Dear Ali,

This is a great question. You have obviously spotted the major groups, insects, chordates and plants, but there are, as you suggest many more. I don't have a 'number' answer to give you, but it is indeed many many times. Life started in the oceans more than 3.5 billion years ago, and by 540 million years ago, all/most of the major animal Phyla were present. Just thinking about animals, we have beautiful fossil deposits from Canada to China that show the amazing diversification of animals at this time. We have annelid worms, molluscs, you name it. All of these groups originated in the seas. It follows that if we find them in terrestrial environments either as fossils, or alive today, they must have made that transition to land. How many times the land has been invaded by animals is hard to tell. It is fair to say that a minimum number must be the number of Phyla that we find on land. However, it isn't necessarily that simple. There are some groups that we think of as being aquatic. An example of this would be the crustaceans. What we forget is the woodlice, or pill bugs, are crustaceans. So, it is fair to say that Arthropoda (a single Phylum) has invaded the land on multiple occasions, giving us the terrestrial Classes of insects, arachnids (spiders and scorpions), myriapods (centipedes and millipedes) and crustaceans. 1 Phylum, 4 (at least) separate invasions. This is a very interesting question. I will try and get you a more complete answer, so keep checking back.

Hi there Grae,

It looks like a tick to me. The easiest way to tell the diference between a bed bug (an insect) and a tick (an arachnid) is to count the number of legs. Insects have 6 legs, arachnids, and therefore ticks,- 8.

Wikipedia has some good information on them: http://en.wikipedia.org/wiki/Tick

Ticks can carry diseases which can affect humans. I was bitten when I lived in the States, in an area with Lymes Disease. I went to my doctor and got some prophylactic treatment to make sure that I avoided Lymes.

Hi There,

You are right, when the frogspawn has a white, not a black centre, that egg has died.  It might be a fungus that has attacked it, but I would guess that the change in colour is due to the breakdown of the proteins, pigments and other material in the egg, which has failed to develop.
I hope this helps to answer your question.

(posted in Evolution)

Another nice book, is Neil Shubin's 'Your Inner Fish' about Tiktaalik.  A good read!

(posted in Evolution)

Hi Alberto,

This is a good question.  The simple answer is 'yes',
sharks have many more primitive characters than do bony fish.  The most
obvious of these characters is the lack of a bony skeleton.  However, a
good reason for using a shark rather than a cod or trout, what most
people recognise as bony fish (the one that we most commonly eat) is to
do with the way that fish evolution has happened.  If we start at the
bottom of the tree and wprk 'up' it, the first chordate group we find is
the amphioxus.  The next in the sequence is the urochordates which
share a surprising similarity with the vertebrates in the sensory
structures in the head.  The next group is what we recognise as a
vertebrate, and is the first 'fishy' group, the cyclostomes (or jawless
fish), the hagfish and lampreys.  They have a skull, the first hint of
vertebrae, and lots of impressive vertebrate anatomy.  The group that we
next find is the cartilaginous fish, which include the sharks.  They
have paired fins, larger brains, and a very robust (although boneless)
skeleton.  The bony fish are the next group, but they are divided into 2
groups, equally close to the sharks, and so the sharks give a good idea
about the primitive characters of each, but each group is less
effective for comparing each other, other than to see or differences. 
The 2 groups are the ray finned fish (including cod and trout) and the
lobe finned fish.  The lobe finned fish are the group to which we humans
belong.  So, if we want to see primitive characters for our group, and
compare ourselves with different fish, we are best to choose sharks as
the group that is most closely related to us, but outside our own group,
and say, a coelacanth or lung fish, both bony fish, but lobe fins. 
That's not to say that cod cannot be useful, but they are a different
branch of the bony fish, with a separate evolutionary history- good for
comparing our differences, but maybe less about our more primitive
similarities.
For the same reason, you would use a shark to look at cod evolution, but ignore lungfishes.

Hi Yuyus,

This is a good question, and at first sight, annelids
and molluscs do not appear to be closely related.  Segmentation is a
defining character of the Annelida.  Segmentation is 'complex'.  The
bilaterally symmetrical animals (animals with a left and right side) are
divided into two super groups, based on their development, the
Protostomia and Deuterostmia.  The deuterostome Phylum Chordata (our
Phylum) is segmented, and the protostome Phyla Annelida (true worms) and
Arthropoda (insects, spiders, crustaceans, etc.) are segmented. 
Traditionally, the Annelida and Arthropoda were grouped together with
segmentation appearing in their last common ancestor.  This was
considered the best way to explain the evolution of segmentation in the
groups.  As I said segmentation is thought to be a complex character
state (lots of changes in DNA 'are required' to make functioning
segments), and so it is most easily explained if it happened as few
times as possible, ie twice, once in the deuterostomes- the chordates,
and once in the protostomes- the common ancestor of the annelids and
arthropods.  This idea prevailed for many decades, until we were able to
sequence DNA from lots of different taxa.  When this was done, looking
at the Hox genes for example it was seen that we have three distinct
clades.  These are the deuterostmes (Chordates and
echinoderms+hemichordates), and two groups in the protostomes,
Ecdysozoa, and Lophotrochozoa.  These two groups were originally the
animals that moult their exoskeletons/cuticle to grow (the Ecdysozoa:
arthropods, lobopods, tardigrades, priapulid worms, loriciferans,
kinorhynchs, nematode worms); and all of the rest (the Lophotrochozoa:
bryozoans, molluscs, annelids, brachiopods). Unlike the Ecdysozoa, who
all share the characteristic moulting using ecdysone hormone, there was
little to unite all of the groups in the Lophotrochozoa, although the
group was made up of organisims that either fed using a lophophore
(lophophorates), or produced a larva called a trochophore
(trochozoans).  The Deuterostomes were a distinct group based on
development, the Ecdysozoa based on moulting and ecdysone hormone, but
the Lophotrochozoa were not defined by a single common feature.  Even so
this resulted in the protostome split, and more importantly splitting
arthropods from annelids, the latter now finding itself with the
molluscs.  However, with another advance in our understanding of the
molecular biology of animal development, we see that in the regulatory
DNA of developing organisms, there are specific sequences producing a
molecule called microRNA which are specific to deuterostomes, others
that are specific to the ecdysozoans, and now crucially microRNAs which a
specific to the Lophotrochozoa!  They are a real group.  This also
tells us that segmentation evolved 3 times, in once each of these
groups, and molluscs and annelids are the most close reletives to each
other.

