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LEC 2,3
Human animal biology
- How come we have different animals all around the world?
the answer is the once all the continents were connected. 250 million years ago al the
continents were connected which was known as “Pangea”. Biogeography allows us to
understand the distribution of animals around the world. where and why they are found the
places they are.
- Time periods:
before we see the emergence of animals, the most important elements to these periods
is known as “Pre-Cambrian” period. which it implies that Cambrian period was really important
that we say any thing before that is Pre-Cambrian.
• Cambrian period is the emergence of animals life forms. This is known as Cambrian
explosion. all of the sudden animals took off and evolved at that time. this period is really
important event
• Ordovician period is the emergence of plants on the land. before the earth was very dry with
a lot of volcanic activities and earthquakes and a lot of toxic gasses in the environment.
Before this period everything was in the ocean. easy animals and plants were aquatic. in this
period plants started to colonize on land from the water. they required energy from the sun in
order to synthesize. this is adaptation on land. first animals to follow out of water to consume
those plants were insects.
• Silurian, on land now we have massive forests, lots of insects, resulted vertebrates animals
in the water and diversity of fish in this period as more animals were trying to get out of the
water to consume whats been developed on land by that time
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• Devonian period was the appearance of terrestrial tetrapods as Amphibia. Amphibia means
animals that can Live in both water and land. they really all representative of evolution of
vertebrate life from water on to land.
• Carboniferous basically the period when these terrestrial tetrapods feeding on pants and
insects.
• Permian we started to approach 250 million years ago… Pangea .. . significance impact on
life at the time. what happened in pavia is the word got a lot more dry and a lot were wet.
Changed the environment. very limited organisms to survive in this condition. Reptiles is one
that was pre adapted to the situation and they were really in good condition to survive.
• Triassic After 250 may we had the evolution of dinosaurs.
• Jurassic abundance of large Herbivore Dinosaurs
• Cretaceous evolution of flowering plants, insects trance and distribute the population.
biodiversity … 65 minion years ago.
65 million years ago the Mesozoic animals era ended and the modern mammal animals took
off. What happened?! meteor and astroids impacts… massive change in climate.. nuclear
winter.. flatttedntr most of the America north and south… massive volcanic activates and toxic
gasses in the environment.. immediately after the impacts.. the earth was clouded with ashes
which cut of a lot of living being. for approximately half a year, there was no life on earth..
plants and large animals and dinosaurs … dark environment for half a year… the organisms
that were able to survive in that environment were the once that already had the feature to
handle that. the ones who were able to survive in dark environment. mammal by definition are
the fury tetrapods which contribute to maintain a regular body temp during the nights or days
or summer or winter.
• Tertiary at 65 million years ago.. the age of modern mammals.
• Human evolution 1.8 almost 2 million years ago
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- Humans have been a huge impact on earth although they were around only for almost 2
million years.
. the smaller the animal, the less intendancy to lose heat … vice versa
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HOMOLOGIES
is any kind of trait that is common to different organism because they have herritated
from a common ancestor. the idea here is that common traits can be used to understand the
evolution history.
fort example, the internal structure of the four limbs of terrestrial tetrapods, 4 limbs of
human arm is the same order and same structure with other tetrapods such as dolphins, bats
and birds.
- Internal skeleton of all vertebrates is structurally identical
- Differences are in proportions and arrangements
- adaptation of common structures to different environments
- Strong evolution evidence is Homology structures. Homologies can be traces all the way
back to the origin of life and the common ancestor.
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- plant cells and animal cells have homologies that indicated that they are both from a
common ancestor. They have all the same units as an evidence to this hypothesis. the
similarities has maintained over their evolution
- Embryo development: cat, chicken, bat human.. we see that through out development of
embryo in uterus , we see all the same structures and all the different looking animals that
we see in the final form. they all have gills that usually developed to glands and gills.. we
know that humans don’t have gills anymore but it is presented in early development of
human embryo
- the fact that it is presented in the embryo, indicated that some time in the past, this
mechanism was useful.
