Cancers aren’t the only thing that evolution continues. The expert explains. : Science Alert

Cancers aren't the only thing that evolution continues.  The expert explains.  : Science Alert
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Charles Darwin believed that evolution createdthe most beautiful of infinite forms“. That’s a nice sentiment, but it doesn’t explain why evolution continues to create cancer.

Scientists have long wondered whether it exists limits what evolution can do or if Darwin had the right idea. The truth may lie somewhere between the two.

Although there appears to be no ceiling on the number of species that can evolve, there may be limits to how many basic forms these species can evolve into. The evolution of crustaceans may be one of the best examples of this, as they evolved not just once. at least five times.

It belongs to the group of crustaceans called crustaceans decapods – literally “ten-legged”, because it has five pairs of walking legs.

Some decapods, such as crabs and shrimp, have thick, muscular bellies, which are the bulk of the animal we eat. Crayfish can quickly throw their abdomen back and escape from predators.

Daggers, on the other hand, have a tight stomach, flattened but expanded thorax and compressed under the shell. This allows them to enter rock crevices for protection. Evolution has hit this solution many times because it works well under similar conditions.

Five groups of “crabs”

The largest group of crabs are arcs Brachyura (true crabs), including edible crab and Atlantic blue crab. They also had an ancestor in the form of cancer. Some species have evolved “backwards” to reshape their abdomens. Another large group is the Anomura (pseudocrabs), which have a more crab-like ancestor.

Red king crab on dark sea background.
king crab (Lithodes longispina), is a species of Anomura. (Karen Gowlett-Holmes/CSIRO Marine Research)

However, at least four groups of Anomura – sponge cancer, porcelain cancer, king crabs and Australian hairy stone crab – evolved independently into a cancer-like form in the same way as true cancers. Like true crustaceans, their compact bodies are more defensive and can move sideways faster.

This means that “crabs” are not a true biological group. They are a collection of identical looking branches on a decagonal tree.

Brown hairy stone crab.
Hairy stone crab (lomis hirta); nor is it a true crab. (Tim Binns/Wikimedia Commons/CC BY-SA 2.0)

But crustaceans are not an exception.

A similar thing happened in the evolution of birds from feathers dinosaurs. Feathers may have originally evolved to insulate, attract mates, protect eggs, and perhaps as a “net”. catch prey. Millions of years later, feathers became elongated and fine-tuned for flight.

Paleontologists disagree on the details, but all modern birds (Neoaves) ancestors living in the land only after the mass extinction that wiped out the other dinosaurs.

However, feathers evolved earlier in other groups of dinosaurs, including wings and flight troodontids and dromaeosaurs. Some of these, such as Microraptor, had four wings.

image of two microraptors
Microraptors had feathers and wings like modern birds (Durbed/Wikimedia Commons/CC-BY-SA 3.0)

Restarting the life bar

Unfortunately, we can’t do evolutionary experiments to see if the same things continue, because that would take hundreds of millions of years.

The history of life has already done something similar for us when closely related lineages evolved and diversified on different continents. In many cases, these ancestors repeatedly came up with solutions to the same or nearly identical problems.

One of the best examples is our own group, mammals.

There are two major groups of living mammals. Placentals (including us) and marsupials (pouched mammals that give birth to their young). Both groups evolved from the same common ancestor 100 million years agomarsupials mainly in Australia and America and elsewhere in placentals.

This isolation led to two almost independent runs of the “experiment” to see what could be done with the mammalian body plan. Moles, mice, anteaters, gliders, and cats have marsupial and placental versions. Even a marsupial wolf (thylacine, It became extinct in 1936), the skull and teeth match that of a placental monster in amazing detail.

The skull and body shapes of the thylacine and the gray wolf are juxtaposed.
The skull of a thylacine (above) and a gray wolf (below). (Feigin et al., Genome Research2019)

It is not only body forms that have evolved independently, but also organs and other structures. People have it compound camera eyes with lens, iris and retina. Squids and octopuses, which are more closely related to molluscs and snails and clams, have also evolved camera eyes with the same components.

The eyes may have evolved more independently 40 times in different groups of animals. Even brainless box jellyfish have lensed eyes at the base of their four tentacles.

Transparent box jellyfish on a black background to visualize their internal structures, such as their tiny eyes under their tentacles.
A box of jellyfish (Tripedalia cystophora). (Bielecki et al., PLOS ONE2014)

The more we look, the more we find. Structures such as jaws, teeth, ears, fins, legs, and wings all develop independently in the tree of life.

Recently, scientists have discovered that convergence also occurs at the molecular level. There are opsin molecules in the eyes that convert light photons into chemical energy and enable people to see close resemblance to those in box jellyfishand developed in this way in parallel.

Even more strangely, there is amazing convergence in the genes of animals as different as whales and bats. allows for reverberation.

Are people really unique?

Many of the things we like to think make humans special have been rediscovered through evolution elsewhere. Corvids, like ravens and crows, have problem-solving intelligence and, along with owls, can use simple tools.

Whales and dolphins has a complex social structure, and their large brains allowed them to develop language. Dolphins use tools like sponges cover their noses while foraging on rocky seabeds. Octopuses also use tools and learn by watching what happens to the other octopuses.

An octopus hiding between two shells on the sandy seabed.
Octopus marginatus hidden between two shells. (Nick Hobgood/Wikimedia/CC BY-SA 3.0)

If things continue to evolve in a similar way on Earth, if life has evolved elsewhere in the Universe, they are likely to follow a similar course. It may mean extraterrestrials seem less alien and more familiar than we expected.Conversation

Matthew WillsProfessor of Evolutionary Paleobiology at the Milner Center for Evolution, University of Bath

This article is being republished Conversation Under Creative Commons license. read it original article.

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