this difference is that rearrangment of the pelvis. The pelvic outlet (the bony ring of the pelvis that limits the size of the birth canal) has been narrowed in humans. It is now just about as wide as a newborn’s head. This makes for a painful childbirth process. In other mammals, the pelvic outlet is much larger relative to the newborn, making their childbirth far less traumatic.

pelvis
A figure showing the relative size of the pelvic outlet and a newborn’s head, chimpanzee on the left, human on right, and early upright hominid in the center (from Evolution and the Prehistory of Man)

This has important implications for child rearing as well. Humans are born altricial – poorly developed. A newborn human is relatively helpless. It can’t move well on its own, can’t obtain food, and can’t communicate well. (Some might argue that this helplessness continues well into their teenage years…) A big reason for this is that humans can’t be born too developed, especially with a much larger brain, because of that limitation of the birth canal size. In contrast, think back to that baby gazelle. Soon after it’s born it can get around on it’s own, and even find it’s own food (although mother’s milk provides the main part of nutrition for a while). This is called precocial development.

A question you should ask yourself after hearing about these trade-offs is why our hominid ancestors took to walking upright in the first place. There are actually a number of theories about this, ranging from freeing the hands to carry objects from place to place, to being able to see over talk savanna grass. The reality is that there were probably numerous reasons why this transition happened, so no one theory can offer an explanation.

Next time we discuss one of the most bizarre quirks of human anatomy that can only be explained through evolution.

The HAPS Video Premiere!

A message from the ComCom
A message from the Communications Committee.

The HAPS video was released this week and it is a great snapshot of all that HAPS can do for its members.  Using interviews of HAPS members to provide the narrative, the video showcases the ways in which people’s lives have improved because of their involvement in HAPS.  From promotions to new positions to getting questions answered on a daily basis, HAPS membership harnesses the power of our members to lift everyone to new heights.

HAPS is well known for its Annual Conference.  Every year a growing number of people come together to share four days of update speakers and workshops, as well as very productive time with exhibitors who share the latest in teaching resources and technology.  And the HAPS Annual is a great conference to attend solo – everyone is happy to meet you, share what they know, and also maybe buy you a drink in the evening. People quickly go from acquaintances to friends.  The HAPS Annual is great, and the more you are able to attend, the better they get.

But there is so much more to HAPS that improves the lives of members all year round.  The HAPS-L discussion group is an incredibly active email discussion group that solves real world problems for HAPS members on a daily basis.  The HAPS “listserv” began in 1998 and has now matured into an online discussion group with a Google Group backend, while retaining its old school name.  

HAPS scholarships and grants make previously unattainable travel or research plans possible.  Many cover expenses to attend the Annual Conference, but others reward using technology in the classroom or just plain old excellent teaching.  

And finally, among most important benefits of being a HAPS member is the career advancement that comes from being part of the HAPS community.  HAPS has an extremely inclusive path to leadership and the video highlights both the ability to join leadership and the benefits that come from it.  

We invite you to watch the video and share it, especially with your A&P friends who are not HAPS members yet.

Journal of a New HAPster: Shani Golovay

HAPS is a society focused on the teaching and learning anatomy and physiology.  We’re always looking for new members to join the community.  Check out some thoughts from new HAPSter, Shani Golovay.  

Meet Shani Golovay, a new HAPSter.
Meet Shani Golovay, a new HAPSter.

“But I have a degree in Plant Biology.  I don’t really know anything about Human Physiology, except what I teach in General Biology.”  And this started my journey to HAPS.

I found the HAPS website to be helpful as soon as I joined. I hunted down the Course Guidelines  and Learning Outcomes right away because I needed a syllabus and some ideas on how much content to cover in the course.  Then I found the Guided Inquiry Activities by Murray Jensen. I tried out the activities with my students right away- and they loved them.  I was starting to feel like I could teach this class after all, and I felt like I had a giant community of people helping me that I didn’t even know.

I learn more from the HAPS email listserv then I do from most professional journals I receive.  I was amazed how open and helpful everyone was with each other.  I look forward to the listserv conversations and I learn so much. It was so refreshing to find a whole group of people willing to share their expertise with those of us way out of our area. If I emailed someone a question, they would explain things and even send me documents or ideas.  I am much more confident about teaching this Human Physiology class because of HAPS.  I think Human Physiology may be my new favorite class to teach because of all the awesome ideas I get from other HAPSters.  I was telling my colleagues about this society where everyone was nice and actually helpful and wanted to share ideas about teaching and everyone was impressed and a bit jealous that I had found such a group.

I am just so grateful to find a community of people where those with experience and lots of talent are willing to help those of us just starting out with these classes.  We need each other because we can’t talk about this sort of stuff over dinner except with each other, right?

The best part for me was the annual meeting, but that is another blog post…..

Why I Decided to View a Dissection

A message from Erin O'Loughlin, honorary HAPSter since she was 3 years old.
A message from Erin O’Loughlin, honorary HAPSter since she was 3 years old.

My name is Erin O’Loughlin, and despite the fact that I am not a HAPS member, I have been attending its conferences since I was three years old. As the daughter of a former HAPS president, I have been granted many incredible opportunities in the realm of science, including the chance to view and assist in the dissection of a cadaver. I hope to interest and enlighten readers by presenting information about the experience through the eyes of a student.

When daydreaming about their summers, most high school students envision themselves lying on the beach, dancing at a concert, or sleeping under the stars; not so much standing over a cadaver. But instead of swimming at the pool or barbecuing, I spent more than 30 hours observing and assisting in a dissection during my vacation. The cold, pungent environment of a lab is no substitute for a warm summer day; however, the experience was well worth my time.

Erin with her mama, HAPS President Emeritus Valerie Dean-O'Loughlin, at her first HAPS Annual Conference in Maui.
Erin with her mama (HAPS President Emeritus Valerie Dean-O’Loughlin) at her first HAPS Annual Conference in Maui.

In a word, my summer break was unusual, and many people were curious as to why I decided to spend it with a cadaver. My reasoning is as follows: Although coming face to face with a deceased human being is an intimidating task, I could not pass up the incredible opportunity to expand my knowledge of anatomy and better understand my own body and its functions at such a young age.

For most of my life, I was unaware of many of the anatomic complexities supporting my existence every second of every day of every year. Being able to visualize and understand the human body is an incredible gift and I encourage any student who is presented with the opportunity to view or partake in a dissection to take full advantage of it.

And to those who spend a lifetime in the presence of cadavers, offering high school students more opportunities to view a human body is a fantastic way to encourage a respect for anatomy and educate a number of individuals who will undoubtedly benefit from the knowledge.

I would also like to thank two incredible HAPS members, Keely Cassidy and Barbie Klein, for their patience, expertise, and generosity in allowing me to observe and assist in their dissections.