Mass Extinction of Earth: A Comprehensive Review

Illustration depicting the timeline of mass extinctions through Earth's history

Intro

The study of mass extinction is a compelling journey through Earth's history, shedding light on the intricate dance between life and the environment. Each extinction event is like turning a page in a dramatic novel, filled with heroes, villains, and sometimes, unexpected twists. Many might believe that understanding extinction is solely a matter for biologists or ecologists, yet it's a topic that interlaces with geology, climate science, and even anthropology. By expressing the past losses of species, we gain insight into our own future. This discussion is timely. With ongoing biodiversity crises, it becomes vital to understand what transpired before to avoid making the same mistakes anew.

Article Overview

Purpose of the Article

The primary aim here is to present a thorough examination of mass extinction events that shaped life on Earth. By sifting through various historical contexts and scientific theories, this article endeavors to elucidate the factors that led to these catastrophic events. Additionally, it will underscore the importance of these events in shaping current biodiversity and conservation efforts. Understanding the ebb and flow of species through extinction gives critical context to present-day challenges, providing a roadmap for future conservation strategies.

Relevance to Multiple Disciplines

Mass extinction is not a subject of isolated interest. It resonates across numerous fields:

Biology: Understanding species loss influences conservation strategies and ecological research.
Geology: Each mass extinction corresponds with geological changes, prompting studies into climate shifts and tectonic activities.
Anthropology: This field examines how human behavior contributes to the decline of species, integrating the social aspects of extinction.
Climate Science: The connection between climate changes and extinction events is increasingly pertinent as the world faces rapid environmental transformations.

This multifaceted approach serves as a reminder that the health of our planet is governed by an intricate web of life forms and the physical world. Therefore, the discourse around mass extinction becomes ever more relevant in our contemporary context.

Research Background

Historical Context

To grasp the enormity of mass extinction, one must glance back through the annals of history. Earth's timeline is dotted with multiple extinction events, each bearing its unique fingerprints:

The Ordovician-Silurian Extinction: Approximately 443 million years ago, this event erased around 85% of species, potentially linked to climate change and sea level fluctuations.
The Late Devonian Extinction: Stretching over several million years, this series of events saw up to 75% of marine species vanish, likely due to anoxic conditions in the oceans.
The Permian-Triassic Extinction: Often dubbed the “Great Dying,” it caused the loss of about 96% of all species, possibly due to volcanic activities and subsequent climate shifts.
The Cretaceous-Paleogene Extinction: Famous for wiping out the dinosaurs, this event was likely triggered by an asteroid impact and volcanic eruptions, radically altering life on Earth.

Key Concepts and Definitions

When diving into mass extinction, some key concepts need clarification:

Mass Extinction: A rapid loss of a significant proportion of species across various habitats on Earth.
Background Extinction Rate: The normal rate at which species go extinct, usually measured on a geological timescale.
Holocene Extinction: Referring to the current period where human activities accelerate species loss, also known as the sixth mass extinction.

Understanding these terms and concepts lays the groundwork for deeper exploration into the causes and consequences of mass extinction events. More importantly, they serve as critical reminders for our ongoing commitment to conservation.

"Each loss is more than a number; it represents a unique strand in the tapestry of life that is forever severed."

"Each loss is more than a number; it represents a unique strand in the tapestry of life that is forever severed."

In summary, the intricate relationships between past extinctions and present biodiversity challenges underscore our responsibility. Insights gained from history can illuminate paths forward, guiding present-day actions towards preserving what remains.

Prelims to Mass Extinction

The concept of mass extinction holds significant weight in both ecological discussions and broader environmental strategies. As ongoing research explores the intricacies of biodiversity, it's crucial to establish a well-rounded understanding of what mass extinction entails. This foundational knowledge not only aids in grasping historical events but also shapes our perception of future challenges and their implications for living organisms on Earth.

Mass extinctions are defined by the rapid loss of a large number of species across various taxa, typically within a relatively short geological timeframe. Understanding these events helps to paint a more comprehensive picture of life's resilience, adaptability, and, at times, vulnerability.

Defining Mass Extinction

When we talk about mass extinction, it’s essential to delineate what constitutes this term. Broadly defined, a mass extinction event is one where at least 75% of species on the planet become extinct within a limited period—usually classified as less than two million years. This stark criterion differentiates mass extinctions from normal background extinction rates, which see species gradually fading out over time due to various factors like environmental changes or evolutionary pressures.

