Sharks are said to have not evolved for tens of millions of years. This is probably true of their basic physicality - they are the apex of the sea predators - but I bet they have spent tens of millions of years evolving to not die from all the other things that can kill you.
Sharks have been around for 350 million years or more (depending on how inclusive you are), and 'modern' sharks have been around for 100 million years (or longer, depending on what counts as modern), but evolution within that family (if that's the right taxonomic rank) has been going on pretty much continuously, as in most families. Great Whites are relative newcomers, ~16 million years ago.
This example [1] of hybridization in the wild has the potential for eventually leading to a new species.
I was not trying to imply that sharks had somehow avoided evolution (probably just could not be bothered to read Darwin's dense prose) !
Merely that if you are the perfect "fit" in size and shape etc already, evolution must focus on the more and more esoteric threats to your reproductive survival.
Once you are basically swimming in a warm buffet, with nothing likely to be able to kill you one on one, evolutions pressures relax on the big obvious things and starts to focus on that liver. which seems to be pretty big even for a predator.
True, but IIRC it's more of eliminating competition or maybe even a blood sport; sharks aren't major part of their diet[1]. Would make sense given that heavy metals and other toxins bio-accumulate up the food chain.
I posit the high heavy metal levels is a defense mechanism for sharks: a slow acting poison.
[1] IIRC again, orcas will leave a shark with the tail cut to just die of asphyxiation, somebody please correct me on this one
I believe the article posted yesterday pointed out that Orcas will eat shark liver, which is about 25% of a shark by weight and also very calorie dense.
Orcas have lots of natural enemies of course. Inside. There is not such thing like a creature that is not eaten by something
I'm sceptic when I see fishermen saying that killer whales are the culprits of killing lots of sharks in the same week for eating their (poisonous?) liver. Fine oils in shark liver are targetted by fishermen. If there are a lot of sharks beached in a small area without its liver, pirate fishing should be counted also in the list of usual suspects.
This example [1] of hybridization in the wild has the potential for eventually leading to a new species.
[1] https://evolution.berkeley.edu/evolibrary/news/120101_sharkh...
Merely that if you are the perfect "fit" in size and shape etc already, evolution must focus on the more and more esoteric threats to your reproductive survival.
Once you are basically swimming in a warm buffet, with nothing likely to be able to kill you one on one, evolutions pressures relax on the big obvious things and starts to focus on that liver. which seems to be pretty big even for a predator.
Orcas are known to hunt and kill sharks [0], and afaik, Orcas have no natural enemies.
[0] https://www.abc.net.au/news/2015-02-04/great-white-killed-by...
I posit the high heavy metal levels is a defense mechanism for sharks: a slow acting poison.
[1] IIRC again, orcas will leave a shark with the tail cut to just die of asphyxiation, somebody please correct me on this one
https://news.ycombinator.com/item?id=19718344
I'm sceptic when I see fishermen saying that killer whales are the culprits of killing lots of sharks in the same week for eating their (poisonous?) liver. Fine oils in shark liver are targetted by fishermen. If there are a lot of sharks beached in a small area without its liver, pirate fishing should be counted also in the list of usual suspects.