GCSE biology Evolution and variation environmental factors and combined effect of genetic factors and environmental factors survival of the fittest Doc Brown's biology revision study notes

GCSE level exam revision notes on Evolution: 4. Variation

Environmental factors and combined effect with genetic factors

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(4) Environmental factors - environmental variation

In many ways an organism's 'full potential' is controlled by its genetic code in the chromosome genes.

However, whether or not an organism develops into a strong healthy specimen can be determined, to some extent, by environmental conditions e.g. the conditions in which the organism grows and develops.

The differences observed between individuals in a species is called environmental variation.

Environmental variations in a phenotype are also known as acquired characteristics. - acquired in the organisms lifetime - NOT due to genetic factors.

Examples of 'survival of the fittest'

(i) In third world countries, where nutritious food and quality medical services are scarce, children cannot grow and develop properly and suffer from malnutrition and are more prone to infectious diseases.

(ii) If fair skinned people are exposed to lots of sunlight, the body responds by producing more of the dark pigment called melanin, and your skin darkens in colour to protect you from the sun's harmful uv rays.

People of e.g. African origin, already have a genetic adaptation to produce a dark skin.

(iii) A plant that receives plenty of water, nutrients and sunlight can grow into a health 'lush' green plant.

If the soil is too dry or the plant grows in the shade, the lack of water, nutrients or light inhibits growth, resulting in e.g. a thin stem and yellowing leaves, and maybe won't even survive such harsher environmental conditions.

(iv) People who eat too much fatty food tend to be larger in size and have higher blood pressure, whereas people who watch their diet (more nutritious and balanced) and take regular exercise tend to be leaner and fitter.

(v) 'In the wild' animals compete for resources including food, water and mates for reproduction.

(vi) How susceptible are animals to a predator?

(vii) How susceptible to a disease?

The net result from ....

All of these acting as selection pressures,

and they all affect the chances of animal/plant surviving and reproducing.

Therefore, those plants/animals best suited/adapted to surviving are more likely to pass on their 'beneficial'/'advantageous' genes - in other words the alleles for the most useful characteristics will be passed on to the next generation and become more common in the population.

Those individuals, and even the whole population of a species (becoming extinct), which are less well adapted, are the least likely to be able to compete and survive and pass on the less effective alleles ....

... in other words the above describes what Darwin called the 'process of natural selection' and the 'survival of the fittest'

more on natural selection

Are environment effects inherited?

Although 'local' conditions can affect an individual organism, the 'negative' characteristics described above are not usually inherited (the theory of Lamarckism).

The children of a couple of fair skinned parents who like sunbathing, are highly likely to be fair skinned too.

(4b) Combined effects of genetic and environmental factors

All scientific research suggests that an individual organisms detailed characteristics are a result of both genetic variation and environmental variation factors.

e.g. in the case of human characteristics - academic ability, body weight, height, physical strength and athleticism, skin colour, teeth condition etc.

For many of your characteristics, your genes provide you initially with your maximum potential (as far as we know),

BUT, e.g. good diet, physical activity, intellectual stimulation and how well you are cared for in your upbringing play a large part in what you become!

Poor lifestyle or poor diet can make you more susceptible to some diseases.

However, no matter how good your 'upbringing' is, some diseases like cancer and heart disease can sometimes be linked to an person's genetic make-up.

See also Part 6

More on genetic variation, mutations, variants, effect on coding and non-coding DNA and the mechanism of natural selection - a modern genetic interpretation

Key points Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Key ideas and examples on variation in evolution due to environmental and genetic factors

Biology notes on Variation, covering both genetic and environmental influences, and why they're crucial in understanding evolution:

Variation in Organisms

Variation refers to the differences in characteristics between individuals of the same species. These differences can be subtle (eye colour) or significant (height, disease resistance).

Types of Variation

Genetic Variation
This type arises from differences in the DNA sequence among individuals. It’s inherited and passed on from parents to offspring.
- Caused by:
  - Different combinations of alleles during sexual reproduction.
  - Mutations — random changes in DNA that can introduce new traits.
- Examples:
  - Blood type
  - Eye colour
  - Natural resistance to certain diseases
Environmental Variation
These are differences caused by external factors, not genes. While they can influence how characteristics are expressed, they are not inherited.
- Caused by:
  - Climate, diet, culture, lifestyle
  - Accidents or injuries
- Examples:
  - Tanning of the skin due to sun exposure
  - Muscle size from exercise
  - Language spoken
Combined Influence
Some traits are affected by both genes and the environment.
- Example: Height — influenced by genetic factors and nutrition during childhood.

Why Variation Matters in Evolution

Variation provides the raw material upon which natural selection acts. Here’s why it’s so important:

Survival of the fittest: Some variations provide advantages (e.g. camouflage, resistance to drought), helping organisms survive and reproduce.
Differential reproduction: Individuals with favorable traits pass on their genes, increasing the prevalence of those traits in the population.
Adaptation over time: Over generations, these advantageous traits become more common — leading to adaptation and eventually, evolution.

Without variation, all individuals would respond the same to changes in the environment — making a species more vulnerable to extinction.

Summary Points

Variation is vital for the diversity and adaptability of species.
Genetic variation is inherited; environmental variation is acquired.
Evolution by natural selection depends on genetic variation within a population.

Summary of learning objectives and key words or phrases

Know that evolution and variation are affected by environmental factors and that the combined effect of genetic factors and environmental factors are major contributions to the 'survival of the fittest'.

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