nothing-without-science:

The story behind DNA’s double helix

The notorious race to uncover the structure of DNA, the molecule of inheritance, began in 1951, when American biologist James Watson  arrived at the University of Cambridge. Here he met Francis Crick, an English physicist and the two began building scale models to test their ideas of what DNA’s appearance might be.

Meanwhile, two scientists at King’s College London called Maurice Wilkins  and Rosalind Franklin were also studying DNA. They were attempting to crystallise the molecule to make an x-ray pattern of it. They hoped this would provide important clues about its structure.

Although the two institutions were effectively competing against each other, Francis Crick (University of Cambridge) and Maurice Wilkins (King’s College London) communicated regularly. Letters sent from Wilkins to Crick reveal their close personal relationship.

It was Rosalind Franklin’s famous x-ray image, nicknamed ‘Photo 51’, that finally revealed the structure of DNA in May 1952. The pattern appeared to contain ‘rungs’, like those on a ladder, set between two strands. The fuzzy “X” pattern indicated DNA’s helix shape. In early 1953, Wilkins showed Watson the image, seemingly without Franklin’s knowledge.

Full story here

American Flamingo - Phoenicopterus ruber

Flamingos aren’t naturally pink! They get their coloration from beta carotene found in the blue-green algae they consume. The flamingos that consume blue-green algae directly are much pinker than flamingos that primarily consume the blue-green algae secondhand (via zooplankton/brine shrimp). 

Flamingos are also unique in their method of eating - their bills are designed to scoop the bottom sediment and then filter out the mud and silt, leaving only the blue-green algae or the brine shrimp in their mouth. They shake their head back and forth under the water after scooping up the sediment. The big, fleshy tongue of the flamingo pushes water back and forth in the mouth and facilitates the filtering of all that mud. They also swallow their food while their head is upside-down! The meaty tongue used to be considered a delicacy among the Roman elite.

Images:
Nature Neighbors: Embracing Birds, Plants, and Minerals. Nathanial Moore Banta for the American Audubon Association, 1914.

Osteologia Avium; or, A sketch of the osteology of birds. T.C. Eyton, 1867.

Osteo-chondro-myxosarcoma before and after surgical intervention

Osteogenic tumors develop bone that displaces soft tissue. Osteo- means “bone”, and -genic means “to form”. In addition to the osteogenic behavior, this patient’s tumor has caused disordered cartilage (chondro-) and mucous membrane (myxo-) growth.

The case report states that it took “many” surgeries to completely remove the tumor and partially reconstruct the jaw, but that the patient lived a further 8 years after removal, and experienced no recurrence of the tumor in that time. While his vision suffered, as the left eye was unsalvagable, and his speech was impeded by both the incomplete jaw reconstruction and the excess skin remaining on the face, he was able to hold down a steady job and communicate. He was reported to be of “average-to-high” intelligence.

Tumors of the Jaws. Charles Locke Scudder, 1912.

Top: Uterine lining at 5 1/2 months, displaying thin maternal separation from fetus, and high level of placental implantation
Center: Relation of placenta to uterus at 5 weeks and 8.5 months
Bottom: Major arteries and veins of the placenta

Did you know that the placenta is a temporary organ that’s actually created by the fetus, and not the woman?

The human female is a curious creature; like our close great ape cousins, but unlike almost all other mammals, they build up a thick barrier in the uterine wall, to protect against any potential embryo that might implant itself. When there’s no embryo implantation, the thickened wall is shed, in the process known as menstruation.

The thing is, most mammals don’t menstruate. They go into heat, and occasionally shed uterine lining (if the uterus is scratched, or an egg tries to implant but fails, for example), but there’s no regular cycle of bloody discharge relating to breeding. This is because other mammals go through triggered decidualization (developing a uterine lining only when a fertilized egg begins to implant itself), while the great apes (and a couple other convergently evolved families, including bats) experience spontaneous decidualization, where they develop a thick uterine lining during every ovulation, before an egg can even attempt to implant itself.

Why the different linings? Well, it turns out that there are three types of mammal placentas (remember, placentas are developed by the embryo/fetus, not the mother):

1. Epitheliochordal, which is completely superficial, and does not connect in any significant way to the mother’s body. The endometrial epithelium, connective tissue, and uterine epithelium are all preserved and undisturbed in the mother. The fetus is separated from the mother by three layers of tissue. Nutrients and waste are delivered and eliminated through diffusion, rather than direct connection. This group includes equids, swine, and ruminants.
2. Endotheliochordal, which is slightly more invasive to the mother, only preserves the uterine epithelium. Nutrients and waste are not exchanged through direct connection to the mother, but the placenta only leaves one layer of tissue between it and the mother. This group includes cats and dogs.
3. Hemochorial is the most invasive form of placenta in the animal kingdom. The embryo directly hooks itself up to the host (mother’s) blood flow, and leaves no tissue layers between the female and the placenta. This allows much more efficient nutrient transfer to the embryo or fetus, but is also potentially the most harmful to the female since the embryo attaches itself so securely to the uterine wall. The female must develop preemptive measures (a thickened uterine lining) to protect herself from a life-form that is literally driven to take all of the nutrients it needs to develop, and which has adapted to connect itself directly to the host. This group includes elephant shrews, most bats, and most primates.

