Coexisting

We know that our own species lived alongside other hominins, but what would those interactions have looked like? Would H. sapiens have recognized other hominins as different from them or would they have looked and seen a creature so similar to themselves that differences could be ignored? We can go through some scenarios and the scientific evidence for these meetings to picture it.

Homo Naledi

Recent evidence (as H. naledi was only discovered in 2015) suggests that H. naledi lived at the same time as our own species. It is thought that the species survived until around 236,000 years ago. Whether or not our species interacted with them has yet to be proven. 

Neandertals

We know that anatomically modern humans interacted with neandertals because of DNA. Many of us have neandertal DNA due to cross-breeding. The meeting between these two groups was inevitable as H. sapiens moved into Europe. As the last two remaining hominins the meeting of the two groups would have meant competition for resources, but the DNA evidence shows that the two were capable of living together and didn’t completely see one another as outsiders. 

It’s easy to see why. These renditions created by artist Tom Björkland are based on neandertal morphology seen in fossils and show just how human they would have looked. It is likely that the early members of our species wouldn’t have seen any difference between neandertals and themselves.

In Summary: The Ardipithecus ramidus Skull and its Implications for Hominid Origins

Ardipithecus ramidus is one of our earliest relatives and one of our best indicators for how humans and chimps diverged from our common ancestor. After the discovery of Ar. ramidus at Aramis Ethiopia in 1994 it took until 2009 for scientists to publish the findings. The skeleton of Ar. ramidus has both ape-like and human-like features and gives us a picture of how us hominids got some of our human traits. In the article ‘The Ardipithecus ramidus Skull and its Implications for Hominid Origins’(https://science-sciencemag-org.proxy006.nclive.org/content/326/5949/68/tab-pdf)  the traits of the skull are focused on in order to highlight the evolutionary process. The features of the skull in general can be divided into three sections: the basicranial structure, the face and vault, and the cranium. These parts can show the unique features of Ar. ramidus. 

Basicranial Structure

The basicranial structure is one of the more important cranial features to consider when looking at the evolution of our species. This is where we examine one of my favorite skull features: the foramen magnum. The article discusses this feature in a rather defensive manner as the original statements regarding the foramen magnum were contested. They note the anterior position of the foramen magnum that suggests bipedalism in Ar. ramidus is within the hominin range of the basi-ovale distance. 

Face and Vault

The face of Ar. ramidus shows us another phase in the evolution of hominins. Compared to chimps the species has a very short face with a small prognathism. The article also focuses in on the fossilized teeth. Both the molars and other teeth give indications of more derived traits. The article brings attention to the large molars for chewing harsher foods as this trait is also seen in robust Australopithecus. The facial bones also show less sexual dimorphism in this species as opposed to apes. 

Cranium

The most important feature of the Ar. ramidus cranium is it’s capacity. The estimated brain size of the species is 300-35cc. The implications of brain size has been highly contested within the scientific community but in the earliest hominins it is particularly interesting to see where we began to increase in brain size. For a hominin Ar. ramidus has an incredibly small brain, but shows evidence of cranial base flexion. This could be an evolutionary link with our bonobo relatives or a derived trait that Australopithecus would later share. 

This article makes an excellent point of how important skull morphology is to the study of human evolution. The efforts of Suwa et al. to reconfigure the hundreds of pieces of Ar. ramidus fossils in order to examine these traits has been hugely influential in the field of human evolution.

(All images are credited to the original article)

How do we know if a creature was bipedal?

One of the most amazing and useful adaptations that humans have is bipedalism. Our ancestors developed this adaptation as a necessity, possibly because of thinning forests or the need to carry their young. But how can we tell that one of these creatures walked on two feet? There are many ways to tell from the shape of bones, to their length. For me the most interesting difference that bipedalism makes is strangely enough in the skull. The foramen magnum is the hole at the base of the skull through which the spinal cord connects to the brain. In quadrupedal vertebrates this hole is at the back of the skull. This is true for our primate relatives as they walk on all fours most of the time. However, in humans the foramen magnum is at the base of the skull. This is due to our spine being vertical as opposed to horizontal. When we look at our hominin relatives we can see the shift from a horizontal spinal position to a vertical one.

If humans came from chimps, why are there still chimps?

I decided to start this post with some personal history to emphasize that I am in no way making fun of this question. I grew up in a traditional Christian home and church that was very against the idea that humans evolved at all. As middle schoolers my peers and I took a class that taught us to “defend our faith” and this question is what we were told to ask when someone brought up evolution. It wasn’t until my 10th grade biology course that I learned that’s not how human evolution took place. After that I grew more interested in the subject, but didn’t really understand our evolutionary history until I began taking biological anthropology courses. I want this post to be a simple informative crash course on human evolution and why the above question is misinformed. In order to do that we need to address a few questions.

How are we related to apes?

https://humanorigins.si.edu/evidence/genetics

The easiest way to understand our relation to apes is to look at our family tree. The primate family tree began roughly 65 million years ago and includes us as well as apes, monkeys, and prosimians. Humans fall in the same category as the great apes, and as shown in the image our last common ancestor with modern chimps lived 8-6 mya. This is the simple answer to our question: no, humans didn’t evolve from chimps, but we do share a common ancestor. 

Human evolution after the split from our chimp-like ancestor wasn’t a direct line to modern humans either. Our closest ancestors and ourselves are referred to as hominins.

https://humanorigins.si.edu/evidence/human-family-tree

This image shows our our own genus as well as our closest relatives. These ancient fossilized hominins help to show us how we’ve evolved from the common ancestor shared with chimps. We can see how and when our ancestors gained some of the traits that make us uniquely human.

How are we different from apes?

Despite our common ancestors and similar DNA humans and our closest living relatives, the apes, have some distinct differences. The first of these major differences was bipedalism which developed between 8-6 mya for humans. The ability to walk upright would have given our ancestors the advantage of speed, sight, and the ability to carry things over greater distances. The second development that helped us differ from apes were tools. While we know that some apes, such as chimps, use tools humans continuously reshaped and redefined tools which gave us an edge in the wild.

Another advantage humans have over our ape relatives is brain size. Human brains average at around 1260cc while chimps brains are between 360-480cc. Our earliest ancestors had much smaller, more chimp like brains.

https://askananthropologist.asu.edu/stories/babies-birth-and-brains

Why aren’t apes evolving?

Short answer: they are, and so are we! Evolution isn’t always a visible process, but it is always happening. In both humans and apes each generation has a new unique set of genes as different individuals mate and share genetic material. There is also visible evolution. For apes, in more recent years, this is unfortunately caused by climate change. For humans it is more subtle but just within the past hundred years the average person has gotten significantly taller. Both us and our living relatives will continue to evolve into the future.

Evolution isn’t a simple or straightforward process, but it is important to understand where we came from and to have a working knowledge of the science of human evolution. I hope this provides at least a jumping off point.