“ONTAGENY RECAPITULATES PHYLOGENY”
Ontogeny is sort of the study of embryonic development and phylogeny is the evolutionary
history. the fact that our embryonic development reflects evolutionary history is another form of
evidence that we all are related to another…
- homologies can be any kind of trait
ANALOGIES
- similarities that are not due to having common ancestor but having the same adaptation to a
certain environment.
- Two swiming creature might be very similar to one another .. shark vs orca … they have very
similar structure and features… you can’t say they have the same ascestor… they only
evolved to the same environment… same adaptation
- Makes confusion
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- similar adaptation in a common environment to do common things.
- analogies is not used to group animals to a common ancestor but to group them in a
common environment.
Observable Evolution
Evolution is currently happening and it is not just limited to the past. such as bacteria
…. Bacterias becoming resistance to treatments. Antibiotic residents by bacteria has occurred
and still occurring. they are becoming stronger and adapted to it. bacteria evolve very quickly
… if after trying to kill off bacteria using antibiotic some of the bacteria survive… those who
have survive will become stronger again the treatment and they will reproduce the stronger
bacteria and eventually they become resistance to the treatment. this happens regularly and is
an evidence that evolution is currently occurring.
another example is “ Pesticide resistance”. when we apply strong selective pressures
which means a really strong agencies that causes death.. if there is any element survived in the
environment, they will be selected to distribute the population. if an element has a gene that
makes it stronger to survive in a certain environment. that element will reproduce and the next
generation will not be effected by that threat.
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Evolutionary change
the story of what happened on the birds beak relatively recently… what was observed
was that:
scientist were measuring the hight of the beaks. there was variation on that trait. variation
means some were smaller.. some bigger and some somewhat in the middle … same is hight of
humans. in the year that they were studying this 1977… there was a drought… drought means
that there was a lot of effects on vegetating and several plants were not able to survive very
well which effected on the kind of foods available. birds that had larger beaks survive better
than the ones who had smaller beaks. smaller beaks could feed on smaller foods and vice
vera.. this drought in 1977 is selected against the birds with smaller beaks that means that
evolution worked the way of favouring one kind and being against another kind.. in this case
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the evolution favoured the birds with lagged beaks because they could feed better and survive
in the environment. in 1978 the number of birds decreased … but the ones that survived were
the ones with larger beaks… there was a shift at the beak size after that period. the next
generation had mostly larger beaks and so on
another example:
about industrial melanism.. melanism refers to colouring of organisms.
moths in their natural variation have two colour forms, light form and dark form. over the past
200 hundred years .. there was a massive boom in industriation in group and this was coal fire
energy.. dark suit was going into the environment an it was depositing everywhere and layered
on the side walk.. forests and everywhere. forest became darker… trees were much darker…
there was a gradual shift in proportion of one moth to another… prior of this event there was
more light moths than the dark moths because they survived better in that environment from
the predators. after everywhere got darker it changed the proportion and now darker moths
survives better that the light colour moths. they are better adapted in hiding from predators.
increased in presentee of dark moths. this has a direct consequence on human activity.
Artificial selection
activities of human being.. purposeful selection of traits in order to survive and
reproduce a certain organism. for example now we when we go to the store we see some
plants or stuff that are not seen naturally in the world. we changed some organism in order to
have what we want to have by artificial selection mechanism. wild common cabbage is the
ancestor of all of these vegetables such as broccoli, kale, cabbage etc… prior to humans none
of these vegetables existed. we are actively controlling which individuals survive and
reproduce… this is a process of evolution even though it is guided by human desires
- by selecting individuals with desired traits and reproducing only them, we can dramatically
change organisms over few generations.
animals are also sometimes artificially selected. modern dogs are all variations of a
common ancestor of a common wolf. all the dogs are all the same species except they have
different variation… much like different looking humans around the world… asian, middle east
and etc… we have an animal that has more variations than other and this happened by human
actives and their artificial selection. same species but massive variation.
