The Ulas family is a large Kurdish

Kurdish people

The Kurdish people, or Kurds , are an Iranian people native to the Middle East, mostly inhabiting a region known as Kurdistan, which includes adjacent parts of Iran, Iraq, Syria, and Turkey...

 family

Family

In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...

 of 19 from rural southern Turkey

Turkey

Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...

, five (except for another, who had died) of whom walk on all fours with their feet and the palms of their hand

Hand

A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...

s in what is called a "bear crawl". Their quadrupedal gait

Gait

Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency...

 has never been reported in anatomically intact adult

Adult

An adult is a human being or living organism that is of relatively mature age, typically associated with sexual maturity and the attainment of reproductive age....

 humans. The gait is different from the knuckle-walking

Knuckle-walking

Knuckle-walking is a form of quadrupedal walking in which the forelimbs hold the fingers in a partially flexed posture that allows body weight to press down on the ground through the knuckles....

 quadrupedal gait of ape

Ape

Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...

s. In 2006, the family was the subject of a documentary

Documentary film

Documentary films constitute a broad category of nonfictional motion pictures intended to document some aspect of reality, primarily for the purposes of instruction or maintaining a historical record...

: The Family That Walks On All Fours

The Family That Walks On All Fours

The Family That Walks On All Fours is a BBC2 documentary that explored the science and the story of five individuals in the Ulas family in Turkey that walk with a previously unreported quadruped gait . The documentary was created by Passionate Productions and was broadcast on Friday 17 March 2006....

.

The affected sibling

Sibling

Siblings are people who share at least one parent. A male sibling is called a brother; and a female sibling is called a sister. In most societies throughout the world, siblings usually grow up together and spend a good deal of their childhood socializing with one another...

s have a form of non-progressive congenital cerebellar ataxia

Ataxia

Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...

. The brain impairments include cerebellar hypoplasia

Cerebellar hypoplasia

Cerebellar hypoplasia is a developmental disorder characterized by the incomplete or underdevelopment of the cerebellum. It may be genetic or occur sporadically. Cerebellar hypoplasia may be caused by thyroid abnormalities, environmental influences such as drugs and chemicals or viral infections or...

, mild cerebral cortex

Cerebral cortex

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

 atrophy

Atrophy

Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

 and a reduced corpus callosum

Corpus callosum

The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...

. They are also mildly retarded

Mental retardation

Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...

 and have problems in balancing

Balance (ability)

In biomechanics, balance is an ability to maintain the center of gravity of a body within the base of support with minimal postural sway. When exercising the ability to balance, one is said to be balancing....

 on two legs

Human leg

The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...

. However, they do not show the poor coordination of hand

Hand

A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...

s, speech

Speech

Speech is the human faculty of speaking.It may also refer to:* Public speaking, the process of speaking to a group of people* Manner of articulation, how the body parts involved in making speech are manipulated...

, and eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

 movements often found in cerebellar ataxia

Ataxia

Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...

. The four sisters can do needlework

Needlework

Needlework is a broad term for the handicrafts of decorative sewing and textile arts. Anything that uses a needle for construction can be called needlework...

. They all share a recessive

Recessive

In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...

 mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 on chromosome 17p.

Source

Uner Tan

Uner Tan

Uner Tan is a Turkish neuroscientist and evolutionary biologist. He is best known for his discovery and study of the human quadrupedal condition he named the Uner Tan syndrome. He taught at Cukurova University until his retirement in 2004 and had previously taught at several other...

 of Cukurova University Medical School in Adana, Turkey, has claimed that they show characteristics of the primate

Primate

A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...

 ancestors of Homo sapiens, before the move to bipedalism. He calls the process "backward evolution" and he named the condition Uner Tan syndrome

Uner Tan syndrome

Uner Tan syndrome, Unertan syndrome or UTS is a syndrome proposed by the Turkish evolutionary biologist Uner Tan. Persons affected by this syndrome walk with a quadrupedal locomotion and are afflicted with primitive speech and severe mental retardation. Tan postulated that this is an example of...

.

However, Nicholas Humphrey

Nicholas Humphrey

Professor Nicholas Keynes Humphrey is an English psychologist, based in Cambridge, who is known for his work on the evolution of human intelligence and consciousness. His interests are wide ranging...

, John Skoyles

John Skoyles (scientist)

John Skoyles is a dyslexic neuroscientist and evolutionary psychologist. He initially studied philosophy of science at the London School of Economics and then did MRC funded research upon neuroscience and dyslexia at University College London....

, and Roger Keynes

Roger Keynes

Roger John Keynes FMedSci is a British medical scientist. He is a Fellow of Trinity College, Cambridge, and a professor within the Department of Physiology, Development and Neuroscience....

 have argued that their gait is due to two rare phenomena coming together. First, instead of initially crawling as infants on their knees, they started off learning

Learning

Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...

 to move around with a “bear crawl” on their feet. Second, due to their congenital brain impairment, they found balancing

Balancing

The concept of balancing derives from the Balance of Power Theory, the most influential theory from the realist school of thought, which assumes that a formation of hegemony in a multistate system is unattainable since hegemony is perceived as a threat by other states, causing them to engage in...

 on two legs

Human leg

The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...

 difficult. Because of this, their motor development was channeled into turning their bear crawl into a substitute for bipedality.