Chapter 7: Geographical Variation and Speciation

Question 1

What is a polymorphic species?

Answer 1

A species formed of several geographic groups that are distinct from one another by certain recognizable traits. The individuals in these groups will be called subspecies or morphs

Question 2

What are ecogeoraphic rules?

Answer 2

models of geographical variation that follow/are cause by climatic gradients for many species

Question 3

What does Bergman’s rule and give an example

Answer 3

This rule states that individuals of a species seem to be larger in size in the northern part of their geographic distribution.

Looking at two woodpecks that are from the same species, but one living in Mexico, and the other living in Alaska, you find that the one from Alaska is much larger in size than the one from Mexico.

Question 4

Explain why this law is true. ( Why is being large in size an adaption for individuals living in the north?)

Answer 4

To understand this, we need to look at the relationship between volume and surface area. For example, a small marble will have a high surface area relative to its volume compared to a soccer ball which will have less surface area relative to its volume.

Translated, for endotherm animals in the northern part, this is an advantage as they will have less surface area relative to their volume which will mean they will have a smaller tendency to lose heat. While being smaller in size means that you will have a higher surface area compared to your volume so you will lose a lot of heat.

Question 5

WHat is Allen’s rule?

Answer 5

It states that animals that live in the north will be shorter and massive, so like have shorter legs and massive bodies, and that animals living in the south will have longer and thinner extremities, so like longer ears and thinner legs.

Question 6

What is Gogler’s rule? Explain why it is true.

Answer 6

It states that individuals of a species will have a darker pigment due to living in humid climates. This is because of the melanin that creates the darker pigment in the feathers. It provides protection from bacterial attacks, which are very prevalent in humid environments. In more open and dry habitats, there are no bacterial attacks so birds there are actually very light as there is no need for melanin to protect them from attacks

Question 7

How many human species existed 2 million years ago?

Answer 7

There was about 6 human species living at the same time

Question 8

What characteristics if found in a fossil duel would let an anthropologist know that its is a hominin fossil?

Answer 8

If the fossil has a foramen magnum whose hole is ventral, meaning the vertebral column will connect directly under the cranium then that means it is a hominin because all human species have ventral holes. Other primates, this hole is dorsal because their heads are in front of their shoulders

Question 9

In what hominin did the evolution of the loss of fur occur

Answer 9

in Homo ergaster and homo Erectus, which are suspected to be the same species

Question 10

The evolution of humans follows what kind of diagram what does this mean?

Answer 10

The evolution of humans follows some kind of a branching diagram, meaning that there are some branches that didn’t necessarily lead to humans, that have their own history and diversity and then went extinct

Question 11

What is an example of a human species that did not lead to humans? What is an interesting characteristic it possesses that humans do not have?

Answer 11

An example is the paranthropus bosei. Looking at its cranium, you can see that they had bony brows, really large lower jaws compared to humans and they had a crest on their cranium. The really large jaw meant that they had a really strong bite. This was also associated with the fact that they had very large teeth. This is often referred to as the nutcracker fossil, meaning they were able to break down really hard structures. In order to have a strong bite, then you need strong muscles. Outside of the lower jaw is attached a muscle, called the temporalis muscle. This muscle covered the whole part of the jaw, went under the zygomatic arch, and attached on the side of the cranium. The muscle was so strong, that the crest on the cranium allowed for more surface area of the muscle. This is why the crest exists. SO in a sense, the cranium was built to bite. This species did not lead to descendants associated with humans. They had a secondary branch that evolved their own morphology.

Question 12

What was the A. Afarensis’s life like 3.7 to 3 million years ago?

Answer 12

They had a very simple way of life. They had toes that were oriented in the same way and were bipedal so they could walk. They had long fingers and hands that allowed to climb trees. Their daily life probably just involved climbing teers, eating fruits from those trees, walking, and moving to other trees

Question 13

What happened 3 million years ago and what impact did this have on the hominin species?

Answer 13

The cooling of the climate probably meant that tropical forests receded and savannas formed, which are open habitats made up of lots of grass and weeds and little trees. The hominin species present, a few of them or atleast populations of them became better adapted to living in open habitats.

Question 14

What are some notable changes that occured for the species living in the savannah?

Answer 14

The species living in the savannah was the homo ergaster. With water and fruits being less available, they had to walk longer distances to hunt for prey and get water. It is with this species that we see the hominin species becoming taller, having larger brains, and have legs that are much longer and better adapted to walking and running.