Hello Laura,

Building cladograms is quite difficult, but I have
got 2 pretty good cladograms for the mammals.  They are similar to each
other, but the first, the one from wikipedia, taken from Dawkins' book
The Ancestor's Tale shows more resolution, that is more branching, while
the tree of life cladogram has more of the branches collapsing at the
base.
http://en.wikipedia.org/wiki/File:The_A … dogram.png
http://tolweb.org/Eutheria/15997

The
first (wikipedia of Dawkins) places horses and seals as most closely
related to each other, equally distant from their next relative, of your
question the bats.  In fact if we made up a tree just with your 4
species we would have a single clade of bats + [horses+seals] with an
outgroup (the next most related group, not in the main group) being the
hare. 
The Tree Of Life web project is less well resolved, but I
think that the relationships are more accurate.  What we see here is
that hare (+rabbits) group with rodents; bats group with primates;
carnivores include the seals and the horses group with all of the other
hoofed animals, with no real resolution with how the individual species
that you have given relate to each other.  This is the problem with
cladistics.  Both trees are correct.  This is because a tree can only be
built from the data that you put into it.  So the trees are correct for
the information they contain.  The more information that we can input,
the better will be the tree.  The only real difference between the trees
is where the bats and hares fall out.  In the two trees, the bats and
hares have swapped places.  In the first the bats group with the mammals
you name, and hares sit by primates.  In the second, bats sit with
primates, and the hares sit with the other mammals.  In order to get the
best trees you need to have as complete a dataset as possible. 
However, the more data that you have, the more time to compute the tree
is required.  It is always important to ook at trees, knowing what data
was used.  I hope that this helps to answer your question.

(posted in Evolution)

Hello PJ, 

You are right species are complex and difficult things to define.  Indeed the definition of a species of plant, animal, fungus, bacteria, or asexual organism is different.  Luckily, you have chosen to ask about dogs, and being animals that is probably the simplest definition of a species.  The biological species concept covers most animals.  It states that a species is a population of 'potentially' interbreeding individuals.  This means that a great dane and a chihuahua must be the same species, because however rare it is, the potential is there for them to interbreed and produce viable, fertile offspring.  In fact under this definition almost all of the 'species' within the Genus Canis could be 'collapsed' into a single wolf/dog species because dogs can interbreed with wolves, coyotes, red wolves and produce fertile offspring.  Examples of interbreeding organisms which are different species include lions and tigers (producing ligers/tigons) or horses and donkeys (producing mules/hinnies).  These offspring are  always infertile and show that the genetic boundries, which are what underpin species, are present. 
The way that an organism looks, a great dane and a chihuahua look so different, is not the best way to define species, although historically this is the starting place for defining a species.  Other groups can look identical, but analysis of behaviour and genetics show that these visually identical populations never interbreed.  An example of this was seen in the Italian Sparrow-http://www.bbc.co.uk/nature/14947902.  The suggestion is that this sparrow group has separated off from populations of House and Spanish Sparrows, interbreeding with neither species.  These birds look very similar, but obviously not to each other.  It highlights another interesting point about species.  Although the Italian Sparrow doesn't breed with the house or spanish 'species', the researchers sugest that the italian species is a hybrid of the house and spanish populations.  If that is true, and the italian sparrow is the fertile daughter species of the House and Spanish species, then these two 'parents' cannot be separate species, because at some point they have produced a fertile population of offspring.  It suggests that again, we have a single parental species of House and Spanish birds, which have given rise to a new Italian species.

Hi Michael,

I hope that one of the entomologists on the site will see this, and correct me if I am wrong, but a quick look in my 3rd Edition of Chinery (Collins Field Guide to Insects of Britain and Northern Europe) suggests that the specimen that you have photographed is a Digger Wasp, a member of the family Sphecidae.  Chinery says that "the yellow and black members of the Sphecidae are often confused with the social waps, but they can be distinguished [from them, by part of the thorax] the pronotum and by the fact that the wings are laid flat at rest", unlike social wasps who fold their wings lengthwise.

If I were to stick my neck out a bit more, I might even suggest that the photograph is of Mellinus sp. http://en.wikipedia.org/wiki/Mellinus_arvensis

I hope that this is helpful.

(posted in Fossils)

Hi Janae,

The process that leads to a dead organism becoming a fossil is called Taphonomy.  It comes from the greek word taphos meaning burial. 

The
very oldest fossils that we have are about 3.2 billion years old, and
are the remains of bacteria and single celled organisms, and that is
pretty much all we find in the fossil record for over 2 billion years. 
Larger body fossils do not show up until about 600 million years ago,
when we get the peculiar Ediacaran fossils.  The first definitively
'animal body' fossils appear about 535 million years ago, and we have
worms, arthropods, echinoderms, primitive chordates, and about 30 other
Phyla!  The most exciting fossil in my opinion also appear around this
time.  They are the fossil embryos from the Late Neoproterozoic (the
fossil embryos are about 580 MYa) and Cambrian (the fossils are about
520 million years old).  They bracket the period just before, and just
after the appearance of animals (a trace made by a bilaterally
symettrical organism) at 542MYa.  They are important because embryology
and development, and changes in the timings of these processes are what
leads to changes in lineages of organisms- evolution.

Why am I
talking about this?  Well, when the fossil embryos were first found,
they were quite controversial.  An embryo is little more than a cell, or
cells, in a protective membrance.  A little fatty bag of water, salts,
nucleic acid and more fat.  How on earth does that preserve?  One of the
ways to test if the fossils were 'preserved biology' and not 'peculiar
geology' was to carry out experimental taphonomy on similar organisms to
what we thought the fossils (if that is what they were) were.  Simple
marine organisms like sponges, worms, arthropods and sea sqirts were
chosen and their eggs collected.  The eggs were allowed to decay under
the conditions that we predicted the fossil material was subjected to
when it died.  These little cells, less than half a millimetre in
diameter preserved beautifully.  Some arthropod eggs even started to
become mineralised!  This whole procedure took a matter of weeks.  When
you think about it that makes perfect sense that the initial
mineralisation event must be rapid.  If the 'biology' isn't preserved
rapidly, a dead organism will quickly become lunch for something else. 
It also explains why we don't see a lot of soft tissue preservation in
the fossil record.  Soft tissues get eaten, decay away, or generally
destroyed by the elements.  When we think of fossils, the first image
that jumps into our heads is a collection of bones or shells, because
these are typically what we find after millions of years.  Bones and
shells don't need to be mineralised, because they are already
mineralised but the muscles and skin of the dinosaur, or the squidgy
body of the snail decay and/or eaten before they can mineralise (most of
the time).
So, I hope that sort of answers your question.  People
are not trying to fossilise things, but we are trying to understand the
processes involved in fossilisation, which in some cases 'mineralises
biology' as an aside.  The initial events that lead to a dead organism
becoming a fossil are not always long and drawn out (sometimes it only
takes a few weeks), in fact if takes too long, then the organism will
decay to very little, before mineralisation can occur.

