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We’ve all seen this poster in our middle school biology classrooms: an ape-like figure on all fours, then the Neanderthal on two, slowly morph into a fully upright human. As kids — or scientists in 1965 — “The March of Progress” generated a real wow-factor.
However, this image oversimplifies the process of evolution. We did not evolve directly from any living primate. Instead, according to the Smithsonian Natural History Museum, chimpanzees and humans have evolved independently since splitting from a common ancestor 8-6 million years ago.
The oversimplification of evolution causes misunderstanding, which in turn can be especially detrimental to the public’s understanding and fields like conservation, which strives to slow global biodiversity losses and, in turn, increase population fitness.
This misunderstanding is reflected in why one 2022 paper states that “coffee production is fragile.” In this production, 58% is coffee arabica, creating a monoculture crop, whereas planting more varieties of coffee species provides a more diverse set of genes and, in turn, confers greater adaptability to climate change’s calamitous effect.
What is evolution?
Evolution is the process wherein a population’s characteristics change over time; picture smooth, colorful sea glass formed by decades of tumbling through waves from larger, colorless, shards.
How did we become what we are? How are all organisms — extant and extinct — related? Why did anteaters evolve their long tongue? How did pangolins and echidnas, too? The answers lie within evolutionary relationships.
“It all gets magnified because how you change in the future is contingent on what you’re like now and how you changed in the past,” Laura Mojonnier, a senior lecturer in the IU Department of Biology, said.
Despite the apparent differences of species today, tracing their lineages through time reveals shared ancestors.
So, the longer the divergence time, the longer these organisms evolved as members of different lineages; this is referred to as their phylogeny.
So what?
Fish don’t exist.
In her novel “Why Fish Don’t Exist,” Lulu Miller points out that a true “fish” clade containing an ancestor and all its descendants is an unrealizable dream, awkwardly grouping organisms with distantly related ancestors
That is, you’d have to backtrack so many millions of years to find the common ancestor of everything we call a “fish,” that you’d end up including tetrapods like cows and humans!
“We don’t call vertebrates with four legs fish, even though they are descended from a fish ancestor,” Mojonnier said, “so the species that we call ‘fish’ do not make up a complete branch of the tree of life... [implying] that the remaining things are more closely related than they actually are.”
For instance, the lungfish and tuna diverged about 429 million years ago, while the lungfish, cattle, and humans diverged from a common ancestor about 408 MYA.
There’s overwhelming scientific evidence that all life forms evolved from a common ancestor arising more than 3.8 billion years ago. Taxonomy and phylogenetic trees best portray this web of life, tangled as it is.
What’s taxonomy?
Organizing nature’s chaos constitutes naming and categorizing its members.
Carl Linnaeus’s system classifies life from domain to genus and species, being the most related, specific and commonly used. However, new evidence can render obsolete categories like Class Reptilia incorrect.
“Theres a hierarchy and that’s manageable because there aren’t too many groups but making it manageable means losing a lot of information,” Mojonnier said, “we don’t have enough categories in the Linnaean system to incorporate all the branching events that have happened in the history of life.”
Maybe because we weren’t there to see much of it, and because of inconsistent teaching, we have trouble understanding and thus appreciating past and present biodiversity.
“I think the world would be a better place if everyone had a better understanding of basic diversity and that’s best illustrated by a tree, you know a tree captures a lot of information,” she said.
How to read phylogenies
Phylogenetic trees, a.k.a. evolutionary trees or time trees, provide a structured and statistically supported representation of the relatedness between organisms.
Time flows from root to tip, past to present. The root grounds the common ancestor of every member of the tree and each node represents the most recent common ancestor of the lineages branching off. Thus, the tip of each branch reaches the most recently living members of a lineage.
“Evolutionary trees are a hypothesis like most things in science, and as data comes in, we might choose to support a different hypothesis,” Mojonnier said.
Misreading them leads to misconceptions.
“Things that are distantly related can look similar in a lot of ways but still have a lot of underlying differences,” Mojonnier said. “Convergence and reversals that go undetected can lead you to the wrong conclusions.”
Even taxonomy can muddy the water.
“Common names definitely mess things up,” she said. “For example, the term ‘worm’ is used for a diverse set of animals that may have little in common other than their long, skinny shape, but people kind of assume that a worm is a worm is a worm.”
Revelations and applications
Below, tuna is the outgroup, revealing that lungfish are more similar to humans than tuna!
A phylogenetic tree shows lungfish share a more recent ancestor with humans than tuna.
Lungfish, subclass Dipnomorpha, share a more recent ancestor with us, Homo sapiens, than tuna, genus Thunnus. Crocodiles, family Crocodylidae, are most closely related to cows, Bos taurus, then lungfish, then tuna.
So, do you still think “fish” exist?
In her final pages, “Miller asks us as readers to be curious about what we will find when we “give up the fish,” as science writer Kate Raphael puts it.
Mojonnier said this is the cornerstone of triage conservation efforts.
“There’s this idea of using phylogenetic diversity as a quick way to maximize the diversity overall that you’re able to preserve,” she said. “If you’re just bioprospecting for new drugs… if you know the relationships you can be much more targeted with that.”
The applications abound: bioprospecting for drugs, supporting biodiversity rather than monocultures and more. However, a lack of effort, interest and understanding hinders approaches such as these.
To “give up the fish” in favor of deeper understanding, try making your own phylogenetic tree with ITOL.
Odessa Lyon (she/her) is a junior studying biology and English.