In the grand scope of Earth's history, the five major mass extinctions mark significant turning points. When we dissect the implications of these extinction events, the relationship between Earth's biosphere and various influencing factors—natural or otherwise—becomes clear. Recognizing this helps navigate the myriad of complexities surrounding biodiversity, ecosystems, and conservation efforts.

Historical Overview

The historical overview provides a lens through which to view the past events that have dramatically altered the course of life. By learning from previous occurrences, we can appreciate the patterns and triggers of extinction. Key points to note include:

Environmental upheavals
Catastrophic events linked to climate changes
Anthropogenic influences that have compounded these effects

Previous Mass Extinctions

The five previous mass extinctions are crucial in understanding contemporary environmental crises and biodiversity loss. Not only do these events exemplify the patterns that can lead to widespread extinction, but they also reveal the resilience and recovery potential of life. Each event has its unique characteristic:

The Ordovician-Silurian Extinction: Linked largely to climatic shifts, it serves as an early indicator of life’s vulnerability to drastic environmental changes.
The Permian-Triassic Extinction: This is often referred to as the Great Dying, showcasing the catastrophic effects of volcanic activity, which led to widespread extinction.
The Cretaceous-Paleogene Extinction: Well-known for the asteroid impact that led to the demise of the dinosaurs, this event highlights how a singular catastrophic occurrence can reshuffle the ecological deck dramatically.

Visual representation of biodiversity loss due to environmental changes

The characteristics of these past mass extinctions make them especially relevant for discussions in this article, as they inform the urgency and strategies in biodiversity conservation today. For instance, understanding the Permian-Triassic event underscores the potential impacts of climate change driven by human actions as we consider ongoing and future extinction risks.

Timeline of Extinction Events

The timeline of extinction events serves as a crucial framework for understanding how often and why these drastic changes occur. By examining the chronological sequence of extinctions, researchers can identify patterns and correlations with climate and geological changes.

The review of these timeframes reveals key characteristics that are particularly beneficial, such as:

Periodic Nature: Extinction events don’t occur randomly; they often coincide with significant environmental shifts.
Resilience and Recovery: Some events provide a sobering reminder that life often rebounds, albeit slowly, after such catastrophic losses.

In laying out the intricate timeline, this narrative deepens our comprehension of how environmental phenomena intertwine with biological survival.

As the discussion unfolds, the context of mass extinctions will bridge past occurrences and present challenges, encouraging a forward-looking perspective on maintaining biodiversity in the modern era.

"Only through understanding the past can we hope to change the future."

"Only through understanding the past can we hope to change the future."

For further exploration of this topic, consider visiting resources such as Britannica, or accessing studies found on academic domains like *.edu and government sites like *.gov.

The Five Major Mass Extinctions

Understanding the five major mass extinctions is crucial for grasping the complex history of life on Earth. These pivotal events reshaped the biosphere, leading to the dramatic loss of biodiversity and altering ecosystems in ways that still resonate today. As we sift through the fossils of the past and study the clues they leave behind, we can discern patterns that inform our current knowledge of evolution and extinction.

Among these five extinctions, each has its unique causes and consequences that reflect the intricate relationship between Earth's geology and biology. The lessons learned from these events are not mere academic exercises; they offer critical insights into our present-day challenges regarding biodiversity. This section carefully examines each extinction event, considering not only the biological ramifications but also the geological and environmental changes that triggered such widespread loss.

"Mass extinctions are rare events that remind us how resilient yet fragile life on Earth can be."

"Mass extinctions are rare events that remind us how resilient yet fragile life on Earth can be."

Ordovician-Silurian Extinction

The first significant mass extinction, occurring around 444 million years ago, is known as the Ordovician-Silurian Extinction. This event wiped out an estimated 85% of marine species, primarily impacting organisms such as trilobites and brachiopods. The primary cause is thought to be a severe ice age that led to changes in sea levels and ocean chemistry. When the climate began to cool significantly, habitats disappeared, leaving many species in dire straits. This extinction emphasizes how climate shifts can overturn the delicate balance of marine life.

