Evolution wasn’t always thought of as we presently understand. Back in the days, fossil-based studies were de-linked from those centered on embryos. But a revolution has been brewing in the past few decades that seeks to combine these and other areas into a broader, holistic view on our journey over the past many millions of years.
The animal kingdom is host to immeasurable complexity and diversity. Starting its journey as a single cell, every organism grows on to become a unique creation, sharing a design from among the millions that are present here on earth. In a generalized distinction of either being a vertebrate or an arthropod, we still see huge differences within the constituent organisms.
Two processes are found to affect the way every creature is formed:
It’s development from the egg stage
Evolution traced back to its ancestors
Understanding these two processes in relation to each organism helps us in knowing the antecedent of the same. As an example, if we have to appreciate fully how 10 trillion cells that make up an average human body start their journey from a fertilized egg, we need to dig deep into our past and document our own biological development with great accuracy. It is only understandable that a few decades ago, a combined study of embryos, evolution, and ancestry was disbanded owing to the complexity. Scientists had expected to crack such cases for each individual species!
People within the field of Evolutionary biology worked without considering the influence genes have on the physical structure of animals. This was challenged and eventually changed by Stephen Jay Gould. A prevalent knowledge of the way genes controls the nature of all creatures was suddenly thrust upon the world of evolution studies, which eventually led to the birth of an entirely new field of interest, Evolutionary Developmental Biology. It lay at the interface of embryology and evolutionary biology. One of the first discoveries led by this new perspective was that all animals, right from the extinct dinosaurs to dogs to humans, all of us contain a common set of genes. This “Master Tool Kit” is behind the growth and functioning of different parts of our bodies.
Our journey over the past 6 million years
Upon further study of this genetic kit, we can uncover the pattern and route that ancient organisms had to take to reach their present form. One of the anomalies that we face is “if there are so many genes shared between us and other animals, how do such massive differences come about”. Evo-Devo (short for Evolutionary Developmental Biology) helps in the learning that much of the difference in physical attributes that we see are a result of genes, switching ON and OFF. What also influences changes to occur in the evolution of species across millions of years is the way genes are used and to what effect. The other part of the equation is handled by ‘regulatory DNA’, which determine the quantity, location, and timing of gene output. Most importantly, what Evo Devo teaches us all is the beauty in the process of how different species evolved to take their present forms. Tiny changes and tweaking over long periods of time that is ever so subtle when viewed individually converge to bring about this beautiful diversity that we are witness to.
Have you ever wondered when you watched a gorilla on TV or in person, “They’re almost humanlike”? The way they move around when they choose to be bipedal, they dexterity of hands, the emotions, its eerie similarity to our own species has surely left some uncomfortable unanswered questions. Well, as it turns out, we share almost all of our genes with say, chimpanzees. Yes, almost 99%.
Around 6 million years ago, it is believed that the ancestors of modern-day humans broke with the line of chimps, and during the course of this time, we grew up differently. So what explains our ability to walk upright, have smaller arms, smaller hands, speech and language, and a unique skull? Evo-Devo may answer some of these, as you’ll learn soon.
As noted a bit earlier, fossil remains point to the fact that the earliest ancestor of us did break away from a common species that also included ancestors of present-day apes, roughly 6 million years ago. In 1856, a Neanderthal fossil discovery in Germany shook the beliefs some held at that point, regarding the uniqueness of humans. The man responsible for rightly identifying the fossil, Thomas Huxley also was one of the pioneers in discussing the similarity between apes and humans. Although a timeline of 160,000 years has been arbitrarily kept as the time humans have existed in present form, more fossil discoveries are bound to push the date around a bit, maybe a few thousand years.
Before continuing further, the reader must understand the meanings of two oft-used words, ‘Homonid’ and ‘Hominin’. Homonid refers to both humans and African apes while the latter is specific to humans and our ancestry from the time we split from the apes and onwards. Of the 6 million years of Hominin evolution, we Homo sapiens occupy a tiny fraction in the timeline. (i.e. around 3%)
Looking back at our origins, we find many ‘chronospecies’, those which are initially slight variations of an existing species, that go on to become completely different over time. A conservative estimate shows that a minimum of 15-20 species predates us in the Hominin era. Sahelonthropus tchadensis happens to be the earliest Hominin discovered as yet. This hominin had a brain equal to that of a modern-day chimpanzee but the structure of the face and teeth was more like ours.
This series is influenced by chapter ‘A beautiful mind: The making of Homo sapiens’ of the book Endless forms most beautiful by Sean Carroll
If you would like to learn more about Evolutionary Developmental Biology you can head over to this link: https://evolution.berkeley.edu/evolibrary/article/evodevo_01