Hi Matt,
Apes tend to live in the tropics, while humans have moved towards the poles.  As this has happened we have encountered different conditions, from our ancestral regions.  Tropical air is warm and moist, while air at higher and lower latitudes is drier and colder.  It is argued that human noses allow cold, dry air to be warmed on the way in, and moisture (to some extent) to be retained when exhaled.  This is a functional reason.  If we look at our closest relative- the Neanderthals (now extinct) the skulls suggest that their noses were enormous.  Neanderthals existed in more extreme climates of northern Europe, where it was very cold.  Their nasal cavities are thought to be adapted for the same reason, warming air on the way into the body.

Hello Sammy, this is a great question!  Chordates, the group to which we belong has about 50000 species, most are vertebrates, which have 2 eyes.  So it is a bit difficult to work out what the ancestor of chordates had from the vertebrates.  Even the most basal vertebrates (those with the most primitive characters and structures) the lamprey and hagfish have 2 eyes.  In the hagfish, these are really only light sensitive spots, because they lack lenses and muscles to help make a sharp picture, and are underneath the skin. 
We need to go back to even more basal groups such as the tunicates to get and idea of the ancestral condition.  Tunicates do not have many eyes across the body, or even 2 like vertebrates.  Tunicates have a single light sensitive cell called the ocellus.  This allows the larva to work out which way is up, because when you are in the sea, light comes from above. 
Having one eye, or eyespot allows you work out what direction light is coming from.  Having two allows you to detect shading.  If you have light from above, and one eyespot, if it goes dark, either it is suddenly night, or you have something between you and the light source.  Maybe a predator.  One eyespot cannot tell you the direction the thing which might eat you is coming from.  If you have two eyespots, you can get direction from shading, so if your right eyespot goes dim, something is on you right side, and you can move away.  It seems that 2 eyes were enough for chordates.  Having 2 eyes allowed a very accurate form of vision, binocular vision, to evolve and that has been enough for chordates to survive and be as successful as they/we are.

(posted in Evolution)

Hello,

I teach this to college students, and they still have a problem with an unconscious 'choice'.  Our words have a weighted meaning, and it is difficult to disentangle them all, or change their meaning to suit what we know they 'mean' in context.
Survival of the fittest is a great example of this.  Herbert Spencer coined this in response to Darwin, and then it has been twisted to mean what we understand- evolution is cruel and the strongest survive.  This is not what it means at all.  'Fittest' in this context means 'best fit' to the environment, to nature. 
In this sense, nature 'chooses' poetically the individuals that best fit their environment.  If you do not fit as well as the next one, you will struggle (find things harder) than the next one, who is a better fit,, who fits better, lets combine these words, and make 'fitter' (not able to run faster, necessarily) but just slots into the surroundings better, and can take advantage of the food, shelter etc.  Now a third comes along.  The third individual fits really well in to the environmental slot, or niche.  This one fits best (combine the words) one might say it is the 'fittest' (fit, fitter, fittest) in the environment.  Because it fits best with the enviroment/nature it is selected (unthinkingly) by nature, to have more offspring than the others, and may even replace the others.
Selection is another word for choosing.  It is perfectly OK to use these words, but they must have the correct contextualisation.   It is good to hear that your daughter is being taught this, and that she is asking questions too!

Hello there,

I think that the top picture is sponge, it appears 'amorphous' that is it has no regular shape, but it seems to have pores, that would allow water to flow through it.  I have no idea what the second picture is, maybe an egg case?
The third (bottom) picture is interesting.  It is not easy to tell, but it may be a sea cucumber, a type of echinoderm.  I am not certain, because I do not know where there photos were taken (geographically speaking).  I hope that this helps a bit.

(posted in Birds)

Hello Joseph,

There is a saying when you wish to describe the low probablity of something as being
'as rare as hen's teeth'.  Well, that saying no longer means what it once did.
Some mutant chicken embryos will start to develop teeth, although, they never hatch.

http://www.scientificamerican.com/artic … grows-alli

However, 2 groups of researchers, one from the University of Wisconsin (from the link above), as well as a group from Manchester (link below) managed to induce tooth growth in normal chickens too.

http://www.sciencedaily.com/releases/20 … 083601.htm

So, the answer to your question is yes it can be done, but it seems that it is only through genetic manipulation (although I am unaware of whether the eggs were allowed to hatch, I would expect not).  When the mutation arises naturally, the bird does not develop normally in other areas, besides the teeth, either and dies before it hatches.

Hello there,

this is a guess, but we had similar 'sounding' insects flying around our Buddlia at home too.  They were 'bee flies'.  This link shows quite a nice picture of one
http://en.wikipedia.org/wiki/Bombyliidae 

Do the insects at this link look like what you saw?

Let us know if it is not one of these, but I think that this is a pretty good guess from the description that you have given.  If you see it again, try and get a photo......

