Human generation times across the past 250,000 years

The generation times of our recent ancestors can tell us about both the biology and social organization of prehistoric humans, placing human evolution on an absolute timescale. We present a method for predicting historic male and female generation times based on changes in the mutation spectrum. Our analyses of whole-genome data reveal an average generation time of 26.9 years across the past 250,000 years, with fathers consistently older (30.7 years) than mothers (23.2 years). Shifts in sex-averaged generation times have been driven primarily by changes to the age of paternity rather than maternity, though we report a disproportionate increase in female generation times over the past several thousand years. We also find a large difference in generation times among populations, with samples from current African populations showing longer ancestral generation times than non-Africans for over a hundred thousand years, reaching back to a time when all humans occupied Africa.

Treatment of Tannery Wastewater with Salt Tolerant Bacteria Basing on Different Culture Mediums

This study was done to access the influence of salinity on the treatment of tannery wastewater, activity of sludge and morphological characteristics of the salt-tolerant bacteria cultivated using tannery wastewater as culture mediums and intermittent aeration as method. The results indicated that， aerobic sludge which contained salt-tolerant bacteria was cultivated under the conditions of temperature of 35°C and pH = 8, the COD removal in simulated and actual tannery wastewater was more than 87% and 85% by the cultivated aerobic sludge, respectively. In addition, the morphological characteristics were related to the composition and concentration of the salt. The average generation time of bacteria was 24.6min ~ 28.6min when the concentration of MLSS was 2.0 ~ 3.0g/L and the concentration of pure NaCl was 1 ~ 5g/L. As the volume ratio of NaCl and Na2SO4 was 4:1 ~ 1:4 with the total concentration of 5g/L, the average generation time of bacteria was 30.8min ~ 39.7min. The relation equation between salt concentration and the average generation time of bacteria under the pure salt, composite salt and actual tannery wastewater conditions was also deduced through four assumptions. The results had significant application on tannery wastewater treatment with great reduction of pollution.

Axenic culture of myxamoebae of the myxomycete Echinostelium minutum

Axenic cultivation of the myxomycete Echinostelium minutum De Bary (Echinosteliales) is reported for the first time. After more than a year of serial passage the average generation time of amoebae during the logarithmic phase is 18 h and a stationary phase yield of over 2 × 106 cells/ml is typical.

LATE DNA REPLICATION PATTERN IN SEX CHROMOSOMES OF MELANDRIUM

DNA replication patterns in somatic cells of female and male Meladrium album were studied with autoradiographic methods. The S-period and the average generation time have been estimated to be 5.7 and 15.5 hours respectively. The heterochromatin observed in interphase nuclei may represent the late replicating and presumably inactivated sex chromosome.One arm of one X chromosome is late replicating in females. In the Y chromosome a region near the centromere replicates late in the S-period. The DNA replication sequence in sex chromosomes of female and male cells of Melandrium album suggests that their pattern is similar to that of mammalian sex chromosomes.

The Intravascular Lifespan of Monocytes

Monocytes, defined as peroxidase positive mononuclear cells in the peripheral blood of healthy rats, were labeled by frequent intermittent injections of tritiated thymidine. About 25 per cent of the monocytes were labeled within 1 day and 82 per cent in 8 days. Both labeled and unlabeled monocytes disappeared from the circulation in accordance with an exponential function with a half-time of about 3 days. Mean grain counts increased asymptotically toward a limit reached in 4 or 5 days. The monocyte turnover rate in the rat is in the neighbourhood of 3.6 x 106 cells per day. It is concluded that monocytes leave the circulation at random and not as a consequence of senescence. It is probable that they are the product of a cell lineage consisting of about 3 generations from the primitive precursor to the mature form, and that the average generation time is about 24 hours. Because of the rapid appearance of large numbers of labeled cells, it is unlikely that they are derived from lymphocytes which acquire label much more slowly.

A SIMPLIFIED CHEMOSTAT FOR THE GROWTH OF MAMMALIAN CELLS: CHARACTERISTICS OF CELL GROWTH IN CONTINUOUS CULTURE

A simplified technique has been described for the continuous growth of mammalian cells in suspension culture. The cell population density increased as the rate of input of fresh medium was decreased, and the average generation time was concommittantly prolonged. At relatively high input rates, the population remained stabilized for an indefinite period, but at low flow rates, there was sometimes a cyclical variation in population density. The factor limiting growth rate at input rates of approximately 0.2 volumes per day was not the exhaustion of the medium; but in some experiments a non-dialyzable material appeared which inhibited cell growth.