Human Impacts on Evolutionary Processes (HL) (DP IB Environmental Systems & Societies (ESS))

Human Impacts on Evolutionary Processes

• Evolution refers to the changes in the genetic diversity of populations over generations

  • Evolution is driven by the process of natural selection

  • Traits that help organisms survive and reproduce are passed on more frequently, allowing species to adapt to their environment

• Human activities have altered natural environments, creating new pressures on species and influencing evolutionary processes

How human activities are affecting evolution

Climate change

• Climate change, mainly caused by burning fossil fuels, is altering ecosystems and habitats

• For example, warmer temperatures are forcing some species to adapt quickly, such as Arctic animals like the polar bear

  • Polar bears are facing evolutionary pressure due to melting sea ice

  • They rely on sea ice to hunt seals, their main food source

  • As ice melts earlier in the year and forms later, polar bears have less time to hunt

  • This has led to:

    • Smaller body size: some polar bears are reaching smaller adult body size due to reduced food availability

    • Shifts in hunting behaviour: polar bears are increasingly forced to hunt on land, where food sources are less abundant, which could eventually lead to long-term evolutionary changes in their diet and behaviour

    • Increased land travel: some polar bears are adapting by moving over larger areas to find food, potentially favouring individuals that are better at long-distance travel

  • Climate change is driving both behavioural and physical adaptations in polar bears

  • As environments change rapidly, only individuals with specific traits may survive, causing evolutionary shifts in the population

    • This could lead to future evolutionary changes in polar bear populations

Hunting, poaching, and harvesting

• Hunting and poaching puts direct pressure on specific species

  • This can lead to changes in the traits that help the individuals of these species to survive

• For example, in Gorongosa National Park, Mozambique, poaching for ivory during the civil war led to an increase in tuskless elephants

  • Poachers were less likely to kill elephants without tusks

  • Over time, tuskless elephants have become more common due to this selective pressure

  • As a result of human actions driving natural selection, the tuskless trait has become more common

• In some fish populations, overfishing of large fish has led to a population dominated by smaller individuals, as larger fish are more likely to be caught

Creation of new habitats and fragmentation

• Human activities like urbanisation and agriculture lead to habitat fragmentation and the creation of new environments

  • This puts pressure on native species to adapt or move away

  • Urban areas favour species that can adapt to human environments, such as pigeons and rats, which evolve to thrive in cities

  • These species may evolve traits such as greater tolerance to pollution or greater ability to find food in human-dominated areas

Artificial Selection

What is artificial selection?

• Artificial selection is the process by which humans deliberately choose specific plants or animals to breed based on desirable traits

  • For example, farmers might breed crops with higher yields or livestock that grow quickly

  • This process is known as selective breeding

  • Humans have been selectively breeding organisms for thousands of years, long before scientists understood the genetics behind it

• Artificial selection is different to natural selection, where environmental pressures determine which traits become more common in a population over time

  • Natural selection is not directed by humans (it is not deliberate)

Selective breeding in animals

• Humans selectively breed animals for a variety of traits, including:

  • Cows, goats and sheep that produce a higher yield of milk or meat

  • Chickens that lay large eggs

  • Domestic dogs that have a gentle nature

  • Sheep with good quality wool

  • Horses with fine features and a very fast pace

• An example of an animal that has been selectively bred by humans in many ways to produce breeds with many different characteristics is the domestic dog, all breeds of which are descended from wolves

Selective breeding in plants

• Humans selectively breed plants to develop a variety of traits, including:

  • Disease resistance in food crops

  • Increased crop yield

  • Hardiness to weather conditions (e.g. drought tolerance)

  • Better tasting fruits

  • Large or unusual flowers

• An example of a plant that has been selectively bred in multiple ways is wild brassica, which has given rise to cauliflower, cabbage, broccoli, Brussels sprouts, kale and kohlrabi

How does artificial selection reduce genetic diversity?

• When breeders choose individuals with specific traits to reproduce, only the genes for those traits are passed on

  • This reduces the overall number of different genes in the population, making the gene pool smaller

• This reduction in genetic diversity can make populations more vulnerable to diseases and environmental changes

  • For example, many commercial crops like bananas and potatoes have very low genetic diversity (they are all very genetically similar), making them vulnerable

  • Panama disease has devastated many banana plantations

• With less genetic variation, populations lack the flexibility to adapt to changes

  • This can reduce their resilience to challenges like climate change or new pests and diseases

Economic and environmental implications

• Economic value:

  • Artificial selection can increase crop yields and livestock productivity, providing short-term economic benefits

    • For example, dairy cows have been selectively bred to produce more milk, benefiting the dairy industry

• Environmental vulnerabilities:

  • The lack of genetic diversity can make artificially selected breeds more vulnerable to sudden environmental changes

  • This can lead to crop failure or large-scale livestock deaths

  • This can have significant long-term economic costs

    • For example, the Irish potato famine in the 1840s was made worse because people depended on a single potato variety that was vulnerable to potato blight disease