Hello just to add to the answer that John has given you, the split
between us and insects is the split between the animal groups called
protostomes and dueterostomes.  These names refer to when the mouth
develops during the formation of the gut; mouth first in protostomes,
while the deuterostomes' mouth secondarily, as the anus develops first. 
Bilaterally symmetrical animals are first found in the fossil record
during the Cambrian (~542-490 Million Years Ago).  We have both
protostomes and deuterostomes (arthropods and chordates- if not actual
vertebrates) are present in Chinese fossil beds, like the Chengjiang
Formation.  This bed is about 530 million years old, so the last common
ancestor of arthropods and chordates has to be older than this. 
The
oldest definitive animal fossils that we have are the embryos from the
Doushantuo Formation also from China.  The Doushantuo is 581 million
years old.  The embryos are 'sponge-like'  so they represent the most
basal animal body form.  The oldest fossil does not (necessarily)
represent the first individuals of a group, only the 'first' to be
preserved, but it is a reasonable estimate for the purposes of your
question to give a range of times when the last common ancestor of
bilaterians might have appeared.  We have about 50 million years
(581-530 MYA)  between the appearance of animals (sponge-like) in, and
the appearance of arthropods and vertebrates in, the fossil record, for
the last common ancestor to have existed.  The second part of your
question is very important to developmental and evolutionary biologists,
because understanding the body plan of an ancestor gives us more
ability to understand how animals develop and evolve.  The way that we
start to get an idea of what an ancestor looks like is based in part on
what its descendants look like.  More importantly, the shared
characteristics of different groups 'hint' at the characteristics of the
ancestor.  For example, vertebrates, arthropods and annelids are
segmented (and although this is contentious) the Last Common Ancestor
(LCA) was probably also segmented, at the very least it likely showed a
banding pattern of gene expression diving up the body.  It had a through
gut a mouth at one end  and an anus at the other.  It had sense organs,
eye spots patterned by a gene called Pax-6.  To give an idea of what it
might have been, I think that the best description is 'kind of
worm-like'.  I hope that this helps to answer your question.

Hello,

it is a wasp of some description.  I do not know what the species is (hopefully someone will be able to tell you), but it looks like a male 'parasitic' wasp, like the Ichneuman Flies.  This group of wasps does not usually sting like a 'yellow jacket'.  The females have long ovipositors (the structure that wasp and bee stings are derived from) to lay their eggs, normally in rotting wood, but sometimes in the bodies of other insects and invertebrates.  From your picture, it does not seem that this individual have a long ovipositor protruding from the rear of the abdomen, so I would suggest this is a male.

I hope that this starts to answer your question

Hello,

An excellent question.  I think that it is the basic body plan for a bilaterally symmetrical animals.  a 'worm' has a head and a tail end, a back and a front (dorsal and ventral) and a left and right.  If a animal is going to evolve with sense organs in one end, a head, and move in that direction, literally 'following its nose', this is an excellent way to do it.

When you think of the 30+ Phyla (major animal groups) in the Bilateria, most have 'worm-like' members.  There are the nematode 'worms'; priapulid 'worms'; annelid worms (true worms); The slugs are fairly 'wormy' when you think about it, although they are not thought of as 'worms'.  Even our own group has worm-like members.  There is the cephaolchordate amphioxus, and even vertebrates like the hagfish and lamprey are 'worms' in a morphological sense. 

I think you are right to ask if this is a primitive condition or convergence?  I am not sure if there is an answer that will satisfy everyone.  Personally I think that it is convergence, because there are a lot of differences between, say annelid worms which develop a long axis through a pattern of segmentation, compared with Nematodes, which are unsegmented, and derive their longitudinal axis by differential extension of cells (that is causing cells to grow in one direction, while inhibiting lateral, or dorso-ventral growth).  However, the last common ancestor of the bilateria is often drawn (hypothetically, because no one has ever seen it) as a worm-like animal. 

I hope that this starts to answer your question.

Hello there,

I do not think that these are jelly fish, but they are similar.  I think that these are Ctenophores, or 'comb jellies'.  I am going to suggest that the species is called Mnemiopsis

The jelly fish are in a group called the Cnidaria (pronounced nigh-dare-rea), while comb jellies are in a group called Ctenophora (pronounced teen-o-four-ra).  They are closely related to each other although exactly how the 'family tree' of the animals branches in this region is still being debated.  Like the jelly fish, comb jellies only have two layers to their bodies.  They have an outer layer called ectoderm, which makes the skin and nervous system; and an inner layer called endoderm, which makes the gut.

The comb jellies get their name because when they are swimming and feeding, they let out long 'tentacles' that have little projections that look like the teeth of a comb.  As they are drifting along on ocean currents these tentacles catch little particles of food or other tiny organisms, and then the comb jelly draws the tentacle in and the food is moved into the gut.

I hope that this answers your question, and I am very excited to see that you found these in Suffolk!

Hello Owen,

Von Baer's Law is pretty good.
http://en.wikipedia.org/wiki/Karl_Ernst_von_Baer
Baer's laws (embryology)
He formulated what would later be called Baer's laws of embryology:

General characteristics of the group to which an embryo
belongs develop before special characteristics.
General structural relations are likewise formed before the most specific appear.
The form of any given embryo does not converge upon other definite
forms but, on the contrary, separates itself from them.
Fundamentally, the embryo of a higher animal form never resembles the adult of another animal form, such as one less evolved, but only its embryo.
This is all before Darwin and evolution was really thought about.  It is a good set of principles!  Especially because it is the opposite of Haeckel's recapitulation ideas (which are wrong), which stated that an organism replayed all of the previous evolutionary forms within its lineage during its development.  Despite von Baer writing his 'law' in the early 'first half' of the 19th century, and Haeckel writing in the 1860s and later, Haeckel seemed to have 'ignored' von Baer.  Simple because of the time it was written, but pretty good.

In animals, we see spatial and temporal colinearity of Hox gene expression.  Hox is crucial for anterio-posterior patterning, that is telling a developing animal where its head is with respect to its tail. Hox genes are found to lie on the chromosome (spatial) in the order in which they are expressed (temporal).  In the case of Hox genes the order in which they are located on chromosomes and the time that they are expressed is also seen in the way that they are expressed in the developing embryo: Hox 1 is anterior most with Hox 2 expressed next to it, but slightly more posteriorly and slightly later, then Hox 3 followed by Hox 4, you get the idea.....

I don't know if this answers your question, if not, let us know.

Hello Christopher,

all animals, even placental mammals have an egg.  It is the female cell that contributes to the embryo, as the sperm is the male cell.  When they fuse they begin to divide into more cells, and then the embryo can implant into the wall of the uterus.  Now, the placenta is not like the yolk.  A yolk in an egg (like we see in a chicken or crocodile) is a food store, and the developing embryo has lots of membranes and blood vessels extending from it that it can use to take up the nutrients.  The placnta is more like these membranes, and it takes up nutrients from the mother in which it finds itself.  So, mammals still have an egg, it is just different from a bird or reptile's.  All animals start from an egg, the mode of development is what differs. We do see some live birth having evolved in some snake species, I will try to get some more information for you on this over the next few days...... I hope that this starts to help to answer your question.

