Many of us return to work or school after spending time with relatives over the summer. Sometimes we may wonder how we are related to certain people (especially an annoying relative) with whom we seem to have nothing in common. But from an evolutionary perspective, we all have common ancestors if we go back far enough. This means that many features of our bodies go back thousands or even millions of years in our great family tree.
In biology, the term “homology” refers to the similarity of structure based on a common ancestor. Consider the similarities between the human hand, bat wing, and whale fin. They all have specific tasks, but the basic body plan of the bones remains the same. This differs from “similar” structures such as the wings of insects and birds. Although dragonfly wings and parrot wings perform a similar function, they arose independently from each other and do not have the same evolutionary origin. Here are five examples of ancient traits that you might be surprised to learn are still found in humans.
One step ahead
What makes us human? This question has plagued scientists and scientists for centuries. Today it seems relatively easy to tell who is human and who is not, but looking at the fossil record quickly becomes unclear. Comparison of the bone structures of the forelimbs of humans, dogs, birds and whales.
Does humanity begin with the origin of our own species, Homo sapiens, 300,000 years ago? Should we trace ancestors like “Lucy” (Afar Australopithecus) from East Africa more than three million years ago? Or even more so, that we are separated from other great apes?
Whichever line you draw in the sand to determine the birth of humanity, one thing is certain. The habitual bipedal gait, known as the “flat gait,” was one of our ancestors’ greatest strides. Almost every part of our skeleton is affected in the transition from crawling to walking upright. These adaptations include the alignment and size of the foot, hip, knee, leg, and spine bones. More importantly, we know from fossil turtles that the rapid increase in the size of our brain occurred shortly after we started walking upright.
This required changes in the pelvic region so that our big-brained babies could pass through enlarged birth canals. Our enlarged pelvis (sometimes called pubic bone enlargement) is a homologous feature shared by several early fossil lineages, as well as all fossils living today. Then our big brains fueled the explosion of art, culture and language, which are important concepts when considering what makes us human.
a hole in your head
You may be surprised to learn that in addition to your pupils sitting in their sockets, there are other large openings (known as fenestrae) in your skull. There is a window on either side of the human skull that connects us to our common ancestors who lived 300 million years ago. Animals with this single window in the skull are known as synapses. The word means “fused arches”, referring to the bony arch located below the opening in the skull behind each eye. Today, all mammals, including humans, are synapses (not reptiles and birds). Other synapses known from prehistoric times include the often misidentified Dimetrodon. An ancient reptile with a sail back is often mistaken for a dinosaur. However, due to its enlarged limbs and single temporal span, it instead belongs to a lineage sometimes called “monster-like reptiles”, although we prefer the more accurate term synapsids.
10 little fingers and 10 little feet
I’m typing this on my computer using my ten fingers (fingers and thumbs; the numbers are also for the toes, but mine doesn’t reach the keyboard). Known as the “five-toed limb,” this five-finger pattern on the human hand or foot is found in most amphibians, reptiles, birds, and mammals. But fish don’t have fingers or toes, so when did fingers first appear? A recent study by myself and my colleagues actually described the first fingers preserved in a fish’s fin.
We used powerful imaging techniques to look inside a 380 million-year-old fossil called Elpistostege from Quebec, Canada, to reveal the oldest fish fingers ever! Somewhat surprisingly, the first fish to develop fingers still had their fin rays around them, so these bones were not visible from the outside of the animal.
The earliest tetrapods (four-legged animals with spines that eventually moved from water to land) “experimented” with the number of toes found, sometimes with six, seven, or eight toes.
These first quadrupeds were probably still aquatic. But when quadrupeds became truly terrestrial, a five-toed limb appeared. Such an arrangement most likely appeared as a practical solution to reduce the load on the ground.
our teeth
Confused while brushing your teeth? Well, have you ever wondered how evolutionarily old your pearly whites are? In 2022, a group of paleontologists described fish fossil teeth isolated from Silurian rocks in China’s Guizhou Province. This remarkable discovery pushes the minimum age of teeth back 14 million years compared to previous discoveries. This means that our teeth date back 439 million years.
A very early jawed vertebrate, this new fish was named Qianodus duplicis and is known only for its individual, specialized teeth known as “curves”. A tooth helix is a peculiar array of teeth that twist together in a spiral (most famously found on the saw shark Helicoprion). However, the teeth of the Chinese jawfish share a number of features common to other modern jawed vertebrates, highlighting their importance for understanding the evolution of our own teeth grinders.
enlarge the spine
To “grow your spine” means to be bolder and more confident. The first animals to do so must have been brave enough to venture into the dangerous ancient seas 500 million years ago. First, these worm-like animals developed a “chordae,” a cartilaginous rod that runs along the back of the body. This allowed attachment of segmented muscle blocks and a long tail that extended beyond the anus. All animals with chordates are called chordates and include everything from ascites to gulls, with more than 65,000 living species.
To get an idea of the early chordates, we can look at animals like the scalpel (known today as Amphioxus or Branchiostoma). Lancers look like small primitive fish without fins. They swim by swinging their bodies from side to side. Then come those in which the head is well organized (cranial) and in adults the chord is replaced by a spine (vertebral). The spine consists of separate segmented bones (vertebrae) that are interconnected in a certain order.
We have some fascinating fossils found in rocks more than 500 million years old, representing the earliest known vertebrate specimens, such as Metaspriggina from Canada or Haikouichthys from China. So, whether it’s your big brain and wide rectus pelvis, single-hole skull and bony arch, fingers, toes, teeth, or spinal cord, we humans share many ancient traits in our bodies. So, according to poet and activist Maya Angelou, we should remember that perhaps we are more alike than we are alike.
Source: Port Altele