Late Devonian Extinction

Following the Ordovician-Silurian, the Late Devonian Extinction spanned a series of events between about 375 and 360 million years ago. It is estimated to have caused the loss of around 75% of species, particularly affecting coral reef ecosystems. Several theories exist regarding its drivers, including prolonged anoxic events in oceans and possible asteroid impacts. The fallout from these changes paints a picture of interconnected organisms reliant on stable environments, which can be easily disrupted by a cascade of changes.

Permian-Triassic Extinction

Often referred to as the "Great Dying," the Permian-Triassic Extinction occurred approximately 252 million years ago, marking the most catastrophic extinction event in Earth's history. Up to 96% of all marine species and 70% of terrestrial vertebrates vanished. This event is linked to massive volcanic eruptions in what is now Siberia, leading to global warming and ocean acidification. The repercussions of this extinction resonate through the ages, illustrating the vulnerability of complex communities to rapid environmental shifts.

Triassic-Jurassic Extinction

The Triassic-Jurassic Extinction, occurring around 201 million years ago, is the fourth major mass extinction. It set the stage for the dominance of dinosaurs in the Jurassic period, as it eliminated roughly 50% of all species. A combination of volcanic activity and climate change is suspected to have contributed to this event. This extinction serves as a reminder of life’s adaptability, as the aftermath gave rise to new groups of animals that would dominate for millions of years ahead.

Cretaceous-Paleogene Extinction

The Cretaceous-Paleogene Extinction, roughly 66 million years ago, is perhaps the most famous, known for the demise of the non-avian dinosaurs. An estimated 75% of species went extinct due to catastrophic events like an asteroid impact and extensive volcanic activity. This extinction emphasized not just the immediate devastation but also the longer-term evolutionary benefits, as mammals and birds began to flourish in the absence of dinosaurs. The evidence found in iridium layers and the Chicxulub crater underscores how sudden changes can reset biological evolution.

In summary, these five major mass extinctions each tell a story of resilience and destruction. They offer a profound understanding of how life can adapt or perish in the face of overwhelming changes. As our planet continues to face challenges that could lead to further extinctions, learning from these historical events becomes even more essential.

Causes of Mass Extinction

Understanding the factors that lead to mass extinction is crucial for grasping the complexities of biodiversity loss through Earth’s history. It provides insights that help not only in analyzing past events but also in recognizing patterns that may play out in our current ecological crisis. The reasons behind these extinctions can be broadly categorized into natural and anthropogenic factors, which interact in complex ways. Highlighting these causes will elucidate the dire consequences they carry for ecosystems and human society alike.

Natural Factors

Volcanic Activity

Volcanic activity has been a significant player in the drama of mass extinction. Massive volcanic eruptions can release copious amounts of ash and gases into the atmosphere, leading to dramatic climatic shifts. The key characteristic of volcanic eruptions that makes them particularly intriguing is their ability to cause both immediate and long-term ecological impacts. For instance, the end of the Permian period is believed to have been exacerbated by the Siberian Traps eruptions, resulting in one of the deadliest extinction events.

One unique feature of volcanic activity is its dual nature. While eruption events can obliterate habitats swiftly, they can also spur innovation in ecosystems during recovery periods. However, the disadvantage lies in the unpredictability of these eruptions; a single catastrophic event can wipe out entire species before they have a chance to adapt.

Asteroid Impacts

Graph showcasing the correlation between anthropogenic activities and species extinction rates

Asteroid impacts represent a colossal force in the annals of extinction. The most famous, the Cretaceous-Paleogene impact, led to the end of the dinosaurs and many other life forms. The key characteristic of these cosmic collisions is their immediate and comprehensive destructiveness. When an asteroid strikes, the consequences can be catastrophic, leading to fires, tsunamis, and a 'nuclear winter' effect, drastically altering global climates.

The unique feature about asteroid impacts is their rarity but significant influence; events like these don’t happen often, but when they do, they leave an indelible mark on Earth's biodiversity. While they can lead to mass extinctions, they sometimes also pave the way for new species to evolve and thrive in the aftermath, showcasing a rather brutal but also transformative aspect of life.

Climate Change

Climate change is not just a modern issue; it has acted as a catalyst for many past extinction events. Dramatic shifts in temperature and precipitation patterns can disrupt ecosystems at staggering rates. One key characteristic of climatic changes is their pervasive reach—when conditions shift, habitats and species can find themselves out of sync with their environments.