Question 15

What is the difference between the A. Afaresis and Homo Ergaster species?

Answer 15

The homo ergaster lived a more active lifestyle of hunter-gatherers where they had to actively look for prey and get water. Also, the homo ergaster species were better adapted to their new open habitat environment. Also, A. Afarensis had fur while homo ergaster lost it and the difference is due to their different lifestyles and environments.

Question 16

How did the evolution of the loss of fur occur in homo ergaster?

Answer 16

With their new lifestyle, homo ergaster needed a good and efficient thermoregulation. The only way to achieve this was to increase the number of sweat glands and have less fur. This is because evapotranspiration is far less efficient with fur, while bare skin allows for better evapotranspiration.

Question 17

What kinds of glands are present in great number in furry animals? What are these responsible for? What do they do in these animals?

Answer 17

Sebaceous and apocrine glands. They secrete proteins and waste and produce oily sweat

Question 18

Why is it hard for furry animals to sweat or perspire?

Answer 18

They have only a few eccrine sweat glands. These glands produce watery sweat. They are found in great numbers in humans, which is why it is not difficult for humans to sweat.

Question 19

Why can humans really good at sweating?

Answer 19

• Humans are really good at sweating because they have this high number of sweat glands that can process a lot of water and the fact that we have lost our fur makes for very easy evapotranspiration. This has evolved as a response to selective pressure associated with species of hominin, specifically the homo ergaster, that lived in open habitat and that adapted a very active lifestyle of hunter-gatherers.

Question 20

What happened at the same time that humans lost their fur? How long ago was this?

Answer 20

At the same time that fur was lost in humans, natural selection favoured darker skin. This was about 1.2 million years ago.

Question 21

What does this say about how old the allele for darkskin is?

Answer 21

The alleles for darker skin must be about 1.2 million years old.

Question 22

How and why did natural selection favour darker skin?

Answer 22

Once the fur was lost in homo ergaster/hominin species, the skin underneath was a pinkish pale colour. There was a variety of skin color due to genetic variation and it so happens that darker skin actually provided protection against bacterial attacks, drought, ultraviolet rays, and vitamin deficiencies. We see here that the functions that were normally performed by the fur had to be taken by the skin. So, it is clear that natural selection would favour individuals with thicker, darker, and more acidic skin over the other skin colours.

Question 23

How long did the skin in hominin species remain dark?

Answer 23

The skin remained dark for 1 million years

Question 24

What is a possible explanation for how paler skin evolved?

Answer 24

Homo sapiens started dispersing from Africa 100,000 years ago and invaded Southeast Asia 70,000 years ago and Europe, 40,000 years ago. The population in southeast Asia moved north away from the equator and into Europe and the selective pressures in this new environment gave rise to paler skin.

Question 25

What is folic acid, why is it important, and how can it be destroyed?

Answer 25

Folic acid is also known as Vitamin B9 and it is a very important vitamin, such as in embryo formation. Not having it would result in vitamin b9 deficiency which can lead to malformations such as developing a spina bifida, amongst other things. It is destroyed by excess UV rays.

Question 26

Why was dark skin favoured in this environment?

Answer 26

Dark skin provided protection from UV rays, meaning that individuals that were dark were safe from b9 deficiency. This dark skin colour became an adaptation because it helped individuals who had it to survive and reproduce more than those who were paler in that environment that contained a lot of UV rays.

Question 27

How and why did paler skin become favoured by selection?

Answer 27

Vitamin D3 is synthesized in the skin by UV rays and it helps in the absorption of calcium and potassium in the gut and a lack of it can lead to diseases such as rickets in the offspring.

People with intense rickets do not have a high survival or reproductive output. So individuals with enough vitamin d3 will survive.

What will ensure that they get enough vitamind3? paler skin

• If you go in the higher latitude, that means that individuals will compensate for the fact that UV rays are less abundant in the northern latitude by having paler skin, so they will absorb more UV rays and this will prevent any possibility of having diseases such as rickets. SO in a population with individuals of dark and pale skin, there would be selection for the paler skin

Question 28

Give a historical example that illustrates/explains the relationship between vitamin D3 deficiency and UV radiation

Answer 28

when black people were freed in the 1800s, many moved from the south to the north of america. The south had a relatively high amount of uv rays. When the black people moved to the north in cities like boston and started reproducing, they found that many of their babies had rickets and di not understanding why this was only found in people of african descent. This was later understood to be due to the lack of uv rays in the north and vitamin d3 defiency.