Interested in more about the science behind reproduction and how amazingly efficient the human embryo is at sucking its host clean, just to obtain its needed resources for development?

PZ Meyers at Pharyngula has an understandable explanation of the article I referenced for this post.

There is also a great site by R. Bowen about the pathophysiology of the reproductive system.

An American Text-Book of Obstetrics for Practitioners and Students. Edited by Richard C. Norris, 1895.

Top left: Hippocampus sp. internal structure
Top right: Short-snouted seahorse - Hippocampus hippocampus
Center: 1. Syngnathus hippocampus [now Hippocampus hippocampus]
2. Pegasus draconis [now Eurypegasus draconis] - the Little Dragonfish (*unrelated to Syngnathidae family*)
3. Syngnathus pelagicus - the Sargassum pipefish
Bottom: Phyllopteryx taeniolatus -the Weedy Sea Dragon

Despite their remarkable appearance, seahorses are true ray-finned bony fishes (class Actinopterygii, infraclass Teleostei), along with bass, mullets, eels, salmon, and lanternfish.

Many people know of the male seahorse incubating the eggs and giving “birth” to 100-1000 offspring after they hatch, but reproduction is similar throughout the order Syngnathidae (including the seahorses, leafy and weedy sea dragons, and pipefish). There’s a persistent myth that seahorses are monogamous, but that’s not strictly true. The majority of species are serially monogamous, and remain together throughout the mating season (until the male births the babies).

Another remarkable thing about seahorses (Hippocampus spp.) is that they’re the only fish with prehensile tails - even their close relatives, the sea dragons and pipefish, don’t have this adaptation. However, since the seahorses are the only ones that swim upright, and they have the poorest locomotive skills, they need to be able to anchor themselves to the sea flora in order to not be swept away. The Guinness Book of World Records has named Hippocampus zosterae, the dwarf seahorse, the slowest fish in the world, moving less than 5 ft [150 cm] an hour.

Aside from the seahorses, the razorfish (Aeoliscus strigatus) is the only other fish to swim “upright”.

Images:
Bulletin of the United States Fish Commission, Vol 1. 1881.
Arcana; or, The Museum of Natural History. George Perry, 1811.

Top: Common Opossum - Didelphis marsupialis
Bottom: Virginia Opossum - Didelphis virginiana

Stay in the pouch, kids! We can’t stop here; this is bat country!

Even though several marsupial families lived in the Americas before the last ice age, opossums are the only ones still remaining. Thanks to their opportunistic omnivorous diet and high rate of reproduction, opossums have survived in their current form for millenia, even despite their extremely low encephalization quotient. While rote brain volume does not in and of itself determine intelligence of an animal, mammals with smaller encephalization quotients tend to be more specialized and quickly speciated when hardships are encountered (such as ice ages).
Opossums in the Americas generally have an EQ around 1/5 that of the raccoons.

Didelphidae (Western hemisphere opossums) have very short lifespans, generally living less than two years in the wild, which is very unusual for a mammal of their size (up to the size of a large housecat). However, they can generally produce two successful litters of up to 13 young each in their short lives.

Australian opossums, while distantly related to those in the Americas, have furry tails, larger brains, and are much less urbanized. They also bear fewer young, live at least twice as long, and are less than half the size of the largest North American opossums.

Dictionnaire Universel d’Histoire Naturelle. Charles d’Orbigny, 1849.

Top: Bichir and trunkfish [top], Electric Catfish [bottom]
Center: Electric “eel” - Electrophorus electricus
Bottom: Indo-Pacific Moray Eel - Muraena nudivomer (now Gymnothorax nudivomer) 

A while ago I saw this Bird and Moon illustration of animals with misleading names, but I kept seeing people asking, “Ok, if they’re not THAT, then what ARE they?” For some reason, I completely forgot that I wanted to cover those questions, but hey, better late than never!

The electric eel isn’t an eel - it’s a knifefish. Knifefish (Gymnotiformes) are actually more closely related to electric catfish (Siluriformes) than they are to true eels (order Anguilliformes), but developed their electroconductive organs through convergent evolution - the first signs of the organ evolution in both the electric eel and the electric catfish appeared after they shared a common ancestor.

In addition to electric eels and electric catfish, electric rays (order Torpediniformes) are the only other “strongly electric” fishes - that is, fish that produce electric shocks over one volt, and use their electrogenerative organs to either stun or kill prey and/or attackers. There are many fish that can produce a small current (“weakly electric”), but it is used for electrolocation and electrocommunication, instead.

Images:
Fishes of Zanzibar: Acanthopterygii. J. Van Voorst, 1866.
The Standard Natural History. John Sterling Kingsley, 1884.
Wild life of the world. Richard Lydekker, 1915.