All animal eyes and eye-spots contain opsin, a protein that captures light. This is the compound eye of Antarctic krill. Photo by Gerd Alberti and Uwe Kills
Gaze deep into any animal eye and you will find opsin, the protein through which we see the world. Every ray of light that you perceive was caught by an opsin first. Without opsin there would be no blue, no red, no green. The entire visible spectrum would be.. just another spectrum.
But opsins haven’t always been the sensitive light detectors that they are today. There is one critter, obscure and small, carries opsins that are blind to light. These opsins aren’t broken, like they are in some cave dwelling species. They never worked to begin with. They are the relics of a distant past, a time in which our ancestors still dwelt in darkness.
Opsin is a member of large family of detector proteins, called the ‘G-protein coupled receptors’ (GPCRs). Like a needle and thread, all GPCRs wind themselves through the outer membrane of the cell seven times. Halfway between cell and outside world, these tiny sensors are perfectly positioned to monitor the surroundings of the cell. Most GPCRs detect the presence of certain molecules. When a certain hormone or neurotransmitter docks their outward facing side they become activated and release signalling molecules on the inside of the cell. But opsin is different. It doesn’t bind molecules physically. Instead, it senses the presence of a more delicate and ephemeral particle: the photon itself, the particles (and waves) that light is made of.
Opsins trap photons with a small molecule in the heart of their architecture, called retinal. In its resting state retinal has a bent and twisted tail. But as soon as light strikes retinal, its tail unbends. This molecular stretching exercise forces the opsin to change shape as well. The opsin is now activated and eventually will cause a nearby nerve to fire, which will relay its message to the brain: light!.
Opsins lie embedded in the outer membrane of the cell, where retinal (grey molecule in the middle) can trap photons.
Scientists have known about the existence of opsins (or rhodopsin, as the retinal-bound form is also called) ever since the 19th century. The German physiologists Wilhelm Kühne and Franz Boll first discovered and isolated rhodopsin in 1876 and 1878, respectively. It took another fifty years before the American biochemist would George Wald discover retinal in 1933.
Since these early days of visual chemistry, scientists have uncovered opsin’s light detecting tricks and resolved its molecular structure in atomic detail. It is safe to say that the physical and chemical nature of opsin are better understood than its history. Many questions about the evolution of opsins have remained unanswered in the past 130 years of opsin research. In which of our many ancestors did opsins evolve? How old is opsin? How old is vision? (...)
Using genetic analyses, scientists have discovered that Northern European populations — including British, Scandinavians, French, and some Eastern Europeans — descend from a mixture of two very different ancestral populations, and one of these populations is related to Native Americans. This discovery helps fill gaps in scientific understanding of both Native American and Northern European ancestry, while providing an explanation for some genetic similarities among what would otherwise seem to be very divergent groups. (...)
This course presents the principles of evolution, ecology, and behavior for students beginning their study of biology and of the environment. It discusses major ideas and results in a manner accessible to all Yale College undergraduates. Recent advances have energized these fields with results that have implications well beyond their boundaries: ideas, mechanisms, and processes that should form part of the toolkit of all biologists and educated citizens.
Stephen C. Stearns is the Edward P. Bass Professor of Ecology and Evolutionary Biology and specializes in life history evolution and evolutionary medicine. He was educated at Yale, the University of Wisconsin, and the University of British Columbia. His books include Evolution, an Introduction; Watching from the Edge of Extinction; and The Evolution of Life Histories, and he is the editor of Evolution in Health and Disease and The Evolution of Sex and Its Consequences. He founded and has served as president of the European Society for Evolutionary Biology and the Tropical Biology Association.
Tiny stone blades from Pinnacle Point Cave 5-6 in South Africa that once tipped arrows or darts represent the oldest known projectile weapons. Image: Simen Oestmo
Archaeologists excavating a cave on the southern coast of South Africa have recovered remains of the oldest known complex* projectile weapons. The tiny stone blades, which were probably affixed to wooden shafts for use as arrows, date to 71,000 years ago and represent a sophisticated technological tradition that endured for thousands of years. The discovery bears on an abiding question about when and how modern human cognition emerged, and suggests a way by which early modern Homo sapiens outcompeted Neandertals to eventually become the last human species standing.
Fossils show that humans who basically looked like us had evolved by around 200,000 years ago. Yet based on the cultural stuff they left behind, it looked as though anatomically modern humansdidn’t begin thinking like us until much later. And when the creative spark did eventually ignite, the flame flickered only briefly before fizzling, only to spark and fade again and again as populations died out, taking their innovations to the grave. Complex projectile weapon technology, for example, seemed to make a brief first appearance sometime between 65,000 and 60,000 years ago and didn’t stick until after 40,000 years ago. But whether this flickering pattern in the archaeological record is real or merely an artifact of the small number of sites excavated has been unclear. The new South African finds, which come from a site called Pinnacle Point 5 – 6 (PP5-6), support the latter scenario.