modern science shows how we’ve done so much wrong

If you look different from your close relatives, you may have felt separated from your family. As a child, during particularly stormy fallouts, you might have even hoped it was a sign that you had been adopted.

As our new research shows, appearances can be deceiving when it comes to family. New DNA technology is shaking up the family trees of many plants and animals.

The primates, to which humans belong, were once considered closest relatives to bats because of some similarities in our skeletons and brains. However, DNA data now places us in a group that includes rodents (rats and mice) and rabbits. Amazingly, bats appear to be more closely related to cows, horses, and even rhinoceroses than to us.

Scientists in Darwin’s time and through most of the 20th century could only determine the branches of the evolutionary tree of life by looking at the structure and appearance of animals and plants. Life forms were grouped according to similarities thought to have evolved together.

About three decades ago, scientists began using DNA data to build “molecular trees.” Many of the first trees based on DNA data were at odds with the classical ones. Sloths and anteaters, armadillos, pangolins (scaly anteaters), and aardvarks were once thought to belong together in a group called edentates (“no teeth”), because they share aspects of their anatomy. Molecular trees showed that these traits evolved independently in different branches of the mammalian tree. It turns out that aardvarks are more closely related to elephants, while pangolins are more closely related to cats and dogs.

Molecular phylogenies show that mammals as different in appearance as aardvarks, manatees, elephant shrews, and elephants really are close cousins.

Getting together

There is another important line of evidence with which Darwin and his contemporaries were familiar. Darwin noted that animals and plants that seemed to share the most common ancestors were often found geographically close together. The location of species is another strong indicator that they are related: species living close together are more likely to share a family tree.

For the first time, our recent paper cross-references location, DNA data, and appearance for a range of animals and plants. We looked at evolutionary trees based on appearance or on molecules for 48 groups of animals and plants, including bats, dogs, monkeys, lizards and pine trees. Evolutionary trees based on DNA data were two-thirds more likely to match the location of the species compared to traditional evolutionary maps. In other words, previous trees showed that different species were related based on appearance. Our research showed that they were much less likely to live near each other compared to species linked by DNA data.

It may seem as if evolution endlessly invents new solutions, almost without limits. But it has fewer tricks up its sleeve than you might think. Animals can be astonishingly similar because they evolved to do the same work or live in a similar way. Birds, bats and the extinct pterosaurs had bony wings for flying, but their ancestors all had front legs for walking on the ground.

The color wheels and key indicate where members of each order can be found geographically. The molecular tree grouped these colors better than the morphological tree, indicating a closer correspondence of the molecules with the biogeography. Figure is from Oyston et al. (2022)
Author provided

Similar wing shapes and muscles developed in different groups because the physics of generating thrust and lift in the air is always the same. It’s about the same with eyes, which may have evolved 40 times in animals, and with just a few basic “designs”.

Our eyes are similar to squid eyes, with a crystalline lens, iris, retina and visual pigments. Cuttlefish are more closely related to snails, snails and clams than we are. But many of their mollusk relatives have only the simplest eyes.

In fact, squid and fish have been separated by more than half a billion years of evolution.
Flickr, CC BY

Moles evolved as blind, burrowing creatures at least four times, on different continents, on different branches of the mammalian tree. The Australian marsupial moles (more closely related to kangaroos), African golden moles (more closely related to aardvarks), African mole rats (rodents), and the Eurasian and North American talpid moles (beloved by gardeners, and more closely related to hedgehogs than these other “moles”) all evolved on a similar path.

The roots of evolution

Until the advent of cheap and efficient gene sequencing technology in the 21st century, all evolutionary biologists had to do was look.

While Darwin (1859) showed that all life on Earth is related to a single evolutionary tree, he did little to map its branches. The anatomist Ernst Haeckel (1834-1919) was one of the first to draw evolutionary trees that tried to show how large groups of life forms are related to each other.

The illustrations of the German zoologist Ernst Haeckel (here, groups of mosses)
Pixaby, CC BY

Haeckel’s drawings made brilliant observations of living things that influenced art and design in the 19th and 20th centuries. His family trees were based almost entirely on what those organisms looked like and developed as embryos. Many of his ideas about evolutionary relationships existed until recently. As it becomes easier and cheaper to obtain and analyze large amounts of molecular data, there will be many more surprises in store.

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