Question 29

Explain the morphological species concept

Answer 29

This concept is used the one that is used most of the time to categorize species. It consists of bringing together under a species name individuals who share similar and unique morphological traits. Here, taxonomists describe a type specimen known as the holotype and identity its unique morphological traits. Then, upon finding specimens that have the same traits, will group them under the same species name. Some of these specimens may have some variations in their morphology and these are called paratypes. There is always one holotype and the other specimens are paratypes.

Question 30

Where does this concept stem from?

Answer 30

It stems from Aristotle’s essentialism which stated that you had to observe nature t understand the essence of things. So you had to look at say a cat to understand what makes a cat a cat

Question 31

What is the biological species concept?

Answer 31

This concept describes a group of populations whose members can interbreed and produce hybrids but do not because of some barriers that prevent them from interbreeding.

Question 32

How would you use it to describe if species are valid or not?

Answer 32

This concept can only be observed in nature and in area of sympathy, or overlap of the two populations. If individuals from the two populations can intebreed and produce viable and fertile offspring, then they are the same species and just different populations. But if, they do not produce viable and fertile offspring, then they are valid species.

Question 33

What is reproductive isolation?

Answer 33

This means that some biological barriers that prevent members of two species from interbreeding and forming viable and fertile hybrids

Question 34

What is is the difference between prezygotic and postzygotic barriers and which is favoured by selection?

Answer 34

Prezygotic barriers are barriers that form between individuals of different species that prevents them from forming hybridized zygotes and there prevents the loss of gametes, while with postzygotic barriers, hybrids are formed but these barriers keep the hybrids from being viable or fertile. This kind of barrier implies the loss of gametes. Here, parents invest energy in caring for offspring that will not be able to pass on their genes because they will either not survive or not reproduce. This is clearly evolutionary disadvantageous and natural selection will favour prezygotic barriers because they prevent this from happening, so they prevent these non-viable and infertile hyrbrids from forming

Question 35

What is phyletic speciation (anagenesis)?

Answer 35

This means that a species modified itself through time to become another species. This does not explain biodiversity. If this mechanism was in place, there would only be one species bu have millions of species and the next mechanism explains how species multiply.

Question 36

How does the multiplication of species work (cladogenesis)?

Answer 36

here you start with one species and get two populations of that one species and are reproductive isolated and will generate different species. This is a very important process of speciation. This is the only mechanism responsible for biodiversity

Question 37

What needs to occur for new speciation to form?

Answer 37

For speciation to occur, so for new species to form, you cannot have gene flow occurring so there needs to be a barrier between populations

Question 38

What are the two kinds of cladogensis speciation that interrupt/prevent gene flow? What is the difference between the two

Answer 38

Allopatric speciation and sympatric speciation.

The first means that individuals from different populations are separated by a geographic barrier that keeps them from coming together and interbreeding, while the later is a barrier that prevents gene flow but that does not require geographic isolation to occur.

Question 39

What is sympatric speciation and how can it occur?

Answer 39

This is the kind of speciatio occurs in populations that live in the same geographic
area. It can occurr if gene flow is reduced by such factors as polyploidy, sexual selection, and habitat differentiation

Question 40

What is polyploidy and what interesting about it?

Answer 40

It is an accident during cell division that results in extra chromosomes. This can lead to the formation of new species, especially in plants, and according to botanists, more than 80% of the plant species we have today have originated from polyploid speciation.

Question 41

What is autopolyploidy and how can it generate new species in the same geographic area?

Answer 41

This occurs when an individual has more than 2 chromosome sets all from one species. So in this case, the individual is a tetraploid, 4n, instead of a diploid, 2n.. So tetraploid plants are reproductvely isolated from diploid plants because when they mate with them, they from 3n plants that have reduced fertility.

Question 42

WHat is allopolyploidy and how can it lead to speciation?

Answer 42

Allopolyploidy is when organisms contain two or more sets of chromosomes that are from 2 different species. Allopolyploid offspring will have the genetic make-up for two different species, which makes it a hybrid and a different species from the parent species. The creation of a new species is known as speciation.

This occurs when two different species interbreed and produce a hybrid offspring. Becasue the hybrid has sets of chromosomes that orginate from different parental species, it will not be able to interbedd with individuals from either of the parent species.

Question 43

WHat are three things that can occur at hybrids zones?

Answer 43

Reinforcement, fusion, or stability