The unique feature of climate change lies in its gradual yet relentless nature, making it harder for species to adapt in real-time. While some organisms exhibit resilience, the clock is ticking for many others. Its long-term effects can lead to a cascading failure of ecosystems—a situation that modern society is now beginning to grasp, recognizing how critical it is to mitigate these changes.

Anthropogenic Factors

Habitat Destruction

Habitat destruction, often fueled by human activities like urbanization, agriculture, and deforestation, is a leading cause of species extinction today. One striking aspect of habitat destruction is its immediacy; entire landscapes can be altered in mere years, leaving many species with no escape routes. Deforestation in the Amazon, for instance, raises alarms about biodiversity loss that can't be ignored and draws attention to the urgency of the issue.

Moreover, the unique feature of habitat destruction is the cascading effect it has—not only does it kill off numerous species directly, but it also destabilizes the complex relationships among them. As habitats are lost, the remaining ecosystems become less resilient and more vulnerable to further threats, creating a vicious cycle that accelerates decline.

Pollution

Pollution, in various forms—chemical, plastic, and noise—creates insurmountable challenges for both terrestrial and marine life. The key characteristic of pollution that sets it apart is its insidious nature; it can infiltrate ecosystems quietly, often unnoticed until the damage is done. This makes pollution a particularly dangerous threat, as the very fabric of life can be eroded without any immediate visual signs.

A unique feature of pollution is its ability to bioaccumulate within food webs, meaning that higher trophic levels suffer disproportionately. Toxins can move through the food chain, affecting species well beyond the original point of contamination. This bioaccumulation presents a stark reality that can render entire ecosystems uninhabitable.

Invasive Species

Invasive species can disrupt local ecosystems by out-competing native species for resources and altering habitat dynamics. Their key characteristic lies in their adaptability; invasive species often thrive in new environments because they lack natural predators. This adaptability can be seen in the case of the brown tree snake in Guam, which led to the extinction of several native bird species.

A particularly concerning unique feature of invasive species is their unpredictable nature; they can spread rapidly and at times not be recognized until significant damage is done. The ramifications can lead to a decline in biodiversity and can alter existing ecosystems profoundly, threatening the survival of species that have evolved over millions of years.

The interplay between natural and anthropogenic factors reveals a complex landscape of extinction causes that demand urgent attention for the sake of conservation and ecological resilience.

The interplay between natural and anthropogenic factors reveals a complex landscape of extinction causes that demand urgent attention for the sake of conservation and ecological resilience.

For further insights and detailed explorations, visit resources such as Britannica, Wikipedia, and government sites like EPA.

Consequences of Mass Extinction

The ramifications of mass extinction are profound and far-reaching. Understanding them is crucial, not just for learning about past events, but for grappling with the ongoing biodiversity crisis. Delving into the consequences allows us to see the delicate web of life that sustains our planet and appreciate the cascading effects that the loss of species can trigger. The following sections elucidate three primary consequences: biodiversity loss, ecosystem changes, and impacts on human society, each underscoring the intricate interconnections that define our biosphere.

Biodiversity Loss

Biodiversity is the term used to describe the variety of life found on Earth, encompassing the different species of plants, animals, fungi, and microorganisms, as well as the genetic diversity within these species. The loss of biodiversity due to mass extinctions is not just a side note in ecological study; it's a central concern. When species disappear, the resilience of ecosystems diminishes, leading to unstable environments.

When a species vanishes from a habitat, it often means that an entire set of relationships could falter. For example, consider the role of bees in pollinating plants. If bee populations decline, many plants struggle to reproduce, which in turn affects the animals that rely on those plants for food, leading to a ripple effect through the food chain. This dependency is not an isolated phenomenon; it's a complex network.

"Biodiversity is not just a feature of natural environments; it shapes the very structure of our societies and economies, supporting food security and health."

"Biodiversity is not just a feature of natural environments; it shapes the very structure of our societies and economies, supporting food security and health."

In essence, the loss of biodiversity can threaten ecosystems' ability to provide services that humanity relies upon, including clean water, climate regulation, and resources for agriculture.

