There has already been, since the late 1970s, much work done to show that whales and dolphins, collectively called cetaceans, evolved from exclusively land-dwelling mammals. Now it appears there is a case to be made that most of the fish we see in oceans today actually arose from freshwater ancestors.
96% of all fish on Earth are in the group called ray-fins. Research summarised by New Scientist shows that 75% of ray-fins share a heritage that arose in freshwater environments. They moved into pelagic habitats perhaps 170 million years ago.
So what happened to the organisms that never left the oceans? Mass extinctions, probably – for instance 95% of marine organisms were extinguished in the Permian-Triassic’s Great Dying – with freshwater habitats somewhat protected from disaster.
National Geographic reported this week on the discovery, in Namibia, of the oldest fossils yet found of a multicellular animal.
At 760 million years old, Otavia antiqua is described as a sponge-like multicellular organism about the size of a grain of rice. These organisms were incredibly hardy, remaining relatively unchanged for 200 million years, and surviving at least two ‘Snowball Earth‘ events.
The previous oldest organism was also a sponge, and had been dated to 650 million years.
These organisms represent the earliest ancestors of all the multicellular organisms which have arisen since, from Dinosaurs to Humans.
Image courtesy Anthony Prave, University of St. Andrews
Here is an interesting theory: noting that certain classes of diseases, including allergies and autoimmune problems, are more prevalent amongst women, researchers in the US are proposing that traditional gender roles have a part to play in limiting the exposure of girls to immune-system ‘challenges’ early in life.
Noting that boys are more likely to be encouraged to play actively while girls tend to be supervised during indoor play and prevented from getting dirty, they suggest that the variation in numbers and kinds of micro-organisms that children encounter is significant.
We’ve heard these ideas before, and the study’s authors are not suggesting that girls should be eating a spoonful of dirt in the backyard. However, this is a trend that they argue is important enough, and notable elsewhere in the world where rapid social change has been observed, that it deserves further consideration in studies of epidemiology.
More here. (Oregon State University)
I went a little bit link crazy a couple of days ago, after I listened to a lecture on stem cells (sometimes called progenitor cells) and cloning. Much of what the presenter discussed sounded like science fiction: healing spinal injuries, reversing retinal damage, replacing damaged cardiac or brain tissue following heart attacks or strokes…
But it turns out this is all current science. Happening right now. Mostly in trials using mice and the like, but in a few noteworthy cases, in actual clinical human trials.
Anyway, if you are comfortable with the basics of embryology and cloning, you might find the links interesting. Otherwise, read up on the basics of stem cells – what they are, how they were found, what they can do – and then get ready to have your mind blown away.
Spinal Cord Injury – Dana Foundation
Regenerative benefit demonstrated in spinal cord injury
Reconstructing neural circuits using transplanted neural stem cells
Retina created from embryonic stem cells
Repairing the optic nerve using stem cells
Now that is old.
According to the scientists studying this find – a piece of fossilised tree sap containing the spider and its web – the structure and composition of the web is very close to the ones of modern spiders.
Beautiful, don’t you think?