|Fossils from Loch Torridon in Scotland is the oldest confirmed |
eukaryote fossils on Earth at 1.1 billion years old
s, powered by mitochondria unimaginable in the bacteria and archaea over 3 billion years previously. While life forms with bilateral symmetry, legs, organs and nervous systems seen in the myriad of animals and plants today, would only evolve 700 million years ago.
Something transformed the eukaryotes seemingly overnight: sexual reproduction. This re-shuffles the genetic pack, gives rise to diversity, complexity and accelerates the pace of evolution in eukaryotes. It seemed the perfect trigger for the sudden and dramatic changes seen in the fossil record 700 million years ago. Yet a study, conducted by William Ratcliff and Michael Travisano from the University of Minnesota, demonstrates that sexual reproduction may have evolved at the same time as multicellularity, explaining why almost all complex organisms use single-celled gametes for reproduction.
|One of the multicellular algal colonies 'evolved' by Ratcliff and Travisano|
Further examination of the colony showed that motile single cells broke off from the cluster at regular intervals. These in turn reproduced to form multicellular colonies of their own. Mathematical models of this propagation process returned surprising results each time: that single cells due to sheer numbers would prove to be more successful in the long run. This is similar to the way corals, humans and indeed most eukaryotes produce millions of sperm cells or a biological equivalent to increase the chances of survival.
|Today almost all eukaryotes use single cells, such as sperm, to reproduce|
While genetic and fossil evidence is required to demonstrate conclusively that the two traits evolved together, Ratcliff and Travisano's work offers a dynamic perspective on the origin of multicellular organisms and one, which in some ways, seems to fit better into the story of life on Earth. As knowledge of life during the Precambrian has increased, the major evolutionary events in the history of eukaryotes have been drawn closer together.