Ecosystem Changes

Mass extinctions come with significant alterations to ecosystems. These transformations can manifest in a multitude of forms, from shifts in species composition to fundamental changes in habitat structure. For instance, after the Permian-Triassic extinction, the dominance of amphibians and reptiles gradually shifted to mammals and birds in subsequent periods. This shift was not merely a change in the types of creatures dwelling on Earth; it dramatically altered the functioning of ecosystems, influencing what plants could thrive and how energy circulated through the food system.

Such transitions can also lead to habitat fragmentation, where once-contiguous environments are broken into smaller, isolated sections. This isolation can prevent species from migrating, adapting, or even breeding with one another, pushing them closer to extinction. The removal of keystone species can also lead to overpopulation of certain organisms, creating imbalances that can devastate remaining species.

Impact on Human Society

The effects of mass extinction extend far beyond the natural world, crashing headlong into human existence. The loss of species and the resulting shifts in ecosystems can have dire consequences on agriculture, fisheries, and overall food security. For example, if certain fish species disappear due to environmental changes linked to human activities, this can disrupt fishing communities and economies, leading to sociopolitical unrest in vulnerable regions.

Moreover, as ecosystems collapse, communities may face increased vulnerability to natural disasters and climate change. More extreme weather patterns or loss of natural barriers (like wetlands that protect against floods) can exacerbate human suffering and displacement. The intertwined fates of humanity and nature underscore the urgency of conservation efforts and sustainable practices.

Conceptual image illustrating conservation efforts and their importance for future biodiversity

While the past can offer valuable lessons, looking ahead, it's essential to foster awareness and actions that can mitigate the effects of potential future extinctions. By understanding these consequences, society can work towards a more sustainable relationship with our environment, recognizing that nature's resilience directly affects our own well-being.

Current Research on Extinctions

The study of mass extinctions is not just about what has happened; it’s also a window into what could happen next. As our planet faces unprecedented biodiversity crises, understanding the intricacies of current research equips us to tackle looming challenges. Today's scientists are using a blend of technology and traditional methods to unlock the secrets of past extinctions, providing crucial insights into prevention strategies for future losses.

Technological Advances

Genetic Studies

Genetic studies stand out as a beacon in the field of extinction research. This approach dissects the very building blocks of life – DNA. By analyzing genetic material from both existing and extinct species, researchers can discern patterns related to adaptation, resilience, and, importantly, vulnerability to extinction. One key characteristic of genetic studies is their ability to track genetic diversity, which is critical in assessing a population’s ability to withstand environmental changes.

"Understanding genetic diversity is like holding a map to survival for species facing extinction. It shows where strength lies and where caution must be exercised."

"Understanding genetic diversity is like holding a map to survival for species facing extinction. It shows where strength lies and where caution must be exercised."

The unique facet of genetic studies is their application in de-extinction efforts, aiming to bring back species that have long vanished. Technologies such as CRISPR are making headlines, paving the way for bold moves in conservation biology. However, while the advantages are compelling—potentially resurrecting lost genetic lines—the disadvantages include ethical dilemmas and potential ecological repercussions that are yet to be fully understood. The journey through genetic research is a double-edged sword, offering hope while demanding responsibility.

Remote Sensing Technologies

Remote sensing technologies have transformed the way researchers monitor and assess ecosystems. By employing satellites and aerial surveys, scientists can gather extensive data on habitat degradation and climate changes over large areas. A major advantage of this technique is its ability to provide real-time information, which is invaluable in identifying trends that might signal impending extinction events.

The key characteristic of remote sensing technologies is their scope; they allow researchers to view entire ecosystems from above, capturing patterns that ground-level studies might miss. A unique feature lies in the integration of geographic information systems (GIS), which enhances spatial analysis capabilities, helping in precise mapping and modeling of biodiversity hotspots.

However, while these technologies are beneficial, there are challenges, including the interpretation of data. High-resolution imagery may produce data overload that can be overwhelming to analyze. Nonetheless, remote sensing remains a strong ally in the quest to understand our planet's health, illustrating the urgent need for conservation efforts.

Conservation Efforts

In-Situ Conservation

In-situ conservation is fundamentally about protecting species in their natural habitats. This method acknowledges that ecosystems are complex and that species thrive best in their native environments. An important advantage of in-situ conservation is that it supports the broader ecosystem, preserving not only individual species but the intricate web of life that surrounds them.