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Evolution of human leg
what was the process of the evolution of our legs?
the story starts in one of the first vertebrate animal. some kind of fish that had hind
limbs about 440 million years ago. 550 million years ago was Cambrian explosion. . there was a
vertebrate that had appendages that was useful in local motion ( meaning to get around)…
didn’t look like leg at the time… however, we the evolution of terrestrial tetrapods meaning
those land vertebrates emerged from the water based on the ancestor of fish… meaning they
had internal skeletons structures that were more supportive… primitive amphibian which is
likely to be the ancestor of all tetrapods because instead of having a loose fin for navigating
and moving in water, it acc had joined the skeleton … linked up to vertebral column which
allowed to provide more support for the organism to pull it self up right on the land. around 385
million years ago
joints in these limbs.. more effective mechanically in order support the body weight
against gravity. rotation of the elbows and knees to support the body occurred in early reptiles
for a upright posture around 220 million years ago. legs and elbow under the body provided
them more support in case of their movement and supporting their body above the ground.
there are atendeges to these limbs which are fingers and toes and nails… useful for
climbing trees or grabbing things… we start to see the evolution of flat nails and toes in
ancestral mammals in about 65 million years ago…. which is the end of dinosaurs and starts of
age of mammals.
ability to walk upright. at some point there was this gradual migration from the trees and
having the ability to walk upright and to remain upright… this resulted the evolution of leg to be
able to support the body weight more… ability to move freely which is common to many of our
cousins such as gibbons and great apes occurred about 25 million years ago.
more recently we started to see adaptations which are unique to humans. around
7million years ago when the first direct true human ancestor started to emerge… having the
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big toe oriented in the same plane as the other toes… opposite toes and thumbs from the rest
of the digits.. meaning they can link up with other.. thumb can touch other fingers… very
important adaptation for the organism to be able to grab the things. very important for animals
living in tree environments. reorientation occurred around 7 million years ago which gave a rise
to the modern human foot which is adapted to walking and running as opposed to adapted to
climbing the trees. ???? :(
Homo sapiens differ form other human species by having a slender leg and an ankle
more adapted for running. the legs gradually became more slender and more articulated in the
ankle for example tore able to be more useful in walking and running.. this happened at about
200,000 years ago.. among the first human species, they were more adapted in walking and
ruining in oppose to climbing the trees.
the history of evolution of human leg is about 440 million years… therefore evolution
doesn’t happen instantly but it is gradual through out the time… the adaptations occur to what
was prior to that adapted need that was modified to the new environmental use of it….
Mechanism of Microevolution
how this happened? what is the process underlying the genetics of a organism that leads
evolution?
changes that occur over geological time .. the emergence of species… a trait changes
drastically or over millions of years… thats MACRO EVOLUTION
Microevolution is what is going on in the genetic level that leads to the changes in
macroevolutionary time. the mechanism of macroevolution which is essentially what causes
the gene frequencies over time from generation to generation… evolution until now was
changes in a trait over time… but what we are really talking about is changes in genes over
generation … the effect on certain type of genes which then will be transferred from generation
to generation… those genes are the ones that effects the trait. chases occur at the genetic
level…
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where to start in this cycle is the production of gametes… gametes are those sex cells
that gives rise to the individuals when they are sexually reproduced. at the start of this cycle
where we are producing the gametes, there is potential to be mutations in being translation and
transcription of our genetic code as we take copies of our dna in our body and divide it into
sex cells … package it up to be the DNA of our off spring…. in this process thing can go
wrong…errors happen during copying the DNA … that could be the source of variation…
Mutation can make differences…
imagine when there is a process of fertilization… which sperm links up with which
egg… in the human reproductive system there is generally one egg to be fertilized with a
sperm.. there is million of sperms racing to be fertilize with the egg… there is a bit of a random
process which sperm to become the part of the next generation … that random proceeds is
called Genetic Drift… result in random variation in the off spring… because there is variation in
the population, some will survive better and some will reproduce better which is the notion of
natural selection…. if they don’t survive or reproduce, their genes will be eliminated from that
cycle… this will have implication on type of gametes that will be present in the cycle… one
other process that will related to the population of adult individuals, is that there is movement
of the individuals around .. as they either leave the population or join other populations or
migration which will add genes in a population or removes them thought the process of
migration. gene frequencies are effected.
