Answer:
speciation is when one species splits off into multiple species.
In-depth answer:
Speciation can happen in 4 different ways, the first being Allopatric Speciation, where 2 groups of the same species are physically separated for extended periods of time, and when they're re-introduced, they don't breed.
Sympatric Speciation is when 2 groups of the same species aren't seperated, but form different behaviors that isolate them reproductively (the groups wont inter-breed)
Parapatric Speciation is when 2 groups of the same species are suddenly placed into a new environmental niche, and adapt in different ways to fill that niche.
Quantum Speciation is much less recognized, but it's when a new species rapidly evolves and 'buds off' from the original group
 
        
             
        
        
        
There are many cases of homeostasis mechanism. In this mechanism, there will be a receptor that will catch a condition. After that, an order will be sent to various place depend on the condition.
One of them is temperature control which was done by shivering or sweating. When your body temperature is too high, the thermoreceptor will detect it and then the brain will send the order to the body sweat glands. Sweat on body surface will evaporate and reduce body temperature.
When the temperature is too low, the brain will tell the muscle to shiver so you can produce heat.
Other than temperature, homeostasis also control blood pressure, or many chemical level(oxygen, glucose).
        
             
        
        
        
There are several ways selection can affect population variation:
stabilizing selection
directional selection
diversifying selection
frequency-dependent selection
sexual selection
As natural selection influences the allele frequencies in a population, individuals can either become more or less genetically similar and the phenotypes displayed can become more similar or more disparate. In the end, natural selection cannot produce perfect organisms from scratch, it can only generate populations that are better adapted to survive and successfully reproduce in their environments through the aforementioned selections.
Hope it helped, much love 
The jokester, hehe
 
        
             
        
        
        
All eukaryote cells lack a nucleus