One notable characteristic of this approach is its focus on creating protected areas, such as national parks and wildlife reserves. The uniqueness of in-situ conservation is that it fosters sustainable practices within their habitats and promotes coexistence between humans and nature. Yet, drawbacks do exist; economic interests and urban development often hinder conservation efforts, leading to habitat loss.

Ex-Situ Conservation

Ex-situ conservation takes a different route, focusing on preserving species outside their natural habitats. This is particularly significant for those species that are critically endangered. The main benefit of ex-situ conservation is the ability to safeguard genetic material and even propagate species in environments where they might otherwise face extinction.

A key characteristic of ex-situ conservation includes techniques like seed banking and breeding programs. These methods can be a lifeline for species facing immediate threats, providing a way to reintroduce them into their habitats when conditions improve. However, the challenge lies in ensuring that these reintroduced species can genuinely thrive in their former ecosystems, as conditions may have changed drastically. Therefore, ex-situ conservation should ideally complement, not replace, efforts to protect natural habitats.

Preventing Future Extinctions

The urgency of preventing future extinctions can hardly be overstated, particularly in a world where the delicate balance of ecosystems hangs by a thread. The ongoing biodiversity crisis necessitates immediate action to mitigate the factors leading to species decline. Understanding the importance of conservation efforts can pave the way for innovative solutions that protect both nature and humanity.

Policy Recommendations

To effectively address the looming shadow of extinction, robust policy measures must be developed and implemented. These recommendations should focus on several key areas:

Strengthening Legal Frameworks: Legislation that protects endangered species and critical habitats is crucial. For instance, the Endangered Species Act in the United States serves as a model that other nations could replicate or build upon to protect biodiversity.
Creating Biodiversity Offsets: Companies that are environmentally impactful should fund conservation projects equivalent to the ecological damage they cause. This “no net loss” approach can help ensure that development does not come at the expense of our planet’s diverse life forms.
International Cooperation: Biodiversity knows no borders, and therefore, effective policy must transcend national lines. Global pacts, such as the Convention on Biological Diversity, underscore the necessity of collective action in combating biodiversity loss.

In summary, policies that advocate for both conservation and sustainable development can form a solid foundation, allowing a balance between ecological health and human progress. As the saying goes, **

Ending

The conclusion serves as a vital synthesis of the multifaceted discussions woven throughout this article. It not only encapsulates the crucial aspects surrounding mass extinctions but also emphasizes the interlinked nature of life and the environment. Grasping the significance of these extinction events helps contextualize the current state of biodiversity, particularly in light of ongoing environmental changes that are largely driven by human actions.

In summarization, the key points discussed provide a compelling narrative about the historical backdrop of mass extinctions, the five significant events that have marked Earth's biological history, and the varied causes behind such phenomena. From volcanic eruptions to habitat destruction, these factors have not only shaped the biosphere but also serve as a warning for the future.

Summary of Key Points

Defining Mass Extinction: Understanding what constitutes mass extinction lays groundwork for comprehending their impacts on biodiversity.
Historical Context: A review of past extinction events connects current threats to their historical precedents.
Natural vs. Anthropogenic Causes: Differentiation between natural occurrences and human-induced factors elucidates pathways for mitigation.
Consequences for Ecosystems and Humans: The loss of species and the subsequent changes in ecosystems affect human societies significantly, leading to disruptions in food chains and loss of ecosystem services.
Current Research: Advancements in technology and conservation strategies present hope, yet clarify the urgency of addressing emerging crises in biodiversity.

Call to Action for Conservation

As we reflect on the lessons presented, there’s an undeniable call for proactive measures. Stakeholders—ranging from individual citizens to governments—must join forces in conservation efforts that emphasize sustainable practices. Notably, some actionable steps include:

Engaging in Conservation: Support organizations dedicated to protecting natural habitats.
Advocacy for Policies: Push for policy changes that prioritize biodiversity, such as emissions reduction initiatives and stricter regulations on pollutants.
Public Education and Awareness: Fostering an understanding of biodiversity's importance within communities encourages responsible actions towards safeguarding it.
Participating in Citizen Science: Opportunities abound for individuals to contribute data that aids scientific research on species and their environments.

"The Earth does not belong to us; we belong to the Earth."
This poignant insight should inspire reflective action, urging society to protect the delicate webs of life we are intricately part of. In doing so, we contribute not only to the preservation of our planet’s natural heritage but also to our own survival as a species.