- mutations happens all the time… hopefully they are neutral .. if not they are not good. over
million year… these mutations will result in emergence of a new trait.. that new trait might be
selected for the survival of the organism at the time and the environment.
- therefore the mutations are the source of variation that is selected for or against depending if
they have positive or negative effect on the the organism
example:
Beatles, they have genetics making them green. we know that genetics within the beatles
might be variation in the genes itself. after generations, traits can appear that weren’t present in
the parents… could be a mutation that resulted in a brown offspring.. in most cases is not
good… but some times if the environment is not uniform in green, maybe having a bit of brown
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might have an advantage for them which it will be selected for and after generations, brown will
be selected against green.
Genetic Drift
term refers to random processes that will effect the genetic makeup. in the production
of gametes, there is a variation in genetic content of gametes…. meaning … that we make
sperm and egg the genetic along the sperm and egg are different from one another… so there
is this sorting process and there is a uniting process that are all largely random… if we consider
that genes have different versions,.. and different version of genes are known as alleles…
whereas the the gene is the genetic unit for production of traits, there will be different version of
genes for different versions of the trait….
the beetle example,.. the gene for colour is either green or brown… so different versions
of that gene are known as alleles. we generally have different versions of a gene or we have the
same version of a gene why ? because we get a copy of our gene from one source and the
other copy from another source. … therefore, for every gene there will be different alleles. so
when we look at the production of gametes, gametes will differ from one another. The
proportion of the alleles or version of the genes do not determine what proportion of those will
be present in the next generation … but it will be a random process based on which of the
sperm containing which of the alleles mixes with the eggs allele…. two copies of dominant or a
copy of dominant and a receive will determine free for example and two copies of recessive will
result in brown colour for example… its a random process. we have tenths of thousands of
genes with different alleles…
Population of Bottlenecks
another kind of genetic drift that acc happens in the adults in a population through
survivorship. survivorship means some survive and some don’t … this process is also
random… natural disasters wipes off some population which is totally random. that is
population reduction though a bottle neck event which is reduced through a process that not
based on genetics but other events. imagine we have a population with three variation in colour
red, yellow, and green… natural disaster occurs and a certain portion of the population dies.
and then you see after the event, you see much less green population.. proportion of the
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frequency of the gene changes,…resulting more variation on some genes presented in a
population… will have an impact in the next generation genes.
example: green and brown frogs… random event that leads the bottle neck and the
frequencies of the brown frogs will be almost zero and therefore the next generation
only green frogs will be presented.
Migration and founder effect
when we leave a population you migrate away… when you start a population you are
known as founder. if we are part of a population and we have a certain genetic makeup, if we
leave that population we have changed the genetic makeup of that population.. by removing
genes or changing the frequencies … animals are mobile and this always happens. migration
from a population will most likely result in starting their own population somewhere else which
is known as founder effect. sometimes it is useful. they will leave with a specific gene variation
and the new generation and population they start it won’t have the gene variety that was
present in the previous population. This will lead to different gene frequencies, and because
different alleles of different genes leads to differences in survival and reproduction, this is
therefore a template to whats its known for “Natural Selection”.
Natural Selection
Process in which some individuals will survive better and or reproduce better than other
individuals, based on those differences that we just described in the amount of genetic
variation and the frequencies of different genes in those populations.
Rephrase : :)
Natural selection as a process, is a process by which the variation in genetic types and
frequencies leads to differences in survival and reproduction within the individuals … and that
difference in survival and reproduction it is the process of natural selection which determines
which genes of the previous generation find themselves in the following generation.