(posted in Evolution)

Well, Hello.  I can assure you that anyone that tells you Darwin did it is wrong.  Darwin was born in 1809, died on the 19th April 1882, and never claimed to have had anything to do with the origin of life!  All he did was explain, in the most 'lyrical' of fashions how species evolve.  Not how life started, not where it came from, just how it has changed over the eons of time that this little tiny planet has cycled around the sun.  There have been many experiments, some better than others that have tried to demonstrate how complex molecules can form naturally.  The Miller and Urey experiment was truly beautiful, even if we now question some of the conditions under which it was carried out.  Miller and Urey made up a soup of organic chemicals, ammonia and other ingredients for 'primordial soup'.  They warmed it and then gave it a burst of electricity, like a lightning bolt, and looked at what they got.  They produced many of the amino acids so important for building protein, and often declared to compex to form by 'chance'. 
Cells are also cited as too difficult to be something that form randomly.  Again, scientists have observed that under certain conditions lipids- fats that make up cell membranes- will form little balls, or bubbles when placed in solution.  These little bubbles absorb more lipids, until at a certain point they 'divide'.  This could be described as a 'protocell'.  I am not claiming that these two examples are perfect, and I am not claiming that this is how life arose, but we see that complex chemicals can form under natural conditions.  As for DNA, I am not sure that there is an answer for it yet, but people are looking all the time, to try and find explanations, that are not pulled out of there butts, so to speak, to understand the universe and life in it.

Hi there.  Richard Dawkins gives this a lot of attention in 'The Greatest Show on Earth' in a chapter entitled 'before your very eyes'.  There have been extensive lab studies carried out, and I would encourage you read Dawkins' book.  However, in a brief summary, Lenski et al. carried out an experiment looking at bacteria over some 45, 000 generations.  They kept and stored a sample of each 'generation' before innoculating another culture and allowing another generatio to develop.  This beautiful experiment allowed a comparison of old and younger generations to be made, and showed how the bacteria, through simple mutations of a couple of genes allowed the individuals in one lineage to evolve and adapt to take advantage of a new food source.  Another example looked at lizard population introduced to an island called Pod Mrcaru. Over just 20 years the population evolved from carnivorous- insect eating lizards into herbivores with all the adaptations required to eat vegetation!  The latter example is not in a lab, so to speak, but it is something that scientists observed experimentally!  Hope this answers yor question.

(posted in Evolution)

Well hello from CNY!  I am not sure that there is anything straight forward that you could do, but please feel free to contact me at SUNY Oswego.  It might be a bit difficult to do things in the classroom directly, but I think that a nice thing that you could do as an earth scientist is look at the fossil record. There are some great outcrops all over the state, so you could take a field trip.  If you just want to decribe evolution 'before your eyes', you could talk about Lenski's experiments using bacteria over thousands of generations, and how they evolved to take advantage of different food sources.  This is detailed in Dawkins' book, The Greatest Show on Earth.  I will have a think and try to give you some more suggestions, but you might hear from other members of the site, so keep an eye out.

That is a good question.  I am not sure that I have a great answer, but I might offer a suggestion that might answer why rabbits in general are not really 'tameable'.  This relates directly to your observation that Dogs are tamed.  I think that this has everything to do with selective breeding.  We have had domestic dogs for the thousands of years, my favourite breed, the beagle (what do you expect, I am an evolutionary biologist, and yes my two are named after Mr and Mrs Darwin) is probably a couple of thousand years old, one of the very oldest breeds.  This means that the domestication of dogs in general is much much longer.  Some suggestions give estimates of 8 thousand years, other still more.  This is a long time.  Now here is my suggestion, and this might be the time to stop your children reading.  Nobody has ever really tried, strictly, to tame rabbits.  Rabbits have only been in the British Isles for the last 1-2000 years, being brought in by the Normans (1000 years ago), or the Romans (2000 years ago), depending on who you ask (children close your ears) for food and fur.  I used to live next door to a family called 'Warren'.  Warren or Warrener are names associated with a trade, like Butcher or Smith.  A Warrener was one that looked after a Warren- where rabbits were kept.  Yes we have selectively bred rabbits to be white, black, piebald, 'blue', large, small, floppy eared etc. but this is very recently, and so we have probably just not had the time that we have had with dogs to select for 'tameness' in the same way.  I hope that this goes some way to answering your question, as I say, I am not sure that it is 'correct' but I think it is sensible.  Thanks for a great question!

Hello Grant,

This is a good question.  The simple answer is no.  There is no other scientific theory of Evolution other than by Natural Selection.  There have been people over the last 150 years (since the Origin of Species was written) that have suggested that Natural Selection is not the only force at play.  I believe that Stephen Jay Gould was a proponent of this idea.  He felt that evolution was not always a gradual process, but there existed long spans of time when organisms changed little, interspersed with times of very rapid evolution and morphological change.  This is the idea of Punctuated Equilibrium, proposed by Gould and Eldridge.  Other people like Dawkins, and to an extent myself, think that you can explain what we see in biological organisms over time, with Darwin, and Natural Selection alone.  Yes, scientists have tweaked what Darwin wrote as we have made new discoveries and developed new understandings of things like DNA and genes.  However, Darwin stands alone in having produced a credible and testable theory that has yet to be 'unsupported' in any substantive way.  If you want to read a great book on the support for evolution I can highly recommend Dawkins' The Greatest Show on Earth, and Coyne's Why Evolution is True.

