Planet Earth is host to a remarkably diverse range of organisms. The variety that exists between different life forms, while very real, may at times be superficial in that some scientists argue whether the differences between humans and other mammals are really so great.
Nonetheless, the uniqueness of at least a few traits that set humans aside from other organisms cannot be so easily debated. Even while certain other species display the use of tools, as well as the rudiments of what were once considered cultural concepts exclusive to humans, no other species on Earth has developed such capabilities to the advanced degree that we have.
Herein lies a great mystery. How is it that humans could have developed so differently--and so much--from other species, enough so that we eventually emerged as the dominant force on this planet?
In 1980, one study carried out at the MRC Laboratory of Molecular Biology in England took its analysis of this question to the microscopic level, looking at what clues might be found in human genetic material.
Appearing in Nature, the paper, titled “Distinctive sequence of human mitochondrial ribosomal RNA genes” by I. C. Eperon, S. Anderson and D. P. Nierlich, called human mitochondria a “radical departure” from that of other organisms,” a conclusion with rather novel implications in terms of the mysterious origins of humanity.
“The nucleotide sequence spanning the ribosomal RNA (rRNA) genes of cloned human mitochondrial DNA reveals an extremely compact genome organization,” the study’s authors wrote in the paper’s abstract, “wherein the putative tRNA genes are probably ‘butt-jointed’ around the two rRNA genes.”
“The sequences of the rRNA genes are significantly homologous in some regions to eukaryotic and prokaryotic sequences, but distinctive” they added, noting that “the tRNA genes also have unusual nucleotide sequences.”
For those among us who aren’t molecular biologists, what the study’s authors present here may seem convoluted. However, the final line of the study’s abstract brought into rather stark focus what the authors interpreted this all to mean.
“It seems that human mitochondria did not originate from recognizable relatives of present-day organisms,” they concluded. But if not “recognizable” ancestors to the kinds of organisms present on Earth today, then what kinds of organisms had they been talking about?
Inherent to the structure of all living cells in higher organisms are mitochondria. These organelles are the areas within cells where functions like respiration and generation of energy take place. Since mitochondria possess their own unique genetic material, scientists have suggested that they might represent the aftermath of an invasion that occurred in the ancient world, in which bacteria stormed the cells of ancient organisms and took up residence within them. The question is, what kind of bacteria might have caused the “radically different” mitochondria found today in modern humans?
The study by Eperon, et al, raises several questions. One has to do with the undeniably unique traits that humans appear to possess when compared with other species on our planet; might it be the case that mitochondria is actually at the root of these distinctions? Another question has to do with whether mitochondrial changes occurring in ancient organisms might have spearheaded the evolutionary trends that eventually led to our ancient hominid ancestors and, eventually, resulted in Homo sapiens.
Other theories exist as well, which give consideration to speculative ideas about the appearance of novel kinds of bacteria from unusual places—possibly even from space—which might have arrived on Earth after being carried over great distances on cosmic debris. This theory that novel kinds of bacteria or viruses could arrive from space, while challenged by most in the scientific community, formed the basis of astronomer Fred Hoyle and his colleague Chandra Wickramasinghe's theory of panspermia or “Cosmic Ancestry,” which entails that all life on Earth may actually have origins in outer space.
Even if ready-made bacteria had not been brought to Earth on cosmic debris, many astrobiologists have entertained the notion that the building blocks of life might have been brought to Earth from elsewhere long ago, having eventually formed into complex proteins over time, and eventually giving rise to simple life forms that evolved over the eons into the biodiversity we see on our planet today.
Is it also possible that some of the evolutionary mysteries about human origins could have been influenced by such cosmic sources at some point in the distant past? Such questions raise a number of possibilities about the likelihood of life existing elsewhere in the cosmos, and whether or not it might differ entirely from what we have come to expect of life on Earth.
In fact, if Earth organisms actually do have their roots in outer space, any prospective aliens out there might not only resemble us, but they might actually be cousins of ours, in a sense. In other words, we Earthlings might be far more “alien” than we even realize.