[⪠INTRO] The purpose of bones might seem obvious. They hold you up, they connect all your muscles together. But lots of animals get along fine without
them. Insects and other inverts donât have them. Sharks use cartilage. Even most fish donât have bones quite like
ours. And no oneâs really sure why our kind of
bones came to be. Researchers have had hypotheses, of course,
but no real evidence. That is, until now. New research published in the journal Science
Advances offers some pretty solid support to one idea: that ancient fish started making
bones like ours because they stored nutrients. And the team got that intel using some super
cool tech that lets us get a more up-close-and-personal look at fossil fish bones than ever before. More than 400 million years ago in the Silurian
Period, ancient jawless fishes evolved bones containing bone cells called osteocytes. And these eventually became all the rage,
All mammals, birds, reptiles, and amphibians, have them. Today, we know osteocytes have a role to play
in sensing pressure and other forces, in repairing bones, and in regulating the abundance of
minerals like calcium and phosphorus. But to understand why this modern take on
bones evolved, the researchers behind this new paper needed a closer look at early examples
of them. And I mean a much closer look: weâre talking
down to a resolution of less than 100 nanometers â and in 3D rather than on a 2D slide. They got that thanks to a technique known
as focused ion-beam scanning electron microscopy, which is usually used in materials science
for studying things like battery materials and thin films. In it, an ion beam scrapes away a tiny amount
of a sample, which is then scanned in 3D in extremely high resolution by an electron microscope. This process is then repeated over and over
to generate a complete, 3D image of the object. It turns out some of the first bones kind
of looked like Swiss cheese. They were riddled with teeny holes where the
osteocytes used to be. And these cavities were linked by tiny channels
a thousand times narrower than a human hair, creating a connective network thatâs structurally
pretty similar to our own bones. But most importantly, the team noticed that
some of the pockets where osteocytes used to be were surrounded by dark, halo-like areas
of lower-density bone. So, basically, bone with less mineral in it. These low-density areas were only found around
some of the pockets and werenât dispersed randomly or evenly. That led the researchers to think that these
regions represent areas where the bone had been leached away through a process called
osteolysis, which releases minerals. And itâs something our bones still do today
â like, when we donât get enough calcium in our diets. Now, in the marine environment, calcium isnât
usually lacking. But fish can and do run low on phosphorus. And these new-fangled bone cells would have
been great at squirreling it away. So their bones could have served as a battery
of sorts to recharge their phosphorus supply, which could have allowed them to go on longer
journeys or take bigger breaks between meals. And the scientists believe that was probably
a good enough reason to keep these fancy new cells in our bones around. Which is why we have them today! Speaking of things that didnât evolve the
way we always thought, scientists reporting in the journal Current Biology have some surprising
news about whales and hippos. Now don't worry! Hippos are still the closest living relatives
of whales, dolphins, and porpoises â the group collectively known as cetaceans. But since both hippos and cetaceans share
some key water-adapted traits â like nearly-hairless bodies and scrotum-less testes â the thinking
was that they had a shared ancestor that had all these traits, most likely because it spent
much of its time in water. Basically, they assumed that the simplest
hypothesis made the most sense. The new findings, however, show that thatâs
just not the case. Instead, hippos and whales evolved from a
land-dwelling ancestor, and separately acquired their water-loving features. To uncover this plot twist, the researchers
studied the animalsâ skin. First, they found that there were actually
some pretty obvious physical differences. Like, cetaceansâ skin was thicker and full
of clusters of fat cells, while hippo skin was much thinner. Hippos also have specialized sweat glands
that produce an orangey liquid known as âblood sweat.â Yes, BLOOD SWEAT. And while whales, porpoises, and dolphins
do have a few whiskers, hippos have both whiskers and some body hair. These little differences hinted that, perhaps,
these groups had acquired their adaptations separately after their respective branches
of the family tree split off in different directions. But this was not quite a slam dunk. So, the team looked at the animalsâ genes. They identified 8 skin genes that were inactive
in both hippos and cetaceans, meaning that at some point, theyâd mutated to the point
that they no longer coded for anything. Now, if this had happened in a shared ancestor,
those changes to the DNA should have been the same. But â drumroll please! â none of them
were. And that suggests that each group turned off
these genes separately. So their shared features didnât come from
a common, water-loving ancestor â theyâre convergent evolution! Furthermore, when the researchers dug into
the timing of these mutation events, they were able to show that they mostly happened
at different times, with whales beating hippos to the punch by 16 million years, on average. Itâs fine, though, if your'e a hippo and you're watching this, you're good, you still win. You have blood sweat, and they don't. Speaking of winners: Iâd like to give a
big shout out to todayâs President of Space, Dave Christopher! Dave is one of the amazing people who supports
SciShow on Patreon. And without him and our other patrons, we
wouldnât be able to make this show happen! So Dave: Thank you! If you want to be like Dave and support what
we do here, you now have even more choices than ever, because we have recently launched separate
Patreon campaigns for all our channels! Thatâs right! SciShow Space, SciShow Psych, and SciShow
Kids now all have their own Patreons! So you can pick the channel you most want
to support by joining that specific Patreon community. Or join them all, and help us make all kinds
of free science content! They are at Patreon.com/SciShowSpace,
Patreon.com/SciShowPsych, and Patreon.comSciShow/Kids. And, as always, you can support this channel
at Patreon.com/SciShow. [⪠OUTRO]
đ