Hello,  this is a realy good question, but starts from a false premise.  As Manabu says, biologists do not say this.  It goes back to an early supporter of Evolution, who made a mistake in interpreting his observations.  Ernst Haeckel stated that Ontogeny recapitulate Phylogeny.  This means that an organism replays its lineage as it goes through development.  For example, this would suggest humans have a single cell stage, like an amoeba; then a primitive animal stage; then a primitive bilaterian worm like stage; followed by a primitive chordate 'amphioxus' stage; a fish stage; an amphibian stage; reptile; early mammal; early primate; ape; and finally -ta-dah a human is born!  Haeckel was wrong! We know he was wrong, the pictures and papers he wrote are in books, if at all, explaining the history of the study of embryology.  Darwin did say that the study of embryology is the surest way to understand descent, but not because he compared embryos of a higher animal with the adult of a lower one.  His ideas came about from the study by another German, some 30 or more years befor the Origin was published.
Karl Ernst von Baer came up with a Law of Embryology.  We don't have a lot of laws in biology, but I like this one.  I have copied it from Wikipedia, and you can read more about it and von Baer at this URL: http://en.wikipedia.org/wiki/Karl_Ernst … ryology.29
<h3><span id="Baer.27s_laws_.28embryology.29" class="mw-headline">Baer's
laws (embryology)</span></h3>
He formulated what would later be called Baer's laws of embryology:
<ol>
<li>General characteristics of the group to which an embryo
belongs develop before special characteristics.</li>
<li>General structural relations are likewise formed before
the most specific appear.</li>
<li>The form of any given embryo does not converge upon other definite
forms but, on the contrary, separates itself from them.</li>
<li>Fundamentally, the embryo of a higher animal form never
resembles the adult of another animal form, such as one less
evolved, but only its embryo.</li>
</ol>It can be summarised as follows: "closely related organisms share developmental pathways for longer than more distantly related ones".  For example if you take 3 embryos, a cow, a chimp and a human, up to a certain point the three look very similar- they are afterall all mammal embryos.
However, at a certain point in development they come to a 'fork in the developmental pathway' if you will and the cow journeys on alone.  The chimp and human embryos share a similar route for longer, because we are both primates.  However, another fork is reached, and the embryos diverge from each other, because one will finish developing as a human, and the other as a chimp.
Noone would suggest comparing a human embryo with an adult chimp or cow, but the embryos do show our common ancestry by the pathways that we follow.

Life is already started before fertilization, because the egg and sperm (the gametes) are living cells.  They divide from cells which are living, so this is a difficult question to answer.  If you mean when does a cell/embryo become a human, I think that is a different question, and I do not think that it can be answered easily.  A zygote (a single fertilized cell) has all the genes it will ever need to make every cell type in every organ in the adult, but not everyone would say that it is a human being, while other people think that it is and has all the rights of you or me.  This is not a question that science answers, but a debate that continues in society everyday.
If I have not answered your question, please respond and we can have another go.  Thanks, and this is a great question!

(posted in Evolution)

Well Jed, I think lots of people have asked this question.  In short the question is actually wrong to start with.  Now this is a common mistake, some of of the blame for which falls on biologists shoulders because we 'say things in short hand'.  People did not come from monkeys that are alive today, humans and living monkeys share a common ancestor, Now that ancestor was probably more monkeylike than humanlike, but it was not a monkey species that is still alive.  So we are 'cousins' of, not descendents of, living monkeys.  You can think if this in human terms, less removed than humans and monkeys, if you look at your own cousins, and use the surname of cousins on your Mum's side, it works well if she has a sister if you can -at last I have found a good reason for using the patronomic- taking the husband's name- if only for this example! Here is a hypothetical situation:

Your name is Smith, your cousin is Jones.

If you ask "if smith came from jones why are there still joneses?" it makes no sense.  You are not descended from your cousins.  You have a common ancestor in your shared grandparents.  Now if your cousins are children of your mother's sister, when each of your respective mothers married their respective husbands, they likely changed their surnames (and for this example they did), so not only are smiths not descended from Jones, but the common ancestor is not a smith or a jones, but a 'Brown'.  Does this answer your question?

You are right.  I cannot think of any mammals do not have green pigment.  We have different types of melanin, which ranges from black, through brown to orangy yellow colours, but no green.  The closest that I can think of is the yellowy grey mix that we see on squirrel monkeys.  These are the small South American monkeys with a white face and black head (roughly speaking) on a grey/yellow body.  I think that this is the closest that I can think of to having green colours as a mammal, and I imagine that it is entirely for camoflage.  Mammals seem to have gone a different way for disguise by breaking up their outline with spots and stripes, rather than colours.  This works well enough, and so green has never (to the best of my knowledge) evolved.

(posted in Evolution)

Hello,
I would just like to add that Hitler actually ordered Darwin's works to be burned.  He wrote a very long book, called Mein Kampf which makes not a single reference to Darwin.
The University of Arizona has a list of books that the Nazis wanted to have destroyed
http://www.library.arizona.edu/exhibits … uments.htm
The relationship between evolution and the Nazis is simply an attempt, as Jim says, to make evolution seem bad by associating it with Nazi ideology, for which there is no evidence.

(posted in Mammals)

Hello,

You have struck on something that early embryologists, in the mid 19th Century observed.  Ernst Haeckel said (wrongly we now know) that vertebrates go through all the stages of evolution that preceded their particular species.  He stated "ontogeny (development) recapitulates (replays) Phylogeny (evolutionary history).  Haeckel said that, for example, humans have a 'fish stage' followed by an amphibian stage, followed by a reptile stage, and then finally a mammal stage.  This is obviously nonsensical but remember Haeckel was one of the first people to look at embryology and evolution, and it is easy with hindsight, and another 150 years of study to 'rubbish' what goes before. 
Another biologist (and like Haeckel, another German) Karl Ernst von Baer came up with a slightly different interpretation of development.  Von Baer's laws of embryology state:

“   1. General characteristics of the group to which an embryo belongs develop before special characteristics.
   2. General structural relations are likewise formed before the most specific appear.
   3. The form of any given embryo does not converge upon other definite forms but, on the contrary, separates itself from them.
   4. Fundamentally, the embryo of a higher animal form never resembles the adult of another animal form, such as one less evolved, but only its embryo.”

From http://en.wikipedia.org/wiki/Karl_Ernst_von_Baer


This is pretty good.  In summary, of 3 animals, the 2 that are more closely related to each other share similar developmental pathways (embryology) for longer than the 3rd more distantly related animal.

Lets work it through.  We will start with 3 bilaterians, animals with fronts and backs, tops & bottoms, and importantly left & right.

Lets have am insect, a  hemichordate (a worm-like animal related to starfish) and a  fish.

All form a ball of cells called a blastula, but the insect is a protostome, while the other two are deuterostomes.  This means that the way that the gut forms (gastrulation) in insects differs from the other two.  The gut forms mouth first in insects, and anus first in the other two.....  The hemichordate and fish share this pattern of development.

Lets add in another animal, and lose the insect, another deuterostome, a frog.

We now have a hemichordate, a fish and a frog.  All are deuterostomes, and share the same basic way of making the gut, anus first.  After gastrulation, the next important stage in development if making a nervous system.  The hemichordate make a diffuse net of nerves, and doesn't make a brain.  The fish and frog (well tadpole at this stage) form a specialised rod of tissue (a precursor to a spinal column) called a notochord.  This lies along the main axis of the body, anterior paosterior (or nose to tail).  This tissue does not form in hemichordates, but it does in frogs and fish.  It acts as a guide for where the nervous system should form, and the central nervous system form directly above it!