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Sexual Selection
There is a subset of natural selection based on reproductive success which is so power
full which we consider has its own category as a process. sexual selection occurs when some
individuals have greater reproductive success because of some features associated wit
improving their attractiveness or their liability are all influence on their ability to produce more
offspring. there are number of features that evolve explicitly to promote reproductive success
particularly in animals wether they are sort of fighting competitive which they acc fight to mate
with females which is very common with mammals … or they elaborate their displays …
showing off their great genes for the female so that they could mate and have grater
reproduction success.
Review:
- Evolution acts on heritable traits that vary among individuals in a population. meaning it
based on the genes.
- those differences lead to differences in fitness : variable ability to survive and reproduce
- adaptation occurs when they improve the fitness of individuals ( more likely to survive)
- evolution acts on populations ( not individuals ) by changing traits throughout different
generations
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LEC 5
The human animal…. molecular evidence … early homo evolution
- humans and chimps share 95% of our DNA in common. The 5% is responsible for the
important difference in body , brain and behaviours.
Early Homo Evolution
- up to 4 species :
• H. habilis
• H. rudolfensis
about 2.5 - 1.5 million years ago. we consider these two as one. the early humans.
Development of rudimentary tools that they made out of stone found in their environment.
development of language and rudimentary culture paintings and etc. gradual progression in
suffictication of our interaction with the world in general… which happens to tool use. the name
of their tools is related to where they were located and the type of their tools.
I.
H. Habilis Tools
- Primitive oldowan tools
They modified stones.. very hard to do … type of rock is really important… they were
able to manipulate their environment in a way where they could be more successful at feeding
in particular …. in order to hunt or having something sharp to slice or skin the animals. there is
evidence of animal bones scratches from their tools.
-Large cats were the main predators… we know they were main predators of homonins
because caves were found with chewed bones. most of the bones found were
Australopithecus which suggests that these early humans were more intelligent to co operate
and were able to use their intelligent for survival and other aspects to be more successful
overall. maybe because of increase in their bran size.
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• H. ergaster
• H. Erectus
The later humans ( more recent). 1.9- 0.5 million years ago. larger brains and height.
they were the ones who migrated out of Africa. they discovered fire use and they were more
advanced in their tools development.
1. Ergaster/ Erectus Tools
Archeulian toolbox, small axes, stone flakes used as knives and blades.
- They were better competitor than earlier homonins. they were smarter.. better
organization, better ability to corporate with one another. they were the first to hunt
large animals. they drove many to extinction either directly or indirectly… Directly by
eating only certain animals, or indirectly by killing the food of other animals and lead
to their extinction. their brain size as mentioned before was much large which
provided them the ability to work in a group and hunt in order to have a greater
success in living.
- the idea of fire extremely important. permitted them for living in cold environments.
( North of China). Fire place could have been first stable social gatherings. Evolution
of :
. Communication
. Cultural transmission
. Community development and stability
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as we move along, we note that there were other humans that existed in parallel in those
species.
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The Hobbit - Homo floresienses
Human discovered recently on Flores island in S. pacific. they were small humans. adult
size equivalent of modern 3 yeas old child. this is very common in islands. because island
compare to continental areas have fewer predators, .. they didn’t more nutrients or energy to
become bigger to taller so they are small. predation is a selective pressure that favours being
bigger. the bigger you are or stronger you are you are more able to hunt and feed yourself or
defend yourself. in Island its waste of energy and nutrients to become larger or taller from
evolutionary preceptive. Dwarfism is common on islands (limited resources, lack of predators)
Homo Neandethalensis
- Species of human that co existed with modern day humans. modern day humans
emerged about 200,000 years ago. happened liked in Europe. they persisted until about 30,000
years ago. their brains were larger than modern human brains. they lived in caves and shelters.
they had well-developed culture… they had decorations, burials. they had tools.
Neanderthal Anatomy
- They were much thicker… they had prominent faces.. their teeth became very worn
with age because they used them as one of their tools. they had stronger and bigger bodies,
they were well adapted to cold environments ( mountain regions ) physically they were well
adapted to cold. they were acc comfortable in cold .. not like other group to necessary have
fire to keep them warm.
