Question

A revolution in the study of human evolution is under way due to the invention of techniques that enable DNA sequencing not only of modern humans but also of ancient humans (introduced in Chapter 20 ). Neanderthals disappeared about 40,000 years ago when the modern human population increased. This is an example of what outcome(s) of secondary contact (see Table 24.3)? Predict one way this result might have come about.

Short answer

The disappearance of Neanderthals and the expansion of modern humans is an example of the extinction of one population as an outcome of secondary contact. This could have occurred due to competitive exclusion, where modern humans were better able to acquire and utilize essential resources, ultimately leading to the extinction of Neanderthals.

Step-by-step solution

Understanding Secondary Contact and Table 24.3 Outcomes

Secondary contact occurs when two distinct populations that evolved separately come into contact again. The outcomes presented in Table 24.3 include 1) Fusion of the two populations, 2) Reinforcement of reproductive barriers, 3) Hybrid zones, and 4) Extinction of one population.

Identifying the Outcome for Neanderthals and Modern Humans

The disappearance of Neanderthals coincided with the expansion of modern humans, which suggests that the outcome of secondary contact between the two species led to extinction of the Neanderthal population. This occurs when one population is unable to survive in the competitive environment upon contact with another population.

Predicting a Potential Explanation for this Outcome

One possible explanation for this outcome is competitive exclusion. This suggests that modern humans and Neanderthals both required similar resources (like food and shelter), and modern humans were better able to acquire and utilize these resources, leading to the Neanderthals' extinction.

Key concepts

DNA Sequencing

The breakthrough of DNA sequencing technologies has been essential in unraveling the complexities of human evolution. By meticulously reading the sequence of nucleotides found in DNA, scientists can unlock historical genetic data which is pivotal to understand our ancestors.

One of the fascinating applications of DNA sequencing is its use in studying ancient DNA, which includes extracting genetic material from archaeological remains. This process has been crucial in confirming connections and genetic flow between modern humans and ancient hominins like Neanderthals and Denisovans.

Moreover, high-throughput sequencing allows for the comparison of genomes across species and time, offering insights into evolutionary changes and patterns that have shaped current human populations. Through DNA sequencing, we've learned that modern humans carry Neanderthal DNA, which is a direct result of interbreeding, demonstrating the intertwined history of these species.

Neanderthals

Neanderthals are an extinct species of archaic humans who lived across Europe and parts of Western Asia. They are closely related to modern humans, differing in DNA by just a small fraction.

Neanderthals are known for their robust build and adaptness to cold climates, characterized by their short limbs and strong bodies. As they evolved in Europe and Asia, they developed unique cultural and survival strategies aligning with the environment of the Pleistocene epoch.

With the advent of DNA sequencing, the genetic relationship between Neanderthals and modern humans has come to light. It has revealed that Neanderthals interbred with ancestors of modern humans, leaving a genetic legacy in the DNA of contemporary individuals outside of Sub-Saharan Africa.

Secondary Contact Outcomes

Secondary contact is a critical phase where previously isolated populations intersect, which can result in a variety of outcomes. Table 24.3 in the textbook outlines these possible scenarios, including the blending of populations, reinforcement of separation, development of hybrid species, or the extinction of one group.

When it comes to Neanderthals, the outcome of secondary contact with modern humans was their eventual extinction. Several factors could explain this, such as competitive exclusion, where modern humans may have outcompeted Neanderthals for resources. Another theory is that diseases carried by modern humans could have contributed to the Neanderthals' decline.

Such outcomes are essential for understanding evolutionary processes, as they reveal how interactions between different hominin species have contributed to our current genetic makeup and diversity.