Lose the hemichordate, add in another vertebrate, a crocodile….

The fish, frog and crocodile all develop a gut- anus first, and all form a notochord and the central nervous system forms bang on top.

We never specified the type of fish that we were talking about, and I am going to say what it is now.  It is a lamprey.  Lampreys do not have jaws.  Their mouth is basically just a suction cup with teeth.  The nice thing about lampreys like all fish, is that they have gills.  The difference between jawed fish (and all jawed vertebrates) and lampreys is in their development.  In the frog and the crocodile the developing structure that forms ‘gill skeleton’ in lampreys at the front of the animal does not form a gill, (in fact, none of the developing structures that form gills in fish form gills in frogs and crocodiles).  The first pharyngeal structure forms a jaw in jawed fish, frogs and crocodiles, but forms a gill skeleton in a lamprey.  At this point we can do away with fish.  The structures –Pharyngeal pouches- that form gills in fish, form jaws and other structures in our throats.  Amphibians and reptiles share development with fish to the point where the pharyngeal pouches form gills in fish but throat structures in land living vertebrates.  We can carry on, all the way up from amphibians and reptiles and mammals, and we see that reptiles and mammals share more developmental similarity that either does with an amphibian; and then we see that a duck billed platypus and a kangaroo develop more similarly for longer than either does with a crocodile.  If we then take a placental mammal, say a cow, and compare this with the Kangeroo and the Platypus we can compare the similarity of development…

All form a ball of cells; all develop the gut anus first; all develop a notochord; all have a central nervous system; all develop jaws from the pharyngeal pouches; the platypus develops in a egg, the other two develop inside the mother and have live birth.  We see that the cow and the kangeroo share a development pathway that is missing in the platypus.  They have internal gestation of their young, not in an egg.

We can lose the platypus, and bring in another placental mammal.  A chimpanzee.  We see that common developmental pathways are seen in the chimp and cow not seen in the kangeroo.  They most obvious is the stage of development at which the chimp and cow give birth to their young.  Compared with the kangeroo, where the baby is very underdeveloped, and would die if it were not in the mothers pouch, cows and chimps are very well developed.  We lose the kangeroo.  Although I am not trying to imply any direction in development, I want to bring us to humans.  However, wherever we have diverged along the way and lost a certain animal. We could have taken it in a different way, and gone to a different ‘pair’, for example we could have added another marsupial to the kangeroo/cow pair, and we would have said goodbye to the cow.  I wanted to get to Homo sapiens , us.  So, we have a cow, a chimpanzee and a human.  Development is near identical in humans and chimps.  We are cousins.  An example of differing development between us and a chimp and a cow is pretty superficial..  All the key development is the same, it is only the very latest things, like the formation of a tail; fingers with nail, not feet with hooves.  These happen really late in our development.  Humans and chimps are 98% identical in our DNA, and our development is almost the same.  It is only at the very end of gestation that our DNA tells a developing human foetus that it is a human, and a chimp’s DNA tells the developing foetus that it is a chimp.  The more closely related 2 animals are to each other, compared to a third, the longer they share a common developmental pathway.  Karl Ernst von Baer was very insightful and proposed a very accurate law of development that explains your observation well.

I hope  that this very long answer helps in some small way.

A tangental answer if you will allow.  I spent several years 'rotting' invertebrate eggs, to better understand how eggs and embryos that we find in the fossil record are preserved.  I used Artemia salina (brine shrimp- sea monkeys) as a model for the 581 million year old cysts that we find in the Doushantuo of China.  They are very resistant to decay, and were a very good model.  Obviously what I was doing used 'dead' cysts.  If you keep yours away from moisture, as David suggests, they will last a very long time.  Indeed, if you go to the Salt Lake, in Utah, and take a core, you can find (dead, but) in man y cases morphologically 'pristine' brine shrimp eggs in 27,000 year old sediments.  One of the reasons we think that they 'survive' so well is that contain glycerol within the cyst.  We use glycerol to stabilise DNA and cells when we store them in the lab.  Sea monkeys are naturally primed to survive in harsh environments, like a dry packet on a shelf, if you will...... I have just been reminded by my research student that the cysts of Brine shrimps have also survived in the vacuum of space.  That is possibly the harshest environment.

Just a quick answer to your question.  I am not sure that an insect would 'work' at that size, but the fossil record shows 2 metre long Myriapods- centipedes and millipedes.

Arthropleura -- http://en.wikipedia.org/wiki/Arthropleura -- was about 1-2.5m long.  This wikipedia link might help.

good luck with your research.

Hi Diane,

This is speculative, but I think that the main difference between ferrets and Dachshunds is the length of time that their anatomies have had to develop.  I suspect that the natural evolution of mustelids has allowed the entire body to 'develop' in a way that is optimal for Mustelids.  Evolution does not always get it right, just think of humans. We have had 6-7 million years of evolutionary time since we diverged from the other apes, and humans suffer from terrible back problems, because of our upright posture. 
I had a friend some years back, who bred ferrets, and I do not believe that ferrets are known to have spinal problems. 
As far a dachshunds go, I think that relatively short time (a few hundred years) that we have artificially selected for 'short legs' has not allowed the 'organism' time to evolve the optimum body plan, balancing morphology with problems associated with it.  Darwin himself recognised, in the Origin of Species, that humans can select only for the grossest of traits, while nature selects with far greater precision.  By forcing the development of short legs, we have not foreseen the problems that we now recogmise are associated with this character.  It is not only Dachshunds that have problems.  Pugs have breathing problems because of a 'short' face, and Bulldogs cannot give birth without assistance.

So, I really think that the differences/problems we observe, are due to the time that the traits/morphologies/characters have had to evolve, artificially and naturally. I don't think that there is a 'quick fix' for this problem.

However, as a dog owner myself (2 beagles) I am very pleased to find, and hear from, responsible breeders.  Good luck with your Dachshunds.