We interacted with neanderthals… they were our first direct enemies… :
Relationship Sapiens- Neanderthals
- they fought with one another… there is evidence that we did interbreed. this evidence
is genetically based and there is reproductive hybridization that went on between neanderthals
and modern day humans and we now have DNA evidence that we can trace back to the
neanderthals … some of the traits today that came form neanderthals is red hair… bone
behind the eyebrow…. other traits that were came from the neandethals were the physiological
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traits…. meaning the desendece of the human neanderthal hybrids would have been better
adapted to cold climates….
- even though they were around and they seemed to have the potential to be successful
and smart… they seem to lack of that ability… they had limited hunting abilities like we did…
we were way more organized … they were lacking some cultural elements… we had more
suffisticated tools at the time including hooks to catch fish, nets, needles …) there is no
evidence that they had those kind of tools. their clothing were much simpler than modern
humans who had needle to acc made some clothes for themselves.
- They got injured more… they didn't’;t live as long. they had short life-span.as they
grew older they had more knowledge and if the older people passed away they would lose
some knowledge or advantage to use the knowledge that older people had. same as internet
that we rely on today to find information, they were relying on the older people in their group.
this lead to the limited knowledge and culture they had.
Neanderthal Tools:
-
scraper
mousterian style
pointed darts for spears
copied modern human tools
. intermediate form of tools
. Did not have sophistication of modern H. Sapiens tools
Neanderthal extinction
- They got wiped out by combat vs modern humans which lead to their extinction. they
were the first human genocide… we know that modern humans won because most of the
injured and dead remaining were mostly neanderthals. other evidence is to counteract the
hypothesis they were extinct due to climate change… because climate was changing greatly
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over the last million years or so… they were very well adapted to cold… they might also be
extinct due to climate change.
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- nowadays we have molecular techniques to trace back the DNA and genes back in
time to see when they first emerged and when they first originated. XX female and XY for
male…. Y chromosome is only for males and always came from fathers,.. Therefore, we can
trace back the Y chromosomes using molecular techniques and knowing rates of mutation that
we know, we can calculate how long that Y chromosome has been existed and how much
change has undergone throughout time and we can find the recent common ancestor for
humans…..
- we can find that the age of genetic atoms is about 200,000-250,000 years ago which
correlate exactly with the fossil records obtained so far. Therefore, MODERN DAY HUMANS
emerged about 200,000 years ago.
- Likewise we can calculated the age of the other sex humans. we know that
mitochondria in our cells are all came from our mother ( female sex). These mitochondrial cells
have DNA which again can undergo molecular studies and we can trace back to find the first
female… which again the age was found to be around 200,000 years ago… This confirms that
Modern humans took off around 200,000 years ago… this doesn’t mean that these two were a
couple … they may have never met.
- those modern day humans are homo sapiens, they look like us … many many aspects
that we share… they had good ability to build something … they had composite tools, we are
very cooperative culture, language and art well- developed, very successful in hunting and
corporation… we had ability to speak at least physically… the history of modern humans also
involved global migration.
⭐ 🔥 BIRTH OF HUMAN SPECIES WAS IN AFRICA AND MODERN HUMANS HAS SEEN TO
BE IN EUROPE AND MIDDLE EAST 🔥 ⭐
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Pleistocene Human
- most recent humans… they were likely very similar in their ecology.. meaning they
were hunter and gatherers over large distances. males more hunters and females more
gatherers… there was division of labour between the sexes… this was likely an important
concept to their extinction between an evolutionary process that would make human males
and human females very different from one another…
- importantly to recognize is when we are talking about hunting and gathering, it also
implies nomadism … because we would essentially complete the local resources and after
move on to another area… there was no ability to harvest regalarly and continuously from a
local environment… “ get what you can from here then move on to another place and get what
you can form there and so on…”
- One of the effects of this would have been development of a very strong spatial
perception which is associated with part of the brain known as “Hippocampus” and we have a
very important ability in a sense to know where we are at the time… because this is an
important feature to not get lost when you are travelling along long distances.
