No animal alive today is ‘primitive’ – why are so many still labeled that way?

• Many animals are still labeled as “primitive” or “ancient,” but modern evolutionary biology shows that all species alive today are equally evolved and have long lineages, rather than being ancestors or descendants.
• The concept of a hierarchical view of evolution, where humans are at the top and other species are lower, is outdated and misleading. This perspective was established by Ernst Haeckel in 1866 but has been debunked by modern evolutionary biology and genomics.
• Species like platypuses, echidnas, and marsupials are often labeled as “primitive” due to their unique characteristics, such as egg-laying or pouch development. However, these traits have evolved to suit their specific ecological niches and make them well-suited for their environments.
• The placement of species on evolutionary trees is not a reflection of their age or evolution, but rather a result of the focus of the tree. For example, marsupials are often shown at the bottom of the page because they are being compared to placental mammals like humans.
• Understanding the tree of life and recognizing that humans are just one branch among many is crucial for advances in fields ranging from animal behavior and physiology to conservation and biomedicine. It helps us appreciate the shared modern status of all animals, from platypuses to people.

We humans have long viewed ourselves as the pinnacle of evolution. People label other species as “primitive” or “ancient” and use terms like “higher” and “lower” animals.

This anthropocentric perspective was entrenched in 1866, when German scientist Ernst Haeckel drew one of the first trees of life. He placed “Man,” clearly labeled, at the top. This illustration helped establish the popular view that we are the ultimate goal of evolution.

Modern evolutionary biology and genomics debunk that flawed perspective, showing there is no hierarchy in evolution. All species alive today, from chimpanzees to bacteria, are cousins that each have equally long lineages, rather than ancestors or descendants.

Unfortunately, these outdated notions remain prevalent in scientific journals and science journalism. In my new book, “Understanding the Tree of Life,” I explore why it is fundamentally misleading to view any current species as primitive, ancient or simple. As an evolutionary biologist, I offer an alternative view that emphasizes evolution’s complex, nonhierarchical, interconnected history.

Not primitive, just different

Egg-laying mammals, the monotremes, are frequently labeled the most “primitive” living mammals. This category includes the platypus and four species of echidnas. Indeed, their egg-laying is an ancient characteristic shared with reptiles.

But platypuses also have many unique recent adaptations that make them well suited to their lifestyle: They have webbed feet for swimming and a bill with specialized electroreceptors that detect prey in the mud. Males have spurs with venom that they can use to defend themselves against rivals. If you take a platypus’s view, they’re the pinnacle of evolution for their specific ecological niche.

Echidnas may seem primitive, especially because they lack a capability that humans have – giving birth to live young. Yet they possess many extraordinary traits that humans lack. Echidnas are known for their outer covering of protective spines. They also have powerful claws for digging, a sensitive beak and a long sticky tongue, all of which they use foraging for ants and termites. In a head-to-head competition foraging for prey in a termite mound, an echidna would easily outperform any human.

Other mammals native to Australia also turn up on lists of primitive mammals, such as many species of marsupials – pouched mammals, including kangaroos, koalas and wombats. These species generally give birth to small, minimally developed young that move to the mother’s pouch where they complete development. Pouch development may seem inferior to the human way, but it does have advantages. For example, kangaroos can simultaneously nurture young at three stages of development.

Evolutionary tree appearance depends on focus

Marsupials such as opossums, or monotremes such as the platypus, are often shown at the bottom or left side of an evolutionary tree. However, that does not mean that they are older, more primitive or less evolved.

Evolutionary trees – what scientists call phylogenies – show cousin relationships. Just as your second or third cousin is no more primitive than you are, it is misleading to think of a koala or echidna as primitive because of where they are depicted on these trees.

When scientists and journalists choose which species to include in the evolutionary trees in their publications, it can influence how the public perceives these species. But species shown lower on the page are not “lower” on some evolutionary scale.

Rather, they are placed there because the focus of many of those trees is on placental mammals, such as humans, other primates, carnivores, rodents and so on. When the focus is on placental mammals, it makes sense to include one or two species of marsupials as comparisons for reference.

In contrast, in a tree focused on marsupials, one or two placental mammals could be included at the bottom of the page for comparison.

Why understanding the tree of life matters

Viewing humans as the goal of evolution leads to a misunderstanding of the entire evolutionary process. Since evolution is the conceptual foundation for all biology, this flawed perspective can hinder all biological and biomedical science.

Mastering a modern understanding of evolutionary trees is crucial to advances in fields ranging from animal behavior and physiology to conservation and biomedicine. For example, because rhesus monkeys are much more closely related to us than are capuchins, rhesus monkeys are generally better subjects for preliminary tests of human vaccines. Opossums, incorrectly considered to be primitive, are a great species for providing a broader framework for studies of neurobiology and aging because they are distantly related to us, not because they are lower or more ancestral.

Grasping the profound reality that humans are not the pinnacle of evolution, but one branch among many, is foundational for all modern biology. Understanding the tree of life is central to fully embracing the shared modern status of all animals, from platypuses to people.

Kevin Omland does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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