I am not sure that this really answers the question in the way that is intended, but I think it applies to the first part.  We must not forget things like the Hox genes.  These are crucial to specifying the regions of embryos, for example, the head, thorax or abdomen of insects.  When the embryo can 'work out' that certain cells sit in certain places, then the next 'tier' of genes can 'know' where they should be expressed to make certain appendages grow.  If cells 'know' that they are in the thorax, then legs and wings can develop.  If cells are 'told' by hox gene expression that they are in the head, they can develop into head appendages like the antennae or mouthparts.  If the cell are confused by having the 'wrong' hox gene in the wrong body area, say thoracic hox gene expressed in the head, a leg will grow where an antenna should be.  So, in this respect, genes do play a crucial role in determining the body plan, of an organism.

Hello Jay,

I cannot be sure, but it looks like you have a soft coral like 'dead man's fingers'.  Alcyonium digitatum is often a pinkish colour, but sometimes it is grey too.  As I have said I am not certain, but I think it is a good possibility.  Maybe someone else on the site will have an idea too.

This is really very interesting.  We don't often get to 'see' this sort of thing in humans, because it is not always well reported.  Thanks for highlighting this!

There were some 'larger' mammals, for example Repenomamus giganticus (http://en.wikipedia.org/wiki/Repenomamus), or, 'Large mammal that ate dinosaurs' was about the size of a dog, or badger.
Or, Castorocauda lutrasimilis, a 'beaver-like animal' from 164 Million years ago (http://scienceblogs.com/pharyngula/2006 … beaver.php).
So, although mammals were small, and probably did move around most at night, there were 'early mammals' that were quite large.

There is a lot of information out there on Archaeopteryx and other early birds.  Fastovsky and Weishampel's evolution and extinction of the dinosaurs is a nice book to start with, and the illustrations in Feathered Dinosaurs-The Origin of Birds, by Long and Schouten, is also very good showing how dinosaurs with feathers might have looked.  There are good descriptions of the dino-birds too.  The references might help you in the right direction too.

Hope that this helps.

Hello Alan,

I was in the lab next door to the person doing the work.  Buddenbrockia was recognised as a 'worm like' animal, or rather that it had a worm like stage in 2002 (or there abouts).  The work was done in Beth Okamura's lab at the University of Reading UK.  I believe that several papers were published on the subject, and I have added a link to a recent one below.

Origin and evolution of a myxozoan worm
Eva Jiménez-Guri, Beth Okamura and Peter W. H. Holland,
icb.oxfordjournals.org/cgi/reprint/47/5/752.pdf

Many of the model organisms that we have chosen because they have a quick generation time (life cycle from 'birth' to reproducing), or their size, or any number of things has meant that they are not always perfect 'models' that can explain more than themselves.  A good example of this is Xenopus -the African Claw Toed Frog found in East Africa.  It  is octoploid, and also has closely related species that are tetraploid.  This is a 'recent' event and there are species in the genus that are tetraploid! 
I don't know if this link to the University of Reading is active, but it is an interesting paper on the subject.....
www.rubic.rdg.ac.uk/amphioxus/supplinfo.pdf

The Ancient Greeks were a clever bunch.  Although I do not know what they thought about frogs and amphibians, Aristotle and others realised that the whale was not a fish! 
I know this is Roman and not Greek, but Pliny the Elder wrote a 'Natural History' (many abridged versions are available).  This gives an idea of what the Romans made of nature, and Pliny's own observations and travels.  Not exactly what you are asking, but it may help point you in the right direction.

Hi Sara,
Peter is right about the insects.  They skew the numbers in favour of terrestrial (land) animals.  However, it depends on the sort of animal that you look at.  If you look at the chordates (the group that we belong to) about half of the species live on the land, and half in water.  This is about the same for molluscs, the second largest (in terms of species) Phylum after the arthropods, where there are probably slightly more than half of molluscan species in the sea/aquatic environment. 
So, it really depends on the type of animal.  The second thing that we must consider is not necessarily the number of species, but different taxonomic levels: classes, orders, families, genera. There may be a a few families with many species, and many families with a few species, and the number of species, might not actually represent the number of individuals. 
Peter is absolutely right in saying that we have not explored the sea as well as the land; indeed it is said that we know more about the surface of the moon than we do about the seabed.  This means that we are much more conscious of land animals and recognise them more readily.  So, there are certainly more species on land, but this is only because of the insects.  If you look at any other Phylum, I don't know that there are really any more land species than aquatic?

Hello,

first off, please remember that we have people of all ages reading these posts, so text speak is not always appropriate, but I have a suspicion that we can help with your question.

Without seeing a photo, it is always hard to identify something conclusively.  However, because of the information about your friend leaving buckets of water out and their sudden appearance, it is sensible to suggest what these might be.  Firstly, they are unlikely to be fish.  Sometimes fish eggs are transplanted from lakes and ponds, to other bodies of water on the feet of water birds like ducks and herons.  However, buckets are not usually places that you find ducks.  So, what else could we have?  You know that they are not tadpoles, so we have to think about what else can get into a bucket.  It is probably an insect that has laid its eggs in the water.  They may well be mosquito larvae.  The larvae are nothing to worry about, but you might want to empty the water onto the garden, to prevent them turning into adults.

http://www.landcareresearch.co.nz/resea … ?Bu_Id=155 

This is a link to a site in New Zealand, which shows all kinds of bugs.  I hope that we have answered you question

Hi Robert,

There is a synonymous site in the US called ask a biologist (no relation) that might be able to help?

askabiologist.asu.edu/

Good luck

Without seeing them it is hard to suggest what they might be.  Often if there is 'dust' around you might get 'woolly-bears'.  These are the grubs of carpet beetles, that are small dark beetles when they are adults.  They don't normally bite, but the very thought of 'bugs' makes me very itchy!  Some species actually eat the fibres of the carpet.  The first thing you should do is  (if you are in the UK) call environmental health.  The council will send someone round to look at your 'infestation, and they can advise you.  Don't panic, they can normally get these things sorted out very well.

Before we work out what the nucleus is, we should think about cells.  In nature, there are two basic cell types, prokaryotic cells, and eukaryotic cells.  The prokaryotic cell is found in bacteria, while eukaryotic cells are found in protozoa, fungi, plants and animals.  The nucleus is a structure that is only found in eukaryotic cells.  The nucleus is a structure within the eukaryotic cell that 'holds' the DNA.  It is the defining structure of a eukaryotic cell- that is, eukaryotic cells have to have a nucleus!  In simple terms, the DNA in a prokaryotic cell, is just floating around within it, it is not in its own little packet, it is not compartmentalised, as we see in eukaryotes.  So the simple answer to your question, the nucleus is the structure in eukaryotic cells that holds the DNA.