Human in North America
- Basic understanding of humans in north America is that it happened at some point
during the most recent glaciation. so glaciations during Pleistocene had been frequent and
there were periods of cold and periods of warm … one of the effects of this is that glaciation
periods would create a bridge between Alaska an (sereyvia !?) ice was the bridge that humans
could walk on …
- This is how human migrated to north America and we see that generally people in
north America seemed to have very related genetic similarities with one another which is due to
the founder effect. small population from Alaska moved to north America and reproduce and
distributed …
- Showed susceptibility to European diseased upon arrival of colonists.
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- These modern humans in north America? were excellent group hunters ( mammoths,
mastodons, giant sloths, bisons).. Facilitated extinction of large predators due to lack of prey
food (e.g large cats)
- they were big animals around up until 12000 years ago which most of them died
off. Most of the animals that did die off were mostly adapted to cold environments such
as Hairy Rhinoceros which existed in Europe at the time was well adapted to cold
environments and it got extinct after the glaciations that happened.. same thing
happened in North America, massive and large elephants, there was this very rapid
extinction that seemed to because of humans . ??????? Pg 4 topic two part two…
- Giant Ape, the humans didn’t like these guys … possible origin of Yeti/ Bigfoot
mythology… humans felt threat and didn’t like these creatures..
- ( Giant sloth, Mastodons, Giant Bison, Mammoths ) all in north America got extinct
which are are fossil evidence that humans were involved in their hunting and extinction … they
didn’t extinct naturally … these extinctions mostly happened all around the world around the
same time… what was going on at that time ? well… modern humans were moving around and
exploring the world… interfering with these giant animals .. felt threat of having them around
and they decided to kill them off and eventually they got extinct.
- Principle Hypothesis: Over hunting ( pleistocene overkill hypothesis)… Evidence:
. Mostly large mammals and birds affected
. extinctions in different places at different times
. extinction correlated with sudden arrival of humans
Questions:
So did these extinctions happened at the same time ? :/
To be continued with Cro-Magnon Artwork LECTURE 6 JAN26th
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THE HUMAN ANIMAL :
SKIN LEC 6-7
what is vertebrate tetrapod skin represent?
- we are vertebrate tetrapods… the story of our skin therefore is traced through
evolutionary history to those animals that left water and colonized on land.. because our skin
carries many features associated with that evolutionary history.
- We look at the evolution of tetrapods to nearest ancient known as Amphibia, we see
that skin at that point was becoming a very important features for tetrapods and continued to
do so for varies different reasons. when we look at Amphibia.. there are organisms that lived in
both aquatic and terrestrial environment. so they really do represent that sort of transitional
type of organism that would have been the ancestor of truly terrestrial or vertebrates, but the
reason that they are amphibian and not truly terrestrial is because they lack features that allow
them to live permanently on dry land. some of those features are reproductive… Amphibians
do not have internal fertilization or shelled eggs that means they are restricted to water for
reproduction.
- Internal fertilization is as mechanism in which sperm is deposited directly into the
female reproductive tracks and one of the benefits of that apart of increasing the fertilization
efficiency, is that the gametes are not free in the environment to be consumed by another
organism or just dry out… “Desiccation” which is a process of being things dry.
- The Amphibian as well is limited in humid environment. because the skin itself is
permeable .. meaning that it can absorb and transmit liquid and other subtense through it .. in
fact this is how amphibians breath.. through their skin. the skin that is highly sense-table to
desiccation. One of the reasons why amphibia represent a transitional organism in the
evolution towards terrestrial vertebrates, they really are transitional because they are somewhat
constrain by requiring to be around water because of the lack of adaptations for their
reproductive elements and for their skin to be allowed to be out in completely dry air.
- The features that allowed reptiles to be terrestrial are those features that were absent
in the amphibia…meaning.. internal fertilization.. having a shelled egg which allowed them lay
their embryos in dry land…. and also a scaly impermeable skin. this repteliance scaly skin is
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one of the main features that gave rise to their ability to dominate on the hot dry continent of
Pangea and not have to return to water.
