When people talk about “missing links” in evolution, they are often referring to the idea of a direct intermediate species between two modern forms, such as an ape and a human. However, scientists today view this concept as outdated. Evolution is now understood more like a branching tree rather than a linear chain, with many branches ending in extinction and others continuing on.
Humans and apes did not evolve directly from one another but share a common ancestor that lived millions of years ago. This means both groups evolved separately from that point onward.
Scientists have found fossils near key points in evolutionary history that help explain major transitions. One example is Tiktaalik, discovered by University of Chicago paleontologist Neil Shubin. This ancient fish fossil has features similar to limbs within its fin skeletons and dates back to the period when animals first started moving from water onto land.
People use the term “missing links” for fossils that show how certain features evolved—such as lungs or feet—but the process is complex. Fossil discoveries, DNA analysis, and laboratory experiments all contribute to understanding how life diversified over time.
“At first glance it seems so utterly impossible. How did fish evolve to walk and breathe and feed on land?” said Prof. Neil Shubin. “But the reality is, as we discover fossils, as we look at genetics and DNA and embryos, that great transition becomes not only possible but highly likely.”
In 2004, Shubin’s team found Tiktaalik in the Arctic—a fish from 375 million years ago with traits of both aquatic and land animals. This find highlighted a significant moment in evolutionary history when some creatures began venturing out of water.
Professors continue to add details to the evolutionary tree through new data and analysis. UChicago Prof. Michael Coates explained: “With the growth of evolutionary biology came recognition that the history of life is tree- shaped,” he said. “Today’s species represent the tips of living shoots and twigs, while the fossil record documents the dead branches and amazing shrubbery of long-lost evolutionary radiations that failed to make it through to the present day.”
The work involves reconstructing patterns of biodiversity over deep time using both living and extinct species.
“We can use living and extinct species to look at changing patterns of biodiversity through deep time,” said Coates. “Every day we fill in more details of this fascinating picture.”
Finding fossils remains difficult because only a small fraction of organisms become fossilized under special conditions such as sudden burial or preservation in places like tar pits. Soft-bodied creatures or those with delicate bones rarely leave fossils behind, making some evolutionary transitions harder to document.
To study these transitions further, scientists compare anatomical structures among different animals—modern and ancient—to identify similarities such as limb bones found across vertebrates like whales and humans. Genetic sequencing also helps trace relationships by revealing how DNA changes over generations.
Experiments with organisms like fruit flies allow researchers to observe how new traits emerge over time or simulate protein evolution computationally.
Fossils remain crucial for identifying transitional forms; paleontologists search likely locations based on geological clues to uncover specimens showing changes such as early tooth structures in ancient fish.
Tiktaalik itself was named after consultation with Indigenous Arctic peoples—the word means shallow-dwelling fish in Inuktitut—and lived around 375 million years ago in streams or ponds near mudflats where movement onto land could be advantageous due to fewer predators outside water.
Shubin described his discovery: “What we saw gradually emerge from these rocks during the fall of 2004 was a beautiful intermediate between fish and land-living animals.” He added: “So every time you bend your wrists, every time you shake your head, you can thank these fish living in streams 375 million years ago… It shows how our bodies contain layer after layer of history, and that history is so important to understand why we look the way we do.”
Other examples include Archaeopteryx—a fossil showing features between reptiles and birds discovered in 1861—and Acanthostega reconstructed by UChicago Prof. Michael Coates; this animal exhibited traits linking fish with amphibians about 360 million years ago.
UChicago research teams have also contributed evidence on early mammals’ adaptations through collaborative discoveries with Beijing-based scientists.
Evolution occurs gradually due to genetic variation passed down by parents or caused by random mutations; these differences may help an organism survive better under certain conditions, leading eventually—over many generations—to new species emerging if changes accumulate enough.
Human evolution follows this pattern too. Since Charles Darwin published On the Origin of Species in 1859 explaining natural selection (https://www.britannica.com/science/evolution-scientific-theory), researchers have identified several hominin species representing our lineage after splitting from chimpanzee ancestors around seven million years ago (https://humanorigins.si.edu/evidence/human-fossils/species).
One notable discovery was Lucy—a partial Australopithecus afarensis skeleton found by Donald Johanson—which dates back about 3.2 million years (https://www.amnh.org/research/paleontology/human-origins/early-hominids/lucy). In 2000, UChicago Prof. Zeresenay Alemseged uncovered Selam—the most complete child skeleton yet found for Lucy’s species—which has provided insight into childhood development among early hominins (https://news.uchicago.edu/story/selam-most-complete-child-skeleton-early-human-ancestor).
Footprints analyzed by UChicago Prof. Russell Tuttle further demonstrate upright walking abilities among ancient hominids (https://www.smithsonianmag.com/science-nature/the-footprints-that-prove-evolution-64228016/).
Ongoing research continues to clarify our place within life’s larger tree—not just among primates but connecting us ultimately even with distant relatives like Tiktaalik or bacteria depending on how far back one looks.