- impermeable meaning water vapour cannot get pass through as well as restricting gas
flow.. they cannot breath through their skin… like amphibia do.. the substance that goes into
making these scales in reptiles is Keratin which is an important protein because the extension
in their skin is made of keratin … their skin, feathers, nails , beaks are all made of keratin.
- mammals are hairy animals. it is features for mammals… others do not have hair…
hair by definition is mammalian trait. as humans we are hairy animals.
SKIN FUNCTIONS
- Protection: mechanical, chemical, thermal, bacterial… generally speaking skin is a
really important organ for vertebrates …. skin is a barrier… mechanical : rubbing against
things, chemical such as acid basis, etc… thermal insulated layer .. very important function …
being capable for containing internal temperature… endothermic animals are able to generate
the heat within and maintain it which is possible by these insulating layers that birds and
mammals has…. another function as protective barrier is against microbial infection…
associated with immune function ( bacterial infection).
- Water proofing
- makes proteins associated with immune system
- regulate body temp
-synthesized Vitamin D ( interaction with UV light)
-Important sensory role.
- darker skin has more filtering effect and therefore it limits the ability of synthesizing vitamin D
which will lead to health related issues…
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How does skin look like (mammalian skin) :
the mammalian skin has an important dermal layer… meaning a thick issue in muscular like
( Epidermis, Dermis, Hypodermis)
Epidermis:
- basically what we see in epidermis which is the surface of our skin, we see some
things coming out… mostly we see hair … there are also pores.
- outer most portion of our skin. its basically what we consider to be our skin for
the most part. the outer most layer in epidermis is “ stratum Corneum”. this is the outer most
section and it is basically dead cells. new cells are produce at the very first section of
epidermis “ Dermis” and they move out wards and by the time they get to strata cornea are
completely dead. they are concisely being shed.. 40,000 cells per minute because they are
basically dead cells. which these dead cell have their own function on our skin. you see dust i
your home.. most of it is your skin cells :)) .. this section in epidermis is very thick compared to
other section in this part .. it absorbs water pretty well.. they don’t transmit water into lower
layers… but it absorbs water which is why your skin shrinks when you spend time in the bath
tub or a pool.
2- Stratum Basale:
•
•
•
•
Is the base layer as its name presents. (base layer in Epidermis).
not a very thick layer.
this is the source of new made skin cells.
they contains keratinocytes.which means they are cells that produce keratin. which is a
very important feature in vertebrate skin which is originated in this layer, stratum basale
• new cells made will move out wars to the outer most part.
other cells present:
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- melanocytes ( are those that produce pigments),
- Langerhaus cells ( those are the ones that have immune function.. anti- microbial
property),
- Merkel cells ( are important for light touch sensateon… not pressure receptors but
very sensitive touch that we can feel).
3- Stratum spunosum:
• much thicker layer
• an area within epidermis which is sort of linking of the cells together by desmosomes.
physical barrier for things to be able to get through between the cells
• where keratinization begin. process in which keratin gets added to cell. it begins here
because the keratin starts becomes active but the cells are not keratinized yet. just a concept
of that process
• looks spiny because we can cell nuclei, there are a lot of metabolic activities going on in the
cells in this point, keratin starting to produce, skins cells starting to grow, desmosomes
getting quite active… so this involves a lot of metabolic activity within the cell and for that
reason the nuclei is more pronounced… se we can see them in that stratum spinosum.
4- stratum granulosum:
• is the stage in which we see the cells really become keratinized , but also much more tightly
bound together. Keratohylin which are kind of proteins where there are fibres of keratin that
are starting to be linked together much more tightly. start to filling the spaces between the
cells. very important process in creating a barrier which what epidormis eventually gonna
become.
•
29:30 6-7
Dermis:
- we see there various kind of receptors, mechanical receptors either for senses or
pressures or pain.… there are nerve cells.skin sensitivity is important.. glands such as sweat
glands and oil glands….
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